[jampekka]

You can donate to get access to faster download mirrors. I'd guess this is the main source of their revenue.

https://annas-archive.org/donate

[glimshe]

Can you donate to them without someone claiming you're donating money to a criminal enterprise and getting you in trouble? I mean, without using bitcoins

[sMarsIntruder]

You can buy Amazon gift cards using bitcoin lighting to add another layer (actually 2) of paranoia :)

[notpushkin]

I suppose it could also be their enterprise users, though there’s not a lot of info on this aspect of their activity.