First Check

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Example Code

from fastapi import FastAPI
from pydantic import BaseModel
from typing import List, Self

app = FastAPI()

class Node(BaseModel):
    id: str
    children: List[Self] = []

@app.get("/node", response_model=Node)
def get_node():
    return Node(
        id="root",
        children=[Node(id="child1"), Node(id="child2")]
    )

Description

pydantic.errors.PydanticUserError: typing.Self is invalid in this context
I expected FastAPI to generate the OpenAPI schema and allow me to see the recursive model structure in the docs. How can I define recursive Pydantic models in FastAPI so that OpenAPI generation works correctly with Self or similar constructs?

Operating System

Linux, Windows

Operating System Details

No response

FastAPI Version

FastAPI Version: 0.121.1

Pydantic Version

Pydantic Version: 2.12.4

Python Version

Python Version: 3.14.0

Additional Context

I want to use recursive models for tree-like data structures (e.g., nested menus, organizational charts) and have proper OpenAPI documentation generated automatically.