fix(langchain): don't check hasSupportForJsonSchemaOutput if specified providerStrategy explictly (#9334)

Author: chiichen

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

@@ -39,7 +39,6 @@ import {
   ProviderStrategy,
   transformResponseFormat,
   ToolStrategyError,
-  hasSupportForJsonSchemaOutput,
 } from "../responses.js";
 
 type ResponseHandlerResult<StructuredResponseFormat> =
@@ -763,15 +762,6 @@ export class AgentNode<
      * check if the user requests a native schema output
      */
     if (structuredResponseFormat?.type === "native") {
-      /**
-       * if the model does not support JSON schema output, throw an error
-       */
-      if (!hasSupportForJsonSchemaOutput(model)) {
-        throw new Error(
-          "Model does not support native structured output responses. Please use a model that supports native structured output responses or use a tool output."
-        );
-      }
-
       const jsonSchemaParams = {
         name: structuredResponseFormat.strategy.schema?.name ?? "extract",
         description: getSchemaDescription(

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

@@ -4,7 +4,7 @@ import { z } from "zod/v3";
 import { ChatOpenAI } from "@langchain/openai";
 import { ChatAnthropic } from "@langchain/anthropic";
 
-import { createAgent, toolStrategy } from "../index.js";
+import { createAgent, toolStrategy, providerStrategy } from "../index.js";
 import { FakeToolCallingModel, FakeToolCallingChatModel } from "./utils.js";
 import { hasSupportForJsonSchemaOutput } from "../responses.js";
 
@@ -306,6 +306,32 @@ describe("structured output handling", () => {
       });
     });
   });
+  describe("providerStrategy", () => {
+    describe("use provider strategy directly", () => {
+      it("should not throw error if use provider strategy directly", async () => {
+        const model = new FakeToolCallingModel({
+          toolCalls: [
+            [{ name: "extract-16", args: { foo: "bar" }, id: "call_2" }],
+          ],
+        });
+        const agent = createAgent({
+          model,
+          tools: [],
+          responseFormat: providerStrategy(
+            z.object({
+              foo: z.string(),
+            })
+          ),
+        });
+
+        await expect(
+          agent.invoke({
+            messages: [{ role: "user", content: "hi" }],
+          })
+        ).resolves.not.toThrowError();
+      });
+    });
+  });
 });
 
 describe("hasSupportForJsonSchemaOutput", () => {