Applied AI Engineer, Autonomous Defense

Get to Know Us Horizon3 is a fast-growing, remote cybersecurity company dedicated to the mission of enabling organizations to proactively find and fix and verify exploitable attack vectors before criminals exploit them. Our flagship product, the NodeZeroTM platform, delivers production-safe autonomous pentests and other key assessment operations that scale across the largest internal, external, cloud, and hybrid cloud environments. NodeZero has been adopted by organizations of all sizes, from small educational institutions to government agencies and Global 100 enterprises. It is used by ITOps/SecOps teams, consulting pentesters, and MSSPs and MSPs.  We are a fusion of former U.S. Special Operations cyber operators, startup engineers, and formerly frustrated cybersecurity practitioners. We're committed to helping solve our common security problems: ineffective security tools, false positives resulting in alert fatigue, blind spots, "checkbox” security culture, cybersecurity skills shortage, and the long lead time and expense of hiring outside consultants. Collectively, we are a team of learn it alls, committed to a culture of respect, collaboration, ownership, and results.   What You'll Do We're looking for an AI Researcher to build the agents that turn our offensive knowledge into defensive action. You'll build agents that reason from a proven attack path to the specific control changes that break it - EDR policy, firewall and segmentation rules, conditional access, detection content, cloud IAM, GPO - apply or stage those changes in the customer's environment, and then prove the fix by re-running the attack. That last part is why this is tractable. Most defensive AI has no ground truth and gets graded on whether its advice sounds reasonable. Ours gets graded on whether the attack still works. You will have a real outcome signal on a short loop, and hundreds of thousands of prior tests to learn from. It is also why this is hard. These agents run inside customer tenants and modify production security controls. A bad change is an outage or a new hole in someone's defense. The reasoning problem and the safety problem are the same problem here, and you will own both. The goal is closed-loop defense: find, fix, verify, running autonomously at enterprise scale. If you want to work on agents where the feedback is real and the stakes are real, this is the job for you. Responsibilities - Build the reasoning systems that map proven attack paths and exploitation telemetry to specific, applicable control changes, ranked by effectiveness against operational blast radius. - Turn our pentest data into training and evaluation data. Extract the signal of why an attack succeeded in one environment and failed in another. - Design and run counterfactual experiments in representative test environments: would this change have broken this attack chain, what does it cost operationally, and does it generalize beyond the tenant it was learned in. - Design the reasoning layer over heterogeneous control planes so an agent can work across vendor APIs with different policy models without a hardcoded playbook per product. - Design the safety architecture for autonomous change — dry-run and simulation, blast-radius classification, approval gates for high-impact actions, staged rollout, rollback, and an audit trail a customer's change board will accept. - Work with our attack engineers and detection engineers to define target agent behavior and diagnose failure modes: ineffective remediations, over-broad changes, business-breaking policy edits, and recommendations that look right and don't hold on re-test. - Own problems end to end in a 0→1 environment where requirements are ambiguous, systems move fast, and reliability matters, becau