According to Sony, any new titles submitted for certification for the PlayStation 4 must be compatible with PlayStation 5 as well, beginning on July 13.
With this system in place, it means that it is up to each game’s developer to make sure this process is implemented. The developer documentation states that developers must make sure that they check to state that each of their titles has been tested for compatibility with the PlayStation 5.
Note that a game can only be deemed compatible with the PlayStation 5 hardware if its submission code runs without issues on this system. In addition, these PlayStation 4 titles must all provide the same features on both the PlayStation 4 and PlayStation 5.
For titles submitted to Sony before July 13, any new patch or remaster after that date would not require this compatibility. However, it would be “strongly recommended” by the company. Note that once a PlayStation 4 game is PlayStation 5 compatible, it must stay that way.
PlayStation themselves is also working on their end to make sure PlayStation 4 titles run on the PlayStation 5, though it previously said it would pass “issues which need adjustment” to each of the developers to field.
You can read the full breakdown from Eurogamer here.