### Pydantic v1

**This version of FastAPI still supports Pydantic v1**. And although Pydantic v1 will be deprecated at some point, it will still be supported for a while.

<code>D0[int, string]</code> and <code>struct{ x int; y string }</code> are
different because the former is an <a href="#Instantiations">instantiated</a>
defined type while the latter is a type literal
(but they are still <a href="#Assignability">assignable</a>).
</p>

<h3 id="Assignability">Assignability</h3>

<p>