240/4 is usually used when 10/8 isn't enough.

Do you have data on that? I've heard rumors, but never seen it actually done.

It was never a viable option for the Internet (million or billions of devices would never support it, and anyway it'd only buy us like 3 months), but in theory it should work better in the (more, but not entirely) controlled environment of a large prod environment.

I know of several massive setups that when running out of 10/8 evaluated 240/4 but deemed it less feasible, riskier, and definitely more work, than to "just" move to IPv6. Sorry, can't namedrop them, since I don't want to doxx myself. I've never seen 240/4 actually chosen.

We use them in AWS as IPv6 hasn't been feasible, though its become better in the last 1-2 years. AWS uses it internally, likely other big providers probably also do. If you can get away with IPv6 only, ie not constrained by provider/device, its likely worth going that direction instead.

Works fine in Linux, doesn't really work on Windows and some BSDs.

https://blog.benjojo.co.uk/post/class-e-addresses-in-the-rea...

240/4 is multicast range, and mobile devices WILL wreak havoc in that range (though it's not impossible to simply drop all such traffic at ingress). I usually see service providers using 172.16/12 instead.

224/4 is multicast. AWS uses it, we use it in AWS, as do others. Works fine with Linux, Windows not so much, afaik android and osx are fine with it.