diff --git a/.claude/settings.json b/.claude/settings.json
new file mode 100644
index 0000000..bba6f84
--- /dev/null
+++ b/.claude/settings.json
@@ -0,0 +1,48 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(git log:*)",
+      "Bash(git branch:*)",
+      "Bash(git remote:*)",
+      "Bash(git fetch:*)",
+      "Bash(git stash:*)",
+      "Bash(git diff:*)",
+      "Bash(git status:*)",
+      "Bash(git show:*)",
+      "Bash(gh repo view:*)",
+      "Bash(gh run list:*)",
+      "Bash(gh run view:*)",
+      "Bash(gh pr view:*)",
+      "Bash(gh pr diff:*)",
+      "Bash(gh pr list:*)",
+      "Bash(gh issue view:*)",
+      "Bash(gh release:*)",
+      "Bash(gh api:*)",
+      "Bash(rake -T:*)",
+      "Bash(bundle show:*)",
+      "Bash(bundle list:*)",
+      "Bash(bundle platform:*)",
+      "Bash(gem search:*)",
+      "Bash(gem list:*)",
+      "Bash(tree:*)",
+      "Bash(grep:*)",
+      "Bash(find:*)",
+      "Bash(echo:*)",
+      "Bash(sort:*)",
+      "Bash(cat:*)",
+      "Bash(head:*)",
+      "Bash(tail:*)",
+      "Bash(less:*)",
+      "Bash(wc:*)",
+      "Bash(ls:*)",
+      "Bash(pwd:*)",
+      "Bash(which:*)",
+      "Bash(type:*)",
+      "Bash(file:*)",
+      "Bash(VCR_MODE=new_episodes bundle exec ruby:*)",
+      "Bash(VCR_MODE=new_episodes bundle exec rake:*)",
+      "Bash(VCR_MODE=new_episodes rake test:*)"
+    ],
+    "deny": []
+  }
+}
diff --git a/.standard.yml b/.standard.yml
new file mode 100644
index 0000000..2bbb355
--- /dev/null
+++ b/.standard.yml
@@ -0,0 +1,5 @@
+# StandardRB configuration
+# https://github.com/standardrb/standard
+
+ignore:
+  - "lib/braintrust/vendor/**/*"  # Vendored code follows upstream conventions
diff --git a/examples/prompt.rb b/examples/prompt.rb
new file mode 100644
index 0000000..f61d541
--- /dev/null
+++ b/examples/prompt.rb
@@ -0,0 +1,100 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+# Example: Loading and executing prompts from Braintrust
+#
+# This example demonstrates how to:
+# 1. Create a prompt (function) on the Braintrust server
+# 2. Load it using Prompt.load
+# 3. Build the prompt with Mustache variable substitution
+# 4. Execute the prompt with OpenAI and get a response
+#
+# Benefits of loading prompts:
+# - Centralized prompt management in Braintrust UI
+# - Version control and A/B testing for prompts
+# - No code deployment needed for prompt changes
+# - Works with any LLM client (OpenAI, Anthropic, etc.)
+# - Uses standard Mustache templating ({{variable}}, {{object.property}})
+
+require "bundler/setup"
+require "braintrust"
+require "openai"
+
+# Initialize Braintrust (auto-instruments OpenAI automatically)
+Braintrust.init
+
+# Create OpenAI client (auto-instrumented for tracing)
+openai = OpenAI::Client.new
+
+project_name = "ruby-sdk-examples"
+prompt_slug = "greeting-prompt-#{Time.now.to_i}"
+
+# First, create a prompt on the server
+# In practice, you would create prompts via the Braintrust UI
+puts "Creating prompt..."
+
+api = Braintrust::API.new
+api.functions.create(
+  project_name: project_name,
+  slug: prompt_slug,
+  function_data: {type: "prompt"},
+  prompt_data: {
+    prompt: {
+      type: "chat",
+      messages: [
+        {
+          role: "system",
+          content: "You are a friendly assistant. Respond in {{language}}. Keep responses brief (1-2 sentences)."
+        },
+        {
+          role: "user",
+          content: "Say hello to {{name}} and wish them a great {{time_of_day}}!"
+        }
+      ]
+    },
+    options: {
+      model: "gpt-4o-mini",
+      params: {temperature: 0.7, max_tokens: 100}
+    }
+  }
+)
+puts "Created prompt: #{prompt_slug}"
+
+# Load the prompt using Prompt.load
+puts "\nLoading prompt..."
+prompt = Braintrust::Prompt.load(project: project_name, slug: prompt_slug)
+
+puts "  ID: #{prompt.id}"
+puts "  Slug: #{prompt.slug}"
+puts "  Model: #{prompt.model}"
+
+# Build the prompt with Mustache variable substitution
+puts "\nBuilding prompt with variables..."
+params = prompt.build(
+  name: "Alice",
+  language: "Spanish",
+  time_of_day: "morning"
+)
+
+puts "  Model: #{params[:model]}"
+puts "  Temperature: #{params[:temperature]}"
+puts "  Messages:"
+params[:messages].each do |msg|
+  puts "    [#{msg[:role]}] #{msg[:content]}"
+end
+
+# Execute the prompt with OpenAI
+puts "\nExecuting prompt with OpenAI..."
+response = openai.chat.completions.create(**params)
+
+puts "\nResponse:"
+content = response.choices.first.message.content
+puts "  #{content}"
+
+# Clean up - delete the test prompt
+puts "\nCleaning up..."
+api.functions.delete(id: prompt.id)
+puts "Done!"
+
+# Flush traces
+OpenTelemetry.tracer_provider.shutdown
diff --git a/lib/braintrust.rb b/lib/braintrust.rb
index ba023fc..7a61327 100644
--- a/lib/braintrust.rb
+++ b/lib/braintrust.rb
@@ -5,6 +5,7 @@
 require_relative "braintrust/state"
 require_relative "braintrust/trace"
 require_relative "braintrust/api"
+require_relative "braintrust/prompt"
 require_relative "braintrust/internal/experiments"
 require_relative "braintrust/internal/env"
 require_relative "braintrust/eval"
diff --git a/lib/braintrust/api/functions.rb b/lib/braintrust/api/functions.rb
index ccfea31..1d569d9 100644
--- a/lib/braintrust/api/functions.rb
+++ b/lib/braintrust/api/functions.rb
@@ -85,6 +85,17 @@ def invoke(id:, input:)
         http_post_json("/v1/function/#{id}/invoke", payload)
       end
 
+      # Get a function by ID (includes full prompt_data)
+      # GET /v1/function/{id}
+      # @param id [String] Function UUID
+      # @param version [String, nil] Retrieve prompt at a specific version (transaction ID or version identifier)
+      # @return [Hash] Full function data including prompt_data
+      def get(id:, version: nil)
+        params = {}
+        params["version"] = version if version
+        http_get("/v1/function/#{id}", params)
+      end
+
       # Delete a function by ID
       # DELETE /v1/function/{id}
       # @param id [String] Function UUID
diff --git a/lib/braintrust/internal/template.rb b/lib/braintrust/internal/template.rb
new file mode 100644
index 0000000..fd9d54a
--- /dev/null
+++ b/lib/braintrust/internal/template.rb
@@ -0,0 +1,91 @@
+# frozen_string_literal: true
+
+require_relative "../vendor/mustache"
+
+module Braintrust
+  module Internal
+    # Template rendering utilities for Mustache templates
+    module Template
+      module_function
+
+      # Render a template string with variable substitution
+      #
+      # @param text [String] Template text to render
+      # @param variables [Hash] Variables to substitute
+      # @param format [String] Template format: "mustache", "none", or "nunjucks"
+      # @param strict [Boolean] Raise error on missing variables (default: false)
+      # @return [String] Rendered text
+      def render(text, variables, format:, strict: false)
+        return text unless text.is_a?(String)
+
+        case format
+        when "none"
+          # No templating - return text unchanged
+          text
+        when "nunjucks"
+          # Nunjucks is a UI-only feature in Braintrust
+          raise Error, "Nunjucks templates are not supported in the Ruby SDK. " \
+                       "Nunjucks only works in Braintrust playgrounds. " \
+                       "Please use 'mustache' or 'none' template format, or invoke the prompt via the API proxy."
+        when "mustache", "", nil
+          # Default: Mustache templating
+          if strict
+            missing = find_missing_variables(text, variables)
+            if missing.any?
+              raise Error, "Missing required variables: #{missing.join(", ")}"
+            end
+          end
+
+          Vendor::Mustache.render(text, variables)
+        else
+          raise Error, "Unknown template format: #{format.inspect}. " \
+                       "Supported formats are 'mustache' and 'none'."
+        end
+      end
+
+      # Find Mustache variables in template that are not provided
+      #
+      # @param text [String] Template text
+      # @param variables [Hash] Available variables
+      # @return [Array<String>] List of missing variable names
+      def find_missing_variables(text, variables)
+        # Extract {{variable}} and {{variable.path}} patterns
+        # Mustache uses {{name}} syntax
+        text.scan(/\{\{([^}#^\/!>]+)\}\}/).flatten.map(&:strip).uniq.reject do |var|
+          resolve_variable(var, variables)
+        end
+      end
+
+      # Check if a variable path exists in a hash
+      #
+      # @param path [String] Dot-separated variable path (e.g., "user.name")
+      # @param variables [Hash] Variables to search
+      # @return [Object, nil] The value if found, nil otherwise
+      def resolve_variable(path, variables)
+        parts = path.split(".")
+        value = variables
+
+        parts.each do |part|
+          return nil unless value.is_a?(Hash)
+          # Try both string and symbol keys
+          value = value[part] || value[part.to_sym]
+          return nil if value.nil?
+        end
+
+        value
+      end
+
+      # Convert hash keys to strings recursively
+      #
+      # @param hash [Hash] Hash with symbol or string keys
+      # @return [Hash] Hash with all string keys
+      def stringify_keys(hash)
+        return {} unless hash.is_a?(Hash)
+
+        hash.transform_keys(&:to_s).transform_values do |v|
+          v.is_a?(Hash) ? stringify_keys(v) : v
+        end
+      end
+    end
+  end
+end
diff --git a/lib/braintrust/prompt.rb b/lib/braintrust/prompt.rb
new file mode 100644
index 0000000..2125075
--- /dev/null
+++ b/lib/braintrust/prompt.rb
@@ -0,0 +1,143 @@
+# frozen_string_literal: true
+
+require "json"
+require_relative "internal/template"
+
+module Braintrust
+  # Prompt class for loading and building prompts from Braintrust
+  #
+  # @example Load and use a prompt
+  #   prompt = Braintrust::Prompt.load(project: "my-project", slug: "summarizer")
+  #   params = prompt.build(text: "Article to summarize...")
+  #   client.messages.create(**params)
+  class Prompt
+    attr_reader :id, :name, :slug, :project_id
+
+    # Load a prompt from Braintrust
+    #
+    # @param project [String] Project name
+    # @param slug [String] Prompt slug
+    # @param version [String, nil] Specific version (default: latest)
+    # @param defaults [Hash] Default variable values for build()
+    # @param api [API, nil] Braintrust API client (default: creates one using global state)
+    # @return [Prompt]
+    def self.load(project:, slug:, version: nil, defaults: {}, api: nil)
+      api ||= API.new
+
+      # Find the function by project + slug
+      result = api.functions.list(project_name: project, slug: slug)
+      function = result.dig("objects")&.first
+      raise Error, "Prompt '#{slug}' not found in project '#{project}'" unless function
+
+      # Fetch full function data including prompt_data
+      full_data = api.functions.get(id: function["id"], version: version)
+
+      new(full_data, defaults: defaults)
+    end
+
+    # Initialize a Prompt from function data
+    #
+    # @param data [Hash] Function data from API
+    # @param defaults [Hash] Default variable values for build()
+    def initialize(data, defaults: {})
+      @data = data
+      @defaults = Internal::Template.stringify_keys(defaults)
+
+      @id = data["id"]
+      @name = data["name"]
+      @slug = data["slug"]
+      @project_id = data["project_id"]
+    end
+
+    # Get the raw prompt definition
+    # @return [Hash, nil]
+    def prompt
+      @data.dig("prompt_data", "prompt")
+    end
+
+    # Get the prompt messages
+    # @return [Array<Hash>]
+    def messages
+      prompt&.dig("messages") || []
+    end
+
+    # Get the tools definition (parsed from JSON string)
+    # @return [Array<Hash>, nil]
+    def tools
+      tools_json = prompt&.dig("tools")
+      return nil unless tools_json.is_a?(String) && !tools_json.empty?
+
+      JSON.parse(tools_json)
+    rescue JSON::ParserError
+      nil
+    end
+
+    # Get the model name
+    # @return [String, nil]
+    def model
+      @data.dig("prompt_data", "options", "model")
+    end
+
+    # Get model options
+    # @return [Hash]
+    def options
+      @data.dig("prompt_data", "options") || {}
+    end
+
+    # Get the template format
+    # @return [String] "mustache" (default), "nunjucks", or "none"
+    def template_format
+      @data.dig("prompt_data", "template_format") || "mustache"
+    end
+
+    # Build the prompt with variable substitution
+    #
+    # Returns a hash ready to pass to an LLM client:
+    #   {model: "...", messages: [...], temperature: ..., ...}
+    #
+    # @param variables [Hash] Variables to substitute (e.g., {name: "Alice"})
+    # @param strict [Boolean] Raise error on missing variables (default: false)
+    # @return [Hash] Built prompt ready for LLM client
+    #
+    # @example With keyword arguments
+    #   prompt.build(name: "Alice", task: "coding")
+    #
+    # @example With explicit hash
+    #   prompt.build({name: "Alice"}, strict: true)
+    def build(variables = nil, strict: false, **kwargs)
+      # Support both explicit hash and keyword arguments
+      variables_hash = variables.is_a?(Hash) ? variables : {}
+      vars = @defaults
+        .merge(Internal::Template.stringify_keys(variables_hash))
+        .merge(Internal::Template.stringify_keys(kwargs))
+
+      # Render Mustache templates in messages
+      built_messages = messages.map do |msg|
+        {
+          role: msg["role"].to_sym,
+          content: Internal::Template.render(msg["content"], vars, format: template_format, strict: strict)
+        }
+      end
+
+      # Build result with model and messages
+      result = {
+        model: model,
+        messages: built_messages
+      }
+
+      # Add tools if defined
+      parsed_tools = tools
+      result[:tools] = parsed_tools if parsed_tools
+
+      # Add params (temperature, max_tokens, etc.) to top level
+      params = options.dig("params")
+      if params.is_a?(Hash)
+        params.each do |key, value|
+          result[key.to_sym] = value
+        end
+      end
+
+      result
+    end
+  end
+end
diff --git a/lib/braintrust/vendor/mustache.rb b/lib/braintrust/vendor/mustache.rb
new file mode 100644
index 0000000..4267497
--- /dev/null
+++ b/lib/braintrust/vendor/mustache.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+# Vendored Mustache template engine
+# From mustache gem v1.1.1 - https://github.com/mustache/mustache
+# License: MIT
+#
+# Modifications from original:
+#   - Namespaced under Braintrust::Vendor to avoid conflicts
+#   - Disabled HTML escaping (LLM prompts don't need HTML entity encoding)
+#
+# This vendored version ensures:
+#   - No external dependency required
+#   - Consistent behavior across all SDK users
+#   - No HTML escaping that would corrupt prompts containing < > & characters
+
+require_relative "mustache/mustache"
diff --git a/lib/braintrust/vendor/mustache/context.rb b/lib/braintrust/vendor/mustache/context.rb
new file mode 100644
index 0000000..fd65d91
--- /dev/null
+++ b/lib/braintrust/vendor/mustache/context.rb
@@ -0,0 +1,180 @@
+# frozen_string_literal: true
+
+# Vendored from mustache gem v1.1.1
+# https://github.com/mustache/mustache
+# License: MIT
+# Modifications: Namespaced under Braintrust::Vendor
+
+require_relative "context_miss"
+
+module Braintrust
+  module Vendor
+    class Mustache
+      # A Context represents the context which a Mustache template is
+      # executed within. All Mustache tags reference keys in the Context.
+      class Context
+        # Initializes a Mustache::Context.
+        #
+        # @param [Mustache] mustache A Mustache instance.
+        #
+        def initialize(mustache)
+          @stack = [mustache]
+          @partial_template_cache = {}
+        end
+
+        # A {{>partial}} tag translates into a call to the context's
+        # `partial` method, which would be this sucker right here.
+        #
+        # If the Mustache view handling the rendering (e.g. the view
+        # representing your profile page or some other template) responds
+        # to `partial`, we call it and render the result.
+        #
+        def partial(name, indentation = "")
+          # Look for the first Mustache in the stack.
+          mustache = mustache_in_stack
+
+          # Indent the partial template by the given indentation.
+          part = mustache.partial(name).to_s.gsub(/^/, indentation)
+
+          # Get a template object for the partial and render the result.
+          template_for_partial(part).render(self)
+        end
+
+        def template_for_partial(partial)
+          @partial_template_cache[partial] ||= Template.new(partial)
+        end
+
+        # Find the first Mustache in the stack.
+        #
+        # If we're being rendered inside a Mustache object as a context,
+        # we'll use that one.
+        #
+        # @return [Mustache] First Mustache in the stack.
+        #
+        def mustache_in_stack
+          @mustache_in_stack ||= @stack.find { |frame| frame.is_a?(Mustache) }
+        end
+
+        # Allows customization of how Mustache escapes things.
+        #
+        # @param [Object] value Value to escape.
+        #
+        # @return [String] Escaped string.
+        #
+        def escape(value)
+          mustache_in_stack.escape(value)
+        end
+
+        # Adds a new object to the context's internal stack.
+        #
+        # @param [Object] new_obj Object to be added to the internal stack.
+        #
+        # @return [Context] Returns the Context.
+        #
+        def push(new_obj)
+          @stack.unshift(new_obj)
+          @mustache_in_stack = nil
+          self
+        end
+
+        # Removes the most recently added object from the context's
+        # internal stack.
+        #
+        # @return [Context] Returns the Context.
+        #
+        def pop
+          @stack.shift
+          @mustache_in_stack = nil
+          self
+        end
+
+        # Can be used to add a value to the context in a hash-like way.
+        #
+        # context[:name] = "Chris"
+        def []=(name, value)
+          push(name => value)
+        end
+
+        # Alias for `fetch`.
+        def [](name)
+          fetch(name, nil)
+        end
+
+        # Do we know about a particular key? In other words, will calling
+        # `context[key]` give us a result that was set. Basically.
