fix(anthropic,openai): handle structured output with v1 output version (#9212)

Author: hntrl

libs/langchain-core/src/language_models/chat_models.ts

@@ -10,6 +10,7 @@ import {
   isAIMessageChunk,
   isBaseMessage,
   isAIMessage,
+  MessageOutputVersion,
 } from "../messages/index.js";
 import {
   convertToOpenAIImageBlock,
@@ -113,7 +114,7 @@ export type BaseChatModelParams = BaseLanguageModelParams & {
    *
    * @default "v0"
    */
-  outputVersion?: "v0" | "v1";
+  outputVersion?: MessageOutputVersion;
 };
 
 /**
@@ -135,6 +136,22 @@ export type BaseChatModelCallOptions = BaseLanguageModelCallOptions & {
    * if used with an unsupported model.
    */
   tool_choice?: ToolChoice;
+  /**
+   * Version of `AIMessage` output format to store in message content.
+   *
+   * `AIMessage.contentBlocks` will lazily parse the contents of `content` into a
+   * standard format. This flag can be used to additionally store the standard format
+   * as the message content, e.g., for serialization purposes.
+   *
+   * - "v0": provider-specific format in content (can lazily parse with `.contentBlocks`)
+   * - "v1": standardized format in content (consistent with `.contentBlocks`)
+   *
+   * You can also set `LC_OUTPUT_VERSION` as an environment variable to "v1" to
+   * enable this by default.
+   *
+   * @default "v0"
+   */
+  outputVersion?: MessageOutputVersion;
 };
 
 function _formatForTracing(messages: BaseMessage[]): BaseMessage[] {
@@ -202,7 +219,7 @@ export abstract class BaseChatModel<
 
   disableStreaming = false;
 
-  outputVersion?: "v0" | "v1";
+  outputVersion?: MessageOutputVersion;
 
   constructor(fields: BaseChatModelParams) {
     super(fields);
@@ -308,6 +325,7 @@ export abstract class BaseChatModel<
         invocation_params: this?.invocationParams(callOptions),
         batch_size: 1,
       };
+      const outputVersion = callOptions.outputVersion ?? this.outputVersion;
       const runManagers = await callbackManager_?.handleChatModelStart(
         this.toJSON(),
         [_formatForTracing(messages)],
@@ -335,7 +353,7 @@ export abstract class BaseChatModel<
             ...chunk.generationInfo,
             ...chunk.message.response_metadata,
           };
-          if (this.outputVersion === "v1") {
+          if (outputVersion === "v1") {
             yield castStandardMessageContent(
               chunk.message
             ) as OutputMessageType;
@@ -440,6 +458,7 @@ export abstract class BaseChatModel<
         handledOptions.runName
       );
     }
+    const outputVersion = parsedOptions.outputVersion ?? this.outputVersion;
     const generations: ChatGeneration[][] = [];
     const llmOutputs: LLMResult["llmOutput"][] = [];
     // Even if stream is not explicitly called, check if model is implicitly
@@ -508,7 +527,7 @@ export abstract class BaseChatModel<
             { ...parsedOptions, promptIndex: i },
             runManagers?.[i]
           );
-          if (this.outputVersion === "v1") {
+          if (outputVersion === "v1") {
             for (const generation of generateResults.generations) {
               generation.message = castStandardMessageContent(
                 generation.message
@@ -650,6 +669,7 @@ export abstract class BaseChatModel<
       );
 
     // Handle results and call run managers
+    const outputVersion = parsedOptions.outputVersion ?? this.outputVersion;
     const generations: Generation[][] = [];
     await Promise.all(
       cachedResults.map(async ({ result: promiseResult, runManager }, i) => {
@@ -666,7 +686,7 @@ export abstract class BaseChatModel<
                 output_tokens: 0,
                 total_tokens: 0,
               };
-              if (this.outputVersion === "v1") {
+              if (outputVersion === "v1") {
                 result.message = castStandardMessageContent(result.message);
               }
             }

libs/providers/langchain-anthropic/src/chat_models.ts

@@ -1224,6 +1224,7 @@ export class ChatAnthropicMessages<
       console.warn(thinkingAdmonition);
 
       llm = this.withConfig({
+        outputVersion: "v0",
         tools,
         ls_structured_output_format: {
           kwargs: { method: "functionCalling" },
@@ -1241,6 +1242,7 @@ export class ChatAnthropicMessages<
       llm = llm.pipe(raiseIfNoToolCalls);
     } else {
       llm = this.withConfig({
+        outputVersion: "v0",
         tools,
         tool_choice: {
           type: "tool",

