Automatic Sonnet 4.5 → Sonnet 4.6 Migration / Claude Code v2.1.67

What

Users whose model setting references claude-sonnet-4-5-20250929 (or its [1m] extended-thinking variant) are automatically migrated to sonnet (or sonnet[1m]). A notification "Model updated to Sonnet 4.6" is shown briefly after the migration.

Details

Applies only to first-party (claude.ai-authenticated) users on Pro, Max, or Team plans
Extended thinking mode ([1m]) is preserved during migration
Users who have already started at least one session will see the notification; brand-new users will not

Evidence

Sonnet 4.5 to 4.6 migration (search for "tengu_sonnet45_to_46_migration" and "Model updated to Sonnet 4.6")

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

See this entry in the whole of v2.1.67 →

The build it came inv2.1.67

4 Mar 2026 · 4 entries, this one is #1.

Either side of it

v2.1.66Older
v2.1.68Newer

Open the release →

Names in this entry

modelclaude-sonnet-4-5-20250929
The dated first-party API id of Sonnet 4.5 (claude-sonnet-4-5 in Claude Code's model table), also used for the anthropic_aws, anthropic_google_cloud and gateway providers. On the first-party provider, when certain account checks pass, a startup migration rewrites a user-settings model of claude-sonnet-4-5-20250929 or sonnet-4-5-20250929 (with or without [1m]) to sonnet or sonnet[1m].
settingsonnet
The 1M-context restriction that blocks certain Sonnet model switches now also blocks opusplan[1m]
flagtengu_sonnet45_to_46_migration
An analytics event, not a feature flag. Claude Code logs it when its startup migration rewrites a user-settings model of Sonnet 4.5 (claude-sonnet-4-5-20250929 or sonnet-4-5-20250929, with or without [1m]) to sonnet or sonnet[1m], which it does only on the first-party provider for Pro, Max or Team (Max 5x tier) subscribers. Fields: from_model and has_1m.

Is this right?

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.