Steam Networking Sockets APIs isn't as flashy (and that "flash" is definitely relative) but is aimed squarely at developers, and could be even more significant to Steam's fortunes given the pressure it's facing from the Epic Games Store: It enables developers to run their game traffic through Valve's own private gaming network, providing players "faster and more secure connections".
The difference between these services is that PlayStation Now and, presumably, xCloud, will be streaming games you don't own via a subscription service model whereas Valve is simply making your own games available to you for free - a model that will appeal to more cost-sensitive gamers and those of us with already-massive Steam libraries. As the name implies, Steam Link Anywhere expands the range of this feature to any Android or Raspberry Pi which is connected to the internet, anywhere. Previously, you could only use Steam Link from home.
Valve indicates that users should enjoy a satisfactory experience as long as "your computer has good upload speed and your Steam Link device has a good network connection".
The feature is in beta for the moment and there are a few caveats to keep in mind, but this is a truly exciting update and helps illuminate just how powerful game streaming will be in the next few years. It supports the Steam Controller over Bluetooth, as well as other Bluetooth controllers, mice, and keyboards. You should be able to pick a game and then stream it to your Android device as if you were on the same network as your host PC.
The platform is compatible with the Steam Link and any device running the Steam Link application. Valve explain the system here, and among the perks for developers are anonymized network traffic (protecting servers and clients from DDOS attacks) and potentially lower pings through Valve's networks.