What: Built-in performance profiling for SDK/headless usage with turn-level metrics. How to enable:
export CLAUDE_CODE_PROFILE_STARTUP=1 # Enable verbose loggingDetails:
- Tracks key checkpoints: system message generation, query start, first response chunk
- Reports metrics via telemetry for 5% of sessions
- Evidence:
e30(),p1A(),A80()functions at lines 445732-445745