Under the hoodTier: how much it should matter to you
1Useful: my rating, 1 to 5
0Signal: worth watching, 1 to 5
ModelsArea: what it touches
ImprovementsKind: in v2.1.219,
ImprovementsSection of the release
What
The two environment-info prompt builders that describe Fast mode now list Opus 5 alongside 4.8 and 4.7, so the model is told Fast mode applies to the new default.
Details
Applies to both environment-info prompt builders.
No gate; the line is emitted for everyone.
Evidence
It can be toggled with /fast and is available on Opus 5/4.8/4.7.
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's release notes agreeFixed the /model picker showing the merged Opus row as plain "Opus" instead of "Opus (1M context)"
