### `response_model` Priority

If you declare both a return type and a `response_model`, the `response_model` will take priority and be used by FastAPI.

It requires a little bit more verbose configurations. And as it is based on WSGI (instead of ASGI), it is not designed to take advantage of the high performance provided by tools like Uvicorn, Starlette and Sanic.

### Technical Details: `root_path`

When you mount a sub-application as described above, FastAPI will take care of communicating the mount path for the sub-application using a mechanism from the ASGI specification called a `root_path`.

That way, the sub-application will know to use that path prefix for the docs UI.

The only thing the function returned by `GzipRequest.get_route_handler` does differently is convert the `Request` to a `GzipRequest`.

Doing this, our `GzipRequest` will take care of decompressing the data (if necessary) before passing it to our *path operations*.

After that, all of the processing logic is the same.

If you can choose a more recent version of Python for your project, you will be able to take advantage of that extra simplicity.

In all the docs there are examples compatible with each version of Python (when there's a difference).

* Running on startup
* Restarts
* Replication (the number of processes running)
* Memory
* Previous steps before starting

Understanding these ideas and how to apply them should give you the intuition necessary to take any decisions when configuring and tweaking your deployments. 🤓

    So, behind the scenes, it will actually work as if everything was the same single app.

!!! check
    You don't have to worry about performance when including routers.

    This will take microseconds and will only happen at startup.

    So it won't affect performance. ⚡

### Include an `APIRouter` with a custom `prefix`, `tags`, `responses`, and `dependencies`

This release has **no breaking changes**. 🎉

It upgrades the version ranges of sub-dependencies to allow applications using FastAPI to easily upgrade them.

Soon there will be a new FastAPI release upgrading Starlette to take advantage of recent improvements, but as that has a higher chance of having breaking changes, it will be in a separate release.

### Features

  - url: https://www.svix.com/
    title: Svix - Webhooks as a service
    img: https://fastapi.tiangolo.com/img/sponsors/svix.svg
  - url: https://www.codacy.com/?utm_source=github&utm_medium=sponsors&utm_id=pioneers
    title: Take code reviews from hours to minutes
    img: https://fastapi.tiangolo.com/img/sponsors/codacy.png
bronze:
  - url: https://www.exoflare.com/open-source/?utm_source=FastAPI&utm_campaign=open_source

The same models are shared among requests, so, it's not one model per request, or one per user or something similar.

Let's imagine that loading the model can **take quite some time**, because it has to read a lot of **data from disk**. So you don't want to do it for every request.