Every model has a **context window** (max tokens it can see). Long-running chats accumulate messages and tool results; once the window is tight, OpenClaw **compacts** older history to stay within limits.
Compaction **summarizes older conversation** into a compact summary entry and keeps recent messages intact. The summary is stored in the session history, so future requests use:
Compaction summarization preserves opaque identifiers by default (`identifierPolicy: "strict"`). You can override this with `identifierPolicy: "off"` or provide custom text with `identifierPolicy: "custom"` and `identifierInstructions`.
You can optionally specify a different model for compaction summarization via `agents.defaults.compaction.model`. This is useful when your primary model is a local or small model and you want compaction summaries produced by a more capable model. The override accepts any `provider/model-id` string:
```json
{
"agents": {
"defaults": {
"compaction": {
"model": "openrouter/anthropic/claude-sonnet-4-5"
}
}
}
}
```
This also works with local models, for example a second Ollama model dedicated to summarization or a fine-tuned compaction specialist:
```json
{
"agents": {
"defaults": {
"compaction": {
"model": "ollama/llama3.1:8b"
}
}
}
}
```
When unset, compaction uses the agent's primary model.
When a session nears or exceeds the model’s context window, OpenClaw triggers auto-compaction and may retry the original request using the compacted context.
