tools-only Context Compression
Strategies for long-running sessions exceeding context windows.
Core Insight
Optimize tokens-per-task (total to completion), not tokens-per-request. Aggressive compression causing re-fetching costs more than better retention.
Compression Methods
| Method | Compression | Quality | Best For |
|---|---|---|---|
| Anchored Iterative | 98.6% | 3.70/5 | Best balance |
| Regenerative Full | 98.7% | 3.44/5 | Readability |
| Opaque | 99.3% | 3.35/5 | Max compression |
Anchored Iterative Summary Template
## Session Intent
Original goal: [preserved]
## Files Modified
- file.py: Changes made
## Decisions Made
- Key decisions with rationale
## Current State
Progress summary
## Next Steps
1. Next action items
On compression: Merge new content into existing sections, don't regenerate.
Compression Triggers
| Strategy | Trigger | Use Case |
|---|---|---|
| Fixed threshold | 70-80% utilization | General purpose |
| Sliding window | Keep last N turns + summary | Conversations |
| Task-boundary | At logical completion | Multi-step workflows |
Artifact Trail Problem
Weakest dimension (2.2-2.5/5.0). Coding agents need explicit tracking of:
- Files created/modified/read
- Function/variable names, error messages
Solution: Dedicated artifact section in summary.
Probe-Based Evaluation
| Probe Type | Tests | Example |
|---|---|---|
| Recall | Factual retention | "What was the error?" |
| Artifact | File tracking | "Which files modified?" |
| Continuation | Task planning | "What next?" |
| Decision | Reasoning chains | "Why chose X?" |
Six Evaluation Dimensions
- Accuracy - Technical correctness
- Context Awareness - Conversation state
- Artifact Trail - File tracking (universally weak)
- Completeness - Coverage depth
- Continuity - Work continuation
- Instruction Following - Constraints
Guidelines
- Use anchored iterative for best quality/compression
- Maintain explicit artifact tracking section
- Trigger compression at 70% utilization
- Merge into sections, don't regenerate
- Evaluate with probes, not lexical metrics