Installing custom software --> caching --> docs unclear to me

I read the docs for installing custom software ( and find I am not 100% clear on whether things I install with apt-get would be cached. The docs say:

Naturally, downloading and compiling this custom software can take time, making your build longer. To reduce the time spent installing dependencies, CircleCI will cache them between builds.

I wasn’t clear if “will cache them between builds” literally meant it happens automatically and I don’t need to do anything further – that I’d only need to specify extra cache directories if I was compiling dependencies.

I tried searching through the forum for posts to clear this up. I found one or two from about a year ago that say the results of apt-get installs are not cached and suggesting a few approaches to work around this. But I didn’t find anything more recent than this and it seems like it was a feature request at some point.

So my question is…what’s the current status?

Software installed with apt-get install will not be cached. One technique would be the cache .DEBs using the cache directory and then install using dpkg -i.