Follow Discord
Sweep 22 Oct 2026 · 21:04Z Build v2.1.309 528 read Stable v2.1.308 Latest v2.1.308 Next v2.1.309 Feeds RSS JSON llms.txt llms-full.txt Unofficial
HomeReleasesv2.1.219entry #35

Claude Code v2.1.219 ·

SDK reports why fast mode is unavailable

SDK messages now tell you exactly why fast mode was unavailable for a request.

Use it now No documentation found New Features
JSON All of v2.1.219
Use it nowTier: how much it should matter to you
3Useful: my rating, 1 to 5
0Signal: worth watching, 1 to 5
SDKArea: what it touches
New FeaturesKind: in v2.1.219,
What probably matters to youSection of the release
What

An optional fast_mode_disabled_reason field now travels on SDK init and result messages, so a client can tell why a request could not use fast mode rather than guessing.

Details
  • Added to the init message and to both the success and error result message schemas.
  • Populated on every result path, including "tool_deferred_unavailable", "budget_exhausted" and "turn_setup_failed".
  • Enum values: free, preference, extra_usage_disabled, network_error, unknown, not_first_party, disabled_by_env, model_not_allowed, sdk_opt_in_required, pending.
  • A companion Set of the first five values normalizes server-supplied reasons: unrecognized values map to unknown, null maps to preference.
  • The field is absent when nothing blocks fast mode; a request may still choose standard speed.
Evidence

Why fast mode can't serve right now. Absent when nothing blocks it (a request may still choose standard speed).

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

Read from
Names in the bundlefast_mode_disabled_reason

See this entry in the whole of v2.1.219 →

Feedback