{"version":"2.0.65","anchor":"headless-profiling-system","canonical_anchor":"headless-profiling-system","heading":"Headless Profiling System","tier":null,"area":null,"scope":null,"heads_up":null,"url":"https:\/\/changelogs.core-directive.com\/v\/2.0.65\/e\/headless-profiling-system","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.0.65","markdown":"### Headless Profiling System\n\n**What:** Built-in performance profiling for SDK\/headless usage with turn-level metrics. **How to enable:**\n\n`export CLAUDE_CODE_PROFILE_STARTUP=1 # Enable verbose logging` **Details:**\n\n- Tracks key checkpoints: system message generation, query start, first response chunk\n- Reports metrics via telemetry for 5% of sessions\n- **Evidence**: `e30()`, `p1A()`, `A80()` functions at lines 445732-445745"}