Is Google Closure Compiler Still Running Online?

Google’s Closure Compiler, which I’ve used for many years, seems to be down (https://closure-compiler.appspot.com/home).

Googling turned up a lot of conflicting data, some of which seems to imply it’s no longer available online, and you have to run it locally. However, none of the download links I tried worked.

Anyone know the current status of the Google Closure Compiler?

All the information is available in the official docs. Indeed both the UI and the API are deprecated. You should download the Java application for local use.

See Getting Started with the Closure Compiler Application:

Download the most recently released JAR file from the Maven repository, and save it in closure-compiler.

Now the Maven web UI is indeed far from obvious, but here's how it goes:

1. In the big table, under the Version heading, click the version you want. At the time of writing, that's v20220803, released on 9 August. (That also answers your question about the current status; new releases are still happening.)
2. In the table at the top, next to Files, click the link named "jar" to start your download.