--- title: 'Senior Software Engineer, Agentic Systems at Horizon3 AI' canonical: 'https://feeny.ai/job/senior-software-engineer-agentic-systems-horizon3-ai-united-states-xkv8szcenmka' type: 'job' last_seen: '2026-09-12' --- # Senior Software Engineer, Agentic Systems at Horizon3 AI - **Company:** [Horizon3 AI](https://feeny.ai/companies/horizon3-ai) - **Location:** United States - **Compensation:** $169k–$208k - **Employment:** full-time - **Work type:** remote - **Posted:** 2026-08-26 - **Last confirmed live:** 2026-09-12 - **Apply:** https://jobs.ashbyhq.com/horizon3ai/e36e9f43-c831-43ac-85b3-782b28bef222/application **Skills:** Python, LLM-powered applications, Agent orchestration, Tool use, Function calling, Structured outputs, Prompt engineering, Context engineering, AWS Bedrock, Testing, Observability, Web application security, IDOR/BOLA, SQLi, XSS, SSRF, SSTI, Agent frameworks, Graph data models, Neo4j > Build and evolve the autonomous agent harness and orchestration layer for an LLM-driven web application penetration tester. The role involves designing tools, validation layers, and evaluation infrastructure to ensure reliable, production-safe, and deterministic attack capabilities without false positives. ## Job description Get to Know Us [Horizon3](http://Horizon3.ai) is a fast-growing, remote cybersecurity company dedicated to the mission of enabling organizations to proactively find, fix, and verify exploitable attack vectors before criminals exploit them. Our flagship product, the NodeZero™ 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, the 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. Summary We're building an autonomous, black-box web application penetration tester. It crawls and attacks real production websites the way a skilled human pentester would, finding broken access control, injection, XSS, SSRF, SSTI, and more, under a strict production-safe, no-false-positives mandate. We have deep offensive expertise on this team: people who know exactly how to find and exploit these vulnerabilities by hand. What we need is an engineer who can turn that expertise into autonomous agent capability, the reasoning, orchestration, tooling, and evaluation that lets an LLM-driven agent do this work reliably, at scale, and unattended. You'd own and evolve the attack-agent layer: the part of the system that decides what to probe, forms and tests hypotheses, exploits, and verifies, without false positives and without touching anything it shouldn't. This is a build role, not a research role. We use models surgically, deterministic-first, LLM-as-scalpel, and the hard problems are in engineering reliability, not chasing benchmarks. Essential Functions - Build and evolve the agent harness and orchestration that turns an LLM into a reliable autonomous pentester, the loop that reasons over an application, forms attack hypotheses, acts, and verifies results. - Design the tools and tool-shaped feedback the agent uses to probe and exploit, and the structured-output and validation layers that keep it reliable (e.g., hook-enforced mandatory validation, schema-constrained outputs). - Translate the team's offensive expertise into repeatable agent capabilities — partnering directly with our attackers to encode how they think into something the agent can do consistently. - Own and grow our evaluation infrastructure: benchmark suites, a failure-mode taxonomy across the pipeline (discovery → hypothesis → exploitation → verification), and regression detection, so we actually know whether the agent is getting better. - Manage LLM inference in production: model selection, prompt and context engineering, and keeping cost and latency under control (we run on AWS Bedrock with centralized cost tracking). - Hold the line on production-safety and no-false-positives, every finding the agent reports has to be real and reproducible. Competencies/Requirements - 5+ years building production software, with strong Python. - Hands-on experience building LLM-powered applications or agents, tool use / function calling, structured outputs, multi-step orchestration, and the glue that makes it all hold together. - A track record of making LLMs reliable in production, you've wrestled nondeterminism, designed around model limitations, and shipped something that worked when it mattered. - Real experience with evaluation: you've built or owned the harness that tells you whether a model or agent change is an improvement, not just a vibe. - Strong instincts for prompt and context engineering, and the judgment to keep the model's job small and well-scoped. - Solid software fundamentals — testing, observability, and the discipline to keep a complex agent debuggable. - Ownership mentality, comfortable owning a critical, fast-moving