TL; DR: With Valve's Steam Deck launch approaching, developers have started working on the units. Valve began shipping development kits on Tuesday. This app allows developers to see how well their games are performing on a handheld device and receive last minute feedback.
On Tuesday, Valve announced that it had begun sending Steam Deck kits to developers. Valve says that "engineering certification tests are underway" similar in performance to the commercial versions coming out at the end of the year. It also provides additional feedback for Valve as it exits the final stage of development.
"As we are still in the final stages of development, the dev-kit gives us the opportunity to guide game developers in the process of downloading their games. On Steam Deck while we're still there we will continue to collect feedback as we prepare for the official launch at the end of the year."
Valve announced the Steam Deck in July. The portable device is somewhat larger than the Nintendo Switch, which is probably its biggest competitor, although Microsoft's Phil Spencer says it could double as a portable Xbox. The Steam Deck pre-purchase was canceled within minutes, and a scalper quickly listed it on eBay at more than three times the retail price. They're the first units, and when the console officially launches in December, shipping begins. However, the delivery date is somewhat ambiguous for those who order now. Subsequent provisions are not said to disappear until some time after the second quarter of 2022.
Valve begins sending Steam Deck kits to developers for testing