In a recent developer walkthrough at Gamescom 2018 it was confirmed that Cyberpunk 2077 will NOT have any loading screens while exploring the open world city.
I did get to see the game in action and developers confirmed this to everyone there. During the 50-minute gameplay demo there was no loading screen at any point. The game looks graphically like next-gen so this coupled with no loading screens is especially promising.
However, it can be assumed that upon death there may be loading screens (as to reload the last checkpoint). And of course during the game’s bootup there would be loading screens but not during gameplay, quests and exploration.