Context Compression Strategies

When agent sessions generate millions of tokens, compression becomes mandatory. Optimize for tokens-per-task (total tokens to complete a task), not tokens-per-request.

Compression Approaches

1. Anchored Iterative Summarization (Recommended)

• Maintain structured summaries with explicit sections
• On compression, summarize only newly-truncated content
• Merge with existing summary instead of regenerating
• Structure forces preservation of critical info

2. Opaque Compression

• Highest compression ratios (99%+)
• Sacrifices interpretability
• Cannot verify what was preserved

3. Regenerative Full Summary

• Generate detailed summary on each compression
• Readable but may lose details across cycles
• Full regeneration rather than merging

Structured Summary Format

## Session Intent
[What the user is trying to accomplish]

## Files Modified
- auth.controller.ts: Fixed JWT token generation
- config/redis.ts: Updated connection pooling

## Decisions Made
- Using Redis connection pool instead of per-request
- Retry logic with exponential backoff

## Current State
- 14 tests passing, 2 failing
- Remaining: mock setup for session service tests

## Next Steps
1. Fix remaining test failures
2. Run full test suite
3. Update documentation

Compression Triggers

Strategy	Trigger	Trade-off
Fixed threshold	70-80% context	Simple but may compress early
Sliding window	Last N turns + summary	Predictable size
Importance-based	Low-relevance first	Complex but preserves signal
Task-boundary	At task completions	Clean but unpredictable

The Artifact Trail Problem

File tracking is the weakest dimension (2.2-2.5/5.0 in evaluations). Coding agents need:

• Which files were created
• Which files were modified and what changed
• Which files were read but not changed
• Function names, variable names, error messages

Solution: Separate artifact index or explicit file-state tracking.

Probe-Based Evaluation

Test compression quality with probes:

Probe Type	Tests	Example
Recall	Factual retention	"What was the original error?"
Artifact	File tracking	"Which files have we modified?"
Continuation	Task planning	"What should we do next?"
Decision	Reasoning chain	"What did we decide about Redis?"

Compression Ratios

Method	Compression	Quality	Trade-off
Anchored Iterative	98.6%	3.70	Best quality
Regenerative	98.7%	3.44	Moderate
Opaque	99.3%	3.35	Best compression

The 0.7% extra tokens buys 0.35 quality points—worth it when re-fetching costs matter.

Three-Phase Workflow (Large Codebases)

1. Research Phase: Explore and compress into structured analysis
2. Planning Phase: Convert to implementation spec (~2,000 words for 5M tokens)
3. Implementation Phase: Execute against the spec

Best Practices

1. Optimize for tokens-per-task, not tokens-per-request
2. Use structured summaries with explicit file sections
3. Trigger compression at 70-80% utilization
4. Implement incremental merging over regeneration
5. Test with probe-based evaluation
6. Track artifact trail separately if critical
7. Monitor re-fetching frequency as quality signal