Versioned documentation in FastAPI, based on https://gist.github.com/Kludex/1c515aa38d22ec28d514da6b6f36da9f

main.py

# uvicorn main:app --host $(hostname) --port 8080 --log-level debug --reload

from fastapi import APIRouter, FastAPI

from utils import create_versioned_docs

VERSION = '2.0.0'
TITLE = 'Sample Versioned API'
DESCRIPTION = 'Sample versioned API blurb'
app = FastAPI(docs_url=None, redoc_url=None, title=TITLE, version=VERSION, description=DESCRIPTION)

v1_router = APIRouter(prefix="/v1")
v2_router = APIRouter(prefix="/v2")

info = {
    'version': '1.2.0',
    'title': 'Sample Versioned API v1',
    'description': 'Version specific blurb for v1'
}
create_versioned_docs(v1_router, **info)

info = {
    'version': '2.0.0',
    'title': 'Sample Versioned API v2',
    'description': 'Version specific blurb for v2'
}
create_versioned_docs(v2_router, **info)


@v1_router.get("/")
def get_hello_world():
    return {
        "version": "v1",
        "message": "Hello World"
    }


@v1_router.get("/foo")
def get_foo():
    return {
        "version": "v1",
        "message": "foo"
    }


@v2_router.get("/")
def get_another_world():
    return {
        "version": "v2",
        "message": "Another World"
    }


@v2_router.get("/bar")
def get_bar():
    return {
        "version": "v2",
        "message": "bar"
    }


app.include_router(v1_router)
app.include_router(v2_router)

requirements.txt

fastapi>=0.68.1
gunicorn>=20.1.0
pydantic>=1.8.2
pylint>=2.10.2
uvicorn>=0.15.0
yapf>=0.31.0

utils.py

import copy
from collections import defaultdict
from typing import Any, DefaultDict, Dict, Optional

from fastapi import APIRouter, Request
from fastapi.openapi.docs import get_redoc_html, get_swagger_ui_html
from fastapi.responses import HTMLResponse

custom_openapi: DefaultDict[str, Optional[Dict[str, Any]]] = defaultdict(lambda: None)


def create_versioned_docs(router: APIRouter, **info) -> None:
    prefix = router.prefix

    @router.get("/openapi.json", include_in_schema=False, name=f"{prefix}_openapi")
    async def get_openapi_json(request: Request) -> dict:
        version = request.url.path.strip("/").split("/")[0]
        if custom_openapi[version] is None:
            custom_openapi[version] = copy.deepcopy(request.app.openapi())
            for key, value in info.items():
                custom_openapi[version]['info'][key] = value

            # Remove other version tags on openapi schema.
            for path in custom_openapi[version]["paths"].copy():
                if not path.startswith(f"/{version}"):
                    del custom_openapi[version]["paths"][path]

        return custom_openapi[version]

    @router.get("/docs", include_in_schema=False, name=f"{prefix}_swagger")
    async def get_swagger(request: Request) -> HTMLResponse:
        return get_swagger_ui_html(
            openapi_url=f"{prefix}/openapi.json",
            title=request.app.title + " - Swagger UI",
        )

    @router.get("/redoc", include_in_schema=False, name=f"{prefix}_redoc")
    async def redoc_html(request: Request) -> HTMLResponse:
        return get_redoc_html(
            openapi_url=f"{prefix}/openapi.json",
            title=request.app.title + " - ReDoc"
        )