Overview

The internet is being rebuilt by AI. The old security model, a binary world of "bots vs. humans", is obsolete. The new frontier is managing the explosion of agentic AI traffic: automated agents that are not just malicious, but productive, analytical, and commercially critical.

We believe the next generation of online trust will not be about blocking bots, but about authenticating agents. We are building the foundational layer for this new reality: a developer-first platform that helps the world's largest consumer companies distinguish between legitimate AI agents and sophisticated abuse.

Our mission is to build the "Stripe for Trust," an API-first platform that serves billions of real-time requests for customers like Rockstar Games, Canva, and Atlassian. Backed by Y Combinator and Index Ventures, we are a profitable team of builders who are passionate about creating beautiful, scalable products. We're looking for an architect to build the hyper-scale infrastructure that will power the future of online trust.

Your Role At Castle

This role is for a strategic infrastructure architect who is obsessed with building for the future. Your mission is to identify and re-architect the core components of our system for 100x scale, ensuring the platform can serve tens of billions of API requests with rock-solid reliability and performance. You will be the technical authority for our infrastructure, designing the foundational systems that will define Castle's next chapter.

Crucially, you will also be the technical voice of Castle's platform, confidently representing our architecture and scaling capabilities in high-stakes customer conversations.

What you will do

• Day-to-day operations: As part of our small team, you'll contribute to larger, high-impact projects while also managing day-to-day infrastructure and security tasks. You'll address team needs and support various aspects of our operations to ensure smooth and secure processes.
• Architect and evolve our core systems, built primarily in Ruby on Rails with a modern stack including AWS, Docker (ECR, ECS, EC2), Kafka, PostgreSQL, and ClickHouse.
• Develop and execute a long-term technical roadmap for our infrastructure, identifying key bottlenecks and designing the next generation of our platform.
• Partner with our Go-to-Market team to provide technical expertise in late-stage sales conversations and key customer reviews, acting as the authority on our platform's reliability and scale.
• Maintain our security and compliance strategy, partnering with the team to ensure our architecture meets SOC-2 standards by design, rather than by checklist.
• Serve as a key member of the on-call rotation, with a focus on building systemic solutions to eliminate recurring alerts.
  
  

Required Skills And Experience

• Deep experience in designing, building, and re-architecting distributed systems for massive scale in an AWS environment.
• Experience in building large-scale, performance-optimized production applications. We treat our SLA very seriously, and our Customers depend on our real-time APIs & data processing.
• Exceptional communication skills, with the ability to clearly articulate complex technical concepts to both engineering and business stakeholders, including enterprise customers.
• The ability to think in systems, not just services, and to make pragmatic, long-term technical decisions that balance immediate needs with a 100x future.
• A strong sense of ownership for the entire infrastructure domain, with a pragmatic approach to balancing cost, performance, and long-term scalability.
• A startup mindset: flexibility, agility, and adaptability. We are passionate about limiting work-in-progress and deeply value work/life balance, but this is a startup, and you will be expected to pivot between projects and priorities regularly.
  
  

Benefits

• Flexible work hours. We value outcomes, not hours.
• Unlimited PTO & Sick Leave
• Paid parental leave
• Employee stock purchase plan with a 10-year post-termination option exercise window