Jim Starlin previously let it be known he wrote a 100-page story for Marvel, and as expected, it's an original Thanos graphic novel.
Marvel announced the news via Newsarama with Starlin on Thanos: The Infinity Revelation.
Thanos: The Infinity Revelation marks Starlin's fifth "Infinity" series, and the new graphic novel will feature the likes of DnA's The Annihilators, the Guardians of the Galaxy, Silver Surfer, Eternity, Infinity, the Living Tribunal - and Adam Warlock (no mention made of Richard Rider Nova).
Thanos: The Infinity Revelation finds the so-called Avatar of Death on the precipice of a universe-wide catastrophe caused by Thanos himself. Rarely seen major cosmic forces such as Eternity, Infinity, and the Living Tribunal come onto the scene to witness this universe-ending threat, and Thanos finds himself working with the man he once killed but might be his only friend, Adam Warlock.
Two pieces of art also debuted. I also believe as this is an original graphic novel that it isn't a part of regular Marvel continuity much like Marvel's Season One OGNs (I could be wrong).