Does the model X come with SIRIUS XM radio i.e. does it have the capabilities to subscribe to XM
On tesla website. MX has XM radio capability with premium upgrade package. I have 2017 MX with premium package and i aint got XM radio. :)
I have premium, and XM. No premium, no XM
Yes with the premium upgrade you can subscribe to Sirius radio I had it on my 2016 MX but cancelled it as I liked Slacker better, there is no free trial like other car makers offer but you can buy it
Options change over time. It is and always has been part of the UHFS (Ultra-High Fidelity Sound) option. For a long time UHFS was a separate option ($2500) and there was an unrelated Premium package. More recently, Tesla changed the options mix, and a new package "Premimum Upgrades" includes UHFS (which has XM).
So if you have or order in some way the UHFS, you get the XM radio hardware. You have to pay for the subscription, although I think it provides 1 demo channel when XM is not yet subscribed.
More on XM radio, options and alternatives: https://teslatap.com/articles/xm-radio-in-teslas/