What just happened? It's safe to say that Google Stadia hasn't been an industry-changing revolution, especially as many of its promised features weren't available at launch. But one of these---4K streaming support on the web---is now rolling out.
Web users should notice an improvement in graphical quality, and you can confirm that 4K is being supported by opening the in-game menu---Shift + Tab or the Stadia button on the Controller---and clicking "Connection." A green "4K" icon will be shown under the "Data Usage" status.
In addition to the $9.99 per month Stadia Pro subscription, which allows access to the "Best visual quality" option, Google says an "excellent" connection of 35Mpbs is required for 4K streaming. 9to5Google does note, however, that it managed to game in 4K with "good" and even "ok" connections.
For those with 1080p or 1440p monitors, it's still not clear if Google is using downscaling for Stadia, or if only those with 4K screens will experience any benefit.
Back in February, Google said Stadia was coming to 18 additional Android smartphones, including 14 Samsung Galaxy devices. It's also introduced the ability to download screenshots and clips. We're still waiting on support for wireless Stadia controllers on the web and expanded Assistant support, but those will reportedly arrive this month.