Claude Opus 5.5 tool_choice 400: 3 SDKs Tested (2026)
September 25, 2026
Claude Opus 5.5 rejects forced tool_choice with a 400. I captured what the AI SDK, LangChain and the raw SDK actually send, and built a preflight check.
#vercel-ai-sdk
Test Vercel AI SDK Code with MockLanguageModelV3 (2026)
June 20, 2026
Unit-test Vercel AI SDK v6 code in TypeScript with MockLanguageModelV3 - no API key, no cost. Mock generateText, tool calls, and streaming in Vitest.