# Managing Long Histories: Trim and Summarise — LangGraph Agents & Multi-Agent Systems

Source: https://www.geekswithgeeks.com/en/langgraph-agents/m-context

> Keep the message list within the model's context window.

## A growing list is a growing bill

Message history grows with every turn and tool call until it exceeds the **context window** and the bill. Strategies: **trim** to the last N messages or a token budget (keeping the system message and any pinned facts); **summarise** older messages into one short message that you keep instead; **filter** bulky tool outputs (store the raw data elsewhere and keep a short result in the messages); and **move durable facts** to long-term memory. Do the trimming in a dedicated node or a message-preparation step before the model call, so the stored history stays complete for audit while the model only sees what it needs.

## Trim for the model, keep the full log

Pass a trimmed copy to the model call but keep the complete history in the checkpoint for debugging and audits.

**Quiz:** Why summarise old messages?

- [ ] To disable tools
- [ ] To delete the thread
- [x] To keep context short and cheap while preserving key information
- [ ] To increase the recursion limit

*Answer:* To keep context short and cheap while preserving key information. Summaries compress history so it fits the window.