Ah crap. I had installed the 9.0 beta on Yosemite prior to installing El Capitan just now. I think it didn't bother updating Safari because it's 9 -> 9 and it figured it's the same version. But it's a very different build, and I'm afraid Yosemite's 9 isn't compatible with El Capitan. Anybody know a fix to this? Can someone upload their Safari.app from the third beta?