Does your TV have "Game Mode" enabled when you play Stadia? A lot of TVs have some kind of special "Game Mode" that disables a lot of post-processing that modern TVs do to improve picture quality at the cost of input latency (which can be quite high). PC monitors typically don't do this, especially gaming-focused monitors.
The other source of input lag would probably come from the wireless controller. I can't tell you exactly why, but tests have shown the input lag to be higher when using the controller wirelessly with the CCU. Wiring up your keyboard/mouse or controller to the device should be better, but the CCU doesn't support this so it will always have a slight disadvantage. It's possible that when Stadia comes to Android TV, you'd be able to plug your controller into your Android TV device.
The third source of input lag would come from the game settings preference, which you can configure in the Stadia mobile app. I think Stadia defaults to "Best Visual Quality", which will prefer 4k/30fps in most games if your screen supports 4k. Input lag is significantly increased when playing a game at 30fps vs 60fps. At the moment, PC/Chrome only supports a maximum of 1080p so Stadia won't be able to "upgrade" the visual quality to 4k/30fps on your PC, which should result in 1080p/60fps but lower input lag on PC/Chrome. I think you can fix it by changing to "balanced", but I'm not sure this guarantees it, maybe someone else can chime it.
Right now, most optimal setup for input lag is to play on PC/Chrome with a wired ethernet internet connection and wired mouse + keyboard. This is the setup I use when playing Destiny 2. For a platformer like Darksiders Genesis, I find the extra input lag from the CCU setup more tolerable.
@Six : I’ve been running wired CCU and no issues with lag, controller is connected to my WiFi on 5 Ghz rather than 2.4 Ghz, and the WiFi access point is also our home router so there are no extra hops before the packets leave the house and make their merry way down to whichever DC it goes to.
Also, the home router is within spitting distance of the controller and I can’t imagine that there is much if any interference with the WiFi signal.
We have quite a highspeed broadband and games are not getting impacted by Netflix or Amazon Video usage, kids are still doing their YouTube and not seeing any impact. Chrome had been a bit laggy in the first couple of weeks of Stadia launch, but CCU has been fine.
I get this issue and my controller is right near the router. I have game mode on and still its just goes crazy at times I find it happens when there is a lot of screen activity the most.
My computer its works pretty well, but its not what I want.
As others have said above me, just make sure you havent got any TV settings on that could be causing the issue. I had this on my TV. I had something enabled that improved the framerate - but at the expense of input lag (I think the TV adds in its own frames to make the image look smoother). Forcing "game-mode" disabled those settings that are not condusive to gaming, like this - and the input lag was back to normal for me.