diff --git a/lib/braintrust.rb b/lib/braintrust.rb
index 7a61327..496fc22 100644
--- a/lib/braintrust.rb
+++ b/lib/braintrust.rb
@@ -6,7 +6,7 @@
 require_relative "braintrust/trace"
 require_relative "braintrust/api"
 require_relative "braintrust/prompt"
-require_relative "braintrust/internal/experiments"
+require_relative "braintrust/dataset"
 require_relative "braintrust/internal/env"
 require_relative "braintrust/eval"
 require_relative "braintrust/contrib"
diff --git a/lib/braintrust/api.rb b/lib/braintrust/api.rb
index 824c362..d808537 100644
--- a/lib/braintrust/api.rb
+++ b/lib/braintrust/api.rb
@@ -25,5 +25,22 @@ def datasets
     def functions
       @functions ||= API::Functions.new(self)
     end
+
+    # Login to Braintrust API (idempotent)
+    # @return [self]
+    def login
+      @state.login
+      self
+    end
+
+    # Generate a permalink URL to view an object in the Braintrust UI
+    # This is for the /object endpoint (experiments, datasets, etc.)
+    # For trace span permalinks, use Trace.permalink instead.
+    # @param object_type [String] Type of object (e.g., "experiment", "dataset")
+    # @param object_id [String] Object UUID
+    # @return [String] Permalink URL
+    def object_permalink(object_type:, object_id:)
+      @state.object_permalink(object_type: object_type, object_id: object_id)
+    end
   end
 end
diff --git a/lib/braintrust/api/datasets.rb b/lib/braintrust/api/datasets.rb
index 44553f1..120d0f7 100644
--- a/lib/braintrust/api/datasets.rb
+++ b/lib/braintrust/api/datasets.rb
@@ -85,7 +85,7 @@ def insert(id:, events:)
       # @param id [String] Dataset UUID
       # @return [String] Permalink URL
       def permalink(id:)
-        "#{@state.app_url}/app/#{@state.org_name}/object?object_type=dataset&object_id=#{id}"
+        @state.object_permalink(object_type: "dataset", object_id: id)
       end
 
