Pi's default auto-compaction only checks after agent_end. This means context can overflow during long multi-tool turns before compaction triggers.

Strategy

This extension checks tokens at three points:

Pre-turn: Before sending any request to the LLM (turn_start)
Mid-turn: After tool execution, before follow-up LLM calls (turn_end)
Emergency: Synchronous truncation in the context event as a last resort

It also handles the session resume case: when an existing session is reopened above the threshold, compaction kicks off as soon as the session starts.

Continuing After Auto-Compaction

ctx.compact() aborts the running agent internally, so without a nudge the session would sit idle once the summary is written. After every auto-triggered compaction this extension sends a short English follow-up user message to make pi resume the in-flight task. The exact wording depends on which check fired (pre-turn, mid-turn, emergency, or session-resume).

The follow-up is suppressed in two cases:

The user ran /compact manually — the callback path used here only fires for compactions this extension started, so manual compaction is never touched.
The agent is no longer idle when the summary finishes, e.g. the user already typed something or another extension started a turn while summarising. Their input acts as the kickoff and we stay quiet.

Compaction Strategies

Strategy	Description
`keep-recent`	Keep only the most recent messages (default)
`keep-bookends`	Keep oldest + newest messages, compact the middle
`summarize-all`	Remove everything except the last user message

Configuration

Use /auto-compact to open the interactive settings menu:

/auto-compact              # Open settings menu
/auto-compact status       # Show current status
/auto-compact reset        # Reset to defaults

Settings

Setting	Default	Options
Auto-compact threshold	90%	80%, 85%, 90%, 95%
Keep recent budget	15%	5%, 10%, 15%, 20%
Strategy	keep-recent	keep-recent, keep-bookends, summarize-all
Debug logging	off	on/off

Example

For a 200K context window model:

Compact at 180K tokens (90%)
Keep 30K recent tokens (15%)

Install

As a pi package:

pi install npm:@capyup/pi-auto-compact

Or via git:

pi install git:github.com/capyup/pi-auto-compact

Or run directly:

pi -e ./extensions/auto-compact.ts

How It Differs from Pi's Default

Aspect	Pi Default	This Extension
Check timing	After `agent_end` only	Before requests + after tools
Overflow protection	None	Emergency truncation
Mid-turn handling	None	Checks after each tool batch
Auto-continue	No	Yes — sends an English follow-up nudge after auto-compaction