If you're just interested in a single value, using the SPARQL endpoint[0] is probably still more simple, since you don't have to filter out deprecated statements, for example.

[0] http://tinyurl.com/ya957wem

I have a lot of goodwill toward wikimedia, but trying to use wiki data made me question my life choices. It doesn’t help that the official API endpoint Times out for anything mildly complicated. (As in a simple aggravation or sorting in the query)

Unfortunately that data isn't granular enough for what I need: I'm looking for the build number, which Wikipedia somehow keeps up to date.

https://en.wikipedia.org/wiki/MacOS has a footnote after the build number. That led me to https://developer.apple.com/news/releases/. I guess that doesn’t do semantic markup, and I didn’t look at the html at all, but it looks like it could provide you what you want fairly easily (likely not 100% reliably if automated, but chances are Wikipedia‘s somehow keeps up to date involves humans, too)

Alternatively, buy a Mac, set it to auto-update, have cron or launchd reboot it reboot it twice a day, and read the version info from the CLI after rebooting (https://coderwall.com/p/4yz8dq/determine-os-x-version-from-t...)