https://www.tomshardware.com/peripherals/controllers-gamepads/valve-steam-controller-developer-interview

I literally got this information from this interview with a valve programmer, which is as much as I looked into it, coupled with this is exactly the same as the first steam controller in terms of connectivity/functionality.

"The Steam Controller is designed for devices that use Steam. It works with Windowsand with Macs, but Steam has to be running. Otherwise, it's seen as a hybrid mouse/keyboard input device. (Even on a PlayStation, it's seen as a mouse. The exception is Linux, where Valve has a driver in the kernel with gamepad functionality).

That's not to say you can't play games purchased outside of Steam — you can add most titles to Steam using the "Add a Non-Steam Game to My Library" option.

But wouldn't letting the Controller work out of the box with more devices and without Steam better follow Valve's PC gaming ethos? Griffais said there are other considerations.

"We're limited in what we can do with things like core operating system drivers and such, right?" he said. "Xbox controllers have built-in support within Windows itself. PlayStation controllers have a driver that they work with Microsoft on."

Of course there are ways around Valve's limitations, like GloSC/GlosSI or people making their own steam controller drivers like the github steamcontroller, but out of the box, (I guess the one difference here being if you use linux, where hypothetically it should work as a generic gamepad) no, the steam controller will not work with xinput, and you're not going to be use it without Steam.