+        def has_key?(key)
+          fetch(key, false)
+        rescue ContextMiss
+          false
+        end
+
+        # Similar to Hash#fetch, finds a value by `name` in the context's
+        # stack. You may specify the default return value by passing a
+        # second parameter.
+        #
+        # If no second parameter is passed (or raise_on_context_miss is
+        # set to true), will raise a ContextMiss exception on miss.
+        def fetch(name, default = :__raise)
+          @stack.each do |frame|
+            # Prevent infinite recursion.
+            next if frame == self
+
+            value = find(frame, name, :__missing)
+            return value if :__missing != value
+          end
+
+          if default == :__raise || mustache_in_stack.raise_on_context_miss?
+            raise ContextMiss.new("Can't find #{name} in #{@stack.inspect}")
+          else
+            default
+          end
+        end
+
+        # Finds a key in an object, using whatever method is most
+        # appropriate. If the object is a hash, does a simple hash lookup.
+        # If it's an object that responds to the key as a method call,
+        # invokes that method. You get the idea.
+        #
+        # @param [Object] obj The object to perform the lookup on.
+        # @param [String,Symbol] key The key whose value you want
+        # @param [Object] default An optional default value, to return if the key is not found.
+        #
+        # @return [Object] The value of key in object if it is found, and default otherwise.
+        #
+        def find(obj, key, default = nil)
+          return find_in_hash(obj.to_hash, key, default) if obj.respond_to?(:to_hash)
+
+          unless obj.respond_to?(key)
+            # no match for the key, but it may include a hyphen, so try again replacing hyphens with underscores.
+            key = key.to_s.tr("-", "_")
+            return default unless obj.respond_to?(key)
+          end
+
+          meth = obj.method(key) rescue proc { obj.send(key) }
+          meth.arity == 1 ? meth.to_proc : meth.call
+        end
+
+        def current
+          @stack.first
+        end
+
+        private
+
+        # Fetches a hash key if it exists, or returns the given default.
+        def find_in_hash(obj, key, default)
+          return obj[key] if obj.has_key?(key)
+          return obj[key.to_s] if obj.has_key?(key.to_s)
+          return obj[key] if obj.respond_to?(:default_proc) && obj.default_proc && obj[key]
+
+          # If default is :__missing then we are from #fetch which is hunting through the stack
+          # If default is nil then we are reducing dot notation
+          if :__missing != default && mustache_in_stack.raise_on_context_miss?
+            raise ContextMiss.new("Can't find #{key} in #{obj}")
+          else
+            obj.fetch(key, default)
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/braintrust/vendor/mustache/context_miss.rb b/lib/braintrust/vendor/mustache/context_miss.rb
new file mode 100644
index 0000000..d30b8ef
--- /dev/null
+++ b/lib/braintrust/vendor/mustache/context_miss.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+# Vendored from mustache gem v1.1.1
+# https://github.com/mustache/mustache
+# License: MIT
+# Modifications: Namespaced under Braintrust::Vendor
+
+module Braintrust
+  module Vendor
+    class Mustache
+      # A ContextMiss is raised whenever a tag's target can not be found
+      # in the current context if `Mustache#raise_on_context_miss?` is
+      # set to true.
+      #
+      # For example, if your View class does not respond to `music` but
+      # your template contains a `{{music}}` tag this exception will be raised.
+      #
+      # By default it is not raised. See Mustache.raise_on_context_miss.
+      class ContextMiss < RuntimeError; end
+    end
+  end
+end
diff --git a/lib/braintrust/vendor/mustache/enumerable.rb b/lib/braintrust/vendor/mustache/enumerable.rb
new file mode 100644
index 0000000..422076d
--- /dev/null
+++ b/lib/braintrust/vendor/mustache/enumerable.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+# Vendored from mustache gem v1.1.1
+# https://github.com/mustache/mustache
+# License: MIT
+# Modifications: Namespaced under Braintrust::Vendor
+
+module Braintrust
+  module Vendor
+    class Mustache
+      Enumerable = Module.new
+    end
+  end
+end
diff --git a/lib/braintrust/vendor/mustache/generator.rb b/lib/braintrust/vendor/mustache/generator.rb
new file mode 100644
index 0000000..c2a6b9b
--- /dev/null
+++ b/lib/braintrust/vendor/mustache/generator.rb
@@ -0,0 +1,188 @@
+# frozen_string_literal: true
+
+# Vendored from mustache gem v1.1.1
+# https://github.com/mustache/mustache
+# License: MIT
+# Modifications: Namespaced under Braintrust::Vendor
+
+module Braintrust
+  module Vendor
+    class Mustache
+      # The Generator is in charge of taking an array of Mustache tokens,
+      # usually assembled by the Parser, and generating an interpolatable
+      # Ruby string. This string is considered the "compiled" template
+      # because at that point we're relying on Ruby to do the parsing and
+      # run our code.
+      #
+      # For example, let's take this template:
+      #
+      #   Hi {{thing}}!
+      #
+      # If we run this through the Parser we'll get these tokens:
+      #
+      #   [:multi,
+      #     [:static, "Hi "],
+      #     [:mustache, :etag, "thing"],
+      #     [:static, "!\n"]]
+      #
+      # Now let's hand that to the Generator:
+      #
+      # >> puts Braintrust::Vendor::Mustache::Generator.new.compile(tokens)
+      # "Hi #{ctx.escape(ctx[:thing])}!\n"
+      class Generator
+        # Options can be used to manipulate the resulting ruby code string behavior.
+        def initialize(options = {})
+          @options = options
+          @option_static_lambdas = options[:static_lambdas] == true
+        end
+
+        # Given an array of tokens, returns an interpolatable Ruby string.
+        def compile(exp)
+          "\"#{compile!(exp)}\""
+        end
+
+        private
+
+        # Given an array of tokens, converts them into Ruby code. In
+        # particular there are three types of expressions we are concerned
+        # with:
+        #
+        #   :multi
+        #     Mixed bag of :static, :mustache, and whatever.
+        #
+        #   :static
+        #     Normal HTML, the stuff outside of {{mustaches}}.
+        #
+        #   :mustache
+        #     Any Mustache tag, from sections to partials.
+        def compile!(exp)
+          case exp.first
+          when :multi
+            exp[1..-1].reduce(+"") { |sum, e| sum << compile!(e) }
+          when :static
+            str(exp[1])
+          when :mustache
+            send(:"on_#{exp[1]}", *exp[2..-1])
+          else
+            raise "Unhandled exp: #{exp.first}"
+          end
+        end
+
+        # Callback fired when the compiler finds a section token. We're
+        # passed the section name and the array of tokens.
+        def on_section(name, offset, content, raw, delims)
+          # Convert the tokenized content of this section into a Ruby
+          # string we can use.
+          code = compile(content)
+
+          # Lambda handling - default handling is to dynamically interpret
+          # the returned lambda result as mustache source
+          proc_handling = if @option_static_lambdas
+            <<-compiled
+              v.call(lambda {|v| #{code}}.call(v)).to_s
+            compiled
+          else
+            <<-compiled
+              t = Braintrust::Vendor::Mustache::Template.new(v.call(#{raw.inspect}).to_s)
+              def t.tokens(src=@source)
+                p = Braintrust::Vendor::Mustache::Parser.new
+                p.otag, p.ctag = #{delims.inspect}
+                p.compile(src)
+              end
+              t.render(ctx.dup)
+            compiled
+          end
+
+          # Compile the Ruby for this section now that we know what's
+          # inside the section.
+          ev(<<-compiled)
+          case v = #{compile!(name)}
+          when NilClass, FalseClass
+          when TrueClass
+            #{code}
+          when Proc
+            #{proc_handling}
+          when Array, Enumerator, Braintrust::Vendor::Mustache::Enumerable
+            v.map { |_| ctx.push(_); r = #{code}; ctx.pop; r }.join
+          else
+            ctx.push(v); r = #{code}; ctx.pop; r
+          end
+          compiled
+        end
+
+        # Fired when we find an inverted section. Just like `on_section`,
+        # we're passed the inverted section name and the array of tokens.
+        def on_inverted_section(name, offset, content, raw, delims)
+          # Convert the tokenized content of this section into a Ruby
+          # string we can use.
+          code = compile(content)
+
+          # Compile the Ruby for this inverted section now that we know
+          # what's inside.
+          ev(<<-compiled)
+          v = #{compile!(name)}
+          if v.nil? || v == false || v.respond_to?(:empty?) && v.empty?
+            #{code}
+          end
+          compiled
+        end
+
+        # Fired when the compiler finds a partial. We want to return code
+        # which calls a partial at runtime instead of expanding and
+        # including the partial's body to allow for recursive partials.
+        def on_partial(name, offset, indentation)
+          ev("ctx.partial(#{name.to_sym.inspect}, #{indentation.inspect})")
+        end
+
+        # An unescaped tag.
+        def on_utag(name, offset)
+          ev(<<-compiled)
+            v = #{compile!(name)}
+            if v.is_a?(Proc)
+              v = #{@option_static_lambdas ? "v.call" : "Braintrust::Vendor::Mustache::Template.new(v.call.to_s).render(ctx.dup)"}
+            end
+            v.to_s
+          compiled
+        end
+
+        # An escaped tag.
+        def on_etag(name, offset)
+          ev(<<-compiled)
+            v = #{compile!(name)}
+            if v.is_a?(Proc)
+              v = #{@option_static_lambdas ? "v.call" : "Braintrust::Vendor::Mustache::Template.new(v.call.to_s).render(ctx.dup)"}
+            end
+            ctx.escape(v)
+          compiled
+        end
+
+        def on_fetch(names)
+          return "ctx.current" if names.empty?
+
+          names = names.map { |n| n.to_sym }
+
+          initial, *rest = names
+          if rest.any?
+            <<-compiled
+              #{rest.inspect}.reduce(ctx[#{initial.inspect}]) { |value, key| value && ctx.find(value, key) }
+            compiled
+          else
+            <<-compiled
+              ctx[#{initial.inspect}]
+            compiled
+          end
+        end
+
+        # An interpolation-friendly version of a string, for use within a
+        # Ruby string.
+        def ev(s)
+          "#\{#{s}}"
+        end
+
+        def str(s)
+          s.inspect[1..-2]
+        end
+      end
+    end
+  end
+end
diff --git a/lib/braintrust/vendor/mustache/mustache.rb b/lib/braintrust/vendor/mustache/mustache.rb
new file mode 100644
index 0000000..7624589
--- /dev/null
+++ b/lib/braintrust/vendor/mustache/mustache.rb
@@ -0,0 +1,260 @@
+# frozen_string_literal: true
+
+# Vendored from mustache gem v1.1.1
+# https://github.com/mustache/mustache
+# License: MIT
+# Modifications:
+#   - Namespaced under Braintrust::Vendor
+#   - Disabled HTML escaping (LLM prompts don't need HTML escaping)
+
+require_relative "enumerable"
+require_relative "template"
+require_relative "context"
+require_relative "settings"
+require_relative "utils"
+
+module Braintrust
+  module Vendor
+    # Mustache is the base class from which your Mustache subclasses
+    # should inherit (though it can be used on its own).
+    #
+    # The typical Mustache workflow is as follows:
+    #
+    # * Create a Mustache subclass: class Stats < Mustache
+    # * Create a template: stats.mustache
+    # * Instantiate an instance: view = Stats.new
+    # * Render that instance: view.render
+    #
+    # You can skip the instantiation by calling `Stats.render` directly.
+    class Mustache
+      # Initialize a new Mustache instance.
+      #
+      # @param [Hash] options An options hash
+      # @option options [String] template_path
+      # @option options [String] template_extension
+      # @option options [String] template_file
+      # @option options [String] template
+      # @option options [String] view_namespace
+      # @option options [String] view_path
+      def initialize(options = {})
+        @options = options
+
+        initialize_settings
+      end
+
+      # Instantiates an instance of this class and calls `render` with
+      # the passed args.
+      #
+      # @return A rendered String version of a template.
+      def self.render(*args)
+        new.render(*args)
+      end
+
+      # Parses our fancy pants template file and returns normal file with
+      # all special {{tags}} and {{#sections}}replaced{{/sections}}.
+      #
+      # @example Render view
+      #   @view.render("Hi {{thing}}!", :thing => :world)
+      #
+      # @example Set view template and then render
+      #   View.template = "Hi {{thing}}!"
+      #   @view = View.new
+      #   @view.render(:thing => :world)
+      #
+      # @param [String,Hash] data A String template or a Hash context.
+      #                           If a Hash is given, we'll try to figure
+      #                           out the template from the class.
+      # @param [Hash] ctx A Hash context if `data` is a String template.
+      # @return [String] Returns a rendered version of a template.
+      def render(data = template, ctx = {})
+        case data
+        when Hash
+          ctx = data
+        when Symbol
+          self.template_name = data
+        end
+
+        tpl = case data
+        when Hash
+          templateify(template)
+        when Symbol
+          templateify(template)
+        else
+          templateify(data)
+        end
+
+        return tpl.render(context) if ctx == {}
+
+        begin
+          context.push(ctx)
+          tpl.render(context)
+        ensure
+          context.pop
+        end
+      end
+
+      # Context accessors.
+      #
+      # @example Context accessors
+      #   view = Mustache.new
+      #   view[:name] = "Jon"
+      #   view.template = "Hi, {{name}}!"
+      #   view.render # => "Hi, Jon!"
+      def [](key)
+        context[key.to_sym]
+      end
+
+      def []=(key, value)
+        context[key.to_sym] = value
+      end
+
+      # A helper method which gives access to the context at a given time.
+      # Kind of a hack for now, but useful when you're in an iterating section
+      # and want access to the hash currently being iterated over.
+      def context
+        @context ||= Context.new(self)
+      end
+
+      # Given a file name and an optional context, attempts to load and
+      # render the file as a template.
+      def self.render_file(name, context = {})
+        render(partial(name), context)
+      end
+
+      # Given a file name and an optional context, attempts to load and
+      # render the file as a template.
+      def render_file(name, context = {})
+        self.class.render_file(name, context)
+      end
+
+      # Given a name, attempts to read a file and return the contents as a
+      # string. The file is not rendered, so it might contain
+      # {{mustaches}}.
+      #
+      # Call `render` if you need to process it.
+      def self.partial(name)
+        new.partial(name)
+      end
+
+      # Override this in your subclass if you want to do fun things like
+      # reading templates from a database. It will be rendered by the
+      # context, so all you need to do is return a string.
+      def partial(name)
+        path = "#{template_path}/#{name}.#{template_extension}"
+
+        begin
+          File.read(path)
+        rescue
+          raise if raise_on_context_miss?
+          ""
+        end
+      end
+
+      # BRAINTRUST MODIFICATION: No HTML escaping for LLM prompts.
+      # Original mustache uses CGI.escapeHTML which would turn
+      # characters like < > & " into HTML entities.
+      # For LLM prompts, we want the raw text without escaping.
+      #
+      # @param [Object] value Value to escape.
+      # @return [String] Unescaped content (just converted to string).
+      def escape(value)
+        value.to_s
+      end
+
+      # @deprecated Use {#escape} instead.
+      # Kept for compatibility but also does no escaping.
+      def escapeHTML(str)
+        str.to_s
+      end
+
+      # Has this instance or its class already compiled a template?
+      def compiled?
+        (@template && @template.is_a?(Template)) || self.class.compiled?
+      end
+
+      private
+
+      # When given a symbol or string representing a class, will try to produce an
+      # appropriate view class.
+      #
+      # @example
+      #   Mustache.view_namespace = Hurl::Views
+      #   Mustache.view_class(:Partial) # => Hurl::Views::Partial
+      def self.view_class(name)
+        name = classify(name.to_s)
+
+        # Emptiness begets emptiness.
+        return Mustache if name.to_s.empty?
+
+        name = "#{view_namespace}::#{name}"
+        const = rescued_const_get(name)
+
+        return const if const
+
+        const_from_file(name)
+      end
+
+      def self.rescued_const_get(name)
+        const_get(name, true) || Mustache
+      rescue NameError
+        nil
+      end
+
+      def self.const_from_file(name)
+        file_name = underscore(name)
+        file_path = "#{view_path}/#{file_name}.rb"
+
+        return Mustache unless File.exist?(file_path)
+
+        require file_path.chomp(".rb")
+        rescued_const_get(name)
+      end
+
+      # Has this template already been compiled? Compilation is somewhat
+      # expensive so it may be useful to check this before attempting it.
+      def self.compiled?
+        @template.is_a? Template
+      end
+
+      # template_partial => TemplatePartial
+      # template/partial => Template::Partial
+      def self.classify(underscored)
+        Mustache::Utils::String.new(underscored).classify
+      end
+
+      # TemplatePartial => template_partial
+      # Template::Partial => template/partial
+      # Takes a string but defaults to using the current class' name.
+      def self.underscore(classified = name)
+        classified = superclass.name if classified.to_s.empty?
+
+        Mustache::Utils::String.new(classified).underscore(view_namespace)
+      end
+
+      # @param [Template,String] obj      Turns `obj` into a template
+      # @param [Hash]            options  Options for template creation
+      def self.templateify(obj, options = {})
+        obj.is_a?(Template) ? obj : Template.new(obj, options)
+      end
+
+      def templateify(obj)
+        opts = {partial_resolver: method(:partial)}
+        opts.merge!(@options) if @options.is_a?(Hash)
+        self.class.templateify(obj, opts)
+      end
+
+      # Return the value of the configuration setting on the superclass, or return
+      # the default.
+      #
+      # @param [Symbol] attr_name Name of the attribute. It should match
+      #                           the instance variable.
+      # @param [Object] default Default value to use if the superclass does
+      #                         not respond.
+      #
+      # @return Inherited or default configuration setting.
+      def self.inheritable_config_for(attr_name, default)
+        superclass.respond_to?(attr_name) ? superclass.send(attr_name) : default
+      end
+    end
+  end
+end
diff --git a/lib/braintrust/vendor/mustache/parser.rb b/lib/braintrust/vendor/mustache/parser.rb
new file mode 100644
index 0000000..f46f3d8
--- /dev/null
+++ b/lib/braintrust/vendor/mustache/parser.rb
@@ -0,0 +1,364 @@
+# frozen_string_literal: true
+
+# Vendored from mustache gem v1.1.1
+# https://github.com/mustache/mustache
+# License: MIT
+# Modifications: Namespaced under Braintrust::Vendor
+
+require "strscan"
+
+module Braintrust
+  module Vendor
+    class Mustache
+      # The Parser is responsible for taking a string template and
+      # converting it into an array of tokens and, really, expressions. It
+      # raises SyntaxError if there is anything it doesn't understand and
+      # knows which sigil corresponds to which tag type.
