Under the hood
Internal list of allowed API request fields switched from an array to a Set
What
A behind-the-scenes list of top-level fields allowed in Claude API requests (things like model, system, and tools) was changed from a plain array to a Set, an internal data structure used for faster membership checks.
Why
This is an internal efficiency change with no visible effect on how Claude Code behaves.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
The finding does not say where this allowlist is used or what request handling it affects.