It's still incredibly limited compared to Samsung's smartwatch platform.

For the past few years, the Gear watches and fitness wearables have been running full Linux. If you enable Wi-Fi debugging, you can actually ssh in to the smartwatch and poke around the file system.

The UI story is a mess though. There's EFL, a C-based GUI layer of somewhat legendary status in Linux circles (it's derived from the Enlightenment window manager). It's plenty fast, as a smartwatch should be, but kind of a bastard to program for.

Alternatively you can write HTML apps, but they run like sedated dogs on the smartwatch.

Last I heard, Samsung was trying to add React Native into the mix. I'm not very convinced that adding in yet another runtime will fix the fundamental problem.