Pixel Watches have an unlocked bootloader [1] and publish factory images [2].

That being said, it appears that the main open source version of WearOS (AsteroidOS) only supports watches that are 5-10 years old [3].

I suspect that if you did try to flash this watch, you would experience a whole host of rough edges.

[1] https://9to5google.com/2022/10/21/pixel-watch-bootloader-unl...

[2] https://developers.google.com/android/images-watch

[3] https://asteroidos.org/watches/

Edit: past pixels watches have an unlocked bootloader, I assume this one will as well. I don't see this information in the announcement post.