The Thesys C1 API is fully compatible with the OpenAI API, making it easy to integrate into your existing applications. You can use any OpenAI SDK or make direct HTTP requests to interact with our models.

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Base URL

The base URL for the Thesys C1 API is: 
https://api.thesys.dev/v1/embed/chat/completions

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Authentication

All requests require an API key to be included in the Authorization header: 
Authorization: Bearer YOUR_API_KEY

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Examples

Manually calling the API via cURL:
curl -X POST https://api.thesys.dev/v1/embed/chat/completions \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "c1/anthropic/claude-sonnet-4/v-20250617",
    "messages": [
      {
        "role": "user",
        "content": "Create a simple contact form"
      }
    ],
    "temperature": 0.7,
    "max_tokens": 1500
  }'

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Streaming Responses

The C1 API also supports streaming responses, just like the OpenAI API: 
stream = client.chat.completions.create(
  model="c1/anthropic/claude-sonnet-4/v-20250617",
  messages=[{"role": "user", "content": "Hello"}],
  stream=True,
)

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Parameters

The C1 API supports most standard OpenAI chat completion parameters:
  • model: The model to use. See Models for more information.
  • messages: Array of message objects with role and content
  • temperature: Controls randomness (0.0 to 1.0)
  • max_tokens: Maximum tokens in the response
  • stream: Whether to stream the response
  • top_p: Nucleus sampling parameter
  • parallel_tool_calls: Whether to call tools in parallel
  • stop: Stop sequences

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Responses

The C1 API represents a JSON object as a XML document which can be rendered by the <C1Component /> or is automatically handled by the <C1Chat /> component if you are building a conversational application. See the integration guide for more information.

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Error

The API returns standard HTTP status codes and error responses compatible with OpenAI’s format: 
{
  "error": {
    "message": "Invalid API key provided",
    "type": "invalid_request_error",
    "code": "invalid_api_key"
  }
}