API Versioning: Strategies That Won't Break Your Clients
APIs evolve. Fields get renamed, endpoints change, entire resources get restructured. The question isn’t whether to version your API—it’s how to do it without breaking every client that depends on you. Versioning Strategies 1. URL Path Versioning The most visible approach—version is part of the URL: G G E E T T / / a a p p i i / / v 1 2 / / u u s s e e r r s s / / 1 1 2 2 3 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 from fastapi import FastAPI, APIRouter app = FastAPI() # Version 1 v1_router = APIRouter(prefix="/api/v1") @v1_router.get("/users/{user_id}") async def get_user_v1(user_id: int): return { "id": user_id, "name": "John Doe", "email": "john@example.com" } # Version 2 - restructured response v2_router = APIRouter(prefix="/api/v2") @v2_router.get("/users/{user_id}") async def get_user_v2(user_id: int): return { "id": user_id, "profile": { "name": "John Doe", "email": "john@example.com" }, "metadata": { "created_at": "2026-01-01T00:00:00Z", "updated_at": "2026-02-11T00:00:00Z" } } app.include_router(v1_router) app.include_router(v2_router) Pros: Explicit, easy to understand, easy to route Cons: URLs change between versions, harder to maintain multiple versions ...