It seems as though you'll still be able to go back and play games on your PS4 after you've upgraded them to the PS5 version.
Earlier today, the post just below appeared on the PS5 subreddit. The user in question asks a PlayStation support agent if they're able to play upgraded PS5 games on their PS4, to which the support agent replies that they will be able to if it's a digital game.
Confirmed: If you take advantage of the PS4-to-PS5 free upgrades on a digital game, you’ll maintain access to both the PS4 version and PS5 version from r/PS5
Elsewhere, things get a little murkier. While a digital game will give you access to both the PS4 and PS5 versions after you've upgraded it, the PlayStation support agent isn't sure if this will be the case with a disc-based version of a game.
With the digital version of a game, it's like "having two versions of the game," the support agent writes. But it's easy to see how physical games can't be treated in the same way, since there's one physical disc for the game that is needed for the game to function on either platform.
It's best to take with this with a pinch of salt. But, for now, it would appear that if you're planning on upgrading a digital game to a PS5 version, you'll effectively be owning the game on two separate platforms, perfect for if you're planning on giving your PS4 to someone else once the next-gen console launches next month.
Speaking of, there's now less than a month to go until the PS5 launches on November 12 in the US, and November 19 in the UK and Europe. For a list of all the games that can currently be upgraded to run on Sony's next-gen console, head over to our PS5 upgrade games guide.
Alternatively, if you're looking to put down a pre-order for the PS5 ahead of its launch next month in November, you should head over to our PS5 pre-orders guide for a complete list of retailers with stock.