Killer Instinct has been announced to be coming out as a F2P game like some other fighters that have been heading that direction. The game is set to launch in November it is unspecified if it is this year or in 2014. Get ready to facepalm guys, because you're only getting 1 free character to play with when its launched. You have to pay for character packs if you want to play as more characters.

Source article. 'Killer Instinct' returns as free-to-play brawler