★ OverviewBeginner9 min
What is LangChain?
The ecosystem, the architecture, and why it exists. One API for every LLM, composable chains via LCEL, and the stability guarantees of v1.0+.
Quick Reference
- →LangChain = unified interface over LLMs, tools, memory, and chains
- →LCEL (pipe operator |) composes any steps declaratively
- →LangChain 1.0 (Oct 2025) — first stable API
- →Agents in LangChain run on LangGraph under the hood
- →langchain-core provides base interfaces; provider packages (langchain-anthropic, langchain-openai…) implement them
The One-Line Definition
Definition
LangChain is a framework that gives you a single, unified API to work with any LLM — plus a composable system for building chains, agents, tools, and memory on top of them.
Without LangChain, you write different code for every provider (OpenAI, Anthropic, Gemini…). With LangChain, you write it once and swap models with a single line. That single-API promise is the reason LangChain exists: it decouples your application logic from the model vendor so you can iterate on prompts, upgrade models, and mix providers without rewriting your stack.