Arceus is one of the most powerful Pokemon in the known universe—possibly strong enough to make its way into Pokemon GO.
Niantic Labs has released several previous legendary Pokemon into Pokemon GO since its release in July 2016. Trainers were quick to catch them all, from Articuno to Victini. However, there are still a handful waiting in the wings. One of these is Arceus, the primary "god" of the universe. It is said that this Pokemon created everything from nothing—existing in a period before time and space. Niantic may be hesitant to let Arceus loose in trainer neighborhoods. After all, how can you capture a god?
Arceus Pokemon GO
Arceus is currently unavailable in Pokemon GO so, no, it cannot be captured at the time of writing. This is likely due to its major combat mechanic from the main series games Diamond, Pearl, and Platinum. In those titles, it was able to adapt to any type desired while holding the corresponding tablet—of which were scattered throughout the map.
Since this is such a key feature, it's possible trainers won't see Arceus for quite some time while Niantic figures out exactly how they want to go about its implementation.
However, despite not yet debuting, some trainer resources have predicted its stats. Arceus may have a CP ceiling of over 4100, with attack, defense, and stamina stats near 230. This would make it one of the most potent opponents in the game. Its base type is normal, meaning its most effective moveset would likely include popular charged moves such as Hyper Beam.
As a normal type, Arceus' best counters include Lucario, Machamp, Conkeldurr, and Breloom—which shouldn't surprise veteran trainers. It may be worth their while to train up the mentioned Pokemon in the event Niantic showcase Arceus as a raid boss.
Arceus originally made its debut in the Sinnoh region as part of Generation IV. Therefore, its PokeDex number is 493. Games describe it as "a Pokemon born before the universe ever existed." Colloquially, it is known as one of the most common answers to the question: "Which was the first Pokemon?" Trainers also tend to take Arceus' name "in vain" as a common community reference.
DBLTAP cannot confirm a date or other credible information concerning the release of Arceus.