Create a chat completion

POST /v1/chat/completions

Model-specific vision and tool support. stream=true returns SSE; usage-only events may have empty choices. Client cancellation closes the upstream connection. Cancelled streams with zero recorded output tokens are not charged; partial usage after output may be estimated and billed. No automatic retry after response starts.

Base URL: https://api.simplellm.eu. Authenticate using Authorization: Bearer $SIMPLELLM_API_KEY.

Request body

Content-Type: application/json

Nested required fields are required only when their containing object is supplied. Extra chat parameters may be provider-specific; acceptance does not guarantee model support.

Example request

curl --fail-with-body https://api.simplellm.eu/v1/chat/completions \
  -H "Authorization: Bearer $SIMPLELLM_API_KEY" \
  -H 'Content-Type: application/json' \
  -d '{
  "model": "qwen3.8-flash-next",
  "messages": [
    {
      "role": "user",
      "content": "Explain what an API is in one sentence."
    }
  ],
  "max_tokens": 1024
}'

Responses

HTTP 200

JSON response or incremental SSE stream ending with data: [DONE].

Content-Type: application/json

Illustrative response shape only; IDs, timestamps and counters below are synthetic, not live limits or customer data.

{
  "id": "chatcmpl-example",
  "object": "chat.completion",
  "created": 1789380000,
  "model": "qwen3.8-flash-next",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "An API lets software communicate."
      },
      "finish_reason": "stop"
    }
  ],
  "usage": {
    "prompt_tokens": 20,
    "completion_tokens": 10,
    "total_tokens": 30,
    "prompt_tokens_details": {
      "cached_tokens": 0
    }
  }
}

Content-Type: text/event-stream

Response type: string.

data: {"choices":[{"delta":{"content":"Hello"}}]}

data: [DONE]

Error handling

Errors can occur in authentication, billing, routing or the upstream service; not every status applies to every route.

See Troubleshooting for response examples and Rate limits & retries for retry rules.

Machine-readable schema

Download OpenAPI JSON. Operation ID: createChatCompletion.