They've had individual -bin versions of a few big builds, like firefox, chromium, and libreoffice for basically forever.

They had something called distcc for a long time too. That let you, the user, cross-compile packages on one machine for installation on different machine(s).

But at the end of 2023, they dramatically expanded the system, adding configuration machinery to install $packagename from source or binary (i.e. not like firefox and firefox-bin). And they set up the server infrastructure to host a much larger number of official binary packages for amd64 and arm64. Around the same time they added a "distribution kernel" as an ebuild, so users no longer had to "compile it yourself". And I think the dist-kernel is now available as a binary.