Principal Security Engineer

Company: Reactor
Location: San Francisco, California
Type: onsite
Posted: Oct 5, 2026
Views: 0

✨ AI Summary

Reactor, an AI inference platform for real-time world models, is hiring a Principal Security Engineer to build its security program from the ground up. The role requires deep experience securing cloud-native infrastructure and GPU clusters, with a hands-on coding approach and prior leadership in AI or cloud infra security. Candidates must have led compliance efforts like SOC 2 and be comfortable with early-stage startup dynamics. The position is in-person in San Francisco with 99th percentile salary and equity, plus visa sponsorship and relocation support.

Reactor is building the inference platform for real-time world models. Our goal is to democratize access to real-time intelligence to unlock next-generation use cases in media, physical AI and omni-directional models. We already run the largest and fastest catalog of world models on the market, and work closely with all major model labs to run and optimize their world models, including Alibaba, Amazon, and NVIDIA. Our team is made of alumni from leading firms such as Apple, Meta, Amazon, Microsoft, Luma AI, Adobe, Stability AI, and more. We've raised $74M led by Lightspeed, with Amplify Partners, WNDR, NVIDIA, Sapphire, and other Tier 1 investors participating. Jeffrey Katzenberg, co-founder of DreamWorks Animation, sits on our board of directors.

The Role
We're hiring a Principal Security Engineer. You'll build Reactor's security program from the ground up, and you'll be the person partners and customers talk to about how we protect their models and data.
  • Set Reactor's security strategy and own it end-to-end
  • Protect the models and data our partners and customers trust us with
  • Threat-model the platform and fix what you find
  • Lead partner and customer security reviews and compliance work
  • Represent Reactor's security work with partners, customers, and the wider security and AI community
  • Build security into how the team ships
  • Set up detection and incident response across the organization
  • You've led security, or been one of the senior people on a security team, at an AI lab, a GPU cloud, or a cloud infra company
  • You write code, and like to be hands-on
  • Deep experience securing cloud-native infrastructure
  • You've taken a company through a compliance framework like SOC 2 and handled enterprise security reviews while keeping engineering moving
  • People in security or AI know your work: talks, published research, open source, or a track record at a company whose name carries weight
  • You are able to communicate complicated technical security problems across both technical and non-technical audiences.
  • You want to work at an early-stage startup: small team, lots of ownership, fast pace, in person in SF
Nice to Have
  • Experience securing model weights or ML infrastructure
  • Real-time or media infrastructure, anywhere p99 matters more than the average
  • GPU cluster security
  • Red team or offensive security experience

What We're Not Looking For
  • Policy or GRC leaders who haven't touched infrastructure in years
  • People who need a team of 10 before anything gets done
  • Compliance checklists with no threat model behind them
Logistics
We're in person in San Francisco
  • Salary and equity at the 99th percentile for our stage (Pave benchmarks).
  • Visa sponsorship and relocation support
  • Generous health, dental, and vision coverage
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Name: Reactor

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