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Reading a new release v2.1.251 Analysing changes · 2/5 Sorting the findings · 1/4 steps 470 findings $18.91 so far

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.

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Claude Code v2.1.196

Fast Mode Model Scope Narrowed

Feature flag
tengu_sunset_penguin_opus47 Not enough to say

Nothing 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 v2.1.196: 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 v2.1.196. It isn't a statement about your account. What a flag value here can and cannot tell you

Fast mode (Opus with faster output, toggled with /fast) is now documented as available on Opus 4.8 and 4.7 only — Opus 4.6 has been removed from the list. Opus 4.7 fast mode is additionally flagged as deprecated with a removal date.

Details
  • Fast-mode eligibility (ig()) passes if the catalog fast_mode capability is set on the resolved model, or if the lowercase model ID contains opus-4-7 or opus-4-8; the previous opus-4-6 string match has been removed.
  • Fast mode is restricted to the first-party Anthropic API (uc() returns false for Bedrock, Vertex, and other providers); toggling on any other provider returns "Fast mode is only available when using the Anthropic API directly".
  • When toggled ON, the active fast-mode model resolves via alias "opus" (or "opus[1m]" for 1M context); iW() returns the display name "Opus 4.8" for the confirmation message.
  • The Opus 4.7 deprecation notice fires only when the currently active model resolves to claude-opus-4-7. The removal date is read from the tengu_sunset_penguin_opus47 GrowthBook flag (default "2026-07-25"); if the date has already passed or is unparseable, no notice is shown.
  • The deprecation notice (SGo()) carries priority: "immediate" and color: "warning", surfacing immediately on the next fast-mode toggle rather than as a background notification.
Evidence

Updated fast mode tip (search for "available on Opus 4.8/4.7.") and deprecation logic (search for "opus47-fast-mode-deprecation" and "tengu_sunset_penguin_opus47")

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.196 →