tengu_sonnet45_to_46_migration
A Claude Code feature flag, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.
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.
Not Anthropic's. Written by Claude Opus 5.5 from reading the v2.1.286 bundle, and it can be wrong.
In the changelogs
1Releases whose published page names tengu_sonnet45_to_46_migration.
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v2.1.67
Automatic Sonnet 4.5 → Sonnet 4.6 Migration
gate cited by this entry, found in this entry's text
Gate readings
0No release here has a gate table behind it for this flag. Most published releases have none at all: the readings exist only for versions the pipeline captured flag state on.
First cited
1The earliest release whose published evidence quoted tengu_sonnet45_to_46_migration was v2.1.67, 4 Mar 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.
Presence across releases
0The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was never mined.
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the feature flag does. All feature flags.