Sony have released firmware update 6.70 for the PS4 yesterday. The release before that one was PS4 firmware 6.51, back in March.
As often for PS4 updates, the changelog is intentionally vague and simply states that “This system software update improves system performance”. In other words, this could be anything from a minor patch for some specific game, to some critical vulnerability fix. Not much has been said so far on popular scene sites whether this updates brings additional security.

You know the drill: if you expect your PS4 to be hacked, we usually don’t recommend you update your console. The highest hackable firmware (publicly) is 5.07. (Check more details on our PS4 Jailbreak page)
Hackers have hinted in the past at hacks available on firmware 6.xx, and there even was a webkit exploit released for 6.20, but no “full" Jailbreak has been announced for recent firmwares by any credible source.
The update appears to be optional for now. But for people not looking to hack their PS4, it is likely you will ultimately have to update to 6.70 in order to retain online service access for your console (PSN, etc…)
Source PS4FWBot