Marvel Comics is ending the current volume of Guardians of the Galaxy with issue #150 in January. The previously solicited #151 will be replaced in February by Infinity Countdown: Adam Warlock #1 and Infinity Countdown Prime #1.
CBR independently confirmed the cancellation news with Marvel, while Guardians of the Galaxy writer Gerry Duggan tweeted the following:
The animated GIF shows Adam Warlock with a caption teasing the introduction of the Soul Gem. Marvel Comics recently changed the Infinity Gems to Infinity Stones, to match their representation in the Marvel Cinematic Universe.
More than likely, the huge story Duggan pitched to Marvel revolves around the Infinity Stones, as the publisher promoted the Infinity Countdown for February with the image of a resurrected Wolverine, Star-Lord and Captain Marvel in possession of the Power, Space, and Reality Stones, respectively.
Below is the solicitation text for Infinity Countdown: Adam Warlock #1 and Infinity Countdown Prime #1: