According to rumors, the "secret" Moto phone, probably the next Moto Z, likely won't arrive before June. If it's the earliest phone supporting the new capabilities, that means the LG G6 and Samsung Galaxy S8 will be left out of the gigabit party this year. All we really know about the new Moto is that it will have a Qualcomm Snapdragon 835 processor and the gigabit abilities.
(For what it's worth: the G6 doesn't have a gigabit modem, and while the S8 will, it may not have the appropriate antennas for Sprint's maximum speeds.)