Marvel Comics is distributing a checklist to the upcoming Infinity Countdown event, noting several issues that lead into the event series which begins in March 2018 - but the checklist isn't including any issues of Infinity Countdown past the first issue - the only issue of the series yet solicited - instead serving as a countdown to Infinity Countdown, of sorts.
Included in the checklist are the upcoming Guardians of the Galaxy #150, Infinity Countdown: Adam Warlock #1, and Infinity Countdown: Prime #1, as well as the previously-released "Communication Breakdown," "Riders of the Sky," and "Infinity Quest" Guardians of the Galaxy story-arcs. The graphic says the location of the Infinity Stones - some already known, some unknown - will be revealed in Guardians #150.
It all builds to March 7's Infinity Countdown #1, the first of a planned five-issue series.
Though Marvel hasn't disclosed what Infinity Countdown itself is counting down to, an Infinity Watch story has been solicited to be included in Marvel's Free Comic Book Day 2018 titles on May 5.