Sony has said in an FAQ of sorts that the "overwhelming majority" of the available 4,000 PlayStation 4 titles will be playable on PS5.
That said, Sony did list 10 PS4 titles that are not compatible PS5.
The backward compatibility information page also stated that select PS4 games will benefit from PS5's Game Boost, which may make current-gen games run with a higher or smoother frame rate on the next-gen system.
It is also noted that some functionalities on PS4 may not be available on the new console and that some may even "exhibit errors or unexpected behavior" when played on PS5.
Sony also warned that before purchasing add-ons, try to boot and play the PS4 games on the new console first to see if you are "happy with the play experience."
The ten games which will not be playable on the new console are below. Any PS4 game on the PS Store that isn't compatible with PS5 will be marked as "Playable on PlayStation 4 only."
PlayStation 4-only games:
- Afro Samurai 2: Revenge of Kuma Volume One (Versus Evil)
- DWVR (Mad Triangles) (PlayStation VR title)
- Hitman Go: Definitive Edition (Square Enix)
- Joe’s Diner (United Independent Entertainment)
- Just Deal With It (Super Punk Creative)
- TT Isle of Man: Ride on the Edge 2 (Nacon)
- Robinson: The Journey (Crytek) (PlayStation VR title)
- Shadow Complex Remastered (Epic Games)
- Shadwen (Frozenbyte)
- We Sing (THQ Nordic)
The page also goes over playing PS4 discs on PS5, transferring digital games from last-gen to next-gen, installing a digital PS4 game on PS5, upgrading eligible PS4 games to the next-gen versions, and more. It also states that the new PlayStation 5 camera will not work with current PS4 PSVR titles.