What changed
Claude Code 2.1.278 makes its server-side auto-mode classifier the default for Claude API and Enterprise users and for Bedrock, Vertex, Foundry and gateway sessions. Anthropic says server-side classification does not charge classifier overhead; affected gateway deployments can opt out, and the CLI now reports whether the server path is active.
Why it matters
Moving a permission classifier changes both billing and a control-path dependency. A proxy or gateway that cannot preserve the required request and response fields may fall back to the billed local path, so teams need evidence that the advertised mode is actually active.
What to do
Pin 2.1.278 in a canary session, inspect the Auto mode server row in /status, exercise one allowed and one blocked command through the real gateway, and reconcile usage records. Test the documented opt-out and billed fallback before changing enterprise defaults.
Caveat
The no-overhead statement is Anthropic's product claim, not an independent billing audit. Eligibility varies by account and provider path, and an incompatible gateway can trigger billed fallback; personal plan behavior is not established by this release note.