The Cyberpunk 2077 gameplay demo stream included a hidden message that was placed in the final frame of the demo and contains a letter from the development team, CD Projekt Red.
Discovered and transcribed on Reddit, the letter from CD Projekt begins by them apologizing for making fans wait so long and goes into detail into what brought them to the decision to finally show Cyberpunk 2077’s gameplay demo to the world.
Source: IGN.com Cyberpunk 2077 Gameplay Demo Stream Included Hidden Message