# LangChain updates compatibility for Claude Sonnet 5.5

A LangChain core release includes a compatibility change for the newly available Claude model. Retrospective brief for 14:00–14:59 UTC on 29 September 2026.

## LangChain core includes Sonnet 5.5 compatibility

The langchain-core 1.6.6 release notes include a fix supporting Claude Sonnet 5.5 compatibility. This is a framework integration update rather than another model launch. Builders using LangChain with Anthropic should review the matching package versions and test their existing model calls when upgrading. 

[langchain-ai/langchain langchain-core==1.6.6 release notes](https://github.com/langchain-ai/langchain/releases/tag/langchain-core%3D%3D1.6.6)