DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.
Fast mode now has a three-state model: "on", "off", and "cooldown" (after a rate limit). Network errors show a temporary unavailability message rather than fully disabling fast mode. The fast_mode_state field is now included in API response schemas.
Evidence
Fast mode state function (search for "Fast mode is temporarily unavailable due to a network error")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.