> ## Documentation Index
> Fetch the complete documentation index at: https://docs.evolink.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# GPT-5.5 - Complete API Reference

> - Use OpenAI SDK format to call GPT-5.5 model
- Synchronous processing mode, real-time response
- **Text conversation**: Single or multi-turn contextual dialogue
- **System prompts**: Customize AI role and behavior
- **Multimodal input**: Supports text + image mixed input
- Quick start? Check out [Quick Start Guide](./gpt-5.5-quickstart)

<Note>
  **BaseURL**: The default BaseURL is `https://direct.evolink.ai`, which has better support for text models and long-lived connections. `https://api.evolink.ai` is the primary endpoint for multimodal services and serves as a fallback address for text models.
</Note>


## OpenAPI

````yaml /en/api-manual/language-series/gpt-5.5/gpt-5.5-reference.json POST /v1/chat/completions
openapi: 3.1.0
info:
  title: GPT-5.5 Complete API Reference
  description: >-
    Complete API reference for GPT-5.5 chat interface, including all parameters
    and advanced features
  license:
    name: MIT
  version: 1.0.0
servers:
  - url: https://direct.evolink.ai
    description: Production (recommended)
  - url: https://api.evolink.ai
    description: Alternative URL
security:
  - bearerAuth: []
tags:
  - name: Chat Completion
    description: AI chat completion related endpoints
paths:
  /v1/chat/completions:
    post:
      tags:
        - Chat Completion
      summary: GPT-5.5 Chat Interface
      description: |-
        - Use OpenAI SDK format to call GPT-5.5 model
        - Synchronous processing mode, real-time response
        - **Text conversation**: Single or multi-turn contextual dialogue
        - **System prompts**: Customize AI role and behavior
        - **Multimodal input**: Supports text + image mixed input
        - Quick start? Check out [Quick Start Guide](./gpt-5.5-quickstart)
      operationId: createChatCompletion
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/ChatCompletionRequest'
            examples:
              simple_text:
                summary: Single-turn text conversation
                value:
                  model: gpt-5.5
                  messages:
                    - role: user
                      content: Please introduce yourself
              multi_turn:
                summary: Multi-turn conversation (context understanding)
                value:
                  model: gpt-5.5
                  messages:
                    - role: user
                      content: What is Python?
                    - role: assistant
                      content: Python is a high-level programming language...
                    - role: user
                      content: What are its advantages?
              system_prompt:
                summary: Using system prompts
                value:
                  model: gpt-5.5
                  messages:
                    - role: system
                      content: >-
                        You are a professional Python programming assistant.
                        Answer questions concisely.
                    - role: user
                      content: How to read a file?
              vision:
                summary: Multimodal input (text + image)
                value:
                  model: gpt-5.5
                  messages:
                    - role: user
                      content:
                        - type: text
                          text: >-
                            Please describe the scene and main elements in this
                            image in detail.
                        - type: image_url
                          image_url:
                            url: https://example.com/image.png
              multi_image:
                summary: Multiple image input
                value:
                  model: gpt-5.5
                  messages:
                    - role: user
                      content:
                        - type: text
                          text: Compare the differences between these two images
                        - type: image_url
                          image_url:
                            url: https://example.com/image1.png
                        - type: image_url
                          image_url:
                            url: https://example.com/image2.png
      responses:
        '200':
          description: Chat completion successful
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ChatCompletionResponse'
        '400':
          description: Invalid request parameters
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 400
                  message: Invalid request parameters
                  type: invalid_request_error
        '401':
          description: Unauthorized, invalid or expired token
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 401
                  message: Invalid or expired token
                  type: authentication_error
        '402':
          description: Insufficient quota, recharge required
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 402
                  message: Insufficient quota
                  type: insufficient_quota_error
                  fallback_suggestion: https://evolink.ai/dashboard/billing
        '403':
          description: Access denied
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 403
                  message: Access denied for this model
                  type: permission_error
                  param: model
        '404':
          description: Resource not found
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 404
                  message: Specified model not found
                  type: not_found_error
                  param: model
                  fallback_suggestion: gpt-5.5
        '413':
          description: Request body too large
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 413
                  message: Image file too large
                  type: request_too_large_error
                  param: content
                  fallback_suggestion: compress image to under 10MB
        '429':
          description: Rate limit exceeded
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 429
                  message: Rate limit exceeded
                  type: rate_limit_error
                  fallback_suggestion: retry after 60 seconds
        '500':
          description: Internal server error
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 500
                  message: Internal server error
                  type: internal_server_error
                  fallback_suggestion: try again later
        '502':
          description: Upstream service error
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 502
                  message: Upstream AI service unavailable
                  type: upstream_error
                  fallback_suggestion: try different model
        '503':
          description: Service temporarily unavailable
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              example:
                error:
                  code: 503
                  message: Service temporarily unavailable
                  type: service_unavailable_error
                  fallback_suggestion: retry after 30 seconds
components:
  schemas:
    ChatCompletionRequest:
      type: object
      required:
        - model
        - messages
      properties:
        model:
          type: string
          description: Model name for chat completion
          enum:
            - gpt-5.5
          default: gpt-5.5
          example: gpt-5.5
        messages:
          type: array
          description: >-
            List of messages for the conversation, supports multi-turn dialogue
            and multimodal input (text, images)
          items:
            $ref: '#/components/schemas/Message'
          minItems: 1
        stream:
          type: boolean
          description: >-
            Whether to stream the response


            - `true`: Stream response, returns content chunk by chunk in
            real-time

            - `false`: Wait for complete response and return all at once
          example: false
        temperature:
          type: number
          description: |-
