The most-studied choke defense in modern combatives - a properly locked rear naked ends the fight in seconds, so the escape lives in the seconds before the lock.
Prevent a rear choke from closing and escape before you lose consciousness.
You have three to five seconds before a locked rear naked takes consciousness. Act on the first sense of the arm across your neck: chin down hard, both hands to their choking wrist.
Turn your head into the crook of their elbow, not away from it. Turning away tightens the seal; turning in creates a channel of air along the inside of their forearm.
Drop your hips and posture forward, hard, breaking their grip and their balance. As they stumble, spin under the arm to face them, then strike or exit. Do not stay in the pocket.