Staff Machine Learning Engineer

Petra Security•San Francisco, CA

26d•Onsite

About The Position

We’re on a mission to stop the most dominant cyberattacks on the planet. Cybersecurity titans are born when a new attack vector overwhelms existing defenses. When ransomware ran rampant, CrowdStrike emerged as the category leader for securing user endpoints. Today, AI has made account compromise the #1 cybercrime. LLM-powered phishing messages get past email security, allowing attackers to compromise accounts and exfiltrate sensitive data in minutes. Incumbents can't keep up. They catch these attacks late, or miss them altogether. Enter Petra, security for when no perimeter remains. We are building an AI-driven Detection and Response platform to catch and remove attackers before they can act. We've grown very quickly, reaching mid-7-figures in ARR in under a year — we now protect over 1.6 million users across 10,000+ businesses. We win 90%+ of head-to-heads. We price premium, yet have extremely low customer churn. Our customers consistently tell us that Petra is the best product they've ever used. This is a rare chance to join early and help scale to $20M+ in revenue in the next 12 months. Our founders are YC W24, ex-Abnormal Security, Palo Alto Networks, and Bridgewater.

Requirements

3+ years of machine learning engineering experience, with meaningful time shipping models in production systems at scale.
Deep expertise in one or more of: anomaly detection, behavioral modeling, NLP, or fraud/abuse detection.
Strong engineering fundamentals — you write clean, production-grade code and are comfortable owning a system end to end, not just the modeling layer.
Experience working with real-time or streaming data pipelines, feature stores, high-performance databases, and distributed systems.
Familiarity with LLMs and LLM-based systems in production — you understand their capabilities and limitations and know how to build around them.
High agency and high output. You don't wait for a spec — you identify the problem, propose the solution, and execute. You ship fast, find the 90/10, and don't let perfect be the enemy of done.
Sharp and scrappy. You learn fast, ask the right questions, and figure it out — whether that's a modeling tradeoff, the right architecture, or the right shortcut.
Comfortable in a small-team, high-autonomy environment. The scope of your work is rarely handed to you, and you wouldn't have it any other way.
Proud of your craft. You care about building things that work well and hold up over time.

Nice To Haves

Bonus if you've worked in security, fraud, or identity.

Responsibilities

Build and evolve our detection models. Working closely with our founding team, you'll help design and build the systems that identify account compromise in real time — spanning behavioral analysis, anomaly detection, and model development.
Take models from research to production. You care about the full loop — not just model performance in a notebook, but how it behaves at scale in a live system with real attackers.
Architect for scale. We're growing fast. Make calls that let us move quickly today without incurring debt that bites us at 10x the user base.
Raise the technical bar. As a senior voice on a lean team, your instincts and opinions shape how we build. You'll establish patterns, push for correctness, and raise the quality of everything around you.