Smarter Models Killed the Harness. Here's What's Left — Jediah Katz, SpaceXAI

Is the agent harness dead? Jediah Katz, Cursor's longest-tenured agent-harness engineer and now at SpaceX, explains why fancy harnesses no longer add coding intelligence: the data flywheel teaches models the skills harnesses used to patch in. He then argues why the harness matters more than ever. It opens new frontiers like Grokbot, and it owns what models can't absorb: infrastructure, trust and security, and efficiency. He closes with predictions, including that 90% of agent work runs off the laptop within six months. Chapters: - 00:00 Is the harness dead? - 01:09 From prompt engineer to harness engineer - 02:02 What's inside an agent harness - 02:59 Peak harness, and the backlash - 05:00 What the research says - 06:16 The data flywheel - 07:34 The harness unlocks the next frontier - 12:07 What models can't absorb: infra, trust, efficiency - 14:21 What's next for harnesses - 17:36 Long live the harness Jediah Katz — X: https://x.com/jediahkatz | https://cursor.com Join us in SF for the second annual AIE CODE summit: https://aie.codes our last flagship summit of 2026. Applications live now!