CSGO update 1.36.4.8 (15/8/2018) Adds the MP5 SD into the game. Whilst there are no skins or the MP5 SD isn’t in match making its very much useable offline and in casual mode.

Iconicly @csgo_dev tweeted this an hour before the update dropped

Oh THAT'S where we put that… pic.twitter.com/l3DeEouHYp

— CS:GO (@csgo_dev) August 15, 2018

Below are some two videos of the MP5 SD in use but if you want to see an analysis by /u/slothsquadron go here. Basically the new MP5 SD is just the MP7 but less accurate when moving, less damage but has a faster reload and moving speed.