This objective (and ending) involves using the two Arming Keys — the one you manufactured and the one you got from Alex — to trigger the station’s self-destruct sequence. This is the explode-y ending.
Since it involves blowing everything up — include the majority of Talos 1’s crew — this is the "evil" or "bad" ending. There’s some subtlety here, though, in who escapes and how. (And, in Prey’s theme of philosophical exploration, it might actually be the better ending — depending on how you interpret some of the statements in "A Hidden Place.")
Access self-destruct consoles
Now that you have both Arming Keys, you can trigger the station to self-destruct. You’re going to be following the same route you took through Life Support in "Reboot."
Make your way down to Life Support. Take the grav lift down to the lower level, and then head into the Power Plant.
The hallway after the security station in the Power Plant has a nasty bundle of typhon tendrils on the right side, so you should either run through or use the monitoring room on your left to skip over it.
Keep going straight through the Coolant Chamber, past Lan Nguyen’s office (where you helped Mikhaila) and down the grav lift to the Reactor Core. Your goal is all the way at the bottom — use the grav lift in the left corner to get down, or just jump and use your suit to soften the fall.
Use the Arming Keys in the Power Plant
There is an access panel on the floor that will open up a hidden stairwell. Take the stairs down below the reactor, then follow the hall around to the back.
Place both of the Arming Keys into the slots and activate them. You’ll black out a little, but the game won’t be over yet — you haven’t triggered the self-destruct.
Trigger the station’s self-destruct
Alex will call you (like he does in "A Mind without Limits" and invite you to the bridge. Head up to the Arboretum and into the Talos 1 Bridge. This time, Alex and January are in the Captain’s Loft (where you completed "Shuttle Advent").
January and Alex will disagree about whether or not blowing up the station is a good idea — their fight will culminate in January knocking Alex out.
You have the opportunity to destroy January before he attacks Alex, but it’s up to you — it doesn’t really change anything. Alex will give you the opportunity to change your mind about blowing up the station, though.
If your mind is made up, use the console to activate (and confirm) the self-destruct sequence. If Alex is still conscious, he’ll be disappointed in you and refuse to leave the station. If January is still functional, he’ll be happy with you.
From here, you have a few choices about how to proceed, depending on which optional objectives you completed.
So you’ve decided to blow up the station. That’s not the last choice you have to make, though. Just because the station is going to explode doesn’t mean you have to. You can, but you don’t have to.
Which of the three conclusions below are available to you depends on which optional objectives you completed earlier in the game. If you didn’t get the EP-01 keycard during "Who is December?," you won’t be able to get into the escape pod. If you killed Dahl, he won’t be there to pilot the shuttle.
Sacrifice yourself to spare Earth ("Perdition" ending)
This is the easiest option to complete — just do what January tells you. Take a seat and watch the credits roll.
Escape Talos 1 ("Who is December?" ending)
We wrote about this before as a way to get the "Abandon Ship" achievement/trophy. With the self-destruct countdown running, head toward Alex’s office. Since the gravity’s off, you don’t have to worry about the bridge or building yourself a GLOO walkway.
Head over to the escape pod and use the EP-01 keycard you got from Alex’s suite in Crew Quarters to get inside. From here, you can launch the escape pod and get away before Talos 1 blows up. (And Dahl’s shuttle will take off as well, saving everyone else.)
Get to the shuttle to escape Talos 1 ("Incapacitate Dahl" ending)
Dahl (and the other survivors) will call you from the Shuttle Bay. The shuttle’s ready to leave with Dahl behind the wheel, and you’re invited. If January is still functional, it’ll call the shuttle with your voice and shorten your countdown significantly.
You’ll have to hurry, but you can make it to the shuttle bay in time even if January cuts your time down. Head down to the Lobby and out into the Shuttle Bay. Everything you did during "The Repo Man" means you have a straight shot from the door to the shuttle.
Sit down in the co-pilot seat, and fly off into the sunset.