Claude Code is more careful with custom API endpoints and gateways

What

ANTHROPIC_BASE_URL sends Claude Code's requests to a different address, such as a company proxy or gateway. Several changes concern what happens when that address is not an Anthropic host.

• The remote settings fetch no longer sends your API key when ANTHROPIC_BASE_URL is not an Anthropic host. It fails with "API key not sent: ANTHROPIC_BASE_URL is not an Anthropic host". Before, the key was always sent as x-api-key. A first-party TLS request path is also checked more strictly.
• Some features that depend on remote settings are turned off by an API provider or a custom base URL. Claude Code now works out who set that: a machine administrator, the process environment, a launch flag, served settings or a settings file. It then tells you which source turned the feature off, or tells you to contact your administrator.
• The attribution header can now end with cc_gateway=1; or cc_gateway=env; when a gateway is in use and the base URL is not a vouched Anthropic host.
• Result messages gain an internal api_error_origin field. It is marked first_party only when an error came from api.anthropic.com over verified TLS, with no base URL override or gateway.
• The SDK result schema, for both success and error, also gains an optional interrupted_by_shutdown field.

Why

If you route Claude Code through your own proxy, the remote settings fetch no longer hands that proxy your Anthropic API key. You also get a reason when a feature is off because of your endpoint. Programs built on the SDK can tell errors from Anthropic's own API apart from errors that passed through a proxy.