Does Stadia work with my existing Chromecast?

You need both a Chromecast Ultra and Stadia controller to play on a TV

By most accounts, Google pretty much bungled the launch of Stadia. As it stands now unless you've bought the Stadia Founders Edition or Premiere Edition you're not going to be able to play Stadia games on your TV.

That's because you'll need both a Chromecast Ultra that has the latest Stadia firmware updates, along with a Stadia controller. That's the only configuration that currently works for TV play, so even if you already own a Chromecast Ultra you will still need to buy a standalone Stadia controller if you want to play on your TV. A software update that adds support for other controllers to be connected to a Chromecast Ultra might come at some point down the line, but for now, the Stadia controller is your only option.

You can still play Stadia through a Chrome browser on your PC with a keyboard and mouse or a controller, albeit only with a controller that's been connected via USB. You can also play on a Google Pixel phone (from the Pixel 2/2 XL up to the latest Pixel 4/4 XL) with any Bluetooth controller you might already own including the Stadia controller. Google has a chart that outlines which controllers are compatible with Stadia, although it's worth noting that any Bluetooth controller that you can connect to your Pixel phone should be able to connect with the Stadia app.

Why can't I use regular Chromecast?

One reason why the Chromecast Ultra is the only Stadia-compatible Chromecast device is simply that it's the only one that supports 4K HDR content. Google wants early adopters to experience the best that Stadia has to offer, which is why they bundled in a three-month Stadia Pro subscription for pre-orders and with the Premiere Edition. Only Stadia Pro subscribers can play in 4K at 60 frames per second with HDR, so if you bought the bundle you get everything you need to enjoy Stadia in blissful 4K. So, following that logic, it seems pretty clear why adding compatibility to older Chromecast devices wasn't a top priority.

It's still relatively early in the Stadia launch cycle and many promised features have yet to arrive on the service. On Google's Stadia FAQ page, it states that there might be future announcements regarding additional Chromecast device compatibility, so we may still see support arrive for older Chromecasts — hopefully alongside Chromecast-enabled smart TVs and other Android TV products with built-in Chromecast functionality.