Claude Code and OpenAI-compatible APIs: what works directly.

Claude Code does not become an OpenAI Chat Completions client when you set ANTHROPIC_BASE_URL. For that setting, its gateway must speak Anthropic Messages. Claude Code also has separate connection modes for Amazon Bedrock and Google Cloud’s Agent Platform.

Match Claude Code’s request format

A service that only exposes /v1/chat/completions does not, by itself, satisfy Claude Code’s Anthropic Messages connection. The formats use different paths and request bodies.

Choose the route from the endpoint you have

• Your endpoint offers only OpenAI Chat Completions: connect it from software that documents OpenAI-compatible Chat Completions. See the ChinaGenAI endpoint compatibility notes.
• You want to use Claude Code: confirm that your gateway exposes Anthropic Messages, or configure Claude Code’s documented Bedrock or Agent Platform mode.
• Your gateway translates between formats: confirm that it accepts Anthropic Messages from Claude Code and forwards the required request fields, tool calls and streaming behavior to its upstream. “OpenAI-compatible” alone does not prove this translation is available.

HTTP_PROXY and HTTPS_PROXY route network traffic through an HTTP proxy. They do not translate a Chat Completions request into Anthropic Messages.

Separate a path error from a credential error

• POST /v1/messages returns 404: check whether that server actually implements Anthropic Messages at the configured base URL. A Chat Completions-only service uses a different route. This points to a protocol or path check; it does not identify the cause by itself.
• The model is missing from /model: model discovery is separate from a chat request. Claude Code’s gateway model discovery is opt-in and uses GET /v1/models for an Anthropic Messages gateway. An empty picker alone does not prove that a configured inference route is broken.
• HTTP 401: inspect the credential variable and authentication header required by that gateway. Do not rotate a key to fix a request sent to the wrong protocol or path.
• HTTP 400 involving tools or message fields: preserve the redacted request shape and check what the adapter forwards. Claude Code adds fields beyond a basic text exchange, and an adapter may not support every feature.

Keep the method, path and response status, but redact authorization headers, tokens, query values and private hostnames before sharing a capture. For a saved response, use the raw response checklist and API error guide.

Model discovery is optional

Claude Code can request a gateway model list when CLAUDE_CODE_ENABLE_GATEWAY_MODEL_DISCOVERY=1 is enabled. The official guide says discovery applies to the Anthropic Messages format; Bedrock and Agent Platform modes use their provider-specific behavior. Check the exact request in the gateway log before treating a failed discovery request as a failed chat route.

To prepare a standard OpenAI Chat Completions body without sending it, use the local request builder. It cannot convert that body into Anthropic Messages.

Official references

Claude Code: Gateway compatibility and API formats
Claude Code: Connect to an LLM gateway

Official Claude Code gateway documentation checked 27 October 2026. No key, Claude Code session or model request was used.