Glock has two magazine styles presently on the market: A newer one with a frame cutout on the front of the magazine, and an older (original) design without a frame cutout.
To the best of my knowledge Glock, GmbH does not yet have a 4th generation Glock Model 21 out on the market - Only 3rd generation standard and SF models. All 3rd generation Glocks will accept both the older and newer magazines styles.
I just bought a brand new 3rd generation G-19. I picked up a number of extra magazines for it when I did. Half came with the front cutout, and half came without. (Who cares!) So, until 4th generation Model 21's hit the market, you don't have a problem.
Quite honestly, there's no way I'd be willing to part with either one of my G-21's. The 3rd generation Glocks are, without question, the most thoroughly field tested and well proven polymer frame pistols in the world. I'm letting, both, the new guys and the gung-ho Glockophiles break-in the recently introduced 4th generation pistols for Glock, GmbH. I've got better things to do with my time.
If the experience is typical: Give the factory another 18 to 24 months, and the 4th generation pistols should finally be reliable enough to defend your life with; but, until Glock's 4th gen. problems COMPLETELY disappear, I'm not going anywhere near one.
(My new G-19, by the way, has been running flawlessly.)
