A minor update hit the PlayStation 4 and Xbox One servers for Grand Theft Auto V back in March. The update (1.08) was around 250 MB on the PS4 and had the intention increasing the stability of GTA Online and offer other minor fixes for both GTA Online and Story Mode.
It appears, however, that update 1.08 has somehow deteriorated the game's graphical quality on the PS4 and Xbox One.
Players have taken to Rockstar support forums to figure out if anything is being done about the apparent downgrade of graphics. Out of the good of their hearts, Rockstar has responded to at least one of the questions and claims to be investigating the issue:
We are aware of some graphical issues on the Xbox One and PS4 versions of GTAV after the most recent Title Update, and we are investigating a fix now.
A similar update hit the PS3 and Xbox 360 on the same day, but the older consoles did not suffer any adverse affects (as far as I know).
Rockstar has not said when a fix would be available, but they will be offering more information to players when it is available.
[Rockstar]