claude-sonnet-4-5-20250929 (text to text) - GPTProto API Documentation

Claude’s openai format for the text to text API.

curl -X POST "https://gptproto.com/v1/chat/completions" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "claude-sonnet-4-5-20250929",
  "messages": [
    {
      "role": "user",
      "content": "Who are you?"
    }
  ],
  "stream": false
}'

{
  "error": {
    "message": "Invalid signature",
    "type": "401"
  }
}

Parameters

Parameter	Type	Required	Default	Range	Description
`model`	string	✅ Yes	`claude-sonnet-4-5-20250929`	-	The model to use for the request. `claude-sonnet-4-5-20250929`
`messages`	array	✅ Yes	-	-	Array of message objects for the conversation. Each message must have a `role` (user/assistant) and `content` (string or array of content blocks)
`max_tokens`	integer	❌ No	-	1-64000	Maximum number of tokens to generate in the response
`temperature`	number	❌ No	`1.0`	0.0-2.0	Controls randomness in output. Use lower values (closer to 0.0) for analytical tasks, higher values (closer to 2.0) for creative tasks
`top_p`	number	❌ No	-	0.0-1.0	Nucleus sampling threshold. Controls diversity by considering only tokens with cumulative probability up to top_p. Recommended for advanced use only. Do not use with temperature
`top_k`	integer	❌ No	-	>0	Only sample from the top K options for each token. Removes low probability responses. Recommended for advanced use only
`stream`	boolean	❌ No	`false`	-	Whether to stream the response incrementally using server-sent events
`stop`	array	❌ No	-	Max 8191 sequences	Custom text sequences that will cause the model to stop generating. Each sequence must contain non-whitespace characters
`presence_penalty`	number	❌ No	`0`	-2.0 to 2.0	Positive values penalize new tokens based on whether they appear in the text so far
`frequency_penalty`	number	❌ No	`0`	-2.0 to 2.0	Positive values penalize new tokens based on their existing frequency in the text so far

Messages Array Structure

Each message object in the messages array should have the following structure:

Field	Type	Required	Range	Description
`role`	string	✅ Yes	-	The role of the message. Can be: `user` or `assistant`
`content`	array/string	✅ Yes	-	The content of the message. Can be a simple string for text-only messages, or an array of content blocks for multimodal content

Content Block Structure (when content is an array)

Field	Type	Required	Range	Description
`type`	string	✅ Yes	-	Must be `text`
`text`	string	✅ Yes	-	The text content

API Reference

​Parameters

​Messages Array Structure

​Content Block Structure (when content is an array)

Parameters

Messages Array Structure

Content Block Structure (when content is an array)