API Platform Architect

About the Company

Callosum is the Intelligent Systems Company. We believe intelligence emerges from the diversity of co-optimised mechanisms working together. We co-evolve models, workflows, and silicon to build the heterogeneous infrastructure required for the next era of Agentic AI.

Responsibilities

• Own the architecture and technical bar for the customer-facing API platform
• Build the orchestration layer including request lifecycle, routing, and state management
• Implement DNS routing, load balancing, and autoscaling
• Design for multi-tenancy, isolation, and per-workflow scaling
• Set design standards, conduct code reviews, and make critical architectural decisions
• Ensure performance and scalability for millions of concurrent requests
• Partner with reliability engineers to ensure production stability

Requirements

• Deep experience designing and operating production API platforms
• Strong distributed-systems fundamentals (stateless/stateful services, routing, queueing, fault tolerance)
• Proven track record of owning architecture for large-scale systems
• Hands-on engineering approach with a bias for action
• Ability to navigate ambiguity and make consequential decisions

Preferred Qualifications

• Experience with high-assurance multi-tenant systems
• Familiarity with high-throughput inference or agent workloads
• Open-source contributions to relevant infrastructure
• Experience in early-stage, AI-native companies

Benefits

• Competitive Salary
• Equity & Ownership
• Private healthcare
• Visa sponsorship and relocation benefits
• In-person collaboration in our London office