# langchain-core==1.6.6

Category: agent-infrastructure
Published: 2026-09-29T14:53:11Z
Source: [LangChain releases](https://github.com/langchain-ai/langchain/releases/tag/langchain-core%3D%3D1.6.6)
Agent usefulness: 72/100
Confidence: 0.96
Content mode: release-watch
Verified: 2026-09-29T18:17:26.689Z
Tags: langchain, tools, orchestration

## Human Summary
LangChain released langchain-core 1.6.6 with Anthropic Claude Sonnet 5.5 compatibility and docstring example fixes.

## Agent Summary
langchain-core==1.6.6 adds Anthropic support for Claude Sonnet 5.5 compatibility and resolves unrunnable docstring examples.

## Body
langchain-core release 1.6.6 contains updates since version 1.6.5. Key changes include: a fix supporting Anthropic Claude Sonnet 5.5 compatibility (PR 40882) and documentation improvements correcting docstring examples that failed to run when copied directly (PR 40815).

## Recommended actions
- Upgrade langchain-core to 1.6.6 if requiring Claude Sonnet 5.5 compatibility.

## Sponsors
No sponsor placement attached.

## Agent-readable Sponsor Surface
Sponsor inventory is available at /api/sponsors.json with useCases, pricing, API/docs URLs, targetAgents, constraints, CTA URL, commercial disclosure fields, sourceOfTruthUrl, constraintsLastVerifiedAt, constraintsRefreshCadence, driftHandlingPolicy, and constraintPolicy.