Context Rot

The progressive degradation of Claude Code's output quality as session length grows, caused by attention dilution across an ever-larger token history.

Key points

• Retrieval accuracy drops from 92% at 256K tokens to 78% at 1M tokens ^[src-011]
• Analysis of 18K thinking blocks across 7K sessions: thinking depth dropped 67% and "edit without reading" behaviour rose from 6% to 34% in long sessions ^[src-011]
• One developer tracked 100+ message chats and found 98.5% of tokens were spent re-reading old conversation history — not producing new output ^[src-011]
• Token cost is exponential: message 30 in a chat can cost 31x more tokens than message 1, because the entire history is re-read each turn ^[src-011]
• Auto-compaction fires at 95% context use and retains only 20–30% of detail — the worst possible moment (most degraded state) ^[src-011]

Symptoms

• Model edits files without reading them first
• Contradicts earlier decisions made in the same session
• Vague or repetitive outputs
• Increasing error rate on tasks it handled correctly earlier in the session

Remediation patterns

• Cap Opus sessions at ~120K tokens (12% of 1M window), then summarise and /clear ^[src-011]
• Use /session-handoff skill to generate a structured context handoff document before clearing ^[src-011]
• Use /re (rewind) to drop failed attempts that silently pollute future responses ^[src-011]
• Convert documents to markdown before ingestion (33–90% token reduction) ^[src-011]
• Use /btw for side questions that don't need to enter conversation history ^[src-011]
• Session chaining: discovery → planning → execution sessions, each consuming only the prior session's output document ^[src-011]

Related entities

• Claude Code — the primary environment where context rot occurs

Related concepts

• Context Management — the broader discipline; context rot is its failure mode
• Session Chaining — structural solution
• Adaptive Thinking — zero-reasoning turns (a symptom of context rot) correlate with hallucinations
• Token Economics — cost model underlying the exponential growth
• Markdown Conversion For Token Reduction — preventive measure

Source references

• ^[src-011] Nate Herk — Claude Code power features cluster (2026-04-20 to 2026-04-27)