LangChain is the most-used open framework for building LLM applications: tool integrations, chains, RAG primitives, and, through the LangGraph spinoff, low-level graph-based agent orchestration. LangChain 1.0 and LangGraph 1.0 both reached general availability in October 2025. It supports Python and JavaScript/TypeScript. Against the opinionated, batteries-included style of CrewAI, LangGraph sits at the low-level end: explicit state machines and graphs the developer wires together. Two facts matter for a 2026 comparison. MCP support is not in the core library; it is provided through the separate langchain-mcp-adapters package, which makes LangChain a later adopter of MCP than the vendor SDKs. License: the core libraries are MIT, but the langgraph-api server runtime used for hosted deployment is under the Elastic License 2.0, which needs a commercial key in production. For open-source AI, LangChain is fully model-agnostic and the default starting point for many teams. LangSmith, the observability and evaluation product, is a separate hosted service that the framework does not require.
The Stack · Agents · Open source
LangChain
Most-used open agent framework; LLM tools, chains, RAG primitives, and LangGraph for low-level agent orchestration. MCP via the langchain-mcp-adapters package.
Sources
- LangChain documentation https://docs.langchain.com/oss/python/langchain/overview
- langgraph LICENSE (MIT core) https://raw.githubusercontent.com/langchain-ai/langgraph/main/LICENSE
- langchain-mcp-adapters (MCP via adapter package) https://github.com/langchain-ai/langchain-mcp-adapters
- LangGraph 1.0 GA announcement https://changelog.langchain.com/announcements/langgraph-1-0-is-now-generally-available
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