How Pi handles context compaction for long coding sessions

bibryam · x · 2026-08-22

Background

LLM context windows are limited. Compaction is essential to maintain long sessions without history overflow.

Pi's Compaction Logic

Pi treats compaction like a shift handoff: keeping recent work active while summarizing older decisions.

Mechanism

Trigger: Activated when history (system prompts, files, tool calls, messages) exceeds the context limit.
Rebuild Process:
First Rebuild: Recomputes everything from the first changed token.
Subsequent: Only computes changes, converting older history into summaries.
Data Flow: Requests carry System, Tools, and conversation history. Compaction prunes this history to fit the window as turns increase.

Significance

This enables agents to handle long-term tasks that exceed the native context window while maintaining continuity.

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