Auto-Compact Based on Model Context Window

[theepicsaxguy]

Goal: Automatically compact sessions when the context window nears its limit to prevent truncation or errors.

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1. Define Triggers and Thresholds

• Context Usage Threshold:
  • Trigger auto-compact when context usage exceeds 80% of the model’s context window (configurable in Settings).
  • Example: For a 128K-token model, auto-compact at 102K tokens.
• Session Length Threshold:
  • Optional: Auto-compact if the session exceeds 50 messages (configurable).
• Idle Trigger:
  • Auto-compact when the user navigates away from the session or after 5 minutes of inactivity.

2. Backend Changes

• Context Monitoring:
  • Extend the existing ContextUsageIndicator [1] to emit events when the threshold is crossed.
  • Use the summarizeSession endpoint to trigger compaction.
• Compaction Logic:
  • Reuse the existing /compact slash command logic but invoke it automatically.
  • Log compaction events for debugging (e.g., "Session auto-compacted at 82% context usage").
• Model Awareness:
  • Fetch the model’s context window from the provider’s metadata (e.g., models[modelID].limit.context ).
  • Fall back to a default (e.g., 128K) if metadata is missing.

3. Frontend UX

• Non-Blocking Toast:
  • Show a toast when auto-compaction starts: "Compacting session to save context space...".
  • Show a success toast: "Session compacted. Tokens reduced from X to Y."
• Manual Override:
  • Add a "Disable Auto-Compact" toggle in Settings.
  • Add a "Compact Now" button in the session header for manual compaction.
• Visual Feedback:
  • Animate the ContextUsageIndicator when auto-compaction is triggered (e.g., pulsing red at 90%+ usage).

4. Edge Cases

• Failed Compaction:
  • If compaction fails, show an error toast: "Auto-compact failed. Try manually or reduce context."
  • Retry once after 30 seconds.
• Rate Limiting:
  • Prevent multiple auto-compacts in a short time (e.g., 1 per 5 minutes).
• Offline Mode:
  • Skip auto-compact if the user is offline (queue for later).

[chriswritescode-dev]

I like this, is this configurable without a plugin in opencode ?

[theepicsaxguy]

I like this, is this configurable without a plugin in opencode ?

Yes you can set it in the config:

Compaction
You can control context compaction behavior through the compaction option.

opencode.json
{
"$schema": "https://opencode.ai/config.json",
"compaction": {
"auto": true,
"prune": true
}
}

auto - Automatically compact the session when context is full (default: true).
prune - Remove old tool outputs to save tokens (default: true).