MarginLab tracker measures a five-day Claude Code drop tied to CLI version 2.1.150

MarginLab's daily SWE-Bench-Pro subset run of Claude Code (50 tasks per day) fell from a 65% Opus 4.7 baseline to 50 to 54% from May 22 to May 26, 2026, and recovered to 66% when version 2.1.153 landed. Tool calls per task rose about 60% over the same days, and MarginLab concluded it was a harness issue, not a model regression.

Who is affected:

Claude Code users on CLI versions 2.1.150 to 2.1.152 in late May 2026.

What to do:

No action needed. Later CLI versions recovered.