Background agents use the main model when your session is on a backup

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.