FastAPI Depends() doesn't cache across requests

Took me a minute. Depends() deduplicates within a single request — if two endpoints in a chain both depend on get_db(), it's resolved once. But the next request gets a fresh resolution.

That's a feature: per-request DB sessions are what you want. But if you expected app-wide singleton behavior (config, cached HTTP client), use a module-level instance or lru_cache:

from functools import lru_cache

@lru_cache
def get_settings() -> Settings:
    return Settings()

# Then in routes:
def handler(settings: Annotated[Settings, Depends(get_settings)]):
    ...

lru_cache makes get_settings a singleton; Depends happily reuses it.