**Note**: You probably don't need `contextvars`, and you should probably avoid using them. But they are powerful and useful in some advanced scenarios, for example, migrating from code that used Flask's `g` semi-global variable.

**Technical Details**: If you want to know more of the technical details you can check out the PR description [#4575](https://github.com/tiangolo/fastapi/pull/4575).

### Internal