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 01 environment where requirements are ambiguous, systems move fast, and reliability matters, because the output lands in someone's production security posture.

What You'll Bring

Required

• Strong ML engineering experience building, evaluating, and deploying production AI systems, with hands-on work in deep learning, transformer models, and PyTorch.
• Hands-on experience with at least one of: post-training large language models (supervised fine-tuning, distillation, preference optimization, RL), or designing agentic systems with tool use, planning, and long-horizon execution that hold up outside a demo.
• A track record of building evaluation systems for open-ended tasks where there is no clean label and success is judged by outcome.
• Experience reasoning over structured, heterogeneous, messy real-world data - configurations, graphs, logs, policy documents - rather than clean benchmark datasets.
• Strong software engineering fundamentals and a track record of shipping and maintaining production-quality code in Python, not just scripts and proofs of concept.
• Experience with data pipelines, distributed systems, and cloud infrastructure, preferably AWS.
• Ability to work across model behavior, APIs, and infrastructure, and to collaborate closely with attack engineers, detection engineers, product, and infrastructure.
• Ability to independently research unfamiliar systems and rapidly become the team's expert.
• Strong written and verbal communication, including clear technical documentation.
• Master's in Computer Science, Machine Learning, or a related field, or equivalent practical experience, plus 4+ years of professional engineering experience.

You do not need to have been a pentester or a SOC analyst. You do need to be seriously interested in how attackers and defenders actually operate, and willing to learn it in depth. The reasoning we are building cannot be designed by someone who does not understand the domain.

Preferred

• Background in detection engineering, purple teaming, security engineering, offensive security, or incident response.
• Hands-on familiarity with security control planes and their APIs and policy models: EDR (CrowdStrike, SentinelOne, Defender), firewalls and segmentation (Palo Alto, Fortinet), identity and conditional access (Entra ID, Okta), SIEM and detection content (Splunk, Sentinel), cloud IAM, WAF, MDM, and GPO.
• Experience with causal or counterfactual inference, or with graph reasoning, planning, and search over large state spaces. Familiarity with Neo4j and attack-path analysis.
• Experience building automation that takes write actions in production systems, along with the safety and change-management machinery around it.
• Experience with adversarial robustness or prompt injection, particularly where an agent consumes untrusted input from the environment it operates in.
• Experience integrating ML into production, multi-tenant SaaS, or running ML systems in customer-controlled or air-gapped environments.

Perks of Horizon3

• Inclusive Team: We value diversity and promote an inclusive culture where everyone can thrive.
• Growth Opportunities: Be part of a dynamic and growing team with numerous career development opportunities.
• Innovative Culture: Work in a collaborative environment that encourages creativity and out-of-the-box thinking.
• Hybrid & Remote Work: We embrace a mix of remote and hybrid work models depending on role and location, including our Chicago office, where some roles require regular in-office presence.
• Competitive Compensation: We offer competitive salary, equity and benefits. Our benefits include health, vision & dental insurance for you and your family, a flexible vacation policy, and generous parental leave.

Compensation and Values

At Horizon3, we believe that our people are our greatest asset, and our compensation philosophy reflects this core value. We are committed to fostering an environment where all employees feel valued, respected, and rewarded for their contributions. Our compensation structure is designed to be fair, competitive, and transparent, ensuring that every team member is recognized and compensated equitably across roles, levels, and locations.

In accordance with various State's transparency regulations, we provide the following salary range information for this position:

• Base salary range: $313,000 - $369,000 annually. The exact salary will be determined based on the selected candidate's location, qualifications, experience, and relevant skills.
• Additional compensation: All full-time roles are eligible for an equity package in the form of stock options.

Other Duties

Please note this job description is not designed to cover or contain a comprehensive listing of activities, duties or responsibilities that are required of the employee. Duties, responsibilities, and activities may change at any time with or without notice.