Support for zod@4 in withStructuredOutput – Types Not Inferred Properly

[weilinzung]

Checked

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Feature request

"langchain": "^0.3.24",
"zod": "^3.25.67",

import { z } from "zod/v4";
import { ChatOpenAI } from '@langchain/openai';

const model = new ChatOpenAI({
  model: 'xxx',
});

const schema = z.object({
  id: z.string(),
  score: z.number()
});

const analysisModel = model.withStructuredOutput(schema);

^^^ "Runnable<BaseLanguageModelInput, Record<string, any>, RunnableConfig<Record<string, any>>>"

The current langchain with Zod 3

Runnable<BaseLanguageModelInput, {
    id: string;
    score: number;
}, RunnableConfig<Record<string, any>>>

Motivation

The current implementation of withStructuredOutput in LangChain v0.3.24 works well with zod@3, providing accurate type inference based on the given ZodSchema. However, when using zod@4 (e.g., via modular import zod/v4), the type inference breaks.

Expected (with Zod 3):

Runnable<BaseLanguageModelInput, {
  id: string;
  score: number;
}, RunnableConfig<Record<string, any>>>

Actual (with Zod 4):

Runnable<BaseLanguageModelInput, Record<string, any>, RunnableConfig<Record<string, any>>>

Even though the API signatures accept z.ZodType, TypeScript cannot infer RunOutput properly from zod@4, leading to a generic Record<string, any> in practice.

This significantly weakens the utility of withStructuredOutput, especially in codebases moving to Zod 4 for its modular build and better tree-shaking.

Proposal (If applicable)

No response

[weilinzung]

langchain-ai/langchainjs#8413 moved as issue