+      #
+      # For example, given this template:
+      #
+      #   Hi {{thing}}!
+      #
+      # Run through the Parser we'll get these tokens:
+      #
+      #   [:multi,
+      #     [:static, "Hi "],
+      #     [:mustache, :etag, "thing"],
+      #     [:static, "!\n"]]
+      class Parser
+        # A SyntaxError is raised when the Parser comes across unclosed
+        # tags, sections, illegal content in tags, or anything of that
+        # sort.
+        class SyntaxError < StandardError
+          def initialize(message, position)
+            @message = message
+            @lineno, @column, @line, _ = position
+            @stripped_line = @line.strip
+            @stripped_column = @column - (@line.size - @line.lstrip.size)
+          end
+
+          def to_s
+            <<-EOF
+#{@message}
+  Line #{@lineno}
+    #{@stripped_line}
+    #{" " * @stripped_column}^
+EOF
+          end
+        end
+
+        # The sigil types which are valid after an opening `{{`
+        VALID_TYPES = ["#", "^", "/", "=", "!", "<", ">", "&", "{"].map(&:freeze)
+
+        def self.valid_types
+          @valid_types ||= Regexp.new(VALID_TYPES.map { |t| Regexp.escape(t) }.join("|"))
+        end
+
+        # Add a supported sigil type (with optional aliases) to the Parser.
+        #
+        # Requires a block, which will be sent the following parameters:
+        #
+        # * content - The raw content of the tag
+        # * fetch- A mustache context fetch expression for the content
+        # * padding - Indentation whitespace from the currently-parsed line
+        # * pre_match_position - Location of the scanner before a match was made
+        #
+        # The provided block will be evaluated against the current instance of
+        # Parser, and may append to the Parser's @result as needed.
+        def self.add_type(*types, &block)
+          types = types.map(&:to_s)
+          type, *aliases = types
+          method_name = :"scan_tag_#{type}"
+          define_method(method_name, &block)
+          aliases.each { |a| alias_method :"scan_tag_#{a}", method_name }
+          types.each { |t| VALID_TYPES << t unless VALID_TYPES.include?(t) }
+          @valid_types = nil
+        end
+
+        # After these types of tags, all whitespace until the end of the line will
+        # be skipped if they are the first (and only) non-whitespace content on
+        # the line.
+        SKIP_WHITESPACE = ["#", "^", "/", "<", ">", "=", "!"].map(&:freeze)
+
+        # The content allowed in a tag name.
+        ALLOWED_CONTENT = /(\w|[?!\/.=-])*/
+
+        # These types of tags allow any content,
+        # the rest only allow ALLOWED_CONTENT.
+        ANY_CONTENT = ["!", "="].map(&:freeze)
+
+        attr_reader :otag, :ctag
+
+        # Accepts an options hash which does nothing but may be used in
+        # the future.
+        def initialize(options = {})
+          @options = options
+          @option_inline_partials_at_compile_time = options[:inline_partials_at_compile_time]
+          if @option_inline_partials_at_compile_time
+            @partial_resolver = options[:partial_resolver]
+            raise ArgumentError.new "Missing or invalid partial_resolver" unless @partial_resolver.respond_to? :call
+          end
+
+          # Initialize default tags
+          self.otag ||= "{{"
+          self.ctag ||= "}}"
+        end
+
+        # The opening tag delimiter. This may be changed at runtime.
+        def otag=(value)
+          regex = regexp value
+          @otag_regex = /([ \t]*)?#{regex}/
+          @otag_not_regex = /(^[ \t]*)?#{regex}/
+          @otag = value
+        end
+
+        # The closing tag delimiter. This too may be changed at runtime.
+        def ctag=(value)
+          @ctag_regex = regexp value
+          @ctag = value
+        end
+
+        # Given a string template, returns an array of tokens.
+        def compile(template)
+          @encoding = nil
+
+          if template.respond_to?(:encoding)
+            @encoding = template.encoding
+            template = template.dup.force_encoding("BINARY")
+          end
+
+          # Keeps information about opened sections.
+          @sections = []
+          @result = [:multi]
+          @scanner = StringScanner.new(template)
+
+          # Scan until the end of the template.
+          until @scanner.eos?
+            scan_tags || scan_text
+          end
+
+          unless @sections.empty?
+            # We have parsed the whole file, but there's still opened sections.
+            type, pos, _ = @sections.pop
+            error "Unclosed section #{type.inspect}", pos
+          end
+
+          @result
+        end
+
+        private
+
+        def content_tags(type, current_ctag_regex)
+          if ANY_CONTENT.include?(type)
+            r = /\s*#{regexp(type)}?#{current_ctag_regex}/
+            scan_until_exclusive(r)
+          else
+            @scanner.scan(ALLOWED_CONTENT)
+          end
+        end
+
+        def dispatch_based_on_type(type, content, fetch, padding, pre_match_position)
+          send(:"scan_tag_#{type}", content, fetch, padding, pre_match_position)
+        end
+
+        def find_closing_tag(scanner, current_ctag_regex)
+          error "Unclosed tag" unless scanner.scan(current_ctag_regex)
+        end
+
+        # Find {{mustaches}} and add them to the @result array.
+        def scan_tags
+          # Scan until we hit an opening delimiter.
+          start_of_line = @scanner.beginning_of_line?
+          pre_match_position = @scanner.pos
+          last_index = @result.length
+
+          return unless @scanner.scan @otag_regex
+          padding = @scanner[1] || ""
+
+          # Don't touch the preceding whitespace unless we're matching the start
+          # of a new line.
+          unless start_of_line
+            @result << [:static, padding] unless padding.empty?
+            pre_match_position += padding.length
+            padding = ""
+          end
+
+          # Since {{= rewrites ctag, we store the ctag which should be used
+          # when parsing this specific tag.
+          current_ctag_regex = @ctag_regex
+          type = @scanner.scan(self.class.valid_types)
+          @scanner.skip(/\s*/)
+
+          # ANY_CONTENT tags allow any character inside of them, while
+          # other tags (such as variables) are more strict.
+          content = content_tags(type, current_ctag_regex)
+
+          # We found {{ but we can't figure out what's going on inside.
+          error "Illegal content in tag" if content.empty?
+
+          fetch = [:mustache, :fetch, content.split(".")]
+          prev = @result
+
+          dispatch_based_on_type(type, content, fetch, padding, pre_match_position)
+
+          # The closing } in unescaped tags is just a hack for
+          # aesthetics.
+          type = "}" if type == "{"
+
+          # Skip whitespace and any balancing sigils after the content
+          # inside this tag.
+          @scanner.skip(/\s+/)
+          @scanner.skip(regexp(type)) if type
+
+          find_closing_tag(@scanner, current_ctag_regex)
+
+          # If this tag was the only non-whitespace content on this line, strip
+          # the remaining whitespace.  If not, but we've been hanging on to padding
+          # from the beginning of the line, re-insert the padding as static text.
+          if start_of_line && !@scanner.eos?
+            if @scanner.peek(2) =~ /\r?\n/ && SKIP_WHITESPACE.include?(type)
+              @scanner.skip(/\r?\n/)
+            else
+              prev.insert(last_index, [:static, padding]) unless padding.empty?
+            end
+          end
+
+          # Store off the current scanner position now that we've closed the tag
+          # and consumed any irrelevant whitespace.
+          @sections.last[1] << @scanner.pos unless @sections.empty?
+
+          return unless @result == [:multi]
+        end
+
+        # Try to find static text, e.g. raw HTML with no {{mustaches}}.
+        def scan_text
+          text = scan_until_exclusive @otag_not_regex
+
+          if text.nil?
+            # Couldn't find any otag, which means the rest is just static text.
+            text = @scanner.rest
+            # Mark as done.
+            @scanner.terminate
+          end
+
+          text.force_encoding(@encoding) if @encoding
+
+          @result << [:static, text] unless text.empty?
+        end
+
+        # Scans the string until the pattern is matched. Returns the substring
+        # *excluding* the end of the match, advancing the scan pointer to that
+        # location. If there is no match, nil is returned.
+        def scan_until_exclusive(regexp)
+          pos = @scanner.pos
+          if @scanner.scan_until(regexp)
+            @scanner.pos -= @scanner.matched.size
+            @scanner.pre_match[pos..-1]
+          end
+        end
+
+        def offset
+          position[0, 2]
+        end
+
+        # Returns [lineno, column, line]
+        def position
+          # The rest of the current line
+          rest = @scanner.check_until(/\n|\Z/).to_s.chomp
+
+          # What we have parsed so far
+          parsed = @scanner.string[0...@scanner.pos]
+
+          lines = parsed.split("\n")
+
+          [lines.size, lines.last.size - 1, lines.last + rest]
+        end
+
+        # Used to quickly convert a string into a regular expression
+        # usable by the string scanner.
+        def regexp(thing)
+          Regexp.new Regexp.escape(thing) if thing
+        end
+
+        # Raises a SyntaxError. The message should be the name of the
+        # error - other details such as line number and position are
+        # handled for you.
+        def error(message, pos = position)
+          raise SyntaxError.new(message, pos)
+        end
+
+        #
+        # Scan tags
+        #
+        # These methods are called in `scan_tags`. Because they contain nonstandard
+        # characters in their method names, they are aliased to
+        # better named methods.
+        #
+
+        # This function handles the cases where the scanned tag does not have
+        # a type.
+        def scan_tag_(content, fetch, padding, pre_match_position)
+          @result << [:mustache, :etag, fetch, offset]
+        end
+
+        def scan_tag_block(content, fetch, padding, pre_match_position)
+          block = [:multi]
+          @result << [:mustache, :section, fetch, offset, block]
+          @sections << [content, position, @result]
+          @result = block
+        end
+        alias_method :'scan_tag_#', :scan_tag_block
+
+        def scan_tag_inverted(content, fetch, padding, pre_match_position)
+          block = [:multi]
+          @result << [:mustache, :inverted_section, fetch, offset, block]
+          @sections << [content, position, @result]
+          @result = block
+        end
+        alias_method :'scan_tag_^', :scan_tag_inverted
+
+        def scan_tag_close(content, fetch, padding, pre_match_position)
+          section, pos, result = @sections.pop
+          if section.nil?
+            error "Closing unopened #{content.inspect}"
+          end
+
+          raw = @scanner.pre_match[pos[3]...pre_match_position] + padding
+          (@result = result).last << raw << [otag, ctag]
+
+          if section != content
+            error "Unclosed section #{section.inspect}", pos
+          end
+        end
+        alias_method :'scan_tag_/', :scan_tag_close
+
+        def scan_tag_comment(content, fetch, padding, pre_match_position)
+        end
+        alias_method :'scan_tag_!', :scan_tag_comment
+
+        def scan_tag_delimiter(content, fetch, padding, pre_match_position)
+          self.otag, self.ctag = content.split(" ", 2)
+        end
+        alias_method :'scan_tag_=', :scan_tag_delimiter
+
+        def scan_tag_open_partial(content, fetch, padding, pre_match_position)
+          @result << if @option_inline_partials_at_compile_time
+            partial = @partial_resolver.call content
+            partial.gsub!(/^/, padding) unless padding.empty?
+            self.class.new(@options).compile partial
+          else
+            [:mustache, :partial, content, offset, padding]
+          end
+        end
+        alias_method :'scan_tag_<', :scan_tag_open_partial
+        alias_method :'scan_tag_>', :scan_tag_open_partial
+
+        def scan_tag_unescaped(content, fetch, padding, pre_match_position)
+          @result << [:mustache, :utag, fetch, offset]
+        end
+        alias_method :'scan_tag_{', :scan_tag_unescaped
+        alias_method :'scan_tag_&', :scan_tag_unescaped
+      end
+    end
+  end
+end
diff --git a/lib/braintrust/vendor/mustache/settings.rb b/lib/braintrust/vendor/mustache/settings.rb
new file mode 100644
index 0000000..f9225ef
--- /dev/null
+++ b/lib/braintrust/vendor/mustache/settings.rb
@@ -0,0 +1,252 @@
+# frozen_string_literal: true
+
+# Vendored from mustache gem v1.1.1
+# https://github.com/mustache/mustache
+# License: MIT
+# Modifications: Namespaced under Braintrust::Vendor
+
+# Settings which can be configured for all view classes, a single
+# view class, or a single Mustache instance.
+module Braintrust
+  module Vendor
+    class Mustache
+      def initialize_settings
+        @template = nil
+        @template_path = nil
+        @template_extension = nil
+        @template_name = nil
+        @template_file = nil
+        @raise_on_context_miss = nil
+      end
+
+      def self.initialize_settings
+        @template = nil
+        @template_path = nil
+        @template_extension = nil
+        @template_name = nil
+        @template_file = nil
+        @raise_on_context_miss = nil
+      end
+
+      initialize_settings
+
+      def self.inherited(subclass)
+        subclass.initialize_settings
+      end
+
+      #
+      # Template Path
+      #
+
+      # The template path informs your Mustache view where to look for its
+      # corresponding template. By default it's the current directory (".")
+      #
+      # A class named Stat with a template_path of "app/templates" will look
+      # for "app/templates/stat.mustache"
+
+      def self.template_path
+        @template_path ||= inheritable_config_for :template_path, "."
+      end
+
+      def self.template_path=(path)
+        @template_path = File.expand_path(path)
+        @template = nil
+      end
+
+      def template_path
+        @template_path ||= self.class.template_path
+      end
+      alias_method :path, :template_path
+
+      def template_path=(path)
+        @template_path = File.expand_path(path)
+        @template = nil
+      end
+
+      # Alias for `template_path`
+      def self.path
+        template_path
+      end
+
+      # Alias for `template_path`
+      def self.path=(path)
+        self.template_path = path
+      end
+
+      #
+      # Template Extension
+      #
+
+      # A Mustache template's default extension is 'mustache', but this can be changed.
+
+      def self.template_extension
+        @template_extension ||= inheritable_config_for :template_extension, "mustache"
+      end
+
+      def self.template_extension=(template_extension)
+        @template_extension = template_extension
+        @template = nil
+      end
+
+      def template_extension
+        @template_extension ||= self.class.template_extension
+      end
+
+      def template_extension=(template_extension)
+        @template_extension = template_extension
+        @template = nil
+      end
+
+      #
+      # Template Name
+      #
+
+      # The template name is the Mustache template file without any
+      # extension or other information. Defaults to `class_name`.
+      #
+      # You may want to change this if your class is named Stat but you want
+      # to re-use another template.
+      #
+      #   class Stat
+      #     self.template_name = "graphs" # use graphs.mustache
+      #   end
+
+      def self.template_name
+        @template_name || underscore
+      end
+
+      def self.template_name=(template_name)
+        @template_name = template_name
+        @template = nil
+      end
+
+      def template_name
+        @template_name ||= self.class.template_name
+      end
+
+      def template_name=(template_name)
+        @template_name = template_name
+        @template = nil
+      end
+
+      #
+      # Template File
+      #
+
+      # The template file is the absolute path of the file Mustache will
+      # use as its template. By default it's ./class_name.mustache
+
+      def self.template_file
+        @template_file || "#{path}/#{template_name}.#{template_extension}"
+      end
+
+      def self.template_file=(template_file)
+        @template_file = template_file
+        @template = nil
+      end
+
+      # The template file is the absolute path of the file Mustache will
+      # use as its template. By default it's ./class_name.mustache
+      def template_file
+        @template_file || "#{path}/#{template_name}.#{template_extension}"
+      end
+
+      def template_file=(template_file)
+        @template_file = template_file
+        @template = nil
+      end
+
+      #
+      # Template
+      #
+
+      # The template is the actual string Mustache uses as its template.
+      # There is a bit of magic here: what we get back is actually a
+      # Mustache::Template object, but you can still safely use `template=`
+      #  with a string.
+
+      def self.template
+        @template ||= templateify(File.read(template_file))
+      end
+
+      def self.template=(template)
+        @template = templateify(template)
+      end
+
+      # The template can be set at the instance level.
+      def template
+        return @template if @template
+
+        # If they sent any instance-level options use that instead of the class's.
+        if @template_path || @template_extension || @template_name || @template_file
+          @template = templateify(File.read(template_file))
+        else
+          @template = self.class.template
+        end
+      end
+
+      def template=(template)
+        @template = templateify(template)
+      end
+
+      #
+      # Raise on context miss
+      #
+
+      # Should an exception be raised when we cannot find a corresponding method
+      # or key in the current context? By default this is false to emulate ctemplate's
+      # behavior, but it may be useful to enable when debugging or developing.
+      #
+      # If set to true and there is a context miss, `Mustache::ContextMiss` will
+      # be raised.
+
+      def self.raise_on_context_miss?
+        @raise_on_context_miss
+      end
+
+      def self.raise_on_context_miss=(boolean)
+        @raise_on_context_miss = boolean
+      end
+
+      # Instance level version of `Mustache.raise_on_context_miss?`
+      def raise_on_context_miss?
+        self.class.raise_on_context_miss? || @raise_on_context_miss
+      end
+
+      def raise_on_context_miss=(boolean)
+        @raise_on_context_miss = boolean
+      end
+
+      #
+      # View Namespace
+      #
+
+      # The constant under which Mustache will look for views when autoloading.
+      # By default the view namespace is `Object`, but it might be nice to set
+      # it to something like `Hurl::Views` if your app's main namespace is `Hurl`.
+
+      def self.view_namespace
+        @view_namespace ||= inheritable_config_for(:view_namespace, Object)
+      end
+
+      def self.view_namespace=(namespace)
+        @view_namespace = namespace
+      end
+
+      #
+      # View Path
+      #
+
+      # Mustache searches the view path for .rb files to require when asked to find a
+      # view class. Defaults to "."
+
+      def self.view_path
+        @view_path ||= inheritable_config_for(:view_path, ".")
+      end
+
+      def self.view_path=(path)
+        @view_path = path
+      end
+    end
+  end
+end
diff --git a/lib/braintrust/vendor/mustache/template.rb b/lib/braintrust/vendor/mustache/template.rb
new file mode 100644
index 0000000..cd8c093
--- /dev/null
+++ b/lib/braintrust/vendor/mustache/template.rb
@@ -0,0 +1,138 @@
+# frozen_string_literal: true
+
+# Vendored from mustache gem v1.1.1
+# https://github.com/mustache/mustache
+# License: MIT
+# Modifications: Namespaced under Braintrust::Vendor
+
+require "cgi"
+
+require_relative "parser"
+require_relative "generator"
+
+module Braintrust
+  module Vendor
+    class Mustache
+      # A Template represents a Mustache template. It compiles and caches
+      # a raw string template into something usable.
