You'll noticeTier: how much it should matter to you
3Useful: my rating, 1 to 5
3Signal: worth watching, 1 to 5
Headless ModeArea: what it touches
New FeaturesKind: in v2.1.304,
New FeaturesSection of the release
What
When Claude Code runs headless (without its interactive screen, driven by another program through the SDK, the toolkit for building on Claude Code), it now reports how far startup has got:
Each startup checkpoint is sent once as a keep_alive line carrying a startup_mark field, provided something is registered to receive it. Marks include before_runHeadlessStreaming and stdin_listen_started.
On the receiving side, the SDK's query reader now reads that text field from keep_alive messages, up to a size limit, and stores it as startupMark together with a timestamp. Before, keep_alive messages were simply ignored.
Why
Programs that host Claude Code can now see startup progress and how long each step takes, which helps when working out why a headless session is slow to start.
