val javaParserVersion = "3.18.0"
// Note: this currently still contains 3/4 logic as we will temporarily have Groovy 3 for the build itself until we move to a Gradle built with Groovy 4
// It can be removed or changed to 4/5 logic (if necessary) at that point.
val groovyVersion = GroovySystem.getVersion()
val isGroovy4 = VersionNumber.parse(groovyVersion).major >= 4

# Using Dataclasses { #using-dataclasses }

FastAPI is built on top of **Pydantic**, and I have been showing you how to use Pydantic models to declare requests and responses.

But FastAPI also supports using <a href="https://docs.python.org/3/library/dataclasses.html" class="external-link" target="_blank">`dataclasses`</a> the same way:

{* ../../docs_src/dataclasses_/tutorial001_py310.py hl[1,6:11,18:19] *}

### Migration

Check out the [Pydantic migration guide](https://docs.pydantic.dev/2.0/migration/).

For the things that need changes in your Pydantic models, the Pydantic team built [`bump-pydantic`](https://github.com/pydantic/bump-pydantic).