You'll noticeTier: how much it should matter to you
2Useful: my rating, 1 to 5
1Signal: worth watching, 1 to 5
Background TasksArea: what it touches
ImprovementsKind: in v2.1.283,
ImprovementsSection of the release
Unclear How often a session is actually running on a backup model is unclear.
What
When the model you normally use is unavailable, a session can switch to a backup model (see fallbackModel). Background agents, the helpers Claude Code runs alongside your conversation, used to take whatever model the session was using, including the backup.
Now, if the session is on its backup model, each new background agent is given the main model instead, as long as that model passes the check for availability and access. Otherwise the agent uses the session's current model.
Why
A temporary switch to a backup model no longer moves every background agent onto the backup too.
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed sinceAnthropic's documentation has since written up fallbackModel, on Agent SDK reference - TypeScript.| `fallbackModel` | `string` | `undefined` | Model to use if the primary model fails. Accepts a comma-separated list. For the order and the cap, see [Fallback model chains](/docs/en/model-config#fallback-model-chains). For guidance, see [C…agent-sdk/typescriptsee the edit
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 doubtHow often a session is actually running on a backup model is unclear.
Anthropic's documentation agreesAnthropic's documentation has since written up fallbackModel, on Agent SDK reference - TypeScript.
