In their 2022 annual report (published October 2023) they listed this as one of their goals:
"Set up a US non-profit branch (501(c)(3)) with a board of governors to become eligible for larger grants from US-based donors and allow US donors to make their contributions tax-deductible"
Annual Report 2022
The 2022 Annual Report is now available for download! As a non-profit organization supported exclusively by donations, we like to keep our community updated on our yearly progress, and 2022 was an interesting year to say the least.
Mastodon Blog (blog.joinmastodon.org)
I'd hardly call setting up that US entity six months later as coming "out of the blue without prior warning"...