WARNING: The following contains spoilers for X-Force #18 by Benjamin Percy, Garry Brown, Guru-eFX & VC's Joe Caramagna, on sale now
The current incarnation of X-Force operates as a mutant spy organization, working with some of the darkest secrets of Krakoa and contending with some of their most dangerous threats. This means the members of X-Force are privy to information that could destroy Krakoa if they were found out, and it explains a secret protocol between X-Force masterminds Beast and Sage that catches other X-Men by surprise.
As revealed in X-Force #18, Beast and Sage have a mutual pact to kill each other if they are seriously injured in some way, proving just how cold the two have had to become since becoming the resident masterminds of X-Force.
Similar to how Domino was previously cloned by the forces associated with XENO, Quentin Quire's telepathy has been turned against the X-Men on Krakoa. This includes a surprisingly brutal psychic series of attacks, striking at mutants when they're less mentally prepared for an assault, such as when asleep, distracted or inebriated. This is first truly noticed by Sage, who was at the Green Lagoon and drinking alone when she began to see Blob as a horrifying monster. Returning to the X-Force base of operations, Sage finds a recently returned Quentin Quire and Phoebe Cuckoo, as well as Beast, who has suffered a massive and debilitating stroke as a result of the psychic assault.
Using his telepathy, Quire is able to probe Beast's mind and discover that a dark version of himself committed these crimes. After revealing everything, Beast pleads with the assembled mutants to kill him. Quire refuses, angrily arguing that he's trying not to be a bad guy anymore. But this just prompts Sage to reveal that she and Beast made an arrangement when they became the backbone of X-Force.
Reasoning that the sheer amount of classified information they possess makes them particularly dangerous assets for Krakoa, having a broken body is akin to being a "damaged hard drive full of invaluable data." Sage notes that this reading of their situation means Beast and her have decided it's better to just go immediately to a backup if they're seriously injured, prompting Sage to swiftly break Beast's neck.
It's a brutal moment for Sage, and it's one that clearly shakes Quire and Phoebe as they witness it. It also speaks to the general coldness with which Beast has been operating since taking a leading role in X-Force. Leading the clandestine branch of Krakoa's government has led Beast to make emotionless and brutal decisions, which have resulted in deaths across the world and even the trust of friends like Jean Grey. Seeing that coldness even extends to his own life helps explain why Beast has grown so dark recently, he hasn't just been hurting his friends like Colossus for no reason. He's even been devaluing his own life if it means helping Krakoa.
It also speaks to just how brutal heroic mutants like Beast and Sage have had to become in the age of Krakoa and the kind of decisions that they'll likely have to continue to make going forward for the good of their country. Only time will tell if Beast ends up forced to reevaluate his previous actions in light of his demise, or if fully cements his new view that anyone, even himself, is an acceptable loss if it means progress for the X-Men.