Yeah they came out with a Glock 20 Gen 4, although it appears that they're a nightmare to find. If you're really intent on buying a G20, wait until they come out with a G20SF (the SF makes a difference). Are you planning on using it for hunting? I mean, 10mm, that's a big ass round heh. I've shot a Glock 20SF Gen 3 and holy crap did my entire right arm and wrist hurt like hell afterward (I have tons of tendon, ligament, and nerve damage in my right wrist). I would never think about buying one. The only thing they're good for is handgun hunting. Home defense, yeah, if you wanna put a hole in the intruder, your wall, and have the round fly into your neighbor's house.
For the record, I hate Gen 4s, they're not worth it when you can get a Gen 3 for cheaper. The only real advantage is that the grip is smaller, which is nice because my hands are small as hell. My G22 Gen 4 is so incredibly inaccurate compared to my G30SF, P226, P229, and XDs. In fact, I'm thinking about selling it and picking up an XD of comparable size. I don't know what it is about my 22 but I have to actually consciously modify the way that I pull the trigger (curl it while I pull) and my finger positioning to hit where I'm aiming My 30SF doesn't do that, XDs is just point and shoot. Sigs, I've had to do a lot of gunsmithing, replaced the hammer springs and installed SRTs, now the DA/SA is nice but stock config...ugh.