Zod schema conversion broken for unions in Zod 4.1.13+ #1709
Description
Confirm this is a Node library issue and not an underlying OpenAI API issue
- This is an issue with the Node library
Describe the bug
Zod recently started emitting oneOf instead of anyOf for discriminated unions:
colinhacks/zod#5453
This is not supported for OpenAI strict mode, so using the Zod conversion helpers will cause API failures upon upgrading to the latest Zod.
To Reproduce
- Define a discriminated union with Zod v4.1.13
- Use one of the
openai/helpers/zodfunctions - Use the result with the appropriate OpenAI endpoint
- It fails because the JSON schema includes
oneOf, which is unsupported by OpenAI
Code snippets
import { z } from "zod"; import { zodResponseFormat } from "openai/helpers/zod"; import { OpenAI } from "openai"; const ResponseSchema = z.object({ data: z.discriminatedUnion("type", [ z.object({ type: z.literal("a") }), z.object({ type: z.literal("b") }), ]), }); const client = new OpenAI({ apiKey: process.env.OPENAI_API_KEY }); const completion = await client.chat.completions.parse({ model: "gpt-4o-mini", messages: [{ role: "user", content: "Choose a or b"}], response_format: zodResponseFormat(ResponseSchema, "choice"), }); // Result: // { // status: 400, // headers: Headers {}, // requestID: 'req_a7f2a1dc6e19439289ff6992bec4a24d', // error: { // message: "Invalid schema for response_format 'choice': In context=('properties', 'data'), 'oneOf' is not permitted.", // type: 'invalid_request_error', // param: 'response_format', // code: null // }, // code: null, // param: 'response_format', // type: 'invalid_request_error' // }OS
N/A
Node version
N/A
Library version
openai v6.9.1