+      #
+      # The idea is this: when handed a Mustache template, convert it into
+      # a Ruby string by transforming Mustache tags into interpolated
+      # Ruby.
+      #
+      # You shouldn't use this class directly, instead:
+      #
+      # >> Braintrust::Vendor::Mustache.render(template, hash)
+      class Template
+        attr_reader :source
+
+        # Expects a Mustache template as a string along with a template
+        # path, which it uses to find partials. Options may be passed.
+        def initialize(source, options = {})
+          @source = source
+          @options = options
+        end
+
+        # Renders the `@source` Mustache template using the given
+        # `context`, which should be a simple hash keyed with symbols.
+        #
+        # The first time a template is rendered, this method is overriden
+        # and from then on it is "compiled". Subsequent calls will skip
+        # the compilation step and run the Ruby version of the template
+        # directly.
+        def render(context)
+          # Compile our Mustache template into a Ruby string
+          compiled = "def render(ctx) #{compile} end"
+
+          # Here we rewrite ourself with the interpolated Ruby version of
+          # our Mustache template so subsequent calls are very fast and
+          # can skip the compilation stage.
+          instance_eval(compiled, __FILE__, __LINE__ - 1)
+
+          # Call the newly rewritten version of #render
+          render(context)
+        end
+
+        # Does the dirty work of transforming a Mustache template into an
+        # interpolation-friendly Ruby string.
+        def compile(src = @source)
+          Generator.new(@options).compile(tokens(src))
+        end
+        alias_method :to_s, :compile
+
+        # Returns an array of tokens for a given template.
+        #
+        # @return [Array] Array of tokens.
+        #
+        def tokens(src = @source)
+          Parser.new(@options).compile(src)
+        end
+
+        # Returns an array of tags.
+        #
+        # Tags that belong to sections will be of the form `section1.tag`.
+        #
+        # @return [Array] Returns an array of tags.
+        #
+        def tags
+          Template.recursor(tokens, []) do |token, section|
+            if [:etag, :utag].include?(token[1])
+              [new_token = nil, new_section = nil, result = ((section + [token[2][2][0]]).join(".")), stop = true]
+            elsif [:section, :inverted_section].include?(token[1])
+              [new_token = token[4], new_section = (section + [token[2][2][0]]), result = nil, stop = false]
+            else
+              [new_token = token, new_section = section, result = nil, stop = false]
+            end
+          end.flatten.reject(&:nil?).uniq
+        end
+
+        # Returns an array of sections.
+        #
+        # Sections that belong to other sections will be of the form `section1.childsection`
+        #
+        # @return [Array] Returns an array of section.
+        #
+        def sections
+          Template.recursor(tokens, []) do |token, section|
+            if [:section, :inverted_section].include?(token[1])
+              new_section = (section + [token[2][2][0]])
+              [new_token = token[4], new_section, result = new_section.join("."), stop = false]
+            else
+              [new_token = token, new_section = section, result = nil, stop = false]
+            end
+          end.flatten.reject(&:nil?).uniq
+        end
+
+        # Returns an array of partials.
+        #
+        # Partials that belong to sections are included, but the section name is not preserved
+        #
+        # @return [Array] Returns an array of partials.
+        #
+        def partials
+          Template.recursor(tokens, []) do |token, section|
+            if token[1] == :partial
+              [new_token = token, new_section = section, result = token[2], stop = true]
+            else
+              [new_token = token, new_section = section, result = nil, stop = false]
+            end
+          end.flatten.reject(&:nil?).uniq
+        end
+
+        # Simple recursive iterator for tokens
+        def self.recursor(toks, section, &block)
+          toks.map do |token|
+            next unless token.is_a? Array
+
+            if token.first == :mustache
+              new_token, new_section, result, stop = yield(token, section)
+              [result] + (stop ? [] : recursor(new_token, new_section, &block))
+            else
+              recursor(token, section, &block)
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/braintrust/vendor/mustache/utils.rb b/lib/braintrust/vendor/mustache/utils.rb
new file mode 100644
index 0000000..4975ceb
--- /dev/null
+++ b/lib/braintrust/vendor/mustache/utils.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+# Vendored from mustache gem v1.1.1
+# https://github.com/mustache/mustache
+# License: MIT
+# Modifications: Namespaced under Braintrust::Vendor
+
+module Braintrust
+  module Vendor
+    class Mustache
+      module Utils
+        class String
+          def initialize(string)
+            @string = string
+          end
+
+          def classify
+            @string.split("/").map do |namespace|
+              namespace.split(/[-_]/).map do |part|
+                part[0] = part.chars.first.upcase
+                part
+              end.join
+            end.join("::")
+          end
+
+          def underscore(view_namespace)
+            @string
+              .dup
+              .split("#{view_namespace}::")
+              .last
+              .split("::")
+              .map do |part|
+                part[0] = part[0].downcase
+                part.gsub(/[A-Z]/) { |s| "_" << s.downcase }
+              end
+              .join("/")
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/test/braintrust/api/functions_test.rb b/test/braintrust/api/functions_test.rb
index 753c1d2..5afef0a 100644
--- a/test/braintrust/api/functions_test.rb
+++ b/test/braintrust/api/functions_test.rb
@@ -378,4 +378,93 @@ def test_helper_validates_prompt_data_has_prompt_key
       end
     end
   end
+
+  def test_functions_get_by_id
+    VCR.use_cassette("functions/get") do
+      api = get_test_api
+      # This test verifies that we can get the full function data by ID,
+      # including prompt_data which is needed for Prompt.load()
+      function_slug = "test-ruby-sdk-get-func"
+
+      # Create a function with prompt_data
+      create_response = api.functions.create(
+        project_name: @project_name,
+        slug: function_slug,
+        function_data: {type: "prompt"},
+        prompt_data: {
+          prompt: {
+            type: "chat",
+            messages: [
+              {role: "system", content: "You are a helpful assistant."},
+              {role: "user", content: "Hello {{name}}"}
+            ]
+          },
+          options: {
+            model: "gpt-4o-mini",
+            params: {temperature: 0.7}
+          }
+        }
+      )
+      function_id = create_response["id"]
+
+      # Get the full function data
+      result = api.functions.get(id: function_id)
+
+      assert_instance_of Hash, result
+      assert_equal function_id, result["id"]
+      assert_equal function_slug, result["slug"]
+
+      # Verify prompt_data is included
+      assert result.key?("prompt_data")
+      prompt_data = result["prompt_data"]
+      assert prompt_data.key?("prompt")
+      assert prompt_data["prompt"].key?("messages")
+      assert_equal 2, prompt_data["prompt"]["messages"].length
+
+      # Verify options are included
+      assert prompt_data.key?("options")
+      assert_equal "gpt-4o-mini", prompt_data["options"]["model"]
+
+      # Clean up
+      api.functions.delete(id: function_id)
+    end
+  end
+
+  def test_functions_get_with_version
+    VCR.use_cassette("functions/get_with_version") do
+      api = get_test_api
+      function_slug = "test-ruby-sdk-get-version"
+
+      # Create a function and capture its version (_xact_id)
+      create_response = api.functions.create(
+        project_name: @project_name,
+        slug: function_slug,
+        function_data: {type: "prompt"},
+        prompt_data: {
+          prompt: {
+            type: "chat",
+            messages: [
+              {role: "user", content: "Version test message"}
+            ]
+          },
+          options: {model: "gpt-4o-mini"}
+        }
+      )
+      function_id = create_response["id"]
+      version_id = create_response["_xact_id"]
+
+      assert version_id, "Expected _xact_id in create response"
+
+      # Get the function with explicit version
+      result = api.functions.get(id: function_id, version: version_id)
+
+      assert_instance_of Hash, result
+      assert_equal function_id, result["id"]
+      assert_equal function_slug, result["slug"]
+      assert result.key?("prompt_data")
+
+      # Clean up
+      api.functions.delete(id: function_id)
+    end
+  end
 end
diff --git a/test/braintrust/internal/template_test.rb b/test/braintrust/internal/template_test.rb
new file mode 100644
index 0000000..05981a6
--- /dev/null
+++ b/test/braintrust/internal/template_test.rb
@@ -0,0 +1,261 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "braintrust/internal/template"
+
+class Braintrust::Internal::TemplateTest < Minitest::Test
+  # render - mustache format
+
+  def test_render_substitutes_variables
+    result = Braintrust::Internal::Template.render(
+      "Hello {{name}}, welcome to {{place}}!",
+      {"name" => "Alice", "place" => "Wonderland"},
+      format: "mustache"
+    )
+    assert_equal "Hello Alice, welcome to Wonderland!", result
+  end
+
+  def test_render_with_symbol_keys
+    result = Braintrust::Internal::Template.render(
+      "Hello {{name}}!",
+      {name: "Bob"},
+      format: "mustache"
+    )
+    assert_equal "Hello Bob!", result
+  end
+
+  def test_render_with_nested_variables
+    result = Braintrust::Internal::Template.render(
+      "User: {{user.name}}, Email: {{user.email}}",
+      {"user" => {"name" => "Alice", "email" => "alice@example.com"}},
+      format: "mustache"
+    )
+    assert_equal "User: Alice, Email: alice@example.com", result
+  end
+
+  def test_render_does_not_escape_html_characters
+    # LLM prompts should NOT have HTML escaping applied
+    result = Braintrust::Internal::Template.render(
+      "Code: {{code}}",
+      {"code" => '<script>alert("test")</script> & other < > stuff'},
+      format: "mustache"
+    )
+    assert_includes result, "<script>"
+    assert_includes result, '"test"'
+    assert_includes result, " & "
+  end
+
+  def test_render_preserves_ampersands_and_quotes
+    result = Braintrust::Internal::Template.render(
+      "Search: {{query}}",
+      {"query" => 'foo & bar "baz"'},
+      format: "mustache"
+    )
+    assert_equal 'Search: foo & bar "baz"', result
+  end
+
+  def test_render_missing_variables_become_empty
+    result = Braintrust::Internal::Template.render(
+      "Hello {{name}}, your task is {{task}}.",
+      {"name" => "Alice"},
+      format: "mustache"
+    )
+    assert_equal "Hello Alice, your task is .", result
+  end
+
+  def test_render_returns_non_string_unchanged
+    result = Braintrust::Internal::Template.render(nil, {}, format: "mustache")
+    assert_nil result
+
+    result = Braintrust::Internal::Template.render(123, {}, format: "mustache")
+    assert_equal 123, result
+  end
+
+  # render - strict mode
+
+  def test_render_strict_raises_on_missing_variable
+    error = assert_raises(Braintrust::Error) do
+      Braintrust::Internal::Template.render(
+        "Hello {{name}}, task: {{task}}",
+        {"name" => "Alice"},
+        format: "mustache",
+        strict: true
+      )
+    end
+    assert_match(/missing.*task/i, error.message)
+  end
+
+  def test_render_strict_succeeds_when_all_variables_provided
+    result = Braintrust::Internal::Template.render(
+      "Hello {{name}}!",
+      {"name" => "Alice"},
+      format: "mustache",
+      strict: true
+    )
+    assert_equal "Hello Alice!", result
+  end
+
+  # render - none format
+
+  def test_render_none_returns_unchanged
+    result = Braintrust::Internal::Template.render(
+      "Literal {{braces}} stay as-is",
+      {"braces" => "REPLACED"},
+      format: "none"
+    )
+    assert_equal "Literal {{braces}} stay as-is", result
+  end
+
+  # render - nunjucks format
+
+  def test_render_nunjucks_raises_error
+    error = assert_raises(Braintrust::Error) do
+      Braintrust::Internal::Template.render(
+        "{% if name %}Hello{% endif %}",
+        {"name" => "Alice"},
+        format: "nunjucks"
+      )
+    end
+    assert_match(/nunjucks/i, error.message)
+    assert_match(/not supported/i, error.message)
+  end
+
+  # render - unknown format
+
+  def test_render_unknown_format_raises_error
+    error = assert_raises(Braintrust::Error) do
+      Braintrust::Internal::Template.render(
+        "Hello {{name}}",
+        {"name" => "Alice"},
+        format: "jinja2"
+      )
+    end
+    assert_match(/unknown template format/i, error.message)
+    assert_match(/jinja2/i, error.message)
+  end
+
+  # render - default format (empty/nil)
+
+  def test_render_empty_format_uses_mustache
+    result = Braintrust::Internal::Template.render(
+      "Hello {{name}}!",
+      {"name" => "Alice"},
+      format: ""
+    )
+    assert_equal "Hello Alice!", result
+  end
+
+  def test_render_nil_format_uses_mustache
+    result = Braintrust::Internal::Template.render(
+      "Hello {{name}}!",
+      {"name" => "Alice"},
+      format: nil
+    )
+    assert_equal "Hello Alice!", result
+  end
+
+  # find_missing_variables
+
+  def test_find_missing_variables_returns_missing
+    missing = Braintrust::Internal::Template.find_missing_variables(
+      "Hello {{name}}, task: {{task}}, priority: {{priority}}",
+      {"name" => "Alice"}
+    )
+    assert_includes missing, "task"
+    assert_includes missing, "priority"
+    refute_includes missing, "name"
+  end
+
+  def test_find_missing_variables_returns_empty_when_all_provided
+    missing = Braintrust::Internal::Template.find_missing_variables(
+      "Hello {{name}}!",
+      {"name" => "Alice"}
+    )
+    assert_empty missing
+  end
+
+  def test_find_missing_variables_handles_nested_paths
+    missing = Braintrust::Internal::Template.find_missing_variables(
+      "User: {{user.name}}, Email: {{user.email}}",
+      {"user" => {"name" => "Alice"}}
+    )
+    assert_includes missing, "user.email"
+    refute_includes missing, "user.name"
+  end
+
+  # resolve_variable
+
+  def test_resolve_variable_finds_simple_key
+    result = Braintrust::Internal::Template.resolve_variable(
+      "name",
+      {"name" => "Alice"}
+    )
+    assert_equal "Alice", result
+  end
+
+  def test_resolve_variable_finds_nested_key
+    result = Braintrust::Internal::Template.resolve_variable(
+      "user.profile.name",
+      {"user" => {"profile" => {"name" => "Alice"}}}
+    )
+    assert_equal "Alice", result
+  end
+
+  def test_resolve_variable_returns_nil_for_missing
+    result = Braintrust::Internal::Template.resolve_variable(
+      "missing",
+      {"name" => "Alice"}
+    )
+    assert_nil result
+  end
+
+  def test_resolve_variable_returns_nil_for_partial_path
+    result = Braintrust::Internal::Template.resolve_variable(
+      "user.profile.name",
+      {"user" => {"name" => "Alice"}}
+    )
+    assert_nil result
+  end
+
+  def test_resolve_variable_handles_symbol_keys
+    result = Braintrust::Internal::Template.resolve_variable(
+      "name",
+      {name: "Alice"}
+    )
+    assert_equal "Alice", result
+  end
+
+  # stringify_keys
+
+  def test_stringify_keys_converts_symbols
+    result = Braintrust::Internal::Template.stringify_keys({name: "Alice", age: 30})
+    assert_equal({"name" => "Alice", "age" => 30}, result)
+  end
+
+  def test_stringify_keys_handles_nested_hashes
+    result = Braintrust::Internal::Template.stringify_keys({
+      user: {name: "Alice", profile: {city: "NYC"}}
+    })
+    expected = {"user" => {"name" => "Alice", "profile" => {"city" => "NYC"}}}
+    assert_equal expected, result
+  end
+
+  def test_stringify_keys_returns_empty_hash_for_nil
+    result = Braintrust::Internal::Template.stringify_keys(nil)
+    assert_equal({}, result)
+  end
+
+  def test_stringify_keys_returns_empty_hash_for_non_hash
+    result = Braintrust::Internal::Template.stringify_keys("not a hash")
+    assert_equal({}, result)
+  end
+
+  def test_stringify_keys_preserves_non_hash_values
+    result = Braintrust::Internal::Template.stringify_keys({
+      name: "Alice",
+      scores: [1, 2, 3],
+      active: true
+    })
+    assert_equal({"name" => "Alice", "scores" => [1, 2, 3], "active" => true}, result)
+  end
+end
diff --git a/test/braintrust/prompt_test.rb b/test/braintrust/prompt_test.rb
new file mode 100644
index 0000000..4869d42
--- /dev/null
+++ b/test/braintrust/prompt_test.rb
@@ -0,0 +1,439 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class Braintrust::PromptTest < Minitest::Test
+  def setup
+    # Sample function data as returned by API
+    @function_data = {
+      "id" => "func-123",
+      "name" => "Test Prompt",
+      "slug" => "test-prompt",
+      "project_id" => "proj-456",
+      "prompt_data" => {
+        "prompt" => {
+          "type" => "chat",
+          "messages" => [
+            {"role" => "system", "content" => "You are a helpful assistant."},
+            {"role" => "user", "content" => "Hello {{name}}, please help with {{task}}."}
+          ]
+        },
+        "options" => {
+          "model" => "claude-3-5-sonnet",
+          "params" => {"temperature" => 0.7, "max_tokens" => 1000}
+        }
+      }
+    }
+  end
+
+  def test_prompt_initialization
+    prompt = Braintrust::Prompt.new(@function_data)
+
+    assert_equal "func-123", prompt.id
+    assert_equal "Test Prompt", prompt.name
+    assert_equal "test-prompt", prompt.slug
+    assert_equal "proj-456", prompt.project_id
+  end
+
+  def test_prompt_messages
+    prompt = Braintrust::Prompt.new(@function_data)
+    messages = prompt.messages
+
+    assert_equal 2, messages.length
+    assert_equal "system", messages[0]["role"]
+    assert_equal "You are a helpful assistant.", messages[0]["content"]
+    assert_equal "user", messages[1]["role"]
+  end
+
+  def test_prompt_model
+    prompt = Braintrust::Prompt.new(@function_data)
+
+    assert_equal "claude-3-5-sonnet", prompt.model
+  end
+
+  def test_prompt_options
+    prompt = Braintrust::Prompt.new(@function_data)
+    options = prompt.options
+
+    assert_equal "claude-3-5-sonnet", options["model"]
+    assert_equal 0.7, options["params"]["temperature"]
+    assert_equal 1000, options["params"]["max_tokens"]
+  end
+
+  def test_prompt_raw_returns_prompt_definition
+    prompt = Braintrust::Prompt.new(@function_data)
+    raw = prompt.prompt
+
+    assert_equal "chat", raw["type"]
+    assert raw.key?("messages")
+  end
+
+  def test_build_substitutes_variables
+    prompt = Braintrust::Prompt.new(@function_data)
+    result = prompt.build(name: "Alice", task: "coding")
+
+    assert_equal "claude-3-5-sonnet", result[:model]
+    assert_equal 2, result[:messages].length
+    assert_equal "You are a helpful assistant.", result[:messages][0][:content]
+    assert_equal "Hello Alice, please help with coding.", result[:messages][1][:content]
+  end
+
+  def test_build_with_string_keys
+    prompt = Braintrust::Prompt.new(@function_data)
+    result = prompt.build("name" => "Bob", "task" => "writing")
+
+    assert_equal "Hello Bob, please help with writing.", result[:messages][1][:content]
+  end
+
+  def test_build_includes_params
+    prompt = Braintrust::Prompt.new(@function_data)
+    result = prompt.build(name: "Alice", task: "coding")
+
+    assert_equal 0.7, result[:temperature]
+    assert_equal 1000, result[:max_tokens]
+  end
+
+  def test_build_with_defaults
+    prompt = Braintrust::Prompt.new(@function_data, defaults: {name: "Default User"})
+    result = prompt.build(task: "testing")
+
+    assert_equal "Hello Default User, please help with testing.", result[:messages][1][:content]
+  end
+
+  def test_build_overrides_defaults
+    prompt = Braintrust::Prompt.new(@function_data, defaults: {name: "Default User"})
+    result = prompt.build(name: "Override User", task: "testing")
+
+    assert_equal "Hello Override User, please help with testing.", result[:messages][1][:content]
+  end
+
+  def test_build_strict_raises_on_missing_variable
+    prompt = Braintrust::Prompt.new(@function_data)
+
+    error = assert_raises(Braintrust::Error) do
+      prompt.build({name: "Alice"}, strict: true)
+    end
+
+    assert_match(/missing.*task/i, error.message)
+  end
+
+  def test_build_non_strict_replaces_missing_variables_with_empty
+    # Mustache standard behavior: missing variables become empty strings
+    prompt = Braintrust::Prompt.new(@function_data)
+    result = prompt.build(name: "Alice")
+
+    assert_equal "Hello Alice, please help with .", result[:messages][1][:content]
+  end
+
+  def test_build_handles_nested_variables
+    data = @function_data.dup
+    data["prompt_data"]["prompt"]["messages"] = [
+      {"role" => "user", "content" => "User: {{user.name}}, Email: {{user.email}}"}
+    ]
+    prompt = Braintrust::Prompt.new(data)
+
+    result = prompt.build(user: {name: "Alice", email: "alice@example.com"})
+
+    assert_equal "User: Alice, Email: alice@example.com", result[:messages][0][:content]
+  end
+
+  def test_build_does_not_escape_html_characters
+    # LLM prompts should NOT have HTML escaping applied.
