input vs. output models described with subtypes

gistfile1.yml

apiVersion: 1.0.0
swaggerVersion: "1.2"
basePath: "http://localhost:8002/api"
resourcePath: /pet
produces: 
  - application/json
  - application/xml
  - text/plain
  - text/html
apis: 
  - path: /user
    operations: 
      - method: POST
        summary: Add a user
        notes: ""
        type: OutputUser
        nickname: addUser
        parameters: 
          - name: body
            description: User to add
            required: true
            allowMultiple: false
            type: User
            paramType: body
        responseMessages: 
          - code: 400
            message: Invalid pet
models: 
  User: 
    id: User
    description: The base user
    required: 
      - name
    properties: 
      username: 
        type: string
    subTypes:
      - OutputUser
  OutputUser: 
    id: OutputUser
    description: A user with internal values
    required: 
      - id
    properties: 
      id: 
        type: integer
        format: int64

gistfile2.json

{
  "apiVersion": "1.0.0",
  "swaggerVersion": "1.2",
  "basePath": "http://localhost:8002/api",
  "resourcePath": "/pet",
  "produces": [
    "application/json",
    "application/xml",
    "text/plain",
    "text/html"
  ],
  "apis": [
    {
      "path": "/user",
      "operations": [
        {
          "method": "POST",
          "summary": "Add a user",
          "notes": "",
          "type": "OutputUser",
          "nickname": "addUser",
          "parameters": [
            {
              "name": "body",
              "description": "User to add",
              "required": true,
              "allowMultiple": false,
              "type": "User",
              "paramType": "body"
            }
          ],
          "responseMessages": [
            {
              "code": 400,
              "message": "Invalid pet"
            }
          ]
        }
      ]
    }
  ],
  "models": {
    "User": {
      "id": "User",
      "description": "The base user",
      "required": [
        "name"
      ],
      "properties": {
        "username": {
          "type": "string"
        }
      },
      "subTypes": [
        "OutputUser"
      ]
    },
    "OutputUser": {
      "id": "OutputUser",
      "description": "A user with internal values",
      "required": [
        "id"
      ],
      "properties": {
        "id": {
          "type": "integer",
          "format": "int64"
        }
      }
    }
  }
}

The OutputUser contains a service-generated id field