Kel-Tec has updated their 9mm SUB2000 carbine to a Gen 3 model. Upgrades include a metal trigger and it will accept a GLOCK 17 magazine. Additionally, the charging handle in the stock features bolt hold open slots in either direction.
But the biggest change is that the barrel twists and folds so that you can keep optics mounted even when folded.
www.keltecweapons.com/firearm/rifles/sub2000