As an OpenStreetMap-contributor: you have to add attribution as per our license agreement: https://www.openstreetmap.org/copyright
CartoDB packages this data into tiles you can use, but that doesn't lift this requirement.
I was implementing OSM the other day (with attribution of course) and noticed Carto seemed to be one of the only players with good dark tiles.
Seems like we can't use them for free, even with attribution, unless I get a grant?
Thank you for this comment, I just fixed it[1], don't know why claude code decided to hide it, I actually should have known this requirement and checked!
1. https://github.com/montanaflynn/ishormuzopenyet/commit/70a8c...