LangChain

LangChain is the standard framework for chaining LLM components. In 2025, the focus shifted to LangGraph for building stateful, cyclic agents.

When to Use

• Orchestration: Chaining "Prompt -> LLM -> Parser".
• Agents: Using LangGraph to build agents that can loop, retry, and keep state.
• Integrations: 1000+ connectors for vector DBs, APIs, and tools.

Core Concepts

LangGraph

The successor to AgentExecutor. A graph-based way to define agent flows with cycles (loops).

LCEL (LangChain Expression Language)

The declarative pipe syntax: prompt | llm | output_parser.