[Release] langchain-ai/langchain langchain==1.3.0a1: langchain==1.3.0a1
LangChain v1.3.0a1 is an alpha release featuring stream_events(version='v3') protocol integration into create_agent, HITL middleware enhancements with a 'respond' decision, and performance optimizations including reduced agent state inlining and LRU caching for type resolution. The release includes updates across multiple partner packages (Fireworks, Anthropic, OpenAI), dependency bumps for security (Pygments CVE-2026-4539, cryptography), and improvements to token counting, middleware initialization speed, and agent configuration. Key infrastructure changes include content-block-centric streaming (v2), dynamic tool registration via middleware, and enhanced LangSmith integration metadata.
Key Points
- •Integrated stream_events(version='v3') protocol into create_agent for improved event streaming capabilities
- •Added 'respond' decision to HITL (Human-in-the-Loop) middleware for enhanced control flow
- •Performance optimization: stopped inlining agent state into tool-dispatch Send operations, reducing overhead
- •Implemented LRU caching for type resolution to improve initialization speed by ~15%
- •Added content-block-centric streaming (v2) protocol for more granular streaming control
- •Enabled dynamic tool registration via middleware for flexible agent configuration
- •Enhanced LangSmith integration with metadata tagging on create_agent and init_chat_model calls
- •Security updates: patched Pygments CVE-2026-4539 and upgraded cryptography dependencies
- •Improved token counting for partial message sequences and ChatAnthropicVertex model support
- •Added ls_agent_type tag on create_agent calls for better tracing and monitoring
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