Short answer is, there is no differences . Actually it's very same hardware.
To be clear GLM 2,3 and 4 are the software part where User Kit (8300-601) is the hardware part.

At the time GLM 2 was the latest software. User kit(8300-601) was sold by named GLM 2.0 Kit.
When GLM 3 came out, it was then sold by name GLM 3.0 Kit.

If you have recently bought a GLM 2.0 Kit and wonder if it is latest GLM Kit.
Worry not because you already have latest hardware.

Latest GLM software can be downloaded at link below
https://www.genelec.com/glm

Happy listening session!