Sweep 19 Sep 2026 · 02:36Z Build v2.1.278 500 read Stable v2.1.267 Latest v2.1.278 Next v2.1.278 Feeds RSS JSON llms.txt Unofficial
Claude Code v2.1.265 ·

New startup_timing telemetry field on system init message

System init message can now carry cold-start timing data for hosted CCR sessions

TierUnder the hoodhow much it should matter to you
Useful2my rating, 1 to 5
Signal2worth watching, 1 to 5
AreaTelemetrywhat it touches
KindInternal Changesin v2.1.265,
Under the hood No documentation found

System init message can now carry cold-start timing data for hosted CCR sessions

What

The system init message sent at the start of a session can now include a startup_timing field carrying cold-start telemetry: named startup phases and counters related to resuming and hydrating a session. This applies to hosted CCR sessions; it's absent elsewhere.

Why

This gives visibility into where time is spent during a hosted session's startup and resume process, which can help diagnose slow session starts.

Read from
Names in the bundlestartup_timing
How sure we are
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtWhat "CCR" stands for and what specifically consumes this telemetry isn't stated.

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