libs/providers/langchain-anthropic/src/tests/chat_models.int.test.ts

@@ -1519,3 +1519,15 @@ describe("Sonnet 4.5", () => {
     expect(response.content.length).toBeGreaterThan(0);
   });
 });
+
+it("won't modify structured output content if outputVersion is set", async () => {
+  const schema = z.object({ name: z.string() });
+  const model = new ChatAnthropic({
+    model: "claude-opus-4-1",
+    outputVersion: "v1",
+  });
+  const response = await model
+    .withStructuredOutput(schema)
+    .invoke("respond with the name 'John'");
+  expect(response.name).toBeDefined();
+});

libs/providers/langchain-openai/src/chat_models.ts

@@ -30,6 +30,7 @@ import {
   BaseChatModel,
   type LangSmithParams,
   type BaseChatModelParams,
+  BaseChatModelCallOptions,
 } from "@langchain/core/language_models/chat_models";
 import {
   isOpenAITool as isOpenAIFunctionTool,
@@ -104,9 +105,11 @@ import {
 import {
   _convertMessagesToOpenAIParams,
   completionsApiContentBlockConverter,
-  ResponsesInputItem,
 } from "./utils/message_inputs.js";
-import { _convertToResponsesMessageFromV1 } from "./utils/standard.js";
+import {
+  _convertToResponsesMessageFromV1,
+  ResponsesInputItem,
+} from "./utils/standard.js";
 import { iife, isReasoningModel, messageToOpenAIRole } from "./utils/misc.js";
 
 const _FUNCTION_CALL_IDS_MAP_KEY = "__openai_function_call_ids__";
@@ -123,7 +126,13 @@ export type { OpenAICallOptions, OpenAIChatInput };
 
 export interface BaseChatOpenAICallOptions
   extends OpenAICallOptions,
+    BaseChatModelCallOptions,
     BaseFunctionCallOptions {
+  /**
+   * Additional options to pass to the underlying axios request.
+   */
+  options?: OpenAICoreRequestOptions;
+
   /**
    * A list of tools that the model may use to generate responses.
    * Each tool can be a function, a built-in tool, or a custom tool definition.
@@ -464,9 +473,13 @@ export abstract class BaseChatOpenAI<
   constructor(fields?: BaseChatOpenAIFields) {
     super(fields ?? {});
 
+    const configApiKey =
+      typeof fields?.configuration?.apiKey === "string"
+        ? fields?.configuration?.apiKey
+        : undefined;
     this.apiKey =
       fields?.apiKey ??
-      fields?.configuration?.apiKey ??
+      configApiKey ??
       getEnvironmentVariable("OPENAI_API_KEY");
     this.organization =
       fields?.configuration?.organization ??
@@ -929,6 +942,7 @@ export abstract class BaseChatOpenAI<
       }
       const asJsonSchema = toJsonSchema(schema);
       llm = this.withConfig({
+        outputVersion: "v0",
         response_format: { type: "json_object" },
         ls_structured_output_format: {
           kwargs: { method: "json_mode" },
@@ -944,6 +958,7 @@ export abstract class BaseChatOpenAI<
       };
       const asJsonSchema = toJsonSchema(openaiJsonSchemaParams.schema);
       llm = this.withConfig({
+        outputVersion: "v0",
         response_format: {
           type: "json_schema",
           json_schema: openaiJsonSchemaParams,
@@ -976,6 +991,7 @@ export abstract class BaseChatOpenAI<
       if (isInteropZodSchema(schema)) {
         const asJsonSchema = toJsonSchema(schema);
         llm = this.withConfig({
+          outputVersion: "v0",
           tools: [
             {
               type: "function" as const,
@@ -1023,6 +1039,7 @@ export abstract class BaseChatOpenAI<
         }
         const asJsonSchema = toJsonSchema(schema);
         llm = this.withConfig({
+          outputVersion: "v0",
           tools: [
             {
               type: "function" as const,
@@ -1944,7 +1961,7 @@ export class ChatOpenAIResponses<
       reasoning.summary.length > 1
         ? reasoning.summary.reduce(
             (acc, curr) => {
-              const last = acc.at(-1);
+              const last = acc[acc.length - 1];
 
               if (last!.index === curr.index) {
                 last!.text += curr.text;

libs/providers/langchain-openai/src/tests/chat_models_responses.int.test.ts

@@ -1,7 +1,7 @@
 import { randomUUID } from "node:crypto";
 
 import { z } from "zod/v3";
-import { test, expect } from "vitest";
+import { describe, it, test, expect } from "vitest";
 
 import {
   AIMessage,
@@ -934,3 +934,15 @@ describe("promptCacheKey", () => {
     ).toBeGreaterThan(0);
   });
 });
+
+it.only("won't modify structured output content if outputVersion is set", async () => {
+  const schema = z.object({ name: z.string() });
+  const model = new ChatOpenAI({
+    model: "gpt-5",
+    outputVersion: "v1",
+  });
+  const response = await model
+    .withStructuredOutput(schema)
+    .invoke("respond with the name 'John'");
+  expect(response.name).toBeDefined();
+});