subsystem end to end. Desired/Nice to Have - Working knowledge of web application security, broken access control, IDOR/BOLA, SQLi, XSS, SSRF, SSTI, enough to collaborate fluently with offensive engineers. - Experience building eval harnesses or benchmarks specifically for agents (synthetic environments, CVE-based test targets, capture-the-flag-style scoring). - Experience with agent frameworks, and strong opinions about when not to reach for one. - Familiarity with graph data models (e.g., Neo4j) for representing application state and attack context. What makes you stand out: - You've shipped an autonomous agent that did real, valuable work unattended in production, and you have scar tissue from making it trustworthy. - You've designed evaluation systems that actually drove improvement, closed the loop between "we changed something" and "it measurably got better." - You pair an offensive-security mindset (CTF, bug bounty, pentesting, or research background) with the engineering chops to turn that intuition into a reliable system. - You have hands-on experience with agent fine-tuning or RL (SFT, GRPO, reward design for tool-using agents) and a grounded view of when it's worth it versus improving the harness. - You've published or spoken on agent reliability, evaluation, or autonomous security tooling. ## 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: $169,000 - $208,000 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. You Belong Here Horizon3 is not just an equal opportunity employer - we are a community that values diversity, equity, and inclusion as fundamental principles of our culture and success. We are dedicated to fostering a workplace where everyone feels welcome and respected, regardless of race, color, religion, sex, national origin, age, disability, veteran status, sexual orientation, gender identity or expression, genetic information, marital status, hair length or any other legally protected status by law. Our commitment to diversity and inclusion means we strive to attract, develop, and retain a workforce that reflects the varied communities we serve. We believe that diverse perspectives drive innovation and strengthen our ability to create cutting-edge cybersecurity solutions. At Horizon3, every team member is valued and supported in an environment that encourages personal and professional growth. We welcome candidates from all backgrounds and experiences, and we encourage all qualified individuals to apply. Come be a part of Horizon3, where your unique contributions are recognized, and your potential is limitless. 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. Application Note In any materials you submit, you may redact or remove age-identifying information such as age, date of birth, or dates of school attendance or graduation. You will not be penalized for redacting or removing this information. ## About Horizon3 AI ## Company Overview - **One-liner**: Horizon3.ai provides an autonomous penetration testing platform (NodeZero) that safely hacks production environments to identify and fix exploitable attack paths using AI. - **Entity Type**: Private (Series D – latest funding round in 2026, led by Prosperity7 Ventures) - **Headquarters**: San Francisco, California, United States (447 Battery Street, San Francisco, CA 94111) - **Founded**: 2019 - **Founders**: Snehal Antani (Co-Founder & CEO); founded by a mix of US Special Operations, US National Security, and cybersecurity industry veterans ## Core Business - **Primary industry**: Cybersecurity (autonomous penetration testing, vulnerability management, continuous security validation) - **Target customers**: B2B – large enterprises, Fortune 100, government agencies (NSA, CISA), healthcare providers, financial services, manufacturing, education, public sector - **Mission**: “Turn the map around” – using the attacker’s perspective to help enterprises prioritize defensive efforts. The company aims to shift the advantage from attackers to defenders by fighting AI with AI. ## Products & Services - **[NodeZero®](https://horizon3.ai/)**: Autonomous penetration testing SaaS platform. Safely runs real attack techniques in production environments (no agents, no disruption). Discovers and chains exploitable vulnerabilities, misconfigurations, harvested credentials, and dangerous defaults across external, identity, on-prem, cloud, and Kubernetes attack surfaces. Also includes Active Directory password auditing and phishing impact testing. Continuously validates fixes and repeats autonomously. ## Market Standing - **Valuation**: Not publicly disclosed - **Key Metrics**: - Annual Revenue: **$35.5M** (per LinkedIn) - Total Funding: **$187M** (per LinkedIn) / **$181M** (per CB Insights – conflicting reports; both