Fast mode is a setting that makes Claude reply faster. To decide its status, Claude Code checks your organization and fetches your profile. It now uses an API key for those checks only when no OAuth login (signing in through your Anthropic account) is available and the key looks like an Anthropic key, starting with sk-ant-. Before, any key in that slot was used.
When the key does not qualify, the reason given for the fast mode guess is now "unknown" instead of "preference".
If you put a gateway or proxy token where the API key goes, Claude Code no longer sends it to fast mode and profile requests that would fail with it.
tengu_penguins_off Not enough to sayNothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.
This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.299: not a boolean we can read
These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.
Read once, for one account on one subscription tier, against v2.1.299. It isn't a statement about your account. What a flag value here can and cannot tell you