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claude-code - 💡(How to fix) Fix [BUG] 2.1.111 introduced ~14% context window bloat at session startup (8% → 22%) [1 comments, 2 participants]

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anthropics/claude-code#49593•Fetched 2026-04-17 08:36:45
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Session startup context usage jumped from ~8% to ~22% with no changes to my project, CLAUDE.md files, MCP servers, or plugins. After extensive investigation, the change correlates exactly with the auto-update from 2.1.110 → 2.1.111 on Apr 16 2026.

Error Message

Error Messages/Logs

Root Cause

Session startup context usage jumped from ~8% to ~22% with no changes to my project, CLAUDE.md files, MCP servers, or plugins. After extensive investigation, the change correlates exactly with the auto-update from 2.1.110 → 2.1.111 on Apr 16 2026.

Fix Action

Fix / Workaround

  • Startup context floor went from ~16K to ~45K tokens (estimated)
  • Effective context burn rate ~5x higher during working sessions
  • All available mitigation (pruning agents, skills, plugins, MCP servers) produced negligible improvement — confirming the bloat is inside Claude Code itself, not user configuration
RAW_BUFFERClick to expand / collapse

Preflight Checklist

  • I have searched existing issues and this hasn't been reported yet
  • This is a single bug report (please file separate reports for different bugs)
  • I am using the latest version of Claude Code

What's Wrong?

Environment

  • Claude Code 2.1.112 (also 2.1.111)
  • Opus 4.6, macOS Darwin 25.3.0
  • 200K context window

Summary

Session startup context usage jumped from ~8% to ~22% with no changes to my project, CLAUDE.md files, MCP servers, or plugins. After extensive investigation, the change correlates exactly with the auto-update from 2.1.110 → 2.1.111 on Apr 16 2026.

Evidence

Binary sizes in ~/.local/share/claude/versions/:

  • 202,932,416 2.1.110 (Apr 15 — 8% startup)
  • 203,956,832 2.1.111 (Apr 16 13:35 — 22% startup)
  • 203,956,832 2.1.112 (Apr 16 15:59 — 22% startup)
  • 14MB increase between .110 and .111. Timing matches exactly. Nothing else changed in the environment.

Impact

  • Startup context floor went from ~16K to ~45K tokens (estimated)
  • Effective context burn rate ~5x higher during working sessions
  • All available mitigation (pruning agents, skills, plugins, MCP servers) produced negligible improvement — confirming the bloat is inside Claude Code itself, not user configuration

What Should Happen?

  • Identify and revert whatever was added to the system prompt / tool schemas in 2.1.111 that caused this, or provide a config flag to opt out of the expanded content.
  • Add a /context command showing a per-component breakdown of startup token usage (system prompt, tool schemas, MCP servers, CLAUDE.md, skills list, memory). Without this, users are forced to do blind archaeology when startup bloat occurs. This is the 6th time I've investigated this class of issue; a breakdown command would have resolved it in 60 seconds.

Error Messages/Logs

None

Steps to Reproduce

Pin to 2.1.110: ln -sfn ~/.local/share/claude/versions/2.1.110 ~/.local/bin/claude Start session, run trivial prompt, note context % Update to 2.1.112, repeat

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

No response

Claude Code Version

2.1.112

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

No response

extent analysis

TL;DR

The most likely fix is to identify and revert the changes introduced in version 2.1.111 that caused the increased context usage.

Guidance

  • Investigate the differences between versions 2.1.110 and 2.1.111 to determine what changes caused the increased context usage.
  • Consider adding a configuration flag to opt out of the expanded content introduced in 2.1.111.
  • Implement a /context command to provide a per-component breakdown of startup token usage for easier debugging.
  • Test the ln -sfn workaround to pin the version to 2.1.110 and verify if the context usage returns to normal.

Example

No code snippet is provided as the issue does not require a specific code change.

Notes

The issue seems to be specific to the Opus model and macOS environment, and the exact cause of the increased context usage is still unknown. Further investigation is needed to determine the root cause.

Recommendation

Apply workaround: Pin the version to 2.1.110 using ln -sfn until the issue is resolved in a future version, as the increased context usage is causing significant performance issues.

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