       # Fetch records from dataset using BTQL
diff --git a/lib/braintrust/api/internal/experiments.rb b/lib/braintrust/api/internal/experiments.rb
new file mode 100644
index 0000000..9c09f92
--- /dev/null
+++ b/lib/braintrust/api/internal/experiments.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+require "net/http"
+require "json"
+require "uri"
+
+module Braintrust
+  class API
+    module Internal
+      # Internal Experiments API
+      # Not part of the public API - use through Eval.run
+      class Experiments
+        def initialize(state)
+          @state = state
+        end
+
+        # Create an experiment
+        # POST /v1/experiment
+        # @param name [String] Experiment name
+        # @param project_id [String] Project ID
+        # @param ensure_new [Boolean] If true (default), fail if exists; if false, return existing
+        # @param tags [Array<String>, nil] Optional tags
+        # @param metadata [Hash, nil] Optional metadata
+        # @return [Hash] Experiment data with "id", "name", "project_id", etc.
+        def create(name:, project_id:, ensure_new: true, tags: nil, metadata: nil)
+          uri = URI("#{@state.api_url}/v1/experiment")
+
+          payload = {
+            project_id: project_id,
+            name: name,
+            ensure_new: ensure_new
+          }
+          payload[:tags] = tags if tags
+          payload[:metadata] = metadata if metadata
+
+          request = Net::HTTP::Post.new(uri)
+          request["Content-Type"] = "application/json"
+          request["Authorization"] = "Bearer #{@state.api_key}"
+          request.body = JSON.dump(payload)
+
+          http = Net::HTTP.new(uri.host, uri.port)
+          http.use_ssl = (uri.scheme == "https")
+          response = http.request(request)
+
+          unless response.is_a?(Net::HTTPSuccess)
+            raise Error, "HTTP #{response.code} for POST #{uri}: #{response.body}"
+          end
+
+          JSON.parse(response.body)
+        end
+      end
+    end
+  end
+end
diff --git a/lib/braintrust/api/internal/projects.rb b/lib/braintrust/api/internal/projects.rb
new file mode 100644
index 0000000..4995a68
--- /dev/null
+++ b/lib/braintrust/api/internal/projects.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+require "net/http"
+require "json"
+require "uri"
+
+module Braintrust
+  class API
+    module Internal
+      # Internal Projects API
+      # Not part of the public API - use through Eval.run
+      class Projects
+        def initialize(state)
+          @state = state
+        end
+
+        # Create or get a project by name (idempotent)
+        # POST /v1/project
+        # @param name [String] Project name
+        # @return [Hash] Project data with "id", "name", "org_id", etc.
+        def create(name:)
+          uri = URI("#{@state.api_url}/v1/project")
+
+          request = Net::HTTP::Post.new(uri)
+          request["Content-Type"] = "application/json"
+          request["Authorization"] = "Bearer #{@state.api_key}"
+          request.body = JSON.dump({name: name})
+
+          http = Net::HTTP.new(uri.host, uri.port)
+          http.use_ssl = (uri.scheme == "https")
+          response = http.request(request)
+
+          unless response.is_a?(Net::HTTPSuccess)
+            raise Error, "HTTP #{response.code} for POST #{uri}: #{response.body}"
+          end
+
+          JSON.parse(response.body)
+        end
+      end
+    end
+  end
+end
diff --git a/lib/braintrust/dataset.rb b/lib/braintrust/dataset.rb
new file mode 100644
index 0000000..f6abb78
--- /dev/null
+++ b/lib/braintrust/dataset.rb
@@ -0,0 +1,185 @@
+# frozen_string_literal: true
+
+require_relative "api"
+require_relative "internal/origin"
+
+module Braintrust
+  # High-level interface for working with Braintrust datasets.
+  # Provides both eager loading and lazy enumeration for efficient access to dataset records.
+  #
+  # @example Basic usage (uses global state)
+  #   Braintrust.init(api_key: "...")
+  #   dataset = Braintrust::Dataset.new(name: "my-dataset", project: "my-project")
+  #   dataset.each { |record| puts record[:input] }
+  #
+  # @example With explicit API client
+  #   api = Braintrust::API.new(state: my_state)
+  #   dataset = Braintrust::Dataset.new(name: "my-dataset", project: "my-project", api: api)
+  #
+  # @example Eager loading for small datasets
+  #   records = dataset.fetch_all(limit: 100)
+  #
+  # @example Using Enumerable methods
+  #   dataset.take(10)
+  #   dataset.select { |r| r[:tags]&.include?("important") }
+  #
+  # @example With version pinning
+  #   dataset = Braintrust::Dataset.new(name: "my-dataset", project: "my-project", version: "1.0")
+  class Dataset
+    include Enumerable
+
+    # Default number of records to fetch per API page
+    DEFAULT_PAGE_SIZE = 1000
+
+    attr_reader :name, :project, :version
+
+    # Initialize a dataset reference
+    # @param name [String, nil] Dataset name (required if id not provided)
+    # @param id [String, nil] Dataset UUID (required if name not provided)
+    # @param project [String, nil] Project name (required if using name)
+    # @param version [String, nil] Optional version to pin to
+    # @param api [API, nil] Braintrust API client (defaults to API.new using global state)
+    def initialize(name: nil, id: nil, project: nil, version: nil, api: nil)
+      @name = name
+      @provided_id = id
+      @project = project
+      @version = version
+      @api = api || API.new
+      @resolved_id = nil
+      @metadata = nil
+
+      validate_params!
+    end
+
+    # Get the dataset ID, resolving from name if necessary
+    # @return [String] Dataset UUID
+    def id
+      return @provided_id if @provided_id
+      resolve_name! unless @resolved_id
+      @resolved_id
+    end
+
+    # Get the dataset metadata from the API
+    # Makes an API call if metadata hasn't been fetched yet.
+    # Note: When initialized with name, metadata is fetched during name resolution.
+    # When initialized with ID, this triggers a separate get_by_id call.
+    # @return [Hash] Dataset metadata including name, description, created, etc.
+    def metadata
+      fetch_metadata! unless @metadata
+      @metadata
+    end
+
+    # Fetch all records eagerly into an array
+    # @param limit [Integer, nil] Maximum records to return (nil for all)
+    # @return [Array<Hash>] Array of records with :input, :expected, :tags, :metadata, :origin
+    def fetch_all(limit: nil)
+      records = []
+      each_record(limit: limit) { |record| records << record }
+      records
+    end
+
+    # Iterate over records lazily (implements Enumerable)
+    # Fetches pages on demand for memory efficiency with large datasets.
+    # @yield [Hash] Each record with :input, :expected, :tags, :metadata, :origin
+    def each(&block)
+      return enum_for(:each) unless block_given?
+      each_record(&block)
+    end
+
+    private
+
+    def validate_params!
+      if @provided_id.nil? && @name.nil?
+        raise ArgumentError, "must specify either :name or :id"
+      end
+
+      if @name && @project.nil?
+        raise ArgumentError, ":project is required when using :name"
+      end
+    end
+
+    # Resolve dataset name to ID (also fetches metadata as side effect)
+    def resolve_name!
+      @metadata = @api.datasets.get(project_name: @project, name: @name)
+      @resolved_id = @metadata["id"]
+    end
+
+    # Fetch metadata explicitly (for when ID was provided directly)
+    def fetch_metadata!
+      if @provided_id
+        @metadata = @api.datasets.get_by_id(id: @provided_id)
+      else
+        resolve_name! unless @metadata
+      end
+    end
+
+    # Core iteration with pagination
+    # @param limit [Integer, nil] Maximum records to return
+    def each_record(limit: nil, &block)
+      dataset_id = id  # Resolve once
+      cursor = nil
+      count = 0
+
+      loop do
+        page_limit = if limit
+          [DEFAULT_PAGE_SIZE, limit - count].min
+        else
+          DEFAULT_PAGE_SIZE
+        end
+
+        result = @api.datasets.fetch(
+          id: dataset_id,
+          limit: page_limit,
+          cursor: cursor,
+          version: @version
+        )
+
+        result[:records].each do |raw_record|
+          record = build_record(raw_record, dataset_id)
+          block.call(record)
+          count += 1
+          break if limit && count >= limit
+        end
+
+        # Stop if we've hit the limit or no more pages
+        break if limit && count >= limit
+
+        cursor = result[:cursor]
+        break unless cursor
+      end
+    end
+
+    # Build a normalized record hash from raw API response
+    # @param raw [Hash] Raw record from API
+    # @param dataset_id [String] Dataset ID for origin
+    # @return [Hash] Normalized record with origin
+    def build_record(raw, dataset_id)
+      record = {}
+      record[:input] = raw["input"] if raw.key?("input")
+      record[:expected] = raw["expected"] if raw.key?("expected")
+      record[:tags] = raw["tags"] if raw.key?("tags")
+      record[:metadata] = raw["metadata"] if raw.key?("metadata")
+
+      origin = build_origin(raw, dataset_id)
+      record[:origin] = origin if origin
+
+      record
+    end
+
+    # Build origin JSON for tracing/linking
+    # @param raw [Hash] Raw record from API
+    # @param dataset_id [String] Dataset ID (fallback if not in record)
+    # @return [String, nil] JSON-serialized origin, or nil if record lacks required fields
+    def build_origin(raw, dataset_id)
+      return nil unless raw["id"] && raw["_xact_id"]
+
+      Internal::Origin.to_json(
+        object_type: "dataset",
+        object_id: raw["dataset_id"] || dataset_id,
+        id: raw["id"],
+        xact_id: raw["_xact_id"],
+        created: raw["created"]
+      )
+    end
+  end
+end
diff --git a/lib/braintrust/eval.rb b/lib/braintrust/eval.rb
index 3e68f6d..0f59326 100644
--- a/lib/braintrust/eval.rb
+++ b/lib/braintrust/eval.rb
@@ -2,8 +2,9 @@
 
 require_relative "eval/scorer"
 require_relative "eval/runner"
-require_relative "internal/experiments"
-require_relative "internal/origin"
+require_relative "api/internal/projects"
+require_relative "api/internal/experiments"
+require_relative "dataset"
 
 require "opentelemetry/sdk"
 require "json"
@@ -200,39 +201,45 @@ def scorer(name, callable = nil, &block)
       # @param metadata [Hash] Optional experiment metadata
       # @param update [Boolean] If true, allow reusing existing experiment (default: false)
       # @param quiet [Boolean] If true, suppress result output (default: false)
-      # @param state [State, nil] Braintrust state (defaults to global state)
+      # @param api [API, nil] Braintrust API client (defaults to API.new using global state)
       # @param tracer_provider [TracerProvider, nil] OpenTelemetry tracer provider (defaults to global)
       # @return [Result]
       def run(project:, experiment:, task:, scorers:,
         cases: nil, dataset: nil,
         parallelism: 1, tags: nil, metadata: nil, update: false, quiet: false,
-        state: nil, tracer_provider: nil)
+        api: nil, tracer_provider: nil)
         # Validate required parameters
         validate_params!(project: project, experiment: experiment,
           cases: cases, dataset: dataset, task: task, scorers: scorers)
 
-        # Get state from parameter or global
-        state ||= Braintrust.current_state
-        raise Error, "No state available" unless state
+        # Get API from parameter or create from global state
+        api ||= API.new
 
