Using the Claude API from mainland China: same protocol, only the Base URL changes

The Anthropic protocol is unchanged: POST /v1/messages with x-api-key and anthropic-version. Point the SDK at a compatible gateway and you keep your code.

• One sentence on the protocol layer: same body, same headers, one variable.
• Two common routes: SDK base_url override, or an OpenAI-compatible wrapper.
• Billing: watch input/output token split and cached-input pricing.