The Google Play edition HTC One began receiving the JWR66Y security update earlier in the week. As of today that same JWR66Y security update has begun rolling out for the other Google Play edition handset -- the Galaxy S 4. While this update is small and focusing on security, this all builds upon the earlier Android 4.3 release which began rolling out for both handsets in the beginning of August.
Anyway, similar to the JWR66Y for the HTC One, there isn't much in terms of specifics for the Galaxy S 4. The update is smaller and has recently begun showing up on user devices. And as we often see, the rollout is likely staged which means you may or may not be seeing it on your handset just yet.
Otherwise, this same JWR66Y update arrived for other devices devices back in August. This one was initial detailed on the T-Mobile support pages for the Nexus 4. Needless to say, it also came available for other Nexus devices as well. Notably for the Galaxy Nexus as well as the 2012 model of the Nexus 7 and Nexus 10 tablets.
As mentioned, this update is on the smaller side and even looking back to that T-Mobile announcement -- we were seeing a file size of just a few MBs. With that, those carrying a Google Play edition Galaxy S 4 should be on the lookout for the update notification and otherwise, those feeling a bit impatient can head into the settings and try to force things.