The current OpenAI TypeScript/JavaScript SDK ( openai @ 5.12.x, released 8 Aug 2025 ) still vendors a copy of zod-to-json-schema that depends on Zod 3-only internals. Trying to pair it with Zod 4 (or with the 3.25.68+ branch that began preparing for v4) leads to compiler/runtime failures such as the missing ZodFirstPartyTypeKind export.