+    # Standard Mustache would turn < into &lt; but we disable this.
+    data = @function_data.dup
+    data["prompt_data"]["prompt"]["messages"] = [
+      {"role" => "user", "content" => "Write code: {{code}}"}
+    ]
+    prompt = Braintrust::Prompt.new(data)
+
+    # These characters would be escaped by standard Mustache
+    code_with_html = '<script>alert("test")</script> & other < > stuff'
+    result = prompt.build(code: code_with_html)
+
+    # Verify NO escaping occurred - raw characters preserved
+    assert_equal "Write code: #{code_with_html}", result[:messages][0][:content]
+    assert_includes result[:messages][0][:content], "<script>"
+    assert_includes result[:messages][0][:content], '"test"'
+    assert_includes result[:messages][0][:content], " & "
+  end
+
+  def test_build_preserves_ampersands_and_quotes
+    # Ampersands and quotes are commonly escaped by HTML escapers
+    data = @function_data.dup
+    data["prompt_data"]["prompt"]["messages"] = [
+      {"role" => "user", "content" => "Search for: {{query}}"}
+    ]
+    prompt = Braintrust::Prompt.new(data)
+
+    result = prompt.build(query: 'foo & bar "baz"')
+
+    # Should be raw, not &amp; or &quot;
+    assert_equal 'Search for: foo & bar "baz"', result[:messages][0][:content]
+  end
+
+  # Template format tests
+
+  def test_template_format_defaults_to_mustache
+    prompt = Braintrust::Prompt.new(@function_data)
+
+    assert_equal "mustache", prompt.template_format
+  end
+
+  def test_template_format_explicit_mustache
+    data = @function_data.dup
+    data["prompt_data"]["template_format"] = "mustache"
+    prompt = Braintrust::Prompt.new(data)
+
+    assert_equal "mustache", prompt.template_format
+
+    # Should render mustache templates
+    result = prompt.build(name: "Alice", task: "coding")
+    assert_equal "Hello Alice, please help with coding.", result[:messages][1][:content]
+  end
+
+  def test_template_format_none_returns_unchanged
+    data = @function_data.dup
+    data["prompt_data"]["template_format"] = "none"
+    data["prompt_data"]["prompt"]["messages"] = [
+      {"role" => "user", "content" => "Literal {{braces}} should stay as-is"}
+    ]
+    prompt = Braintrust::Prompt.new(data)
+
+    assert_equal "none", prompt.template_format
+
+    # Should NOT render - return template unchanged
+    result = prompt.build(braces: "REPLACED")
+    assert_equal "Literal {{braces}} should stay as-is", result[:messages][0][:content]
+  end
+
+  def test_template_format_nunjucks_raises_error
+    data = @function_data.dup
+    data["prompt_data"]["template_format"] = "nunjucks"
+    data["prompt_data"]["prompt"]["messages"] = [
+      {"role" => "user", "content" => "{% if name %}Hello {{name}}{% endif %}"}
+    ]
+    prompt = Braintrust::Prompt.new(data)
+
+    assert_equal "nunjucks", prompt.template_format
+
+    error = assert_raises(Braintrust::Error) do
+      prompt.build(name: "Alice")
+    end
+
+    assert_match(/nunjucks/i, error.message)
+    assert_match(/not supported/i, error.message)
+    assert_match(/ruby sdk/i, error.message)
+  end
+
+  def test_template_format_unknown_raises_error
+    data = @function_data.dup
+    data["prompt_data"]["template_format"] = "jinja2"
+    prompt = Braintrust::Prompt.new(data)
+
+    error = assert_raises(Braintrust::Error) do
+      prompt.build(name: "Alice", task: "coding")
+    end
+
+    assert_match(/unknown template format/i, error.message)
+    assert_match(/jinja2/i, error.message)
+  end
+
+  # Tools tests - basic behavior without schema assumptions
+
+  def test_tools_returns_nil_when_not_defined
+    prompt = Braintrust::Prompt.new(@function_data)
+    assert_nil prompt.tools
+  end
+
+  def test_tools_returns_nil_for_empty_string
+    data = @function_data.dup
+    data["prompt_data"]["prompt"]["tools"] = ""
+    prompt = Braintrust::Prompt.new(data)
+
+    assert_nil prompt.tools
+  end
+
+  def test_tools_returns_nil_for_invalid_json
+    data = @function_data.dup
+    data["prompt_data"]["prompt"]["tools"] = "not valid json"
+    prompt = Braintrust::Prompt.new(data)
+
+    assert_nil prompt.tools
+  end
+
+  def test_build_excludes_tools_when_not_defined
+    prompt = Braintrust::Prompt.new(@function_data)
+    result = prompt.build(name: "Alice", task: "coding")
+
+    refute result.key?(:tools)
+  end
+end
+
+class Braintrust::PromptLoadTest < Minitest::Test
+  def setup
+    flunk "BRAINTRUST_API_KEY not set" unless ENV["BRAINTRUST_API_KEY"]
+    @project_name = "ruby-sdk-test"
+  end
+
+  def get_test_api
+    get_integration_test_api(enable_tracing: false)
+  end
+
+  def test_prompt_load
+    VCR.use_cassette("prompt/load") do
+      api = get_test_api
+      slug = "test-prompt-load"
+
+      # Create a prompt first
+      api.functions.create(
+        project_name: @project_name,
+        slug: slug,
+        function_data: {type: "prompt"},
+        prompt_data: {
+          prompt: {
+            type: "chat",
+            messages: [
+              {role: "user", content: "Say hello to {{name}}"}
+            ]
+          },
+          options: {
+            model: "gpt-4o-mini"
+          }
+        }
+      )
+
+      # Load the prompt using Prompt.load
+      prompt = Braintrust::Prompt.load(project: @project_name, slug: slug, api: api)
+
+      assert_instance_of Braintrust::Prompt, prompt
+      assert_equal slug, prompt.slug
+      assert_equal "gpt-4o-mini", prompt.model
+      assert_equal 1, prompt.messages.length
+
+      # Test build
+      result = prompt.build(name: "World")
+      assert_equal "Say hello to World", result[:messages][0][:content]
+
+      # Clean up
+      api.functions.delete(id: prompt.id)
+    end
+  end
+
+  def test_prompt_load_not_found
+    VCR.use_cassette("prompt/load_not_found") do
+      api = get_test_api
+
+      error = assert_raises(Braintrust::Error) do
+        Braintrust::Prompt.load(project: @project_name, slug: "nonexistent-prompt-xyz", api: api)
+      end
+
+      assert_match(/not found/i, error.message)
+    end
+  end
+
+  def test_prompt_load_with_version
+    VCR.use_cassette("prompt/load_with_version") do
+      api = get_test_api
+      slug = "test-prompt-version"
+
+      # Create a prompt and capture its version (_xact_id)
+      created = api.functions.create(
+        project_name: @project_name,
+        slug: slug,
+        function_data: {type: "prompt"},
+        prompt_data: {
+          prompt: {
+            type: "chat",
+            messages: [
+              {role: "user", content: "Version test: {{name}}"}
+            ]
+          },
+          options: {
+            model: "gpt-4o-mini"
+          }
+        }
+      )
+
+      version_id = created["_xact_id"]
+      assert version_id, "Expected _xact_id in response"
+
+      # Load the prompt with explicit version
+      prompt = Braintrust::Prompt.load(
+        project: @project_name,
+        slug: slug,
+        version: version_id,
+        api: api
+      )
+
+      assert_instance_of Braintrust::Prompt, prompt
+      assert_equal slug, prompt.slug
+      assert_equal "gpt-4o-mini", prompt.model
+
+      # Build and verify content
+      result = prompt.build(name: "World")
+      assert_equal "Version test: World", result[:messages][0][:content]
+
+      # Clean up
+      api.functions.delete(id: prompt.id)
+    end
+  end
+
+  def test_prompt_load_with_tools
+    VCR.use_cassette("prompt/load_with_tools") do
+      api = get_test_api
+      slug = "test-prompt-tools"
+
+      # Tools in OpenAI format - stored as JSON string per API schema
+      tools = [
+        {
+          type: "function",
+          function: {
+            name: "get_weather",
+            description: "Get the current weather in a location",
+            parameters: {
+              type: "object",
+              properties: {
+                location: {type: "string", description: "City name"}
+              },
+              required: ["location"]
+            }
+          }
+        }
+      ]
+
+      # Create a prompt with tools
+      api.functions.create(
+        project_name: @project_name,
+        slug: slug,
+        function_data: {type: "prompt"},
+        prompt_data: {
+          prompt: {
+            type: "chat",
+            messages: [
+              {role: "user", content: "What is the weather in {{city}}?"}
+            ],
+            tools: JSON.dump(tools)
+          },
+          options: {model: "gpt-4o-mini"}
+        }
+      )
+
+      # Load the prompt
+      prompt = Braintrust::Prompt.load(project: @project_name, slug: slug, api: api)
+
+      # Verify tools accessor
+      assert_instance_of Array, prompt.tools
+      assert_equal 1, prompt.tools.length
+      assert_equal "get_weather", prompt.tools[0]["function"]["name"]
+
+      # Build and verify tools are included
+      result = prompt.build(city: "Seattle")
+      assert result.key?(:tools), "Expected build result to include :tools"
+      assert_equal prompt.tools, result[:tools]
+      assert_equal "What is the weather in Seattle?", result[:messages][0][:content]
+
+      # Clean up
+      api.functions.delete(id: prompt.id)
+    end
+  end
+end
diff --git a/test/fixtures/vcr_cassettes/functions/get.yml b/test/fixtures/vcr_cassettes/functions/get.yml
new file mode 100644
index 0000000..908caac
--- /dev/null
+++ b/test/fixtures/vcr_cassettes/functions/get.yml
@@ -0,0 +1,449 @@
+---
+http_interactions:
+- request:
+    method: get
+    uri: https://api.braintrust.dev/v1/function/eaa1d7fa-ddfc-487e-bdf1-8c83c9e5e216
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '650'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:22:45 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 999f045e-52bf-431a-ab23-4231e84c599b
+      X-Bt-Internal-Trace-Id:
+      - 69611d45000000001d09e277b8e05ffb
+      X-Amz-Apigw-Id:
+      - W7GC7HqrIAMEBEQ=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"28a-o+EOs8vizZBvL0+kfKefNOgxPc0"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611d45-406960f37e85c137106930c0;Parent=0943949cf2b37855;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 f8debc28b6c73eb3dc7540e2ac2f0e18.cloudfront.net (CloudFront), 1.1 d9b04a822e1c215374729ec159356140.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - UeZO45ONY1S230A3ccsinel_eSg2umCVj5z3YObzFX1Y_j2Q3IXy6w==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"id":"eaa1d7fa-ddfc-487e-bdf1-8c83c9e5e216","_xact_id":"1000196458014160880","project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","log_id":"p","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","name":"test-ruby-sdk-get-func","slug":"test-ruby-sdk-get-func","description":null,"created":"2026-01-09T15:06:49.196Z","prompt_data":{"prompt":{"type":"chat","messages":[{"role":"system","content":"You
+        are a helpful assistant."},{"role":"user","content":"Hello {{name}}"}]},"options":{"model":"gpt-4o-mini","params":{"temperature":0.7}}},"tags":null,"metadata":null,"function_type":null,"function_data":{"type":"prompt"},"origin":null,"function_schema":null}'
+  recorded_at: Fri, 09 Jan 2026 15:22:45 GMT
+- request:
+    method: delete
+    uri: https://api.braintrust.dev/v1/function/eaa1d7fa-ddfc-487e-bdf1-8c83c9e5e216
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '282'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:22:47 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - b46eee9c-fcb5-4035-897c-fae539611a0e
+      X-Bt-Internal-Trace-Id:
+      - 69611d47000000005cc7572f079de445
+      X-Amz-Apigw-Id:
+      - W7GDKGoaoAMEg5g=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"11a-P+3A9L3licMg9JgEGiq9t1aKens"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611d47-4a348ed101c9c9fc6fdb1b86;Parent=14e14957b2cba183;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 6e202b767e6bdee837ba15ada7e3120e.cloudfront.net (CloudFront), 1.1 b601959712c1f21193a489b5759f70ba.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - VsS0_f9QROIT-ckZpbiAmMpiT6skqE6pHr-hGzREkFyqEXIihNwgNA==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","slug":"test-ruby-sdk-get-func","id":"eaa1d7fa-ddfc-487e-bdf1-8c83c9e5e216","created":"2026-01-09T15:22:47.106Z","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","_object_delete":true,"_xact_id":"1000196458076954719"}'
+  recorded_at: Fri, 09 Jan 2026 15:22:47 GMT
+- request:
+    method: post
+    uri: https://www.braintrust.dev/api/apikey/login
+    body:
+      encoding: UTF-8
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - www.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Access-Control-Allow-Credentials:
+      - 'true'
+      Access-Control-Allow-Headers:
+      - X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5,
+        Content-Type, Date, X-Api-Version
+      Access-Control-Allow-Methods:
+      - GET,OPTIONS,PATCH,DELETE,POST,PUT
+      Access-Control-Allow-Origin:
+      - "*"
+      Cache-Control:
+      - public, max-age=0, must-revalidate
+      Content-Length:
+      - '257'
+      Content-Security-Policy:
+      - 'script-src ''self'' ''unsafe-eval'' ''wasm-unsafe-eval'' ''strict-dynamic''
+        ''nonce-MzQ5OGZkZjYtMmJlOC00NDY2LWE1MzAtODY5N2ViZjI5YzFl''  *.js.stripe.com
+        js.stripe.com maps.googleapis.com ; style-src ''self'' ''unsafe-inline'' *.braintrust.dev
+        btcm6qilbbhv4yi1.public.blob.vercel-storage.com fonts.googleapis.com www.gstatic.com
+        d4tuoctqmanu0.cloudfront.net; font-src ''self'' data: fonts.gstatic.com btcm6qilbbhv4yi1.public.blob.vercel-storage.com
+        cdn.jsdelivr.net d4tuoctqmanu0.cloudfront.net fonts.googleapis.com mintlify-assets.b-cdn.net
+        fonts.cdnfonts.com; object-src ''none''; base-uri ''self''; form-action ''self'';
+        frame-ancestors ''self''; worker-src ''self'' blob:; report-uri https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16;
+        report-to csp-endpoint-0'
+      Content-Type:
+      - application/json; charset=utf-8
+      Date:
+      - Fri, 09 Jan 2026 15:26:29 GMT
+      Etag:
+      - '"ubzjf1iqqj75"'
+      Reporting-Endpoints:
+      - csp-endpoint-0="https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16"
+      Server:
+      - Vercel
+      Strict-Transport-Security:
+      - max-age=63072000
+      X-Clerk-Auth-Message:
+      - Invalid JWT form. A JWT consists of three parts separated by dots. (reason=token-invalid,
+        token-carrier=header)
+      X-Clerk-Auth-Reason:
+      - token-invalid
+      X-Clerk-Auth-Status:
+      - signed-out
+      X-Content-Type-Options:
+      - nosniff
+      X-Frame-Options:
+      - SAMEORIGIN
+      X-Matched-Path:
+      - "/api/apikey/login"
+      X-Nonce:
+      - MzQ5OGZkZjYtMmJlOC00NDY2LWE1MzAtODY5N2ViZjI5YzFl
+      X-Vercel-Cache:
+      - MISS
+      X-Vercel-Id:
+      - iad1::iad1::vhxvp-1767972389112-bcc3207d4501
+    body:
+      encoding: UTF-8
+      string: '{"org_info":[{"id":"5ba6d482-b475-4c66-8cd2-5815694764e3","name":"matt-test-org","api_url":"https://api.braintrust.dev","git_metadata":null,"is_universal_api":null,"proxy_url":"https://api.braintrust.dev","realtime_url":"wss://realtime.braintrustapi.com"}]}'
+  recorded_at: Fri, 09 Jan 2026 15:26:29 GMT
+- request:
+    method: get
+    uri: https://api.braintrust.dev/v1/project?project_name=ruby-sdk-test
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '269'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:26:29 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - df8c7dca-c9f8-4554-bc08-c4003c5faaaa
+      X-Bt-Internal-Trace-Id:
+      - 69611e25000000002d2feed003d7844a
+      X-Amz-Apigw-Id:
+      - W7Gl4FNZIAMET2Q=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"10d-jHt6t+s3DyzhLf+d20I2XKvIjGQ"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611e25-0e71a6817e098cd12d46df1e;Parent=55ae8824648bf68a;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 6e202b767e6bdee837ba15ada7e3120e.cloudfront.net (CloudFront), 1.1 f25b89e7ef738cb8bb7e28e041d8fe54.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - Z8Zuf3NfTPdgGMykdiyvlEx-Hfpr-8BgDvslAhNlF-FBzdse37eiWQ==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"objects":[{"id":"c532bc50-7094-4bbb-8704-42344c9728b9","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","name":"ruby-sdk-test","description":null,"created":"2025-10-22T02:53:49.779Z","deleted_at":null,"user_id":"855483c6-68f0-4df4-a147-df9b4ea32e0c","settings":null}]}'
+  recorded_at: Fri, 09 Jan 2026 15:26:29 GMT
+- request:
+    method: post
+    uri: https://api.braintrust.dev/v1/function
+    body:
+      encoding: UTF-8
+      string: '{"project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","slug":"test-ruby-sdk-get-func","name":"test-ruby-sdk-get-func","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"system","content":"You
+        are a helpful assistant."},{"role":"user","content":"Hello {{name}}"}]},"options":{"model":"gpt-4o-mini","params":{"temperature":0.7}}}}'
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Content-Type:
+      - application/json
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '545'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:26:29 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 601a8e03-eb46-49c4-8d2a-facdecc0274a
+      X-Bt-Internal-Trace-Id:
+      - 69611e25000000004e9aa6fbc35c2222
+      X-Amz-Apigw-Id:
+      - W7Gl8EE0IAMEBuw=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"221-MYmA2S4f3IZPIdPfajiNHs1EESA"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611e25-605279d552cb95a6336cea62;Parent=3d0b812115b7dd19;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 c4d0da6268789cfda9bb5da1f3f8fc58.cloudfront.net (CloudFront), 1.1 537c1727cc67e6d2567bb61ae0478182.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - 5P3DoYCNcIvlRYIrkJ6CQY-dCflpP0eCy6XrAmn2kJObAN6B1_kgsA==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","slug":"test-ruby-sdk-get-func","name":"test-ruby-sdk-get-func","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"system","content":"You
+        are a helpful assistant."},{"role":"user","content":"Hello {{name}}"}]},"options":{"model":"gpt-4o-mini","params":{"temperature":0.7}}},"id":"9c763edd-0474-4034-8869-8bbe307fcd32","created":"2026-01-09T15:26:29.742Z","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","_xact_id":"1000196458091495183"}'
+  recorded_at: Fri, 09 Jan 2026 15:26:29 GMT
+- request:
+    method: get
+    uri: https://api.braintrust.dev/v1/function/9c763edd-0474-4034-8869-8bbe307fcd32
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '650'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:26:30 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 9a293bcc-24ab-4ec0-9b3f-842c0fce7b76
+      X-Bt-Internal-Trace-Id:
+      - 69611e250000000002effecf6f118ea1
+      X-Amz-Apigw-Id:
+      - W7Gl_FW4IAMEI8w=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"28a-dA3pKxLHq2B0teWLcR3HocUdXLs"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611e25-2ebc8ae9137051f60738d543;Parent=66f232e4b293ec11;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 ab734ad5d81cc9d470b6176a05dd968e.cloudfront.net (CloudFront), 1.1 8ca36406fe3aa11c1641e5bc917c8a74.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - vOXNwjsPTHAO-Am1MlqnlLjUiJfihdYMdlRvPf-vQW1B3CP7ogmIAw==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"id":"9c763edd-0474-4034-8869-8bbe307fcd32","_xact_id":"1000196458091495183","project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","log_id":"p","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","name":"test-ruby-sdk-get-func","slug":"test-ruby-sdk-get-func","description":null,"created":"2026-01-09T15:26:29.742Z","prompt_data":{"prompt":{"type":"chat","messages":[{"role":"system","content":"You
+        are a helpful assistant."},{"role":"user","content":"Hello {{name}}"}]},"options":{"model":"gpt-4o-mini","params":{"temperature":0.7}}},"tags":null,"metadata":null,"function_type":null,"function_data":{"type":"prompt"},"origin":null,"function_schema":null}'
+  recorded_at: Fri, 09 Jan 2026 15:26:30 GMT
+- request:
+    method: delete
+    uri: https://api.braintrust.dev/v1/function/9c763edd-0474-4034-8869-8bbe307fcd32
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '282'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:26:30 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - d1b4a95f-c311-4b54-8332-a8d893a10e09
+      X-Bt-Internal-Trace-Id:
+      - 69611e260000000011fd6ec6f9aad01f
+      X-Amz-Apigw-Id:
+      - W7GmDGdooAMERvQ=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"11a-G6BnvsesfXj6YiI3nDotOemHZaM"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611e26-6993aa0d4516e67113188a3e;Parent=7678979c42d17017;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 b5fe18267507cb61755963d8928a60f4.cloudfront.net (CloudFront), 1.1 b601959712c1f21193a489b5759f70ba.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - 8gF7-nfICr1kX_ArRuSfyuBcWIjLCSubLVjOW_gAi3mvyB_fNxsaxw==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","slug":"test-ruby-sdk-get-func","id":"9c763edd-0474-4034-8869-8bbe307fcd32","created":"2026-01-09T15:26:30.444Z","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","_object_delete":true,"_xact_id":"1000196458091561660"}'
+  recorded_at: Fri, 09 Jan 2026 15:26:30 GMT
+recorded_with: VCR 6.4.0
diff --git a/test/fixtures/vcr_cassettes/functions/get_with_version.yml b/test/fixtures/vcr_cassettes/functions/get_with_version.yml
new file mode 100644
index 0000000..a6f4092
--- /dev/null
+++ b/test/fixtures/vcr_cassettes/functions/get_with_version.yml
@@ -0,0 +1,328 @@
+---
+http_interactions:
+- request:
+    method: post
+    uri: https://www.braintrust.dev/api/apikey/login
+    body:
+      encoding: UTF-8
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - www.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Access-Control-Allow-Credentials:
+      - 'true'
+      Access-Control-Allow-Headers:
+      - X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5,
+        Content-Type, Date, X-Api-Version
+      Access-Control-Allow-Methods:
+      - GET,OPTIONS,PATCH,DELETE,POST,PUT
+      Access-Control-Allow-Origin:
+      - "*"
+      Cache-Control:
+      - public, max-age=0, must-revalidate
+      Content-Length:
+      - '395'
+      Content-Security-Policy:
+      - 'script-src ''self'' ''unsafe-eval'' ''wasm-unsafe-eval'' ''strict-dynamic''
+        ''nonce-MmYwZmFiMWQtNjg4NC00YTE2LWE5OTItMzE0ZTg3MGFhNTNh''  *.js.stripe.com
+        js.stripe.com maps.googleapis.com ; style-src ''self'' ''unsafe-inline'' *.braintrust.dev
+        btcm6qilbbhv4yi1.public.blob.vercel-storage.com fonts.googleapis.com www.gstatic.com
+        d4tuoctqmanu0.cloudfront.net; font-src ''self'' data: fonts.gstatic.com btcm6qilbbhv4yi1.public.blob.vercel-storage.com
+        cdn.jsdelivr.net d4tuoctqmanu0.cloudfront.net fonts.googleapis.com mintlify-assets.b-cdn.net
+        fonts.cdnfonts.com; object-src ''none''; base-uri ''self''; form-action ''self'';
+        frame-ancestors ''self''; worker-src ''self'' blob:; report-uri https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16;
+        report-to csp-endpoint-0'
+      Content-Type:
+      - application/json; charset=utf-8
+      Date:
+      - Tue, 03 Feb 2026 16:33:08 GMT
+      Etag:
+      - '"12n7ok4b5phaz"'
+      Reporting-Endpoints:
+      - csp-endpoint-0="https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16"
+      Server:
+      - Vercel
+      Strict-Transport-Security:
+      - max-age=63072000
+      X-Clerk-Auth-Message:
+      - Invalid JWT form. A JWT consists of three parts separated by dots. (reason=token-invalid,
+        token-carrier=header)
+      X-Clerk-Auth-Reason:
+      - token-invalid
+      X-Clerk-Auth-Status:
+      - signed-out
+      X-Content-Type-Options:
+      - nosniff
+      X-Frame-Options:
+      - SAMEORIGIN
+      X-Matched-Path:
+      - "/api/apikey/login"
+      X-Nonce:
+      - MmYwZmFiMWQtNjg4NC00YTE2LWE5OTItMzE0ZTg3MGFhNTNh
+      X-Vercel-Cache:
+      - MISS
+      X-Vercel-Id:
+      - cle1::iad1::ghmxj-1770136388123-be3269ddef3e
+    body:
+      encoding: UTF-8
+      string: '{"org_info":[{"id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"braintrustdata.com","api_url":"https://staging-api.braintrust.dev","git_metadata":{"fields":["commit","branch","tag","author_name","author_email","commit_message","commit_time","dirty"],"collect":"some"},"is_universal_api":true,"proxy_url":"https://staging-api.braintrust.dev","realtime_url":"wss://realtime.braintrustapi.com"}]}'
+  recorded_at: Tue, 03 Feb 2026 16:33:08 GMT
+- request:
+    method: get
+    uri: https://staging-api.braintrust.dev/v1/project?project_name=ruby-sdk-test
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '269'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:33:08 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 458bdb37-c7dd-435d-8b11-880cf64b9c4e
+      X-Bt-Internal-Trace-Id:
+      - 69822344000000003d66a0003e2d8e5c
+      X-Amz-Apigw-Id:
+      - YNpywFagoAMEUiw=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"10d-SEV8zdYyFxsGQVbFPF9yW/SqrIE"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822344-1313d1613b18b7be36fb3789;Parent=08d66bd32e72fe64;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 1f25a64e755f195dbccfdacb5a82a7ce.cloudfront.net (CloudFront), 1.1 7e4c775b563a7a47cbdf48a806a6bd2a.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - z5qWg4SAuaivZsVRtH8qKQSSd1FzU4aOuMdPyk-H1abMXlKwM6uqiQ==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"objects":[{"id":"ac86d18e-af78-4caf-918d-b89ad108ec67","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"ruby-sdk-test","description":null,"created":"2025-10-22T03:32:12.324Z","deleted_at":null,"user_id":"f2ddc4e6-a51a-4a60-9734-9af4ea05c6ef","settings":null}]}'
+  recorded_at: Tue, 03 Feb 2026 16:33:08 GMT
+- request:
+    method: post
+    uri: https://staging-api.braintrust.dev/v1/function
+    body:
+      encoding: UTF-8
+      string: '{"project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","slug":"test-ruby-sdk-get-version","name":"test-ruby-sdk-get-version","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Version
+        test message"}]},"options":{"model":"gpt-4o-mini"}}}'
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Content-Type:
+      - application/json
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '469'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:33:09 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 96c75162-20f9-4e1c-be0d-782d3f07547c
+      X-Bt-Internal-Trace-Id:
+      - 698223440000000036800c79695f4502
+      X-Amz-Apigw-Id:
+      - YNpyyEd4IAMEr3g=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"1d5-EXDd/m5R7AuOv8m7Q9If7CqJm/0"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822344-6d5737ee59077c897584a5e1;Parent=7f672d0dc8bad837;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 ff2cda2997d759f25d189d4bd5288a18.cloudfront.net (CloudFront), 1.1 ed11b381965875f4766a15a39ce86a5a.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - bjsF6cAsgNc1zvIAsWUKMM3qWY5jWp747Xi_Qikk9wTF1xF8FkDbEQ==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","slug":"test-ruby-sdk-get-version","name":"test-ruby-sdk-get-version","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Version
+        test message"}]},"options":{"model":"gpt-4o-mini"}},"id":"51619c9a-c450-4532-9be2-ddc07f667f88","created":"2026-02-03T16:33:08.808Z","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","_xact_id":"1000196599911306390"}'
+  recorded_at: Tue, 03 Feb 2026 16:33:09 GMT
+- request:
+    method: get
+    uri: https://staging-api.braintrust.dev/v1/function/51619c9a-c450-4532-9be2-ddc07f667f88?version=1000196599911306390
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '574'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:33:09 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - fc2331fc-7760-421d-8ef5-81a6844478cb
+      X-Bt-Internal-Trace-Id:
+      - 6982234500000000437008e428860d4c
+      X-Amz-Apigw-Id:
+      - YNpy5H8HIAMEUxQ=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"23e-1wXcVKhMbpJMjZHunom3G8oHbyY"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822345-0dc09d0173d5027d260d4cad;Parent=64a5f852d88955f5;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 c2b321e4bf2baad609809abdec469ff6.cloudfront.net (CloudFront), 1.1 1aba603d822d5b3ffcc843f252edb6ea.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - CJK4qcYkg2yeFO1ZFxLBolJ4-wt-OJl-1OmzbV6adUzCP16R2invFg==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"id":"51619c9a-c450-4532-9be2-ddc07f667f88","_xact_id":"1000196599911306390","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","log_id":"p","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"test-ruby-sdk-get-version","slug":"test-ruby-sdk-get-version","description":null,"created":"2026-02-03T16:33:08.808Z","prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Version
+        test message"}]},"options":{"model":"gpt-4o-mini"}},"tags":null,"metadata":null,"function_type":null,"function_data":{"type":"prompt"},"origin":null,"function_schema":null}'
+  recorded_at: Tue, 03 Feb 2026 16:33:09 GMT
+- request:
+    method: delete
+    uri: https://staging-api.braintrust.dev/v1/function/51619c9a-c450-4532-9be2-ddc07f667f88
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '285'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:33:10 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 9750ea43-9ce6-47a8-a4a3-7b33062e464b
+      X-Bt-Internal-Trace-Id:
+      - 69822345000000003e5cfec1015329e3
+      X-Amz-Apigw-Id:
+      - YNpy-Gx4oAMEh7g=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"11d-TXf4dI6R04Mz+mUFVNDns6262HQ"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822345-190babb759c148332924f5f0;Parent=2b3b7f6f7276be2e;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 ff2cda2997d759f25d189d4bd5288a18.cloudfront.net (CloudFront), 1.1 7e4c775b563a7a47cbdf48a806a6bd2a.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - bH8q5cDjQz8j8jkSIUFRfgUNBx6VUWAkkvD3OSXcTIfyOEqjaBvKuw==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","slug":"test-ruby-sdk-get-version","id":"51619c9a-c450-4532-9be2-ddc07f667f88","created":"2026-02-03T16:33:10.053Z","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","_object_delete":true,"_xact_id":"1000196599911439840"}'
+  recorded_at: Tue, 03 Feb 2026 16:33:10 GMT
+recorded_with: VCR 6.4.0
diff --git a/test/fixtures/vcr_cassettes/prompt/load.yml b/test/fixtures/vcr_cassettes/prompt/load.yml
new file mode 100644
index 0000000..9df95d7
--- /dev/null
+++ b/test/fixtures/vcr_cassettes/prompt/load.yml
@@ -0,0 +1,389 @@
+---
+http_interactions:
+- request:
+    method: post
+    uri: https://www.braintrust.dev/api/apikey/login
+    body:
+      encoding: UTF-8
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - www.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Access-Control-Allow-Credentials:
+      - 'true'
+      Access-Control-Allow-Headers:
+      - X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5,
+        Content-Type, Date, X-Api-Version
+      Access-Control-Allow-Methods:
+      - GET,OPTIONS,PATCH,DELETE,POST,PUT
+      Access-Control-Allow-Origin:
+      - "*"
+      Cache-Control:
+      - public, max-age=0, must-revalidate
+      Content-Length:
+      - '257'
+      Content-Security-Policy:
+      - 'script-src ''self'' ''unsafe-eval'' ''wasm-unsafe-eval'' ''strict-dynamic''
+        ''nonce-MGQzNDRiYjctMzcyZC00ODEzLTg0MmYtYjYwNmFiZWY0Nzc5''  *.js.stripe.com
+        js.stripe.com maps.googleapis.com ; style-src ''self'' ''unsafe-inline'' *.braintrust.dev
+        btcm6qilbbhv4yi1.public.blob.vercel-storage.com fonts.googleapis.com www.gstatic.com
+        d4tuoctqmanu0.cloudfront.net; font-src ''self'' data: fonts.gstatic.com btcm6qilbbhv4yi1.public.blob.vercel-storage.com
+        cdn.jsdelivr.net d4tuoctqmanu0.cloudfront.net fonts.googleapis.com mintlify-assets.b-cdn.net
+        fonts.cdnfonts.com; object-src ''none''; base-uri ''self''; form-action ''self'';
+        frame-ancestors ''self''; worker-src ''self'' blob:; report-uri https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16;
+        report-to csp-endpoint-0'
+      Content-Type:
+      - application/json; charset=utf-8
+      Date:
+      - Fri, 09 Jan 2026 15:31:57 GMT
+      Etag:
+      - '"ubzjf1iqqj75"'
+      Reporting-Endpoints:
+      - csp-endpoint-0="https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16"
+      Server:
+      - Vercel
+      Strict-Transport-Security:
+      - max-age=63072000
+      X-Clerk-Auth-Message:
+      - Invalid JWT form. A JWT consists of three parts separated by dots. (reason=token-invalid,
+        token-carrier=header)
+      X-Clerk-Auth-Reason:
+      - token-invalid
+      X-Clerk-Auth-Status:
+      - signed-out
+      X-Content-Type-Options:
+      - nosniff
+      X-Frame-Options:
+      - SAMEORIGIN
+      X-Matched-Path:
+      - "/api/apikey/login"
+      X-Nonce:
+      - MGQzNDRiYjctMzcyZC00ODEzLTg0MmYtYjYwNmFiZWY0Nzc5
+      X-Vercel-Cache:
+      - MISS
+      X-Vercel-Id:
+      - iad1::iad1::478kl-1767972717018-8f1c4449dd71
+    body:
+      encoding: UTF-8
+      string: '{"org_info":[{"id":"5ba6d482-b475-4c66-8cd2-5815694764e3","name":"matt-test-org","api_url":"https://api.braintrust.dev","git_metadata":null,"is_universal_api":null,"proxy_url":"https://api.braintrust.dev","realtime_url":"wss://realtime.braintrustapi.com"}]}'
+  recorded_at: Fri, 09 Jan 2026 15:31:57 GMT
+- request:
+    method: get
+    uri: https://api.braintrust.dev/v1/project?project_name=ruby-sdk-test
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '269'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:31:57 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 6308ae43-6aef-4e2a-b677-6eeb03896599
+      X-Bt-Internal-Trace-Id:
+      - 69611f6d000000007e25f8ac6b23187b
+      X-Amz-Apigw-Id:
+      - W7HZIGr1IAMEjxA=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"10d-jHt6t+s3DyzhLf+d20I2XKvIjGQ"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611f6d-6e2659e44897bfc601214fab;Parent=168da3c03f62beb4;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 ad22d4e4410fd07809425488bf6e79be.cloudfront.net (CloudFront), 1.1 f391dfb0806f29cccc5f1df3e1ae836e.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - dEzh8blLXvYXHkMRSBV5zi5DiwpekBQFkgXMWtmtiirn4jCsm4dU8w==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"objects":[{"id":"c532bc50-7094-4bbb-8704-42344c9728b9","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","name":"ruby-sdk-test","description":null,"created":"2025-10-22T02:53:49.779Z","deleted_at":null,"user_id":"855483c6-68f0-4df4-a147-df9b4ea32e0c","settings":null}]}'
+  recorded_at: Fri, 09 Jan 2026 15:31:57 GMT
+- request:
+    method: post
+    uri: https://api.braintrust.dev/v1/function