-        # Ensure state is logged in (to populate org_name, etc.)
+        # Ensure logged in (to populate org_name, etc.)
         # login is idempotent and returns early if already logged in
-        state.login
+        api.login
 
         # Resolve dataset to cases if dataset parameter provided
         if dataset
-          cases = resolve_dataset(dataset, project, state)
+          cases = resolve_dataset(dataset, project, api)
         end
 
-        # Register project and experiment via API
-        result = Internal::Experiments.get_or_create(
-          experiment, project, state: state,
-          tags: tags, metadata: metadata, update: update
+        # Register project and experiment via internal API
+        projects_api = API::Internal::Projects.new(api.state)
+        experiments_api = API::Internal::Experiments.new(api.state)
+
+        project_result = projects_api.create(name: project)
+        experiment_result = experiments_api.create(
+          name: experiment,
+          project_id: project_result["id"],
+          ensure_new: !update,
+          tags: tags,
+          metadata: metadata
         )
 
-        experiment_id = result[:experiment_id]
-        project_id = result[:project_id]
-        project_name = result[:project_name]
+        experiment_id = experiment_result["id"]
+        project_id = project_result["id"]
+        project_name = project_result["name"]
 
         # Instantiate Runner and run evaluation
         runner = Runner.new(
@@ -242,7 +249,7 @@ def run(project:, experiment:, task:, scorers:,
           project_name: project_name,
           task: task,
           scorers: scorers,
-          state: state,
+          api: api,
           tracer_provider: tracer_provider
         )
         result = runner.run(cases, parallelism: parallelism)
@@ -286,104 +293,29 @@ def validate_params!(project:, experiment:, cases:, dataset:, task:, scorers:)
       end
 
       # Resolve dataset parameter to an array of case records
-      # @param dataset [String, Hash] Dataset specifier
-      # @param project [String] Project name (used as default if not specified in hash)
-      # @param state [State] Braintrust state
+      # @param dataset [String, Hash, Dataset] Dataset specifier or instance
+      # @param project [String] Project name (used as default if not specified)
+      # @param api [API] Braintrust API client
       # @return [Array<Hash>] Array of case records
-      def resolve_dataset(dataset, project, state)
-        require_relative "api"
+      def resolve_dataset(dataset, project, api)
+        limit = nil
 
-        # Parse dataset parameter
-        dataset_opts = case dataset
+        dataset_obj = case dataset
+        when Dataset
+          dataset
         when String
-          # String: dataset name in same project
-          {name: dataset, project: project}
+          Dataset.new(name: dataset, project: project, api: api)
         when Hash
-          # Hash: explicit options
-          dataset.dup
+          opts = dataset.dup
+          limit = opts.delete(:limit)
+          opts[:project] ||= project
+          opts[:api] = api
+          Dataset.new(**opts)
         else
-          raise ArgumentError, "dataset must be String or Hash, got #{dataset.class}"
+          raise ArgumentError, "dataset must be String, Hash, or Dataset, got #{dataset.class}"
         end
 
-        # Apply defaults
-        dataset_opts[:project] ||= project
-
-        # Create API client
-        api = API.new(state: state)
-
-        # Resolve dataset ID
-        dataset_id = if dataset_opts[:id]
-          # ID provided directly
-          dataset_opts[:id]
-        elsif dataset_opts[:name]
-          # Fetch by name + project
-          metadata = api.datasets.get(
-            project_name: dataset_opts[:project],
-            name: dataset_opts[:name]
-          )
-          metadata["id"]
-        else
-          raise ArgumentError, "dataset hash must specify either :name or :id"
-        end
-
-        # Fetch records with pagination
-        limit_per_page = 1000
-        max_records = dataset_opts[:limit]
-        version = dataset_opts[:version]
-        records = []
-        cursor = nil
-
-        loop do
-          result = api.datasets.fetch(
-            id: dataset_id,
-            limit: limit_per_page,
-            cursor: cursor,
-            version: version
-          )
-
-          records.concat(result[:records])
-
-          # Check if we've hit the user-specified limit
-          if max_records && records.length >= max_records
-            records = records.take(max_records)
-            break
-          end
-
-          # Check if there's more data
-          cursor = result[:cursor]
-          break unless cursor
-        end
-
-        # Filter records to only include Case-compatible fields
-        # Case accepts: input, expected, tags, metadata, origin
-        records.map do |record|
-          filtered = {}
-          filtered[:input] = record["input"] if record.key?("input")
-          filtered[:expected] = record["expected"] if record.key?("expected")
-          filtered[:tags] = record["tags"] if record.key?("tags")
-          filtered[:metadata] = record["metadata"] if record.key?("metadata")
-
-          origin = build_dataset_origin(record, dataset_id)
-          filtered[:origin] = origin if origin
-
-          filtered
-        end
-      end
-
-      # Build origin JSON for a dataset record
-      # @param record [Hash] Record from dataset fetch API
-      # @param dataset_id [String] Dataset ID (fallback if not in record)
-      # @return [String, nil] JSON-serialized origin, or nil if record lacks required fields
-      def build_dataset_origin(record, dataset_id)
-        return nil unless record["id"] && record["_xact_id"]
-
-        Internal::Origin.to_json(
-          object_type: "dataset",
-          object_id: record["dataset_id"] || dataset_id,
-          id: record["id"],
-          xact_id: record["_xact_id"],
-          created: record["created"]
-        )
+        dataset_obj.fetch_all(limit: limit)
       end
     end
   end
diff --git a/lib/braintrust/eval/runner.rb b/lib/braintrust/eval/runner.rb
index 6040f3d..dfc1b79 100644
--- a/lib/braintrust/eval/runner.rb
+++ b/lib/braintrust/eval/runner.rb
@@ -18,14 +18,14 @@ class Runner
       MAX_PARALLELISM = Internal::ThreadPool::MAX_PARALLELISM
 
       def initialize(experiment_id:, experiment_name:, project_id:, project_name:,
-        task:, scorers:, state:, tracer_provider: nil)
+        task:, scorers:, api:, tracer_provider: nil)
         @experiment_id = experiment_id
         @experiment_name = experiment_name
         @project_id = project_id
         @project_name = project_name
         @task = task
         @scorers = normalize_scorers(scorers)
-        @state = state
+        @api = api
         @tracer_provider = tracer_provider || OpenTelemetry.tracer_provider
         @tracer = @tracer_provider.tracer("braintrust-eval")
         @parent_attr = "experiment_id:#{experiment_id}"
@@ -61,7 +61,7 @@ def run(cases, parallelism: 1)
         duration = Time.now - start_time
 
