Factory Anchored Iterative Summarization: Structured Context Compression Beats OpenAI by 0.35 and Anthropic by 0.26 Across 36,000 Real Engineering Session Messages

Factory AI·high signal

Factory AI evaluated three context compression approaches on 36,000 production session messages spanning PR review, testing, bug fixes, and feature implementation. Their 'anchored iterative summarization' maintains a structured persistent summary with explicit sections for session intent, file modifications, decisions made, and next steps. When compression triggers, only the newly-truncated span is summarized and merged. Factory scores 4.04 accuracy vs Anthropic 3.74 vs OpenAI 3.43. The key insight: structure forces preservation — dedicated sections act as checklists preventing silent information loss.