+    body:
+      encoding: UTF-8
+      string: '{"project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","slug":"test-prompt-load","name":"test-prompt-load","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Say
+        hello to {{name}}"}]},"options":{"model":"gpt-4o-mini"}}}'
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Content-Type:
+      - application/json
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '452'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:31:57 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 411104c9-b444-450f-b49c-d7cd030b9b18
+      X-Bt-Internal-Trace-Id:
+      - 69611f6d000000007281a26ff26ab68f
+      X-Amz-Apigw-Id:
+      - W7HZKEbxIAMEDJQ=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"1c4-HTfX1Q46VKOG3lasMWxS8J85LCQ"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611f6d-27b6279359f4794e35dcdbc5;Parent=5158f835fa228c4a;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 6ea9421ec132e3640100792ef9535494.cloudfront.net (CloudFront), 1.1 d3041c3025b9205db460853b5b9626bc.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - hL_HuFng0i2Jeib3N83UPHx5g9XfA0nnGHSST1ARKxpzagyH3dd-2g==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","slug":"test-prompt-load","name":"test-prompt-load","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Say
+        hello to {{name}}"}]},"options":{"model":"gpt-4o-mini"}},"id":"2ee042ed-2971-47f4-a73c-7abe38ab1a38","created":"2026-01-09T15:31:57.524Z","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","_xact_id":"1000196458112984917"}'
+  recorded_at: Fri, 09 Jan 2026 15:31:57 GMT
+- request:
+    method: get
+    uri: https://api.braintrust.dev/v1/function?project_name=ruby-sdk-test&slug=test-prompt-load
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '571'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:31:58 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - af75d70c-ba8f-4244-a61e-fb6e643abd74
+      X-Bt-Internal-Trace-Id:
+      - 69611f6d0000000079da7c9d7c78e29e
+      X-Amz-Apigw-Id:
+      - W7HZNF8ooAMErzg=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"23b-zKRi5DEcuekPd/TsGth74hG9tXw"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611f6d-17dd36184ab7c9202e705efa;Parent=4103abe6bc9216e0;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 6e202b767e6bdee837ba15ada7e3120e.cloudfront.net (CloudFront), 1.1 ef73a156d5c211fdbb7e4231f2a0edca.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - 78ntxSmfza39FAmaCa-exUtRnNXyNWRnHxcQ77_UZoLQ1D-gcWcmHg==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"objects":[{"id":"2ee042ed-2971-47f4-a73c-7abe38ab1a38","_xact_id":"1000196458112984917","project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","log_id":"p","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","name":"test-prompt-load","slug":"test-prompt-load","description":null,"created":"2026-01-09T15:31:57.524Z","prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Say
+        hello to {{name}}"}]},"options":{"model":"gpt-4o-mini"}},"tags":null,"metadata":null,"function_type":null,"function_data":{"type":"prompt"},"origin":null,"function_schema":null}]}'
+  recorded_at: Fri, 09 Jan 2026 15:31:58 GMT
+- request:
+    method: get
+    uri: https://api.braintrust.dev/v1/function/2ee042ed-2971-47f4-a73c-7abe38ab1a38
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '557'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:31:58 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 9e3c6ab3-0160-4a1e-94a9-35ab9f19913e
+      X-Bt-Internal-Trace-Id:
+      - 69611f6e0000000071b8a71148470d4f
+      X-Amz-Apigw-Id:
+      - W7HZTHd7oAMESTw=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"22d-ma3D4t+NO2VLj1JEXruVnj40R7s"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611f6e-71c865c4585fcb7f648bd594;Parent=407f3261d889f0cb;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 f9aa0e4086fcbefc20f307d96a8e3b44.cloudfront.net (CloudFront), 1.1 b601959712c1f21193a489b5759f70ba.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - ccO14e2OKjR_YWWVAAiYlvQ148Mh72XPFQUJP7-mfkXI8h4tmQjX1g==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"id":"2ee042ed-2971-47f4-a73c-7abe38ab1a38","_xact_id":"1000196458112984917","project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","log_id":"p","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","name":"test-prompt-load","slug":"test-prompt-load","description":null,"created":"2026-01-09T15:31:57.524Z","prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Say
+        hello to {{name}}"}]},"options":{"model":"gpt-4o-mini"}},"tags":null,"metadata":null,"function_type":null,"function_data":{"type":"prompt"},"origin":null,"function_schema":null}'
+  recorded_at: Fri, 09 Jan 2026 15:31:58 GMT
+- request:
+    method: delete
+    uri: https://api.braintrust.dev/v1/function/2ee042ed-2971-47f4-a73c-7abe38ab1a38
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '276'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:31:59 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 2fd59f3d-1ab3-4711-a36d-cc8f4a571f38
+      X-Bt-Internal-Trace-Id:
+      - 69611f6e000000006407a3df038879bd
+      X-Amz-Apigw-Id:
+      - W7HZYFE2oAMEF7g=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"114-DQ3SOr2UfgKZ6FbXE8ta7C0iQ+0"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611f6e-4980fe2e0131dc962a5a453b;Parent=21b6b931be060230;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 38bc9c97daf30f968ccac44ef89e14e0.cloudfront.net (CloudFront), 1.1 92672fff57a11d8cf4f64313a69242d0.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - t19MgdmAEgAvifEHWTWB_Eg5GrWxHuhgmBzUCXkGWFh0UPmXSQsLKA==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"c532bc50-7094-4bbb-8704-42344c9728b9","slug":"test-prompt-load","id":"2ee042ed-2971-47f4-a73c-7abe38ab1a38","created":"2026-01-09T15:31:58.990Z","org_id":"5ba6d482-b475-4c66-8cd2-5815694764e3","_object_delete":true,"_xact_id":"1000196458113118216"}'
+  recorded_at: Fri, 09 Jan 2026 15:31:59 GMT
+recorded_with: VCR 6.4.0
diff --git a/test/fixtures/vcr_cassettes/prompt/load_not_found.yml b/test/fixtures/vcr_cassettes/prompt/load_not_found.yml
new file mode 100644
index 0000000..aeafd82
--- /dev/null
+++ b/test/fixtures/vcr_cassettes/prompt/load_not_found.yml
@@ -0,0 +1,143 @@
+---
+http_interactions:
+- request:
+    method: post
+    uri: https://www.braintrust.dev/api/apikey/login
+    body:
+      encoding: UTF-8
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - www.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Access-Control-Allow-Credentials:
+      - 'true'
+      Access-Control-Allow-Headers:
+      - X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5,
+        Content-Type, Date, X-Api-Version
+      Access-Control-Allow-Methods:
+      - GET,OPTIONS,PATCH,DELETE,POST,PUT
+      Access-Control-Allow-Origin:
+      - "*"
+      Cache-Control:
+      - public, max-age=0, must-revalidate
+      Content-Length:
+      - '257'
+      Content-Security-Policy:
+      - 'script-src ''self'' ''unsafe-eval'' ''wasm-unsafe-eval'' ''strict-dynamic''
+        ''nonce-ZDE5MmFhODgtNjU5Ny00OWVmLTgzZjAtNDRmMDJlYTY5MmQ1''  *.js.stripe.com
+        js.stripe.com maps.googleapis.com ; style-src ''self'' ''unsafe-inline'' *.braintrust.dev
+        btcm6qilbbhv4yi1.public.blob.vercel-storage.com fonts.googleapis.com www.gstatic.com
+        d4tuoctqmanu0.cloudfront.net; font-src ''self'' data: fonts.gstatic.com btcm6qilbbhv4yi1.public.blob.vercel-storage.com
+        cdn.jsdelivr.net d4tuoctqmanu0.cloudfront.net fonts.googleapis.com mintlify-assets.b-cdn.net
+        fonts.cdnfonts.com; object-src ''none''; base-uri ''self''; form-action ''self'';
+        frame-ancestors ''self''; worker-src ''self'' blob:; report-uri https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16;
+        report-to csp-endpoint-0'
+      Content-Type:
+      - application/json; charset=utf-8
+      Date:
+      - Fri, 09 Jan 2026 15:32:03 GMT
+      Etag:
+      - '"ubzjf1iqqj75"'
+      Reporting-Endpoints:
+      - csp-endpoint-0="https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16"
+      Server:
+      - Vercel
+      Strict-Transport-Security:
+      - max-age=63072000
+      X-Clerk-Auth-Message:
+      - Invalid JWT form. A JWT consists of three parts separated by dots. (reason=token-invalid,
+        token-carrier=header)
+      X-Clerk-Auth-Reason:
+      - token-invalid
+      X-Clerk-Auth-Status:
+      - signed-out
+      X-Content-Type-Options:
+      - nosniff
+      X-Frame-Options:
+      - SAMEORIGIN
+      X-Matched-Path:
+      - "/api/apikey/login"
+      X-Nonce:
+      - ZDE5MmFhODgtNjU5Ny00OWVmLTgzZjAtNDRmMDJlYTY5MmQ1
+      X-Vercel-Cache:
+      - MISS
+      X-Vercel-Id:
+      - iad1::iad1::c7rlk-1767972723551-c064f07e7248
+    body:
+      encoding: UTF-8
+      string: '{"org_info":[{"id":"5ba6d482-b475-4c66-8cd2-5815694764e3","name":"matt-test-org","api_url":"https://api.braintrust.dev","git_metadata":null,"is_universal_api":null,"proxy_url":"https://api.braintrust.dev","realtime_url":"wss://realtime.braintrustapi.com"}]}'
+  recorded_at: Fri, 09 Jan 2026 15:32:03 GMT
+- request:
+    method: get
+    uri: https://api.braintrust.dev/v1/function?project_name=ruby-sdk-test&slug=nonexistent-prompt-xyz
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '14'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - JFK50-P2
+      - JFK50-P5
+      Date:
+      - Fri, 09 Jan 2026 15:32:03 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - e525a4b0-3de5-43ce-9b4f-fedef9b6d867
+      X-Bt-Internal-Trace-Id:
+      - 69611f73000000005ccf167cee9e9974
+      X-Amz-Apigw-Id:
+      - W7HaJFBAIAMEF8w=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"e-xZKibKAiOxxBbzTm2byfFNRkvtA"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69611f73-2656d761732ae2725b2c54f8;Parent=0f5f3e756009b8f2;Sampled=0;Lineage=1:24be3d11:0
+      Via:
+      - 1.1 ab734ad5d81cc9d470b6176a05dd968e.cloudfront.net (CloudFront), 1.1 baec235d174153a8f2e92ea724643824.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - CcRV9GjE2YYavLYeGWNDevFa9mY2YldGSV-TUg4E5QrLLfsnxL3cJQ==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"objects":[]}'
+  recorded_at: Fri, 09 Jan 2026 15:32:03 GMT
+recorded_with: VCR 6.4.0
diff --git a/test/fixtures/vcr_cassettes/prompt/load_with_tools.yml b/test/fixtures/vcr_cassettes/prompt/load_with_tools.yml
new file mode 100644
index 0000000..74dd701
--- /dev/null
+++ b/test/fixtures/vcr_cassettes/prompt/load_with_tools.yml
@@ -0,0 +1,397 @@
+---
+http_interactions:
+- request:
+    method: post
+    uri: https://www.braintrust.dev/api/apikey/login
+    body:
+      encoding: UTF-8
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - www.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Access-Control-Allow-Credentials:
+      - 'true'
+      Access-Control-Allow-Headers:
+      - X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5,
+        Content-Type, Date, X-Api-Version
+      Access-Control-Allow-Methods:
+      - GET,OPTIONS,PATCH,DELETE,POST,PUT
+      Access-Control-Allow-Origin:
+      - "*"
+      Cache-Control:
+      - public, max-age=0, must-revalidate
+      Content-Length:
+      - '395'
+      Content-Security-Policy:
+      - 'script-src ''self'' ''unsafe-eval'' ''wasm-unsafe-eval'' ''strict-dynamic''
+        ''nonce-ZDFkMGEyMzAtYmU1Zi00ZTE0LWI4MjItYjY3YTNhYWZjMjE5''  *.js.stripe.com
+        js.stripe.com maps.googleapis.com ; style-src ''self'' ''unsafe-inline'' *.braintrust.dev
+        btcm6qilbbhv4yi1.public.blob.vercel-storage.com fonts.googleapis.com www.gstatic.com
+        d4tuoctqmanu0.cloudfront.net; font-src ''self'' data: fonts.gstatic.com btcm6qilbbhv4yi1.public.blob.vercel-storage.com
+        cdn.jsdelivr.net d4tuoctqmanu0.cloudfront.net fonts.googleapis.com mintlify-assets.b-cdn.net
+        fonts.cdnfonts.com; object-src ''none''; base-uri ''self''; form-action ''self'';
+        frame-ancestors ''self''; worker-src ''self'' blob:; report-uri https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16;
+        report-to csp-endpoint-0'
+      Content-Type:
+      - application/json; charset=utf-8
+      Date:
+      - Tue, 03 Feb 2026 16:42:24 GMT
+      Etag:
+      - '"12n7ok4b5phaz"'
+      Reporting-Endpoints:
+      - csp-endpoint-0="https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16"
+      Server:
+      - Vercel
+      Strict-Transport-Security:
+      - max-age=63072000
+      X-Clerk-Auth-Message:
+      - Invalid JWT form. A JWT consists of three parts separated by dots. (reason=token-invalid,
+        token-carrier=header)
+      X-Clerk-Auth-Reason:
+      - token-invalid
+      X-Clerk-Auth-Status:
+      - signed-out
+      X-Content-Type-Options:
+      - nosniff
+      X-Frame-Options:
+      - SAMEORIGIN
+      X-Matched-Path:
+      - "/api/apikey/login"
+      X-Nonce:
+      - ZDFkMGEyMzAtYmU1Zi00ZTE0LWI4MjItYjY3YTNhYWZjMjE5
+      X-Vercel-Cache:
+      - MISS
+      X-Vercel-Id:
+      - cle1::iad1::h84s4-1770136944328-d672984a107e
+    body:
+      encoding: UTF-8
+      string: '{"org_info":[{"id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"braintrustdata.com","api_url":"https://staging-api.braintrust.dev","git_metadata":{"fields":["commit","branch","tag","author_name","author_email","commit_message","commit_time","dirty"],"collect":"some"},"is_universal_api":true,"proxy_url":"https://staging-api.braintrust.dev","realtime_url":"wss://realtime.braintrustapi.com"}]}'
+  recorded_at: Tue, 03 Feb 2026 16:42:24 GMT
+- request:
+    method: get
+    uri: https://staging-api.braintrust.dev/v1/project?project_name=ruby-sdk-test
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '269'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:42:24 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 64ed7b2f-c6af-4fe3-9a5c-dfe27d66375c
+      X-Bt-Internal-Trace-Id:
+      - 698225700000000073d4803fef0b51bd
+      X-Amz-Apigw-Id:
+      - YNrJpH4GoAMEvVw=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"10d-SEV8zdYyFxsGQVbFPF9yW/SqrIE"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822570-02a97bb7600882560cae1380;Parent=04f434b89e4e7c8b;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 a325baefc1f21c1691e3e84bbf7b8906.cloudfront.net (CloudFront), 1.1 e076775a891ac80c1e3adb1434253734.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - jFjTHgK9HY--VEoaSl8Srz9HR0m0L0p5iRwogo4e6lDoakm0mlx20A==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"objects":[{"id":"ac86d18e-af78-4caf-918d-b89ad108ec67","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"ruby-sdk-test","description":null,"created":"2025-10-22T03:32:12.324Z","deleted_at":null,"user_id":"f2ddc4e6-a51a-4a60-9734-9af4ea05c6ef","settings":null}]}'
+  recorded_at: Tue, 03 Feb 2026 16:42:24 GMT
+- request:
+    method: post
+    uri: https://staging-api.braintrust.dev/v1/function
+    body:
+      encoding: UTF-8
+      string: '{"project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","slug":"test-prompt-tools","name":"test-prompt-tools","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"What
+        is the weather in {{city}}?"}],"tools":"[{\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"description\":\"Get
+        the current weather in a location\",\"parameters\":{\"type\":\"object\",\"properties\":{\"location\":{\"type\":\"string\",\"description\":\"City
+        name\"}},\"required\":[\"location\"]}}}]"},"options":{"model":"gpt-4o-mini"}}}'
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Content-Type:
+      - application/json
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '746'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:42:25 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 898ddabf-814d-4d58-b383-2590fb58fe9a
+      X-Bt-Internal-Trace-Id:
+      - 6982257000000000022807ed4476bdfa
+      X-Amz-Apigw-Id:
+      - YNrJrFK6IAMEvXw=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"2ea-LYRoVaHbEKEatY1aVi6aOl18504"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822570-30e10891009922183e64f79e;Parent=7b452c25456c1491;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 597391769ad998307dcc74a3c790e7c6.cloudfront.net (CloudFront), 1.1 8cfefd272d22e2fc7f6429802eca79b0.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - KA3EiiqSY6neuoto7Z3UgBnshyT0zYSSM2jjG6jIfGo0LSbDVUScyw==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","slug":"test-prompt-tools","name":"test-prompt-tools","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"What
+        is the weather in {{city}}?"}],"tools":"[{\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"description\":\"Get
+        the current weather in a location\",\"parameters\":{\"type\":\"object\",\"properties\":{\"location\":{\"type\":\"string\",\"description\":\"City
+        name\"}},\"required\":[\"location\"]}}}]"},"options":{"model":"gpt-4o-mini"}},"id":"54bf3889-e339-4869-9dea-2d9524fc0540","created":"2026-02-03T16:42:24.919Z","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","_xact_id":"1000196599947750956"}'
+  recorded_at: Tue, 03 Feb 2026 16:42:25 GMT
+- request:
+    method: get
+    uri: https://staging-api.braintrust.dev/v1/function?project_name=ruby-sdk-test&slug=test-prompt-tools
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '865'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:42:26 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 56c51e8b-f77b-4175-aba3-83aae0476841
