Very brief specs are listed on the Mobil 1 website under data sheets. It is not listed in the viscosity list on the left hand side of the page in the data sheets. Just click on data sheets and look in the middle of the table. If you enter "Mobil 1 0W20" in Google it will take you to a website (might be Mobil UK) with an "official Mobil" full-page spread on 0W20.
PS Castrol has debuted a 0W20 version of SLX
"Castrol Formula SLX mit sensationeller-Viskosität