[tomjakubowski]

Unfortunately, it seems Apple has forced us to choose between Meltdown mitigation and a somewhat working OS. The recent Sierra security updates didn’t include the Meltdown patch.

https://twitter.com/theregister/status/949358083431546880

[sgolestane]

Apple has actually backported the fix to Sierra and even El Capitan. https://support.apple.com/en-us/HT208331

[bangonkeyboard]

The tweet in the post you replied to points out that the page that you linked to was altered today to no longer say the fixes extended to those two.

[alwillis]

My educated guess, based on 14-years working for MIT’s IT department: the fixes for Sierra and El Capitan broke something important, so they got pulled.

When they get fixed, they’ll be re-released…