The SGI 5.45 is a unique variant of the SGI-5k that was scheduled to appear in S.T.A.L.K.E.R.: Clear Sky. It was modified to fire 5.45x39mm rounds, similar to the "Tunder" 5.45 from S.T.A.L.K.E.R.: Shadow of Chernobyl. Only the name and description remain in the game files. The variant was replaced by an upgrade that changes the SGI-5k caliber from the 5.56x45mm caliber to 5.45x39mm rounds.