How Claude Code's Context Eviction Is Silently Destroying Developer Work

This is context eviction. And it's costing developers hours of work every day.

Claude Code doesn't work like ChatGPT where each message is fresh. It runs in long sessions — reading files, running commands, tracking changes — all inside one giant running memory called a context window.

Think of it like a whiteboard. Every file Claude reads, every error it sees, every rule you give — it all gets written there. Claude Sonnet holds around 200,000 tokens. Claude Opus holds up to 1,000,000. That sounds enormous until you're deep inside a real codebase — then it fills up faster than you expect.

When the whiteboard hits 95% full, something triggers automatically: context compaction.

Claude Code takes your entire conversation history, sends it to a separate internal model call, compresses it into a shorter summary, and replaces the original with that summary. You don't get a warning. You don't get asked. The session continues as if nothing happened.

The problem: the summary is imperfect. Specific decisions, subtle preferences, nested rules, and exact reasoning from earlier in your session — all of it gets compressed, truncated, or silently dropped.

What Survives — and What Doesn't

Survives compaction:

Your root CLAUDE.md file

Main project structure

Recent messages

Gets lost or badly summarised:

Specific decisions made earlier in the session

Nested CLAUDE.md rules in subdirectories

Preferences you mentioned in passing

The reasoning behind earlier architectural choices

A developer ran an always-on Claude Code agent for 200 minutes. After compaction triggered, it forgot a security rule set at the beginning of the session and introduced a vulnerability it had explicitly been told to avoid. No warning was given. The session logs showed nothing unusual.

In March 2026, Claude Code's source code was accidentally exposed publicly — 1,900 files, 512,000+ lines of TypeScript. The leak revealed the internal compaction logic in detail. The dev community spent weeks analysing exactly how context eviction works under the hood, and confirmed what many had suspected: the summarisation process is lossy by design.

Meanwhile, Microsoft began cancelling thousands of internal Claude Code licences, with its Experiences & Devices team winding down usage by June 30, 2026. Context management friction was cited alongside the push to consolidate on GitHub Copilot CLI.

Context management tools are improving fast. Persistent project memory, plan mode, and automatic compaction are all getting smarter. In 2026, more of the orchestration burden sits with the tool rather than the developer.

But the fundamental constraint remains: context windows are finite, and the compaction process is imperfect. The developers who understand this will ship faster and lose less work than those who don't.