langchain

Facts

Openness

Open source

Licence

MIT

Language

Python

Pinned version

be854a1 (2026-09-28)

Topics checked

28 of 33

Kind of agent

General framework

Source repository (opens another site)

What it does notably well

• Compaction

  SummarizationMiddleware._find_safe_cutoff_point (a static method) walks backward from the cutoff when the message there is a ToolMessage, finds the AIMessage whose tool_calls ids…

  SummarizationMiddleware has no default trigger (trigger=None, so it never fires until configured); a trigger can be a (tokens, N), (fraction, F) or (messages, N) tuple, a dict…

• Concurrency

  Of the three pieces the lead names, only the token-bucket rate limiter (InMemoryRateLimiter, opt-in through BaseChatModel.rate_limiter) is defined in the langchain repository…

• Config and routing

  langchain_v1 routes models through init_chat_model over 30 built-in providers with provider:model strings, and its LLMToolSelectorMiddleware docstring shows a smaller model…

• Message model

  create_agent keeps the system prompt out of the stored state: it turns system_prompt into a SystemMessage, passes it as ModelRequest.system_message, and prepends it to the…

  In HumanInTheLoopMiddleware, a reject decision adds a ToolMessage with status error carrying the original tool_call_id, and a respond decision adds one with status success; an…