diff --git a/packages/openai/src/index.ts b/packages/openai/src/index.ts
index 5b69e093c..42304f5c8 100644
--- a/packages/openai/src/index.ts
+++ b/packages/openai/src/index.ts
@@ -1,2 +1,31 @@
 export { observeOpenAI } from "./observeOpenAI.js";
 export * from "./types.js";
+export type { WithLangfuseIds } from "./langfuseIds.js";
+
+/**
+ * Module augmentation for OpenAI SDK response types.
+ *
+ * When `observeOpenAI` wraps a client, all response objects are augmented
+ * with Langfuse observation and trace IDs at runtime. These declarations
+ * make TypeScript aware of those properties so consumers don't need casts.
+ *
+ * The properties are marked optional because the base OpenAI types are also
+ * used without `observeOpenAI`.
+ */
+declare module "openai/resources/chat/completions/completions" {
+  interface ChatCompletion {
+    /** Langfuse observation ID — present when the client is wrapped with `observeOpenAI` */
+    langfuseObservationId?: string;
+    /** Langfuse trace ID — present when the client is wrapped with `observeOpenAI` */
+    langfuseTraceId?: string;
+  }
+}
+
+declare module "openai/resources/responses/responses" {
+  interface Response {
+    /** Langfuse observation ID — present when the client is wrapped with `observeOpenAI` */
+    langfuseObservationId?: string;
+    /** Langfuse trace ID — present when the client is wrapped with `observeOpenAI` */
+    langfuseTraceId?: string;
+  }
+}
diff --git a/packages/openai/src/langfuseIds.ts b/packages/openai/src/langfuseIds.ts
new file mode 100644
index 000000000..60ca022fd
--- /dev/null
+++ b/packages/openai/src/langfuseIds.ts
@@ -0,0 +1,47 @@
+import type { LangfuseGeneration } from "@langfuse/tracing";
+
+/**
+ * Extends a response object with Langfuse observation and trace IDs.
+ *
+ * @public
+ */
+export type WithLangfuseIds<T> = T & {
+  /** The Langfuse observation ID for this generation */
+  langfuseObservationId: string;
+  /** The Langfuse trace ID for this generation */
+  langfuseTraceId: string;
+};
+
+/**
+ * Attaches Langfuse observation and trace IDs to a response object as non-enumerable properties.
+ *
+ * The properties are non-enumerable so they don't appear in JSON.stringify output
+ * or for-in loops, but are directly accessible on the response object.
+ *
+ * @internal
+ */
+export function attachLangfuseIds<T>(
+  result: T,
+  generation: LangfuseGeneration,
+): asserts result is T & WithLangfuseIds<T> {
+  if (result && typeof result === "object") {
+    try {
+      Object.defineProperty(result, "langfuseObservationId", {
+        value: generation.id,
+        enumerable: false,
+        writable: false,
+        configurable: false,
+      });
+      Object.defineProperty(result, "langfuseTraceId", {
+        value: generation.traceId,
+        enumerable: false,
+        writable: false,
+        configurable: false,
+      });
+    } catch {
+      // In practice this never happens: OpenAI SDK responses are plain objects
+      // from JSON parsing (never frozen/sealed), and this function is only called
+      // once per response. Guard kept for defensive robustness.
+    }
+  }
+}
diff --git a/packages/openai/src/traceMethod.ts b/packages/openai/src/traceMethod.ts
index bafe35ca1..49e4ea7fb 100644
--- a/packages/openai/src/traceMethod.ts
+++ b/packages/openai/src/traceMethod.ts
@@ -5,6 +5,7 @@ import {
 } from "@langfuse/tracing";
 import type OpenAI from "openai";
 
+import { attachLangfuseIds } from "./langfuseIds.js";
 import {
   getToolCallOutput,
   parseChunk,
@@ -129,6 +130,8 @@ const wrapMethod = <T extends GenericMethod>(
                 })
                 .end();
 
+              attachLangfuseIds(result, generation);
+
               return result;
             })
             .catch((err) => {
@@ -258,5 +261,8 @@ function wrapAsyncIterable<R>(
       .end();
   }
 
-  return tracedOutputGenerator() as R;
+  const generator = tracedOutputGenerator();
+  attachLangfuseIds(generator, generation);
+
+  return generator as R;
 }