Full Spoilers for The Umbrella Academy season three follow, you've been warned! Readers of The Umbrella Academy comic series were likely surprised to watch the most recent season and frequently see a "Hotel Obsidian" throughout the new episodes. Though the name sure sounds like Hotel Oblivion from the source material, and Hotel Oblivion does make an appearance, and though there are some similarities, there's also some stark differences. It's not until the new season is complete however that it's revealed just how different this version of Hotel Oblivion that appears in the TV series is from its counterpart in the comics.
In The Umbrella Academy TV series it's revealed that the Hotel Obsidian was constructed by Sir Reginald Hargreeves, having realized that a portal existed in this location to the Hotel Oblivion on the other side. As per Hargreeves tradition though, it was a foil, something to cover up his true intentions. On the other side of the portal, the Hotel Oblivion was a machine sitting in another dimension. As Hargreeves himself revealed in the finale, it was created by "whoever created the universe," and was done so as a Break Glass In Case of Emergency scenario, one that would allow for the universe to be reset if needed.
With season three featuring the devastating effects of the kugelblitz, the blackhole that ate reality as a result of the grandfather paradox at play in this new universe. Later after entering the hotel and defeating its "guardians," giant samurais that appear to be made out of cockroaches, Hargreeves uses the machine in the hotel to try and reset the universe. Powering hte machine? The Umbrella Academy, and the leftover Sparrows, with Hargreeves noting that "the particles inside their bodies are the only things that fuel the machine," the particles he's referencing being the ones that seemingly gave birth to them and gave them their powers.
In the pages of The Umbrella Academy comic series, Hotel Oblivion is very different. For the comics, the building is a creation of Sir Reginald Hargreeves but it's not a place with large, samurai-like guardians or even a machine to reset the universe, at least that we know of. Gerard Way & Gabriel Bá's comic series uses Hotel Oblivion as a prison, one that houses all the enemies that The Umbrella Academy has faced over the years, at least it appears to be a prison.
Throughout volume 3 of the comic series, the villains that appear in the Hotel Oblivion, ranging from characters like Dr. Terminal, Perseus IX, The Murder Magician, and Obscura (none of whom have appeared in the TV series), plan an elaborate escape out of their confines. It coincides with a number of other characters and plot threads that culminate in the hotel becoming emptied and the Umbrellas reuniting. There's also a major twist with the Hotel that hasn't been fully explored within the pages of the comic series. At a certain point it becomes clear that the Hotel wasn't just a prison for villains, but a lure and a tarp, meant to ensnare some unseen monster from deep within the universe.
There's no mention of this plan for the Hotel Oblivion or this giant intergalactic monster anywhere in the new season of The Umbrella Academy TV series, but that doesn't completely mean it won't ever happen. Gerard Way & Gabriel Bá's confirmed when the first season came out that they provided an outline to series creator Steve Blackman and the writers about where the comic is headed, meaning the show knows where to plant seeds for the future and where they can divulge.
Perhaps the TV series will come back to the Hotel Oblivion, it's unclear, but the new season of the series reveals an all-new world, one where the Umbrellas have no powers and Sir Reginald Hargreeves has remade the world in his own image. Something that also appears to be a deviation from the source material.