Cold start context usage increased significantly between versions

Description

Cold start context usage jumped from ~4% to ~11% overnight with zero config changes on user side.

Environment

• Claude Code v2.1.105
• macOS (Darwin 25.4.0)
• 1 MCP server (Playwright)
• 2 lean CLAUDE.md files (~2.5KB each)
• 27 auto-memory files (only MEMORY.md index loaded at start)
• 5 custom slash commands

What changed

Nothing on my end. Same CLAUDE.md files, same MCP servers, same memory setup, same settings. The increase appears to come entirely from system prompt growth — tool schemas, auto-memory instructions, skill definitions, agent definitions, etc.

Impact

• ~7% of the context window is now consumed before the user sends a single message
• Per-message context cost also feels higher due to less remaining headroom
• Power users who have already optimized their configs have no way to reclaim this space since the system prompt is not user-controllable

Request

• Transparency on what changed in the system prompt between recent versions
• Consideration for keeping system prompt size stable or providing opt-out for unused features
• Ideally, lazy-load tool schemas and instructions that aren't relevant to every session

🤖 Generated with Claude Code