In the past decade, the US and South Korea faced a relatively narrow set of challenges in cyberspace, notably North Korea’s cyber crime facilitating sanctions evasion. In the next decade, however, the two countries will face a more diversified set of challenges with growing North Korean ties with Russia, its involvement in the war in Ukraine, and intensifying US-China competition. The US and South Korea must develop a joint playbook for responding to scenarios of disruptive cyber operations targeting South Korean public and private sectors and prepare for an even more difficult environment for curbing North Korea’s cyber crime as Russia provides a way out. Over the past two years, the US and South Korea have significantly deepened and broadened cooperation on cyber issues and have expanded cooperation further to trilateral and multilateral settings. The two countries established several regular high-level and working-level dialogues, have issued joint sanctions and threat advisories, and deepened mil-to-mil cooperation. However, 2024 has been a watershed in terms of shifting geopolitical dynamics on and around the Korean peninsula. Cyber threats will become more diversified, and the bilateral relationship will be tested at the seams without a clear joint strategic concept and operational plan.