[Release] langchain-ai/langchain langchain==1.3.0a2: langchain==1.3.0a2

LangChain v1.3.0a2 is an alpha release featuring improvements to stream events protocol (v3), ordered schema resolution, and agent middleware enhancements. The release includes performance optimizations, bug fixes across multiple integrations (OpenAI, Anthropic, Fireworks), and new features like HITL middleware respond decision and dynamic tool registration. Key updates involve dependency bumps, security patches, and refinements to the agent creation and model initialization systems.

Key Points

• •Stream events v3 protocol integrated into create_agent for improved event streaming capabilities
• •Ordered schema resolution fix ensures state_schema takes precedence by using list instead of set
• •HITL (Human-in-the-Loop) middleware enhanced with respond decision capability
• •Performance improvements including 15% init speed reduction and LRU cache for type resolution
• •Dynamic tool registration via middleware enables runtime tool updates without agent recreation
• •Content-block-centric streaming (v2) added to core for better streaming architecture
• •Multiple security patches including CVE-2026-4539 (Pygments) and cryptography/urllib3 updates
• •Enhanced model provider support including Azure AI Foundry, Anthropic Bedrock, and OpenRouter
• •Improved token counting for partial message sequences and approximate token counter accuracy
• •LangSmith integration metadata added to create_agent and init_chat_model for better tracing

Workflow Diagram

Concepts