First spotted by CharlieIntel, two videos supposedly from a cancelled Xbox 360-era Call of Duty game called "Future Warfare" or "NX1" internally have been shared on Twitter. Their provenance has seemingly been confirmed by a former senior Neversoft developer who worked on the project.
The first video was shared by an account with the handle @mangafigurines (I've embedded a YouTube upload of the same video), and shows a first person cinematic sequence where the player's space suit is breached on the surface of the moon, and they have to flee into a nearby base while under attack.
The second video, shared by Twitter user @catgurlfriend, purports to show NX1 multiplayer in a map with a ruined desert town theme. The player switches between dual Glock 18 pistols (pretty standard for CoD) and a far more interesting futuristic DMR-looking rifle.
The moon base video especially strikes me as being too high-quality to be a convincing mod, but the most compelling supporting evidence for their veracity comes from Brian Bright, a Neversoft developer who worked on Guitar Hero and 2013's Call of Duty: Ghosts. Neversoft is most famous as the developer of the Tony Hawk's Pro Skater series, later taking up work on Guitar Hero and Call of Duty before ultimately merging with Infinity Ward in 2014.
Regarding the moon base video, Bright commented that NX1 was Neversoft's first experiment with the Call of Duty engine after the studio was pulled off Guitar Hero to work on the series. "Neversoft pivoted from Guitar Hero to make a futuristic CoD game," Bright wrote. "This mission was on the moon, some experiments with low g and was really about the team learning the engine.
"I believe this would have been in place of Ghosts, trying to remember. We had 2-3 campaign missions, and a bunch of MP work done (I was mp lead on this) before cancellation."
Bright further mentioned that the multiplayer map in the second clip may have been named "Sandstorm," and that NX1 would have included an "Escort" game mode years before we saw something similar in 2020's Black Ops: Cold War.
Though NX1 is a direct predecessor to 2013's Call of Duty: Ghosts, it's also strongly reminiscent of 2016's Infinite Warfare, a sci-fi, solar system-spanning CoD whose ideas the series hasn't revisited since. It remains unclear how the Twitter users in question acquired their footage of NX1, nor how many instances of the unfinished game remain out there in the wild.