I'm confident it's not temp wikis. In editor_month, all of the temp users have the user_is_temporary flag, and our active editor query simply users WHERE NOT user_is_temporary in both of the appropriate places.

I also broke down new active editors by "main wiki" (the wiki where the new editor made the most edits). By far the biggest April–July changes (note: not the same as the year-over-year change) were at Wikidata and Commons, which haven't had temp accounts deployed yet.

Source code for this analysis.

thanks @nshahquinn-wmf , I checked YoY numbers using your code and the growth seems to be from Commons and wikidata as well.
In conjunction to the growth in Commons, I saw that net new content on Commons has increased, we usually attribute this to bot contributions but surprisingly this month we had a lot of new content added by non-bot users on Commons and Wikidata!

We continue to see these trends in August as well.
Wikidata seems to be pulling most of the weight in the new active editor growth in July and Aug 2025. here's why -
in July 2025, Wikidata accounted for more than half the growth in new active ed increases; and in Aug 2025 Wikidata increases were more than the overall new active editor increases.

raw numbers -
July 2025, had an increase of 2113 new active editors compared to july 2024, and wikidata saw an inc of 1204, while commons had an increase of 921 new active editors.
Aug 2025, had an inc of 849 new active editors compared to last yr; wikidata saw 116% inc ie 938 new active editors growth, while commons had an increase of 334 new active editors.