yeah unfortunately it seems to only be available for their larger devices, which is a bummer because the way I'm using mine, I intentionally want it to not look like a watch but instead more like a bracelet so I don't look like some weirdo wearing two watches :)
The SDK is pure JavaScript and seems friendly enough (I only got a few examples working and lost interest) - https://dev.fitbit.com/build/tutorials/examples/
I don't know if the SDK can target the luxe BTW