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Sweep 22 Oct 2026 · 04:32Z Build v2.1.308 527 read Stable v2.1.308 Latest v2.1.308 Next v2.1.308 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.1.221 ·

claude attach now measures time-to-interactive

Attaching to a background session now times how long it takes to paint and reach an idle prompt.

Under the hood Internal Changes
JSON All of v2.1.221
Under the hoodTier: how much it should matter to you
2Useful: my rating, 1 to 5
0Signal: worth watching, 1 to 5
SessionsArea: what it touches
Internal ChangesKind: in v2.1.221,
Internal ChangesSection of the release
What

Attaching to a background session records how long it takes to reach first paint and an idle prompt, alongside how much of the transcript was loaded and rendered.

Details
  • A gesture record is created up front and the child's output is watched for content-paint and prompt-idle marks.
  • tengu_bg_attach_outcome gained attach_ms, content_paint_ms, prompt_idle_ms, msgs_loaded, msgs_in_jsonl, msgs_rendered_at_first_paint, first_frame_kind and marks_expected.
  • Daemon boot is marked when the daemon starts.
  • Error exits (crash loop, respawn failure, daemon unavailable) flush the gesture with a 750 ms race before exiting.
Evidence

msgs_rendered_at_first_paint

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Read from
Names in the bundleclaude attach

See this entry in the whole of v2.1.221 →

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