Terribly sorry about the short notice – this is not a planned thing,
it's an emergency fix. Most wikis (but not the biggest ones) will be
read-only for up to 30 minutes at 07:00 UTC AM tomorrow, 17 January.
Depending on your time zone, that might be late 16 January. It'll
probably be shorter than 30 minutes.
There's a Phab task here with more information and a list of affected wikis:
That list is very long, so to make it easier, I've put a list of wikis
that are *not* affected here:
Please help spread this in your community, if it's affected.