LangChain Core 1.5.1 adds LangSmith gateway support for Anthropic, Fireworks, OpenAI

LangChain has released langchain-core version 1.5.1, a patch update that brings two notable improvements for developers building with LLM tools. The headline feature is support for the LangSmith gateway through environment variables, now available for Anthropic, Fireworks, and OpenAI integrations. This allows teams to easily route API calls through LangSmith's observability and tracing infrastructure without modifying their existing code—just set the relevant env vars.

The second fix addresses token counting in base tools. Previously, the count_tokens_approximately method did not use the cached tool_call_schema, potentially leading to inaccurate token estimates when calling tools. By leveraging the schema cache, the release ensures more reliable token accounting, which is critical for cost management and context window planning. This is a minor but stable release for the core library, and all users are encouraged to upgrade.