What probably matters to youSection of the release
What
Running /model with a model name now consults any registered model-switch hooks before the model changes. A hook can block the switch outright, in which case you see "model switch blocked by a PreModelSwitch hook" and are told to run /model to confirm, or it can answer "ask", which leaves the model unchanged and directs you to /model interactively. Hooks can also attach their own messages to the confirmation, so a switch that needs a second look explains why instead of failing silently.
Details
Only engaged when model-switch hooks are registered by the caller; with none registered, switching behaves exactly as before.
A hook answering "ask" changes nothing and defers to the interactive /model picker.
The check on whether a model is available now gives up and reports "Couldn't confirm model '" rather than hanging indefinitely when it stalls.
Evidence
Couldn't confirm model ', model switch blocked by a PreModelSwitch hook
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed sinceAnthropic's documentation has since written up PreModelSwitch, on Hooks reference.| PreModelSwitch | `hookSpecificOutput` or top-level `decision` | `permissionDecision` (allow/deny/ask), `permissionDecisionReason`. `decision: "block"` also [cancels the switch](#premodelswitch-decision-control) |hookssee the edit
Confirmed sinceAnthropic's documentation has since written up /model, on All settings.Cap the [effort level](/docs/en/model-config#adjust-effort-level) a session can use, leaving lower levels available. Any higher level runs at the cap instead, including one from `/effort`, the `/model` picker, `--effort`, [`CLAUDE_CODE_EFF…settings-referencesee the edit
Added sinceA small documentation edit on Agent SDK reference - TypeScript touched a line naming /model after this was published.`effortLevel` accepts an [effort level](/docs/en/model-config#adjust-effort-level) name. It also accepts `"ultracode"`, which requests `xhigh` effort with [ultracode](/docs/en/workflows#let-claude-decide-with-ultracode) on. `applyFlagSetti…agent-sdk/typescriptsee the edit
How sure we are
Two sources agreeTwo things we can check say the same as this entry.
Anthropic's documentation agreesA small documentation edit on Agent SDK reference - TypeScript touched a line naming /model after this was published.
Anthropic's release notes agreeAdded PreModelSwitch and PostModelSwitch hook events (block, confirm, or annotate a model switch); SessionStart resume hooks now receive…
