AI Security Cost Asymmetry Favors Closed Source

AI equalizes the defender’s security cost across open and closed source but varies the attacker’s cost by source availability. This inverts Linus’s Law: openness helps the attacker more than the defender. The defender always has source access and frontier models; their cost is the floor: tokens. What changes is the attacker’s cost. Open source: point a model at the public repository (tokens). Closed binary: decompile first (lossy, noisier analysis). Service API: black box, limited attempts, highest cost. The defender’s posture is constant in all three cases. Source availability is now a variable in the attacker’s equation only.