fix(langchain): enable Anthropic native structured output with create agent (#9562)

Author: christian-bromann

libs/langchain/package.json

@@ -207,4 +207,4 @@
     "./package.json": "./package.json"
   },
   "module": "./dist/index.js"
-}
+}

libs/langchain/src/agents/nodes/AgentNode.ts

@@ -849,6 +849,13 @@ export class AgentNode<
           type: "json_schema",
           json_schema: jsonSchemaParams,
         },
+        output_format: {
+          type: "json_schema",
+          schema: structuredResponseFormat.strategy.schema,
+        },
+        headers: {
+          "anthropic-beta": "structured-outputs-2025-11-13",
+        },
         ls_structured_output_format: {
           kwargs: { method: "json_schema" },
           schema: structuredResponseFormat.strategy.schema,

libs/langchain/src/agents/tests/responses.int.test.ts

@@ -5,7 +5,7 @@ import { tool } from "@langchain/core/tools";
 import { HumanMessage, AIMessage } from "@langchain/core/messages";
 import z from "zod/v3";
 
-import { createAgent, toolStrategy } from "../index.js";
+import { createAgent, toolStrategy, providerStrategy } from "../index.js";
 import type { JsonSchemaFormat } from "../responses.js";
 
 import responsesSpec from "./specifications/responses.json";
@@ -180,6 +180,43 @@ describe("structured output handling", () => {
       );
     });
   });
+
+  describe("providerStrategy", () => {
+    it("should support native structured output for newer Anthropic models", async () => {
+      const model = new ChatAnthropic({
+        model: "claude-sonnet-4-5-20250929",
+        temperature: 0, // Make it deterministic
+      });
+      const captialCatalogTool = tool(
+        () => {
+          return "Paris";
+        },
+        {
+          name: "capital_catalog",
+          description: "Get the capital of a country",
+          schema: z.object({
+            location: z.string(),
+          }),
+        }
+      );
+      const agent = createAgent({
+        model,
+        tools: [captialCatalogTool],
+        responseFormat: providerStrategy(
+          z.object({
+            answer: z.string().describe("The capital of the country in 1 word"),
+          })
+        ),
+      });
+      const result = await agent.invoke({
+        messages: [new HumanMessage("What is the capital of France?")],
+      });
+      expect(result.structuredResponse.answer).toBe("Paris");
+      expect(result.messages.length).toBe(4);
+      expect(result.messages.at(-1)?.content).toContain('{"answer": "Paris"}');
+      expect((result.messages.at(-1) as AIMessage).tool_calls?.length).toBe(0);
+    });
+  });
 });
 
 describe("Strategy Selection", () => {

libs/langchain/src/load/import_constants.ts

@@ -1,9 +1,9 @@
 /** Auto-generated by import-constants plugin. Do not edit manually */
 
 export const optionalImportEntrypoints: string[] = [
-  "langchain_langchain/chat_models/universal",
-  "langchain_langchain/cache/file_system",
-  "langchain_langchain/storage/file_system",
-  "langchain_langchain/hub/index",
-  "langchain_langchain/hub/node",
+  "langchain/chat_models/universal",
+  "langchain/cache/file_system",
+  "langchain/storage/file_system",
+  "langchain/hub/index",
+  "langchain/hub/node",
 ];