What just happened? While many people have Valve's Steam app installed on their mobile devices, it's often used for little more than the Steam Guard account authentication feature. The company knows this, and so is testing an updated version of the app that's a lot more appealing to users.
The updated Steam Mobile app is now available in beta form. Valve itself has joked about the current app's ancient design, writing that "2015 called and wants its app back."
The refreshed version offers QR code sign-in, smarter notifications, an improved Library, and multi-account support. All the previous features will remain, including the Steam Guard codes, being able to browse the Steam store, and confirming trades.
"[The beta test] helps us test our assumptions, learn what you like and don't like, and find things that need to be fixed. This is especially important when the app can be used on so many different phones and devices," Valve writes.
If you already have the Steam mobile app installed and want to try out the beta while offering feedback to Valve, you can do so by clicking on the link and waiting for the update to arrive on the Steam app. That's the process for Android users; those on iOS will need to install Apple's TestFlight and join via that app. Valve is also limiting iOS participant numbers to 10,000.
This is a limited beta, but Valve does write that even if all the slots are full, it will still be possible to join the group and give your opinion on what new features you'd like to see.
Having briefly checked out the updated app, it does seem to be a noticeable improvement over the previous version---you can tell pretty much straight away that it's been built on a new framework. The lagginess that some were complaining about earlier seems to have gone, the new layout and navigation bar are certainly welcome additions, and using the QR code to sign into the desktop site was quick and painless.
Valve says it is still working on ironing out the bugs and polishing, so don't let those put you off. Expect more changes in the final version of the Steam app based on user feedback from the beta, but it's looking pretty promising so far.