         # Generate permalink
-        permalink = "#{state.app_url}/app/#{state.org_name}/object?object_type=experiment&object_id=#{experiment_id}"
+        permalink = @api.object_permalink(object_type: "experiment", object_id: experiment_id)
 
         Result.new(
           experiment_id: experiment_id,
@@ -78,7 +78,7 @@ def run(cases, parallelism: 1)
       private
 
       attr_reader :experiment_id, :experiment_name, :project_id, :project_name,
-        :task, :scorers, :state, :tracer, :parent_attr
+        :task, :scorers, :tracer, :parent_attr
 
       # Run a single test case with OpenTelemetry tracing
       # Creates eval span (parent) with task and score as children
diff --git a/lib/braintrust/internal/experiments.rb b/lib/braintrust/internal/experiments.rb
deleted file mode 100644
index a5a64a1..0000000
--- a/lib/braintrust/internal/experiments.rb
+++ /dev/null
@@ -1,129 +0,0 @@
-# frozen_string_literal: true
-
-require "net/http"
-require "json"
-require "uri"
-require_relative "../logger"
-
-module Braintrust
-  module Internal
-    # Experiments module provides internal API methods for registering projects and experiments
-    # Methods are marked private to prevent direct user access - use through Eval.run
-    module Experiments
-      # Public convenience method to register/get both project and experiment
-      # @param experiment_name [String] The experiment name
-      # @param project_name [String] The project name
-      # @param state [State] Braintrust state with API key and URL
-      # @param tags [Array<String>, nil] Optional experiment tags
-      # @param metadata [Hash, nil] Optional experiment metadata
-      # @param update [Boolean] If true, allow reusing existing experiment (default: false)
-      # @return [Hash] Hash with :experiment_id, :experiment_name, :project_id, :project_name
-      def self.get_or_create(experiment_name, project_name, state:,
-        tags: nil, metadata: nil, update: false)
-        # Register/get project first
-        project = register_project(project_name, state)
-
-        # Then register/get experiment
-        experiment = register_experiment(
-          experiment_name,
-          project["id"],
-          state,
-          tags: tags,
-          metadata: metadata,
-          update: update
-        )
-
-        {
-          experiment_id: experiment["id"],
-          experiment_name: experiment["name"],
-          project_id: project["id"],
-          project_name: project["name"]
-        }
-      end
-
-      # Register or get a project by name
-      # POST /v1/project with {name: "project-name"}
-      # Returns existing project if already exists
-      # @param name [String] Project name
-      # @param state [State] Braintrust state
-      # @return [Hash] Project data with "id", "name", "org_id", etc.
-      # @raise [Braintrust::Error] if API call fails
-      def self.register_project(name, state)
-        Log.debug("Registering project: #{name}")
-
-        uri = URI("#{state.api_url}/v1/project")
-        request = Net::HTTP::Post.new(uri)
-        request["Content-Type"] = "application/json"
-        request["Authorization"] = "Bearer #{state.api_key}"
-        request.body = JSON.dump({name: name})
-
-        http = Net::HTTP.new(uri.hostname, uri.port)
-        http.use_ssl = true if uri.scheme == "https"
-
-        response = http.start do |http_session|
-          http_session.request(request)
-        end
-
-        Log.debug("Register project response: [#{response.code}]")
-
-        # Handle response codes
-        unless response.is_a?(Net::HTTPSuccess)
-          raise Error, "Failed to register project '#{name}': [#{response.code}] #{response.body}"
-        end
-
-        project = JSON.parse(response.body)
-        Log.debug("Project registered: #{project["id"]} (#{project["name"]})")
-        project
-      end
-      private_class_method :register_project
-
-      # Register or get an experiment by name
-      # POST /v1/experiment with {project_id:, name:, ensure_new:, tags:[], metadata:{}}
-      # @param name [String] Experiment name
-      # @param project_id [String] Project ID
-      # @param state [State] Braintrust state
-      # @param tags [Array<String>, nil] Optional tags
-      # @param metadata [Hash, nil] Optional metadata
-      # @param update [Boolean] If true, allow reusing existing experiment (ensure_new: false)
-      # @return [Hash] Experiment data with "id", "name", "project_id", etc.
-      # @raise [Braintrust::Error] if API call fails
-      def self.register_experiment(name, project_id, state, tags: nil, metadata: nil, update: false)
-        Log.debug("Registering experiment: #{name} (project: #{project_id}, update: #{update})")
-
-        uri = URI("#{state.api_url}/v1/experiment")
-        request = Net::HTTP::Post.new(uri)
-        request["Content-Type"] = "application/json"
-        request["Authorization"] = "Bearer #{state.api_key}"
-
-        payload = {
-          project_id: project_id,
-          name: name,
-          ensure_new: !update  # When update=true, allow reusing existing experiment
-        }
-        payload[:tags] = tags if tags
-        payload[:metadata] = metadata if metadata
-
-        request.body = JSON.dump(payload)
-
-        http = Net::HTTP.new(uri.hostname, uri.port)
-        http.use_ssl = true if uri.scheme == "https"
-
-        response = http.start do |http_session|
-          http_session.request(request)
-        end
-
-        Log.debug("Register experiment response: [#{response.code}]")
-
-        # Handle response codes
-        unless response.is_a?(Net::HTTPSuccess)
-          raise Error, "Failed to register experiment '#{name}': [#{response.code}] #{response.body}"
-        end
-
-        experiment = JSON.parse(response.body)
-        Log.debug("Experiment registered: #{experiment["id"]} (#{experiment["name"]})")
-        experiment
-      end
-      private_class_method :register_experiment
-    end
-  end
-end
diff --git a/lib/braintrust/state.rb b/lib/braintrust/state.rb
index a56181e..f8c6275 100644
--- a/lib/braintrust/state.rb
+++ b/lib/braintrust/state.rb
@@ -139,6 +139,16 @@ def login
       end
     end
 
