The first operational Soviet GLATGM was Songster as fitted to the T-64B and using the 125mm gun. Newer missiles exist, but you're going to have to Google for the details.
In addition, the Soviets went on to produce variants in 100mm and 115mm for retrofit to T-55 and T-62. The missile guidance equipment can also be retro-fitted to T-72, was standard on T-80 and is standard on the T-90. And they'll sell you 105mm and 120mm variants now for Western gun tubes.
They are all laser beam riding, that is the laser is aimed at the base of the missile and the missile manoeuvres to keep it centred, so beam moves up, missile follows and so on. This means that it is more difficult to detect the laser on the target than using a laser for illumination.
Hence missile exhausts will be on the sides, and motor burn times may be very short to allow better manoeuvering. After all, it comes out of the gun pretty fast to start with.