While many may have thought Sony already had Insomniac games, PlayStation announced via Twitter today it has formally acquired the Spider-Man developer.
Despite having worked with Sony for over 20 years, starting with Spyro the Dragon in 1998, Insomniac was an independent developer for over 25 years. Many of their games have been developed exclusively for PlayStation. The studio had branched out with a few games recently though, most notably Sunset Overdrive which was exclusive to the Xbox One.
Check out the press release from Sony for more info and bit more about the history between the two companies.