            Sampling temperature, controls randomness of output

            **Notes**:
            - Lower values (e.g., 0.2): More deterministic and focused output
            - Higher values (e.g., 1.5): More random and creative output
          minimum: 0
          maximum: 2
          example: 0.7
        top_p:
          type: number
          description: >-
            Nucleus sampling parameter


            **Notes**:

            - Controls sampling from tokens with cumulative probability

            - For example, 0.9 means sampling from tokens with top 90%
            cumulative probability

            - Default: 1.0 (considers all tokens)


            **Recommendation**: Do not adjust both temperature and top_p
            simultaneously
          minimum: 0
          maximum: 1
          example: 0.9
        top_k:
          type: integer
          description: >-
            Top-K sampling parameter


            **Notes**:

            - For example, 10 means only considering the top 10 most probable
            tokens during each sampling step

            - Smaller values make output more focused

            - Default: unlimited
          minimum: 1
          example: 40
    ChatCompletionResponse:
      type: object
      properties:
        id:
          type: string
          description: Unique identifier for the chat completion
          example: chatcmpl-20251010015944503180122WJNB8Eid
        model:
          type: string
          description: The model used for completion
          example: gpt-5.5
        object:
          type: string
          enum:
            - chat.completion
          description: Response type
          example: chat.completion
        created:
          type: integer
          description: Unix timestamp when the completion was created
          example: 1760032810
        choices:
          type: array
          description: List of completion choices
          items:
            $ref: '#/components/schemas/Choice'
        usage:
          $ref: '#/components/schemas/Usage'
    ErrorResponse:
      type: object
      properties:
        error:
          type: object
          properties:
            code:
              type: integer
              description: HTTP status error code
            message:
              type: string
              description: Error message
            type:
              type: string
              description: Error type
            param:
              type: string
              description: Related parameter name
            fallback_suggestion:
              type: string
              description: Suggestion for handling the error
    Message:
      type: object
      required:
        - role
        - content
      properties:
        role:
          type: string
          description: |-
            Message role

            - `user`: User message
            - `assistant`: AI assistant message (for multi-turn dialogue)
            - `system`: System prompt (sets AI role and behavior)
          enum:
            - user
            - assistant
            - system
          example: user
        content:
          type: array
          description: >-
            Message content. Supports two formats:


            **1. Plain text string**: Pass a string directly, e.g.,
            `"content":"Please introduce yourself"`


            **2. Object array** (supports text input, multimodal input): See
            structure below
          items:
            $ref: '#/components/schemas/ContentPart'
    Choice:
      type: object
      properties:
        index:
          type: integer
          description: Index of this choice
          example: 0
        message:
          $ref: '#/components/schemas/AssistantMessage'
        finish_reason:
          type: string
          description: Reason why the completion finished
          enum:
            - stop
            - length
            - content_filter
          example: stop
    Usage:
      type: object
      description: Token usage statistics
      properties:
        prompt_tokens:
          type: integer
          description: Number of tokens in the input
          example: 13
        completion_tokens:
          type: integer
          description: Number of tokens in the output
          example: 1891
        total_tokens:
          type: integer
          description: Total number of tokens used
          example: 1904
        prompt_tokens_details:
          type: object
          description: Input token details
          properties:
            cached_tokens:
              type: integer
              description: Number of cached tokens
              example: 0
            text_tokens:
              type: integer
              description: Number of text tokens
              example: 13
            audio_tokens:
              type: integer
              description: Number of audio tokens
              example: 0
            image_tokens:
              type: integer
              description: Number of image tokens
              example: 0
        completion_tokens_details:
          type: object
          description: Output token details
          properties:
            text_tokens:
              type: integer
              description: Number of text tokens
              example: 0
            audio_tokens:
              type: integer
              description: Number of audio tokens
              example: 0
            reasoning_tokens:
              type: integer
              description: Number of reasoning tokens
              example: 1480
        input_tokens:
          type: integer
          description: Number of input tokens (compatibility field)
          example: 0
        output_tokens:
          type: integer
          description: Number of output tokens (compatibility field)
          example: 0
        input_tokens_details:
          type: object
          nullable: true
          description: Input token details (compatibility field)
          example: null
    ContentPart:
      oneOf:
        - $ref: '#/components/schemas/TextContent'
        - $ref: '#/components/schemas/ImageContent'
    AssistantMessage:
      type: object
      properties:
        role:
          type: string
          description: Role of the message sender
          enum:
            - assistant
          example: assistant
        content:
          type: string
          description: AI's response content
          example: >-
            Hello! I'm GPT-5.5, with enhanced reasoning and understanding
            capabilities. I excel at handling complex problems, multi-step
            reasoning, and code generation.\n\nKey features include:\n- Stronger
            logical reasoning\n- Better context understanding\n- More accurate
            code generation
    TextContent:
      title: Text content
      type: object
      required:
        - type
        - text
      properties:
        type:
          type: string
          enum:
            - text
          description: Content type
        text:
          type: string
          description: Text content
          example: Please describe this image in detail
    ImageContent:
      title: Image content
      type: object
      required:
        - type
        - image_url
      properties:
        type:
          type: string
          enum:
            - image_url
          description: Content type
        image_url:
          type: object
          required:
            - url
          properties:
            url:
              type: string
              format: uri
              description: >-
                Image URL


                **Limits**:

                - Max size per image: `10MB`

                - Supported formats: `.jpeg`, `.jpg`, `.png`, `.webp`

                - URL requirements: Must be publicly accessible, typically ends
                with image extension
              example: https://example.com/image.png
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      description: >-
        ## All APIs require Bearer Token authentication ##


        **Get API Key:**


        Visit [API Key Management Page](https://evolink.ai/dashboard/keys) to
        get your API Key


        **Add to request header:**

        ```

        Authorization: Bearer YOUR_API_KEY

        ```

````