Agent Runtime & Systems - Member of Technical Staff

The role

This person will own the runtime and programming model for long-running agent systems. They will develop core software for durable execution, distributed scheduling, and secure tool execution.

What you will do

• Design and build stateful, asynchronous agent runtimes across distributed environments
• Define event histories, checkpoint and resume semantics, deterministic reconstruction, retries, cancellation, timeouts, and recovery from partial failure
• Build traces and replay, time-travel debugging, and hierarchical tracing
• Develop clear Python APIs, libraries, and DSLs
• Design scheduling, placement, backpressure, resource accounting, sandboxing, permissions, and isolation for secure tool execution at scale
• Develop tooling for trajectory collection and visualisation, performance profiling, experiment comparison, failure attribution, and regression detection

Required qualifications

• Strong distributed systems background with hands-on experience in durable workflows, actor systems, schedulers, workflow engines, distributed databases, or stream processors
• Experience designing a library, framework, runtime, or DSL that other engineers or researchers adopted
• Deep Python expertise
• Proficiency in a systems language such as Rust, C++, or Go
• Hands-on debugging skills across APIs, runtimes, and distributed infrastructure

Nice to have

• Experience building a production-grade runtime, compiler, workflow engine, distributed training system, database, debugger, or orchestration platform
• Meaningful contributions to systems such as Ray, Temporal, Kafka, Erlang/BEAM, PyTorch, JAX, TensorFlow, or comparable projects
• Strong API design judgement, open-source collaboration, and disciplined approaches to testing, versioning, compatibility, and reproducibility
• Experience in ML systems or large-scale inference and training

Benefits

• Competitive Salary
• Equity & Ownership
• Private healthcare
• Visa sponsorship
• Relocation benefits

About the company

Callosum is the Intelligent Systems Company building infrastructure that unifies heterogeneous compute across the full stack. They are engineers and scientists based in London.