+    # Generate a permalink URL to view an object in the Braintrust UI
+    # This is for the /object endpoint (experiments, datasets, etc.)
+    # For trace span permalinks, use Trace.permalink instead.
+    # @param object_type [String] Type of object (e.g., "experiment", "dataset")
+    # @param object_id [String] Object UUID
+    # @return [String] Permalink URL
+    def object_permalink(object_type:, object_id:)
+      "#{@app_url}/app/#{@org_name}/object?object_type=#{object_type}&object_id=#{object_id}"
+    end
+
     # Login to Braintrust API in a background thread with retry logic
     # Retries indefinitely with exponential backoff until success
     # Idempotent: returns early if already logged in
diff --git a/test/braintrust/dataset_test.rb b/test/braintrust/dataset_test.rb
new file mode 100644
index 0000000..8ad15f7
--- /dev/null
+++ b/test/braintrust/dataset_test.rb
@@ -0,0 +1,224 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "braintrust/dataset"
+
+class Braintrust::DatasetTest < Minitest::Test
+  # ============================================
+  # Initialization tests
+  # ============================================
+
+  def test_initialize_with_name_and_project
+    api = mock_api
+    dataset = Braintrust::Dataset.new(name: "my-dataset", project: "my-project", api: api)
+
+    assert_equal "my-dataset", dataset.name
+    assert_equal "my-project", dataset.project
+  end
+
+  def test_initialize_with_id
+    api = mock_api
+    dataset = Braintrust::Dataset.new(id: "dataset-123", api: api)
+
+    assert_equal "dataset-123", dataset.id
+  end
+
+  def test_initialize_requires_name_or_id
+    api = mock_api
+    error = assert_raises(ArgumentError) do
+      Braintrust::Dataset.new(api: api)
+    end
+
+    assert_match(/must specify either :name or :id/, error.message)
+  end
+
+  def test_initialize_requires_project_when_using_name
+    api = mock_api
+    error = assert_raises(ArgumentError) do
+      Braintrust::Dataset.new(name: "my-dataset", api: api)
+    end
+
+    assert_match(/:project is required when using :name/, error.message)
+  end
+
+  def test_initialize_with_version
+    api = mock_api
+    dataset = Braintrust::Dataset.new(name: "my-dataset", project: "my-project", version: "1.0", api: api)
+
+    assert_equal "1.0", dataset.version
+  end
+
+  def test_initialize_defaults_api_from_global_state
+    # Set up global state
+    state = get_unit_test_state
+    Braintrust::State.global = state
+
+    dataset = Braintrust::Dataset.new(name: "my-dataset", project: "my-project")
+
+    assert_equal "my-dataset", dataset.name
+  ensure
+    Braintrust::State.global = nil
+  end
+
+  # ============================================
+  # ID resolution tests
+  # ============================================
+
+  def test_id_returns_provided_id_directly
+    api = mock_api
+    dataset = Braintrust::Dataset.new(id: "dataset-123", api: api)
+
+    # Should return ID without making API calls
+    assert_equal "dataset-123", dataset.id
+  end
+
+  # ============================================
+  # Enumerable tests
+  # ============================================
+
+  def test_dataset_is_enumerable
+    api = mock_api
+    dataset = Braintrust::Dataset.new(id: "dataset-123", api: api)
+
+    assert dataset.respond_to?(:each)
+    assert dataset.respond_to?(:map)
+    assert dataset.respond_to?(:select)
+    assert dataset.respond_to?(:take)
+  end
+
+  # ============================================
+  # Origin generation tests
+  # ============================================
+
+  def test_build_origin_creates_valid_json
+    api = mock_api
+    dataset = Braintrust::Dataset.new(id: "dataset-123", api: api)
+
+    raw_record = {
+      "id" => "record-456",
+      "_xact_id" => "1000196022104685824",
+      "dataset_id" => "dataset-123",
+      "created" => "2025-10-24T15:29:18.118Z",
+      "input" => "test"
+    }
+
+    origin = dataset.send(:build_origin, raw_record, "dataset-123")
+
+    assert origin
+    parsed = JSON.parse(origin)
+    assert_equal "dataset", parsed["object_type"]
+    assert_equal "dataset-123", parsed["object_id"]
+    assert_equal "record-456", parsed["id"]
+    assert_equal "1000196022104685824", parsed["_xact_id"]
+  end
+
+  def test_build_origin_uses_fallback_dataset_id
+    api = mock_api
+    dataset = Braintrust::Dataset.new(id: "dataset-123", api: api)
+
+    raw_record = {
+      "id" => "record-456",
+      "_xact_id" => "1000196022104685824"
+      # No dataset_id in record
+    }
+
+    origin = dataset.send(:build_origin, raw_record, "fallback-id")
+
+    parsed = JSON.parse(origin)
+    assert_equal "fallback-id", parsed["object_id"]
+  end
+
+  def test_build_origin_returns_nil_when_missing_required_fields
+    api = mock_api
+    dataset = Braintrust::Dataset.new(id: "dataset-123", api: api)
+
+    # Missing id
+    record_no_id = {"_xact_id" => "123"}
+    assert_nil dataset.send(:build_origin, record_no_id, "dataset-id")
+
+    # Missing _xact_id
+    record_no_xact = {"id" => "record-123"}
+    assert_nil dataset.send(:build_origin, record_no_xact, "dataset-id")
+  end
+
+  # ============================================
+  # Integration tests with VCR
+  # ============================================
+
+  def test_fetch_all_returns_records_with_origin
+    VCR.use_cassette("dataset/fetch_all") do
+      state = get_integration_test_state
+      api = Braintrust::API.new(state: state)
+
+      # Create/reuse test dataset
+      project_name = "ruby-sdk-test"
+      dataset_name = "test-ruby-sdk-dataset-fetch"
+
+      result = api.datasets.create(
+        name: dataset_name,
+        project_name: project_name
+      )
+      dataset_id = result["dataset"]["id"]
+
+      # Insert test record
+      api.datasets.insert(
+        id: dataset_id,
+        events: [{input: "fetch-test", expected: "FETCH-TEST"}]
+      )
+
+      # Use Dataset class to fetch
+      dataset = Braintrust::Dataset.new(name: dataset_name, project: project_name, api: api)
+      records = dataset.fetch_all(limit: 1)
+
+      assert records.any?, "Expected at least one record"
+
+      record = records.first
+      assert record[:input], "Record should have input"
+      assert record[:origin], "Record should have origin"
+
+      # Verify origin structure
+      origin = JSON.parse(record[:origin])
+      assert_equal "dataset", origin["object_type"]
+    end
+  end
+
+  def test_each_iterates_lazily
+    VCR.use_cassette("dataset/each_lazy") do
+      state = get_integration_test_state
+      api = Braintrust::API.new(state: state)
+
+      # Create/reuse test dataset
+      project_name = "ruby-sdk-test"
+      dataset_name = "test-ruby-sdk-dataset-lazy"
+
+      result = api.datasets.create(
+        name: dataset_name,
+        project_name: project_name
+      )
+      dataset_id = result["dataset"]["id"]
+
+      # Insert test records
+      api.datasets.insert(
+        id: dataset_id,
+        events: [
+          {input: "lazy-1", expected: "LAZY-1"},
+          {input: "lazy-2", expected: "LAZY-2"}
+        ]
+      )
+
+      # Use take to only fetch what we need
+      dataset = Braintrust::Dataset.new(name: dataset_name, project: project_name, api: api)
+      first_record = dataset.take(1).first
+
+      assert first_record, "Expected to get first record"
+      assert first_record[:input], "Record should have input"
+    end
+  end
+
+  private
+
+  def mock_api
+    # Create a minimal mock API that won't make real calls
+    Minitest::Mock.new
+  end
+end
diff --git a/test/braintrust/eval/functions_test.rb b/test/braintrust/eval/functions_test.rb
index cef3e91..d985f21 100644
--- a/test/braintrust/eval/functions_test.rb
+++ b/test/braintrust/eval/functions_test.rb
@@ -181,7 +181,7 @@ def test_use_remote_task_in_eval_run
             output.to_s.include?(expected) ? 1.0 : 0.0
           end
         ],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -246,7 +246,7 @@ def test_use_remote_scorer_in_eval_run
         ],
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         quiet: true
       )
 