+      X-Bt-Internal-Trace-Id:
+      - 69822571000000003e48a514d09e88a5
+      X-Amz-Apigw-Id:
+      - YNrJyHh0oAMETAw=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"361-O3S4Sbw84UNJFYmmKW8EAmWnk28"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822571-6fb5640633651db97d7df84c;Parent=478ef94a42d603d5;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 597391769ad998307dcc74a3c790e7c6.cloudfront.net (CloudFront), 1.1 784ffc262e0c17e3566b62b0f85f34d0.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - gH9jk_MH0CT3lTYjHOmUVdzWAW4RkpI9WaSUBZsoPeGNeHl4wRx_NQ==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"objects":[{"id":"54bf3889-e339-4869-9dea-2d9524fc0540","_xact_id":"1000196599947750956","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","log_id":"p","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"test-prompt-tools","slug":"test-prompt-tools","description":null,"created":"2026-02-03T16:42:24.919Z","prompt_data":{"prompt":{"type":"chat","tools":"[{\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"description\":\"Get
+        the current weather in a location\",\"parameters\":{\"type\":\"object\",\"properties\":{\"location\":{\"type\":\"string\",\"description\":\"City
+        name\"}},\"required\":[\"location\"]}}}]","messages":[{"role":"user","content":"What
+        is the weather in {{city}}?"}]},"options":{"model":"gpt-4o-mini"}},"tags":null,"metadata":null,"function_type":null,"function_data":{"type":"prompt"},"origin":null,"function_schema":null}]}'
+  recorded_at: Tue, 03 Feb 2026 16:42:26 GMT
+- request:
+    method: get
+    uri: https://staging-api.braintrust.dev/v1/function/54bf3889-e339-4869-9dea-2d9524fc0540
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '851'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:42:26 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 05d3c865-33f7-4adc-b255-8e3ea2e06338
+      X-Bt-Internal-Trace-Id:
+      - 6982257200000000624807f7fb72df2b
+      X-Amz-Apigw-Id:
+      - YNrJ5HcmoAMEBGw=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"353-R0sY6kMiNsBCrx543jboP5r6O70"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822572-5d8d21811e4871550e692e44;Parent=28e49ed67466dc55;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 7d742df65452f74d1ef6daa93f595db8.cloudfront.net (CloudFront), 1.1 788c5a18883f334d0b09e6cda9d22c86.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - 6TwiapmAgQoawdDSZ19MIkBCKmI-WW7woUQePg50ENerX416PMFdYA==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"id":"54bf3889-e339-4869-9dea-2d9524fc0540","_xact_id":"1000196599947750956","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","log_id":"p","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"test-prompt-tools","slug":"test-prompt-tools","description":null,"created":"2026-02-03T16:42:24.919Z","prompt_data":{"prompt":{"type":"chat","tools":"[{\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"description\":\"Get
+        the current weather in a location\",\"parameters\":{\"type\":\"object\",\"properties\":{\"location\":{\"type\":\"string\",\"description\":\"City
+        name\"}},\"required\":[\"location\"]}}}]","messages":[{"role":"user","content":"What
+        is the weather in {{city}}?"}]},"options":{"model":"gpt-4o-mini"}},"tags":null,"metadata":null,"function_type":null,"function_data":{"type":"prompt"},"origin":null,"function_schema":null}'
+  recorded_at: Tue, 03 Feb 2026 16:42:26 GMT
+- request:
+    method: delete
+    uri: https://staging-api.braintrust.dev/v1/function/54bf3889-e339-4869-9dea-2d9524fc0540
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '277'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:42:27 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - db1d0f4b-0533-4584-8d62-b30b3afc176f
+      X-Bt-Internal-Trace-Id:
+      - 69822572000000002917c3a08e258b31
+      X-Amz-Apigw-Id:
+      - YNrJ-Hm_IAMEjXA=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"115-DyUp6466yAVGFZroE14vpI62SXI"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822572-49dedce72c152701310955c8;Parent=282dd59264c300c8;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 597391769ad998307dcc74a3c790e7c6.cloudfront.net (CloudFront), 1.1 a325baefc1f21c1691e3e84bbf7b8906.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - 2VzPBA3zxdDfWmKlG9iU57yS_fHYINtWuSGjxebGgeSrXvPienHA6A==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","slug":"test-prompt-tools","id":"54bf3889-e339-4869-9dea-2d9524fc0540","created":"2026-02-03T16:42:26.748Z","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","_object_delete":true,"_xact_id":"1000196599947884626"}'
+  recorded_at: Tue, 03 Feb 2026 16:42:27 GMT
+recorded_with: VCR 6.4.0
diff --git a/test/fixtures/vcr_cassettes/prompt/load_with_version.yml b/test/fixtures/vcr_cassettes/prompt/load_with_version.yml
new file mode 100644
index 0000000..3befff3
--- /dev/null
+++ b/test/fixtures/vcr_cassettes/prompt/load_with_version.yml
@@ -0,0 +1,389 @@
+---
+http_interactions:
+- request:
+    method: post
+    uri: https://www.braintrust.dev/api/apikey/login
+    body:
+      encoding: UTF-8
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - www.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Access-Control-Allow-Credentials:
+      - 'true'
+      Access-Control-Allow-Headers:
+      - X-CSRF-Token, X-Requested-With, Accept, Accept-Version, Content-Length, Content-MD5,
+        Content-Type, Date, X-Api-Version
+      Access-Control-Allow-Methods:
+      - GET,OPTIONS,PATCH,DELETE,POST,PUT
+      Access-Control-Allow-Origin:
+      - "*"
+      Cache-Control:
+      - public, max-age=0, must-revalidate
+      Content-Length:
+      - '395'
+      Content-Security-Policy:
+      - 'script-src ''self'' ''unsafe-eval'' ''wasm-unsafe-eval'' ''strict-dynamic''
+        ''nonce-NDk0M2EwZTYtM2M0YS00N2Y3LWFlMTEtNzVhMzA1MjZiNGFl''  *.js.stripe.com
+        js.stripe.com maps.googleapis.com ; style-src ''self'' ''unsafe-inline'' *.braintrust.dev
+        btcm6qilbbhv4yi1.public.blob.vercel-storage.com fonts.googleapis.com www.gstatic.com
+        d4tuoctqmanu0.cloudfront.net; font-src ''self'' data: fonts.gstatic.com btcm6qilbbhv4yi1.public.blob.vercel-storage.com
+        cdn.jsdelivr.net d4tuoctqmanu0.cloudfront.net fonts.googleapis.com mintlify-assets.b-cdn.net
+        fonts.cdnfonts.com; object-src ''none''; base-uri ''self''; form-action ''self'';
+        frame-ancestors ''self''; worker-src ''self'' blob:; report-uri https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16;
+        report-to csp-endpoint-0'
+      Content-Type:
+      - application/json; charset=utf-8
+      Date:
+      - Tue, 03 Feb 2026 16:27:59 GMT
+      Etag:
+      - '"12n7ok4b5phaz"'
+      Reporting-Endpoints:
+      - csp-endpoint-0="https://o4507221741076480.ingest.us.sentry.io/api/4507221754380288/security/?sentry_key=27fa5ac907cf7c6ce4a1ab2a03f805b4&sentry_environment=production&sentry_release=16"
+      Server:
+      - Vercel
+      Strict-Transport-Security:
+      - max-age=63072000
+      X-Clerk-Auth-Message:
+      - Invalid JWT form. A JWT consists of three parts separated by dots. (reason=token-invalid,
+        token-carrier=header)
+      X-Clerk-Auth-Reason:
+      - token-invalid
+      X-Clerk-Auth-Status:
+      - signed-out
+      X-Content-Type-Options:
+      - nosniff
+      X-Frame-Options:
+      - SAMEORIGIN
+      X-Matched-Path:
+      - "/api/apikey/login"
+      X-Nonce:
+      - NDk0M2EwZTYtM2M0YS00N2Y3LWFlMTEtNzVhMzA1MjZiNGFl
+      X-Vercel-Cache:
+      - MISS
+      X-Vercel-Id:
+      - cle1::iad1::l8kjr-1770136079348-08771e3e847b
+    body:
+      encoding: UTF-8
+      string: '{"org_info":[{"id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"braintrustdata.com","api_url":"https://staging-api.braintrust.dev","git_metadata":{"fields":["commit","branch","tag","author_name","author_email","commit_message","commit_time","dirty"],"collect":"some"},"is_universal_api":true,"proxy_url":"https://staging-api.braintrust.dev","realtime_url":"wss://realtime.braintrustapi.com"}]}'
+  recorded_at: Tue, 03 Feb 2026 16:27:59 GMT
+- request:
+    method: get
+    uri: https://staging-api.braintrust.dev/v1/project?project_name=ruby-sdk-test
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '269'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:27:59 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - '011186a0-0fb2-4634-bc00-95af84cf3343'
+      X-Bt-Internal-Trace-Id:
+      - 6982220f000000003c26a0c34f0470ae
+      X-Amz-Apigw-Id:
+      - YNpCgHGaIAMEh_g=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"10d-SEV8zdYyFxsGQVbFPF9yW/SqrIE"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-6982220f-24cc6cc24f85645b30a5c468;Parent=0654b02348779b8a;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 7d742df65452f74d1ef6daa93f595db8.cloudfront.net (CloudFront), 1.1 eb377f5086ebfe1cf72cecf255a055ac.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - 659ozGzduTOLgQjEvY1CUHaGiZ8qWTG-5CC22P6BzmgmoRkpX4sn0Q==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"objects":[{"id":"ac86d18e-af78-4caf-918d-b89ad108ec67","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"ruby-sdk-test","description":null,"created":"2025-10-22T03:32:12.324Z","deleted_at":null,"user_id":"f2ddc4e6-a51a-4a60-9734-9af4ea05c6ef","settings":null}]}'
+  recorded_at: Tue, 03 Feb 2026 16:27:59 GMT
+- request:
+    method: post
+    uri: https://staging-api.braintrust.dev/v1/function
+    body:
+      encoding: UTF-8
+      string: '{"project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","slug":"test-prompt-version","name":"test-prompt-version","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Version
+        test: {{name}}"}]},"options":{"model":"gpt-4o-mini"}}}'
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Content-Type:
+      - application/json
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '459'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:28:00 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 1163b7e1-fedc-4625-b894-2f07340664e4
+      X-Bt-Internal-Trace-Id:
+      - 6982220f00000000761b361d77c86ede
+      X-Amz-Apigw-Id:
+      - YNpCiGaCoAMEtNQ=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"1cb-HOafIp8cLL2WM5C1XzbOXaTM8cs"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-6982220f-463a656e25da7fc85b393b23;Parent=4620d658222ee05c;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 ea4a33625617615e13496b292edda6d6.cloudfront.net (CloudFront), 1.1 0a864429e4c3205f41fe9901ea675d26.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - pqUODqWhWTDArZe979C6DS6H4ioLhfm_PA-GUclt1HKhRMdWlK86_g==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","slug":"test-prompt-version","name":"test-prompt-version","function_data":{"type":"prompt"},"prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Version
+        test: {{name}}"}]},"options":{"model":"gpt-4o-mini"}},"id":"688afbf1-2138-4b26-83c4-0ae9c5ff18f3","created":"2026-02-03T16:27:59.956Z","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","_xact_id":"1000196599891140962"}'
+  recorded_at: Tue, 03 Feb 2026 16:28:00 GMT
+- request:
+    method: get
+    uri: https://staging-api.braintrust.dev/v1/function?project_name=ruby-sdk-test&slug=test-prompt-version
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '578'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:28:01 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 46b9edb0-b604-4457-8f05-3c4eeb5b42cc
+      X-Bt-Internal-Trace-Id:
+      - 69822210000000006e8e7b10d1aea3d7
+      X-Amz-Apigw-Id:
+      - YNpCpE8HoAMEvwg=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"242-lXp8Iw1uJp0p+kj/h9BNJF+gKls"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822210-79e7075e502b51fa5bef8186;Parent=7dd3fbe5f74712d0;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 7d742df65452f74d1ef6daa93f595db8.cloudfront.net (CloudFront), 1.1 784ffc262e0c17e3566b62b0f85f34d0.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - ULGFrn5On5yV4Z_QRBLWik3Eti8Hs7Bxj4pgsgd3pm3FIsCGlYZi5A==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"objects":[{"id":"688afbf1-2138-4b26-83c4-0ae9c5ff18f3","_xact_id":"1000196599891140962","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","log_id":"p","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"test-prompt-version","slug":"test-prompt-version","description":null,"created":"2026-02-03T16:27:59.956Z","prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Version
+        test: {{name}}"}]},"options":{"model":"gpt-4o-mini"}},"tags":null,"metadata":null,"function_type":null,"function_data":{"type":"prompt"},"origin":null,"function_schema":null}]}'
+  recorded_at: Tue, 03 Feb 2026 16:28:01 GMT
+- request:
+    method: get
+    uri: https://staging-api.braintrust.dev/v1/function/688afbf1-2138-4b26-83c4-0ae9c5ff18f3?version=1000196599891140962
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '564'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:28:01 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 90cdb81b-df18-42cb-902b-fff81078a6bd
+      X-Bt-Internal-Trace-Id:
+      - 69822211000000002386aaf7bfc14b99
+      X-Amz-Apigw-Id:
+      - YNpCvHNMIAMEdYw=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"234-4hFqSCp1semAPAQ5IIwmnQAzn5w"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822211-4077df0b132ec38a3447312c;Parent=26b77a22cb47f50a;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 7d742df65452f74d1ef6daa93f595db8.cloudfront.net (CloudFront), 1.1 d250acc8f0df4d0f6cf0c8da374c8b8e.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - 9ASx7SGX48NXo-vT80dGwGGu_s_V4-QqPRHW-P4A101GElFY5sxOAg==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"id":"688afbf1-2138-4b26-83c4-0ae9c5ff18f3","_xact_id":"1000196599891140962","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","log_id":"p","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","name":"test-prompt-version","slug":"test-prompt-version","description":null,"created":"2026-02-03T16:27:59.956Z","prompt_data":{"prompt":{"type":"chat","messages":[{"role":"user","content":"Version
+        test: {{name}}"}]},"options":{"model":"gpt-4o-mini"}},"tags":null,"metadata":null,"function_type":null,"function_data":{"type":"prompt"},"origin":null,"function_schema":null}'
+  recorded_at: Tue, 03 Feb 2026 16:28:01 GMT
+- request:
+    method: delete
+    uri: https://staging-api.braintrust.dev/v1/function/688afbf1-2138-4b26-83c4-0ae9c5ff18f3
+    body:
+      encoding: US-ASCII
+      string: ''
+    headers:
+      Accept-Encoding:
+      - gzip;q=1.0,deflate;q=0.6,identity;q=0.3
+      Accept:
+      - "*/*"
+      User-Agent:
+      - Ruby
+      Host:
+      - staging-api.braintrust.dev
+      Authorization:
+      - Bearer <BRAINTRUST_API_KEY>
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Content-Type:
+      - application/json; charset=utf-8
+      Content-Length:
+      - '279'
+      Connection:
+      - keep-alive
+      X-Amz-Cf-Pop:
+      - CMH68-P1
+      - CMH68-P1
+      Date:
+      - Tue, 03 Feb 2026 16:28:02 GMT
+      Access-Control-Allow-Credentials:
+      - 'true'
+      X-Amzn-Requestid:
+      - 46c9d966-a18d-4f27-843a-a8b54e14b404
+      X-Bt-Internal-Trace-Id:
+      - 69822211000000002299cfa4323934bf
+      X-Amz-Apigw-Id:
+      - YNpC0FuYoAMETAw=
+      Vary:
+      - Origin, Accept-Encoding
+      Etag:
+      - W/"117-C2YbqIF11ONeL97loSFeQl9ViCI"
+      Access-Control-Expose-Headers:
+      - x-bt-cursor,x-bt-found-existing,x-bt-query-plan
+      X-Amzn-Trace-Id:
+      - Root=1-69822211-0eb3ef63003280cb41e086b6;Parent=674223659ffb9119;Sampled=0;Lineage=1:fc3b4ff1:0
+      Via:
+      - 1.1 ea4a33625617615e13496b292edda6d6.cloudfront.net (CloudFront), 1.1 9c05c6d9d9e659ba5e3eeea02120bf34.cloudfront.net
+        (CloudFront)
+      X-Cache:
+      - Miss from cloudfront
+      X-Amz-Cf-Id:
+      - IJHrfGSMjXuuGZzMGIaPA2PAMCGURCjdtZppidV4mqh99i919fERBw==
+    body:
+      encoding: ASCII-8BIT
+      string: '{"log_id":"p","project_id":"ac86d18e-af78-4caf-918d-b89ad108ec67","slug":"test-prompt-version","id":"688afbf1-2138-4b26-83c4-0ae9c5ff18f3","created":"2026-02-03T16:28:01.929Z","org_id":"5d7c97d7-fef1-4cb7-bda6-7e3756a0ca8e","_object_delete":true,"_xact_id":"1000196599891209069"}'
+  recorded_at: Tue, 03 Feb 2026 16:28:02 GMT
+recorded_with: VCR 6.4.0
diff --git a/test/support/braintrust_helper.rb b/test/support/braintrust_helper.rb
index e5e8002..b5ff6c0 100644
--- a/test/support/braintrust_helper.rb
+++ b/test/support/braintrust_helper.rb
@@ -64,6 +64,15 @@ def get_integration_test_state(**options)
         Braintrust.init(set_global: false, blocking_login: true, **options)
       end
 
+      # Creates an API client for integration tests (without polluting global state)
+      # This is the preferred way to get an API client for tests.
+      # @param options [Hash] Options to pass to get_integration_test_state
+      # @return [Braintrust::API]
+      def get_integration_test_api(**options)
+        state = get_integration_test_state(**options)
+        Braintrust::API.new(state: state)
+      end
+
       # Helper to run eval internally without API calls for testing
       def run_test_eval(experiment_id:, experiment_name:, project_id:, project_name:,
         cases:, task:, scorers:, state:, parallelism: 1, tracer_provider: nil)