According to the Lowlands Music Festival website, Radiohead will be playing the Dutch festival along with Arcade Fire and Pearl Jam the weekend of August 17th.
We do want to stress that nothing has been announced by the band themselves so please consider this a rumor until made official.
http://www.lowlandsfestival.nl/ (click on “Programma”)
(thanks to psychodandy)
UPDATE: We have been told that this is not the official Lowlands site so this may all be crap. Whatever. 🙂