Watermark

LangChain JS 0.3 Can Cost Sonnet 4.6 Its Watermark

Anthropic's 3 November release note added Sonnet 4.6, Opus 4.7 and Mythos 5 to its text watermark, and the doc warns that on Sonnet 4.6 a request setting temperature, top_p or top_k to a non-default value might not carry the mark, including values a framework sets for you. Capturing request bodies from 17 client setups against a local stub: current Anthropic SDKs, LangChain (Python and JS), LiteLLM, Pydantic AI, DSPy, Instructor, the Vercel AI SDK, Claude Code and the Agent SDK send none. LangChain JS 0.3.x sends temperature 1, top_p -1 and top_k -1 on every Sonnet 4.6 call (19.5% of last week's downloads), DSPy before 3.0.4 sends 0.0, and LlamaIndex 0.12.3 crashes on a fresh install and sends 0.1 once the Anthropic SDK is pinned below 1.0. Claude Code sends temperature 1 only with thinking off.