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Example Code

import json
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str


class Config(BaseModel):
    item: Item


class User(BaseModel):
    config: Config


@app.post("/users", response_model=User)
async def create_user(user: User):
    return user


print(json.dumps(app.openapi(), indent=2))

Description

Hello 👋

In the provided code example, there is no default value for User, Config or Item models so I would not expect any -Input or -Output"schemas in openapi.json, but I do get User-Input and User-Output schemas, which are identical :

{
  // ...
  "components": {
    "schemas": {
      "Config": {
        "properties": {
          "item": {
            "$ref": "#/components/schemas/Item"
          }
        },
        "type": "object",
        "required": [
          "item"
        ],
        "title": "Config"
      },
      "Item": {
        "properties": {
          "name": {
            "type": "string",
            "title": "Name"
          }
        },
        "type": "object",
        "required": [
          "name"
        ],
        "title": "Item"
      },
      "User-Input": {
        "properties": {
          "config": {
            "$ref": "#/components/schemas/Config"
          }
        },
        "type": "object",
        "required": [
          "config"
        ],
        "title": "User"
      },
      "User-Output": {
        "properties": {
          "config": {
            "$ref": "#/components/schemas/Config"
          }
        },
        "type": "object",
        "required": [
          "config"
        ],
        "title": "User"
      }
    }
  }
}

Any Idea what could cause that ? Thanks a lot !

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.121.0

Pydantic Version

2.12.3

Python Version

3.13.3

Additional Context

No response