Anthropic Messages Endpoint¶

DeltaLLM exposes an Anthropic Messages API-compatible endpoint at POST /v1/messages. Requests are converted to the gateway's canonical chat format and routed through the same deployment routing, budgets, rate limits, and failover as /v1/chat/completions, so the target model can be served by any configured provider — not only Anthropic.

Authentication¶

The endpoint uses the same authentication as every other proxy endpoint: Authorization: Bearer YOUR_API_KEY.

Note

The Anthropic SDKs send the API key in an x-api-key header by default, which this endpoint does not accept. Configure your client to send a bearer token instead. With the Python SDK: Anthropic(auth_token="YOUR_API_KEY", base_url="http://localhost:8000").

Example¶

curl http://localhost:8000/v1/messages \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "Hello from DeltaLLM"}
    ]
  }'

The model value is a DeltaLLM public model name, resolved through the gateway's routing configuration like any other endpoint.

Supported¶

Text conversations with system prompts (string or text-block form)
text, tool_use, and tool_result content blocks, including the is_error flag on tool_result (forwarded as an Error: prefix on the tool message content)
Tool calling: tools, tool_choice (auto, any, tool, none), including full pass-through to Anthropic and Bedrock deployments in their native formats
Streaming via "stream": true — responses use Anthropic SSE event types (message_start, content_block_start, content_block_delta, content_block_stop, message_delta, message_stop), including streamed tool use
max_tokens (required), temperature, top_p, stop_sequences, metadata

Not Supported¶

Unsupported input is rejected with a 400 invalid_request_error — never silently dropped. This includes:

image and document content blocks (and any other non-text, non-tool block types)
top_k
Extended thinking (top-level thinking field), prompt caching (cache_control on any block), citations (citations on text blocks), and any other unrecognized top-level field or block field

Errors¶

Errors use the Anthropic error envelope:

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "messages[0].content[1]: unsupported content block type 'image'; this endpoint only forwards text and tool blocks"
  }
}

Gateway-level errors (rate limits, budget exhaustion, upstream failures) return the same status codes as the OpenAI-compatible endpoints.