Claude Code sends up to 36K tokens before you type, measurement finds

A developer measured 58 Claude Code versions from July 2025 to October 2026: the fixed system prompt and tool definitions grew from 19,498 to a peak of 36,309 tokens (+86%), then dropped 39% to 18,055 in version 2.1.293 on October 7. The figure has since crept back to 18,841 tokens in 2.1.310.

• The block grew from 19,498 to 36,309 tokens between 1.0.60 and 2.1.150
• Version 2.1.293 cut it by 39% to 18,055 tokens
• It rose 4% over the 15 releases after 2.1.293
• In versions 2.1.83–2.1.140 connectors added about 395K tokens