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POST
/
v1
/
chat
/
completions
gemini-3-pro-image-preview (Image Edit (Chat))
curl --request POST \
  --url https://api.example.com/v1/chat/completions

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API Key Authentication

GPTProto API uses Bearer token authentication. All API requests must include your API key (sk-xxxxx) in the Authorization header.

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Getting Your API Key

  1. Sign up for a GPTProto account at https://gptproto.com
  2. Navigate to the API Keys section in your dashboard
  3. Generate a new API key
  4. Copy and securely store your API key For authentication details, please refer to the Authentication section.

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Initiate Request

curl --location --request POST 'https://gptproto.com/v1/chat/completions' \
--header 'Authorization: GPTPROTO_API_KEY' \
--header 'Content-Type: application/json' \
--data-raw '{
  "model": "gemini-3-pro-image-preview",
  "messages": [
    {
      "role": "user",
      "content": [
        {
          "type": "text",
          "text": "Put a hat on the cat"
        },
        {
          "type": "image_url",
          "image_url": {
            "url": "https://tos.gptproto.com/resource/cat.png"
          }
        }
      ]
    }
  ]
}'

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Response Example

{
    "choices": [
        {
            "finish_reason": "stop",
            "index": 0,
            "message": {
                "content": "![image](data:image/jpeg;base64,*****)",
                "role": "assistant"
            }
        }
    ],
    "created": 1766481392,
    "id": "chatcmpl-**",
    "model": "gemini-3-pro-image-preview",
    "object": "chat.completion",
    "usage": {
        "completion_tokens": 1319,
        "completion_tokens_details": {
            "accepted_prediction_tokens": 0,
            "audio_tokens": 0,
            "reasoning_tokens": 116,
            "rejected_prediction_tokens": 0
        },
        "prompt_tokens": 265,
        "prompt_tokens_details": {
            "audio_tokens": 0,
            "cached_tokens": 0
        },
        "total_tokens": 1584
    }
}

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Parameters

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Core Parameters

ParameterTypeRequiredDefaultRangeDescription
modelstring✅ Yes--Model ID used to generate the response. OpenAI offers a wide range of models with different capabilities, performance characteristics, and price points. Refer to the model guide to browse and compare available models.
messagesarray✅ Yes--A list of messages comprising the conversation so far. Depending on the model you use, different message types (modalities) are supported, like text, images, and audio.
>messages.rolestring✅ Yes-developer
user
system		The role of the messages author.
>messages.namestring❌ No--An optional name for the participant. Provides the model information to differentiate between participants of the same role.
>messages.contentstring / array✅ Yes--The contents of the developer message.
>>messages.content.typestring✅ Yes-text
image_url		The type of the content part
>>messages.content.textstring❌ No--The text content
>>messages.content.image_urlobject❌ No--The image URL content
>>messages.content.image_url.urlstring❌ No--The URL of the image

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Error Codes

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Common Error Codes

Error CodeError NameDescription
401UnauthorizedAPI key is missing or invalid
403ForbiddenYour API key doesn’t have permission to access this resource, or insufficient balance for the requested operation
429Too Many RequestsYou’ve exceeded your rate limit
500Internal server errorAn internal server error occurred
503Content policy violationContent blocked due to safety concerns (actual status code is 400)