Stamen will tiles will be migrated to stadia on october 31 ref :
Stadia Maps has partnered with Stamen Design to host their iconic map styles. If you are currently accessing Stamen map tiles via the Fastly CDN or a Stamen domain, you'll need to make a few (small!) changes to keep on using these maps after August 31, 2023. After this point, we will start progressive brownouts before the old URLs stop working entirely on October 31, 2023.
Stamen will tiles will be migrated to stadia on october 31 ref :
https://docs.stadiamaps.com/guides/migrating-from-stamen-map-tiles/ https://stamen.com/here-comes-the-future-of-stamen-maps/