cited) - **225,000+** production-safe tests completed - **5,000+** customers - **Notable Investors/Partners**: - SignalFire (lead in Seed, Series A, Series B) - Craft Ventures (lead Series C) - Prosperity7 Ventures (lead Series D – 2026) - **Growth Signals**: - Ranked **#1 in Security** on the 2025 Inc. 5000 list - **#3 overall** on the 2025 Deloitte Technology Fast 500 - Fast Company’s **Most Innovative Companies** (2026) – #1 in Security - Named to the **Fortune Cyber 60** (2023 & 2025) - Two-time **Black Unicorn Award** winner - Headcount grew **115.5% YoY** to 341 employees (LinkedIn) - Active job postings up **168.2% YoY**; operates in 14 countries ## Competitive Advantages - **AI-driven autonomous testing** that learns from hundreds of thousands of tests and uses the right AI (ML, GenAI) for each problem – delivers evidence-based results with **zero hallucinations**. - **Production-safe** – zero downtime across all production tests, trusted by the world’s most sensitive high-security environments (NSA, CISA, Fortune 10, major healthcare). - **No agents required** – fully self-service SaaS, safe to run continuously. - **Real attack techniques** – not a scanner; shows actual attacker paths and impact. - **Rapid verification** – instantly confirms fixes and repeats the cycle, enabling a continuous validation loop. ## Strategic Focus - **Continuous validation** – driving a loop of test-fix-verify-repeat autonomously. - **Fighting AI with AI** – building NodeZero to operate at machine speed against AI-powered attacks. - **Global expansion** – already in 14 countries, with active hiring in EMEA, APAC, and the Americas. - **Scaling the team** – 59 active job postings (as of mid-2026), with emphasis on engineering, sales, and customer success roles. ## Why Work Here - **Culture**: Rated **5.0/5.0 on LinkedIn** (76 reviews) with perfect scores for Culture (5.0), Career (4.9), Compensation (4.7), and Work-Life (4.6). Described as a “kick-ass organization hell bent on disrupting an industry” with a team of “motivated learn-it-alls.” - **Work Policy**: Remote-friendly (most roles listed as remote, HQ in San Francisco, CA). Offers flexibility across time zones. - **Notable Perks** (from Built In and LinkedIn): - Comprehensive healthcare (medical, dental, vision, FSA) - Life insurance, disability insurance - 401(k) with company matching - Equity and employee stock purchase plan - Generous parental leave and family medical leave - Performance bonuses - Job training, conferences, and customized development tracks - Promotion policies and career growth support - **Engineering Culture**: Built by US Special Operations and National Security veterans. Emphasis on high autonomy, real-world impact, and cutting-edge AI/security work. “If you want to be part of a kick-ass organization hell bent on disrupting an industry and keeping attackers at bay, let’s talk.” ## Sources 1. [horizon3.ai – Homepage](https://horizon3.ai/) 2. [horizon3.ai – About/Team](https://horizon3.ai/about-us/) 3. [LinkedIn – Horizon3.ai Company Page](https://www.linkedin.com/company/horizon3ai) 4. [Built In – Horizon3.ai Careers & Perks](https://builtin.com/company/horizon3ai) 5. [CB Insights – Horizon3.ai Profile](https://www.cbinsights.com/company/horizon-3-ai) ## Other roles at Horizon3 AI - [Account Executive, MSP (East)](https://feeny.ai/job/account-executive-msp-east-horizon3-ai-east-q4w5atyf2a5p) — East - [Senior Channel Field Marketing Manager, META](https://feeny.ai/job/senior-channel-field-marketing-manager-meta-horizon3-ai-dubai-0d5m3qsarw9t) — Dubai, United Arab Emirates - [Channel Account Manager, Midatlantic](https://feeny.ai/job/channel-account-manager-midatlantic-horizon3-ai-united-states-fj7veyksksrn) — United States - [Senior Manager, Sales Compensation & Incentive Strategy](https://feeny.ai/job/senior-manager-sales-compensation-incentive-strategy-horizon3-ai-united-states-nyed00v8m8gz) — United States - [Manager, Commercial Sales](https://feeny.ai/job/manager-commercial-sales-horizon3-ai-washington-tzanjykxxkvy) — Washington, DC - [Commercial Account Executive, DC](https://feeny.ai/job/commercial-account-executive-dc-horizon3-ai-washington-p55jz13x238t) — Washington, DC - [Sales Engineer (Enterprise, Pacific NorthWest)](https://feeny.ai/job/sales-engineer-enterprise-pacific-northwest-horizon3-ai-united-states-qja22wvgb4sq) — United States - [Partner Operations, MSSP](https://feeny.ai/job/partner-operations-mssp-horizon3-ai-united-states-338jd1v1m3nm) — United States - [Product & Privacy Counsel](https://feeny.ai/job/product-privacy-counsel-horizon3-ai-united-states-6c6sgefxegx0) — United States - [Sales Engineer (SouthWest)](https://feeny.ai/job/sales-engineer-southwest-horizon3-ai-southwest-vrtjjnpsxa8b) — Southwest