diff --git a/test/braintrust/eval/runner_test.rb b/test/braintrust/eval/runner_test.rb
index 570a8fe..09d11e5 100644
--- a/test/braintrust/eval/runner_test.rb
+++ b/test/braintrust/eval/runner_test.rb
@@ -24,7 +24,7 @@ def test_runner_run_returns_result_object
       project_name: "test-project",
       task: ->(input) { input.upcase },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| (o == e) ? 1.0 : 0.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -43,7 +43,7 @@ def test_runner_run_populates_result_fields
       project_name: "test-project",
       task: ->(input) { input.upcase },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -71,7 +71,7 @@ def test_runner_run_generates_correct_permalink
       project_name: "test-project",
       task: ->(input) { input },
       scorers: [Braintrust::Eval.scorer("test") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -95,7 +95,7 @@ def test_runner_run_executes_task_for_each_case
         input.upcase
       },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -127,7 +127,7 @@ def test_runner_run_executes_scorers_with_correct_args
           1.0
         }
       ],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -156,7 +156,7 @@ def test_runner_run_accepts_array_of_hashes
       project_name: "test-project",
       task: ->(input) { input },
       scorers: [Braintrust::Eval.scorer("test") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -174,7 +174,7 @@ def test_runner_run_accepts_cases_object
       project_name: "test-project",
       task: ->(input) { input },
       scorers: [Braintrust::Eval.scorer("test") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -193,7 +193,7 @@ def test_runner_run_accepts_enumerable
       project_name: "test-project",
       task: ->(input) { input },
       scorers: [Braintrust::Eval.scorer("test") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -220,7 +220,7 @@ def test_runner_run_collects_task_errors
         input.upcase
       },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -250,7 +250,7 @@ def test_runner_run_collects_scorer_errors
           1.0
         }
       ],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -279,7 +279,7 @@ def test_runner_run_continues_after_task_error
         input.upcase
       },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -307,7 +307,7 @@ def test_runner_run_collects_multiple_errors
         input.upcase
       },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -339,7 +339,7 @@ def test_runner_run_with_parallelism_greater_than_1
         input.upcase
       },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -368,7 +368,7 @@ def test_runner_run_sequential_preserves_order
         input.upcase
       },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -395,7 +395,7 @@ def test_runner_run_default_parallelism_is_sequential
         input.upcase
       },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -419,7 +419,7 @@ def test_runner_run_creates_eval_spans
       project_name: "test-project",
       task: ->(input) { input.upcase },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -442,7 +442,7 @@ def test_runner_run_creates_task_spans
       project_name: "test-project",
       task: ->(input) { input.upcase },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -465,7 +465,7 @@ def test_runner_run_creates_score_spans
       project_name: "test-project",
       task: ->(input) { input.upcase },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -491,7 +491,7 @@ def test_runner_run_records_scores_on_span
         Braintrust::Eval.scorer("accuracy") { |i, e, o| 0.95 },
         Braintrust::Eval.scorer("relevance") { |i, e, o| 0.87 }
       ],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -526,7 +526,7 @@ def test_runner_can_be_run_multiple_times
         input.upcase
       },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -551,7 +551,7 @@ def test_runner_runs_are_independent
         input.upcase
       },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| 1.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -575,7 +575,7 @@ def test_runner_scores_is_reset_between_runs
       project_name: "test-project",
       task: ->(input) { input.upcase },
       scorers: [Braintrust::Eval.scorer("exact") { |i, e, o| (o == e) ? 1.0 : 0.0 }],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
diff --git a/test/braintrust/eval_test.rb b/test/braintrust/eval_test.rb
index ff28e7e..17511f8 100644
--- a/test/braintrust/eval_test.rb
+++ b/test/braintrust/eval_test.rb
@@ -16,7 +16,7 @@ def test_eval_scorer_helper
 
   def test_eval_run_basic
     VCR.use_cassette("eval/run_basic") do
-      state = get_integration_test_state
+      api = get_integration_test_api
 
       task = ->(input) { input.upcase }
       scorer = Braintrust::Eval.scorer("exact") do |input, expected, output|
@@ -32,7 +32,7 @@ def test_eval_run_basic
         ],
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -45,7 +45,7 @@ def test_eval_run_basic
 
   def test_eval_run_with_task_error
     VCR.use_cassette("eval/run_task_error") do
-      state = get_integration_test_state
+      api = get_integration_test_api
 
       task = ->(input) {
         raise "Task failed!" if input == "bad"
@@ -65,7 +65,7 @@ def test_eval_run_with_task_error
         ],
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -77,7 +77,7 @@ def test_eval_run_with_task_error
 
   def test_eval_run_with_scorer_error
     VCR.use_cassette("eval/run_scorer_error") do
-      state = get_integration_test_state
+      api = get_integration_test_api
 
       task = ->(input) { input.upcase }
 
@@ -95,7 +95,7 @@ def test_eval_run_with_scorer_error
         ],
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -125,7 +125,7 @@ def test_eval_scorer_error_records_exception_event
       cases: [{input: "bad", expected: "BAD"}],
       task: task,
       scorers: [good_scorer, failing_scorer],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -149,7 +149,7 @@ def test_eval_scorer_error_records_exception_event
 
   def test_eval_run_with_multiple_scorers
     VCR.use_cassette("eval/run_multiple_scorers") do
-      state = get_integration_test_state
+      api = get_integration_test_api
 
       task = ->(input) { input.upcase }
 
@@ -169,7 +169,7 @@ def test_eval_run_with_multiple_scorers
         ],
         task: task,
         scorers: [scorer1, scorer2],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -179,7 +179,7 @@ def test_eval_run_with_multiple_scorers
 
   def test_eval_run_with_callable_task
     VCR.use_cassette("eval/run_callable_task") do
-      state = get_integration_test_state
+      api = get_integration_test_api
 
       callable_task = Class.new do
         def call(input)
@@ -199,7 +199,7 @@ def call(input)
         ],
         task: callable_task,
         scorers: [scorer],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -220,16 +220,14 @@ def test_eval_run_validates_required_params
 
   def test_eval_run_validates_task_callable
     # Test that task must be callable (no API call needed)
-    state = get_unit_test_state
-
+    # Note: Validation happens before API is used, so we can pass nil
     error = assert_raises(ArgumentError) do
       Braintrust::Eval.run(
         project: "test",
         experiment: "test",
         cases: [],
         task: "not callable",  # String is not callable
-        scorers: [],
-        state: state
+        scorers: []
       )
     end
 
