The HTTP Client API was incubated in Java 9. Essentially, this means that this API wasn't a part of the Java SE. It was defined in the jdk.incubator.httpclient package. The incubated features should explicitly be added to a project's classpath. The incubated features are released by Oracle to enable developers to use and experiment with them and provide their feedback, which decides the fate of HTTP Client API. In a future Java version, incubated APIs and features are either included as a full feature or just dropped off. There is no partial inclusion.

Just in case you need a quick refresher on HTTP, we will provide one here.