@@ -238,7 +236,7 @@ def test_eval_run_validates_task_callable
 
   def test_eval_run_with_method_scorer
     VCR.use_cassette("eval/run_method_scorer") do
-      state = get_integration_test_state
+      api = get_integration_test_api
 
       task = ->(input) { input.upcase }
       # Use a lambda instead of nested method
@@ -252,7 +250,7 @@ def test_eval_run_with_method_scorer
         ],
         task: task,
         scorers: [test_method_scorer],  # Pass lambda directly
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -279,7 +277,7 @@ def test_eval_task_error_records_exception_on_task_span
       cases: [{input: "bad", expected: "BAD"}],
       task: task,
       scorers: [scorer],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -308,7 +306,7 @@ def test_eval_run_with_tracing
       rig = setup_otel_test_rig
 
       # Initialize and login
-      state = get_integration_test_state
+      api = get_integration_test_api
 
       task = ->(input) { input.upcase }
       scorer = Braintrust::Eval.scorer("exact") { |i, e, o| (o == e) ? 1.0 : 0.0 }
@@ -319,7 +317,7 @@ def test_eval_run_with_tracing
         cases: [{input: "hello", expected: "HELLO"}],
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         tracer_provider: rig.tracer_provider,
         quiet: true
       )
@@ -367,8 +365,7 @@ def test_eval_run_with_tracing
   # Test dataset integration: dataset as string (same project as experiment)
   def test_eval_run_with_dataset_string
     VCR.use_cassette("eval/dataset_string") do
-      state = get_integration_test_state
-      api = Braintrust::API.new(state: state)
+      api = get_integration_test_api
 
       # Create a test dataset with records
       project_name = "ruby-sdk-test"
@@ -403,7 +400,7 @@ def test_eval_run_with_dataset_string
         dataset: dataset_name,  # String - should fetch from same project
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -417,8 +414,7 @@ def test_eval_run_with_dataset_string
   # Test dataset integration: dataset as hash with name + project
   def test_eval_run_with_dataset_hash_name_project
     VCR.use_cassette("eval/dataset_hash_name_project") do
-      state = get_integration_test_state
-      api = Braintrust::API.new(state: state)
+      api = get_integration_test_api
 
       # Create a test dataset
       project_name = "ruby-sdk-test"
@@ -446,7 +442,7 @@ def test_eval_run_with_dataset_hash_name_project
         dataset: {name: dataset_name, project: project_name},
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -457,8 +453,7 @@ def test_eval_run_with_dataset_hash_name_project
   # Test dataset integration: dataset as hash with id
   def test_eval_run_with_dataset_hash_id
     VCR.use_cassette("eval/dataset_hash_id") do
-      state = get_integration_test_state
-      api = Braintrust::API.new(state: state)
+      api = get_integration_test_api
 
       # Create a test dataset
       project_name = "ruby-sdk-test"
@@ -486,7 +481,7 @@ def test_eval_run_with_dataset_hash_id
         dataset: {id: dataset_id},  # By ID only
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -497,8 +492,7 @@ def test_eval_run_with_dataset_hash_id
   # Test dataset integration: dataset with limit option
   def test_eval_run_with_dataset_limit
     VCR.use_cassette("eval/dataset_limit") do
-      state = get_integration_test_state
-      api = Braintrust::API.new(state: state)
+      api = get_integration_test_api
 
       # Create a test dataset with multiple records
       project_name = "ruby-sdk-test"
@@ -537,7 +531,7 @@ def test_eval_run_with_dataset_limit
         dataset: {name: dataset_name, project: project_name, limit: 2},
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         quiet: true
       )
 
@@ -549,7 +543,7 @@ def test_eval_run_with_dataset_limit
   # Test dataset integration: error when both dataset and cases provided
   def test_eval_run_with_both_dataset_and_cases_errors
     VCR.use_cassette("eval/run_both_dataset_and_cases_error") do
-      state = get_integration_test_state
+      api = get_integration_test_api
 
       task = ->(input) { input.upcase }
       scorer = Braintrust::Eval.scorer("exact") { |i, e, o| (o == e) ? 1.0 : 0.0 }
@@ -563,7 +557,7 @@ def test_eval_run_with_both_dataset_and_cases_errors
           cases: [{input: "test"}],
           task: task,
           scorers: [scorer],
-          state: state
+          api: api
         )
       end
 
@@ -599,7 +593,7 @@ def test_eval_run_with_parallelism_executes_all_cases
       task: task,
       scorers: [scorer],
       parallelism: 3,
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -635,7 +629,7 @@ def test_eval_run_parallelism_1_matches_sequential
       task: task,
       scorers: [scorer],
       parallelism: 1,
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -666,7 +660,7 @@ def test_eval_run_parallel_collects_errors_from_threads
       task: task,
       scorers: [scorer],
       parallelism: 3,
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -692,7 +686,7 @@ def test_eval_run_parallelism_exceeds_max_raises
         task: task,
         scorers: [scorer],
         parallelism: max_parallelism + 1,
-        state: rig.state,
+        api: rig.api,
         tracer_provider: rig.tracer_provider
       )
     end
@@ -724,7 +718,7 @@ def test_eval_run_invalid_parallelism_falls_back_to_sequential
       task: task,
       scorers: [scorer],
       parallelism: 0,
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
     assert result.success?
@@ -744,7 +738,7 @@ def test_eval_run_invalid_parallelism_falls_back_to_sequential
       task: task,
       scorers: [scorer],
       parallelism: -1,
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
     assert result.success?
@@ -757,30 +751,6 @@ def test_eval_run_invalid_parallelism_falls_back_to_sequential
   # Origin is automatically generated when using remote datasets.
   # It links eval spans back to their source dataset records in the UI.
 
-  def test_build_dataset_origin_uses_fallback_dataset_id
-    # Some API responses may not include dataset_id in the record itself
-    record = {
-      "id" => "record-123",
-      "_xact_id" => "1000196022104685824",
-      "created" => "2025-10-24T15:29:18.118Z"
-    }
-
-    origin = Braintrust::Eval.send(:build_dataset_origin, record, "fallback-dataset-id")
-
-    parsed = JSON.parse(origin)
-    assert_equal "fallback-dataset-id", parsed["object_id"]
-  end
-
-  def test_build_dataset_origin_returns_nil_when_missing_required_fields
-    # Missing id - can't link to a specific record
-    record_no_id = {"_xact_id" => "1000196022104685824"}
-    assert_nil Braintrust::Eval.send(:build_dataset_origin, record_no_id, "dataset-id")
-
-    # Missing _xact_id - can't identify the transaction
-    record_no_xact = {"id" => "record-123"}
-    assert_nil Braintrust::Eval.send(:build_dataset_origin, record_no_xact, "dataset-id")
-  end
-
   def test_runner_does_not_set_origin_when_case_has_no_origin
     # Inline cases (not from remote datasets) have no origin
     rig = setup_otel_test_rig
@@ -796,7 +766,7 @@ def test_runner_does_not_set_origin_when_case_has_no_origin
       cases: [{input: "hello", expected: "HELLO"}],
       task: task,
       scorers: [scorer],
-      state: rig.state,
+      api: rig.api,
       tracer_provider: rig.tracer_provider
     )
 
@@ -813,10 +783,8 @@ def test_eval_with_remote_dataset_sets_origin_from_api_response
     VCR.use_cassette("eval/dataset_origin") do
       # Set up span capture (uses unit test state internally, but we override state for API calls)
       rig = setup_otel_test_rig
-      # Get integration state for real API calls via VCR
-      state = get_integration_test_state
-
-      api = Braintrust::API.new(state: state)
+      # Get integration API for real API calls via VCR
+      api = get_integration_test_api
 
       # Create/reuse test dataset (idempotent)
       project_name = "ruby-sdk-test"
@@ -845,7 +813,7 @@ def test_eval_with_remote_dataset_sets_origin_from_api_response
         dataset: dataset_name,
         task: task,
         scorers: [scorer],
-        state: state,
+        api: api,
         tracer_provider: rig.tracer_provider,
         quiet: true
       )
diff --git a/test/braintrust/internal/experiments_test.rb b/test/braintrust/internal/experiments_test.rb
deleted file mode 100644
index ef4d11f..0000000
--- a/test/braintrust/internal/experiments_test.rb
+++ /dev/null
@@ -1,84 +0,0 @@
-# frozen_string_literal: true
-
-require "test_helper"
-require "braintrust/internal/experiments"
-
-class Braintrust::Internal::ExperimentsTest < Minitest::Test
-  def test_get_or_create_basic
-    VCR.use_cassette("experiments/get_or_create_basic") do
-      state = get_integration_test_state
-
-      result = Braintrust::Internal::Experiments.get_or_create(
-        "test-ruby-sdk-experiment-basic",
-        "ruby-sdk-test",
-        state: state
-      )
-
-      assert result[:experiment_id]
-      assert result[:experiment_name]
-      assert result[:project_id]
-      assert_equal "ruby-sdk-test", result[:project_name]
-    end
-  end
-
-  def test_get_or_create_with_tags_and_metadata
-    VCR.use_cassette("experiments/get_or_create_with_tags") do
-      state = get_integration_test_state
-
-      result = Braintrust::Internal::Experiments.get_or_create(
-        "test-ruby-sdk-experiment-tags",
-        "ruby-sdk-test",
-        state: state,
-        tags: ["test", "ruby"],
-        metadata: {version: "1.0", author: "claude"}
-      )
-
-      assert result[:experiment_id]
-      assert result[:project_id]
-    end
-  end
-
-  def test_get_or_create_with_update_flag
-    VCR.use_cassette("experiments/get_or_create_with_update") do
-      state = get_integration_test_state
-
-      # First create with update: false (new experiment)
-      result1 = Braintrust::Internal::Experiments.get_or_create(
-        "test-experiment-update",
-        "ruby-sdk-test",
-        state: state,
-        update: false
-      )
-
-      # Then with update: true (should allow reusing)
-      result2 = Braintrust::Internal::Experiments.get_or_create(
-        "test-experiment-update",
-        "ruby-sdk-test",
-        state: state,
-        update: true
-      )
-
-      # Both should succeed and return experiment IDs
-      assert result1[:experiment_id]
-      assert result2[:experiment_id]
-    end
-  end
-
-  def test_register_project_is_private
-    # Test that register_project is private and cannot be called directly
-    error = assert_raises(NoMethodError) do
-      Braintrust::Internal::Experiments.register_project("test", nil)
-    end
-
-    assert_match(/private method|undefined method/, error.message)
-  end
-
-  def test_register_experiment_is_private
-    # Test that register_experiment is private and cannot be called directly
-    error = assert_raises(NoMethodError) do
-      Braintrust::Internal::Experiments.register_experiment("test", "proj_id", nil)
-    end
-
-    assert_match(/private method|undefined method/, error.message)
-  end
-end
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new file mode 100644
index 0000000..7490df6
--- /dev/null
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diff --git a/test/support/braintrust_helper.rb b/test/support/braintrust_helper.rb
index b5ff6c0..43232a4 100644
--- a/test/support/braintrust_helper.rb
+++ b/test/support/braintrust_helper.rb
@@ -64,8 +64,8 @@ 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.
+      # Creates an API for integration tests
+      # This is the preferred way to get an API for tests.
       # @param options [Hash] Options to pass to get_integration_test_state
       # @return [Braintrust::API]
       def get_integration_test_api(**options)
@@ -74,8 +74,9 @@ def get_integration_test_api(**options)
       end
 
       # Helper to run eval internally without API calls for testing
+      # @param api [API] Braintrust API client
       def run_test_eval(experiment_id:, experiment_name:, project_id:, project_name:,
-        cases:, task:, scorers:, state:, parallelism: 1, tracer_provider: nil)
+        cases:, task:, scorers:, api:, parallelism: 1, tracer_provider: nil)
         runner = Braintrust::Eval::Runner.new(
           experiment_id: experiment_id,
           experiment_name: experiment_name,
@@ -83,7 +84,7 @@ def run_test_eval(experiment_id:, experiment_name:, project_id:, project_name:,
           project_name: project_name,
           task: task,
           scorers: scorers,
-          state: state,
+          api: api,
           tracer_provider: tracer_provider
         )
         runner.run(cases, parallelism: parallelism)
diff --git a/test/support/tracing_helper.rb b/test/support/tracing_helper.rb
index 3a0ace7..4be57b4 100644
--- a/test/support/tracing_helper.rb
+++ b/test/support/tracing_helper.rb
@@ -37,6 +37,12 @@ def initialize(tracer_provider, exporter, state)
           @state = state
         end
 
+        # Get API client for the test state
+        # @return [Braintrust::API]
+        def api
+          @api ||= Braintrust::API.new(state: @state)
+        end
+
         # Get a tracer from the provider
         # @param name [String] tracer name (default: "test")
         # @return [OpenTelemetry::Trace::Tracer]