2 months ago
London, United KingdomSenior
Responsibilities
- Design and build stateful, asynchronous agent runtimes across distributed environments.
- Define event histories, checkpointing and resume semantics, deterministic reconstruction, retries, cancellation, timeouts, and partial-failure recovery.
- Build tracing, replay, time-travel debugging, and hierarchical observability across models, tools, handoffs, state changes, and runtime decisions.
- Develop Python APIs, libraries, and DSLs with stable extension points for tools, backends, and execution models.
- Design scheduling, placement, backpressure, resource accounting, sandboxing, permissions, and isolation for secure tool execution at scale.
- Develop tooling for trajectory collection and visualization, profiling, experiment comparison, failure attribution, and regression detection.
Requirements
- 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 adopted by other engineers or researchers.
- Deep Python expertise and proficiency in a systems language such as Rust, C++, or Go.
- Hands-on debugging skills across APIs, runtimes, and distributed infrastructure, including practical understanding of nondeterminism, side effects, and reproducibility.
- Preferred experience building production-grade runtimes, compilers, workflow engines, distributed training systems, databases, debuggers, or orchestration platforms.
- Preferred meaningful contributions to Ray, Temporal, Kafka, Erlang/BEAM, PyTorch, JAX, TensorFlow, or comparable projects.
- Preferred strong API design judgment, open-source collaboration, and disciplined approaches to testing, versioning, compatibility, and reproducibility.
- Preferred experience in ML systems or large-scale inference and training.
Benefits
- Competitive salary determined by skills and experience.
- Equity and ownership.
- Private healthcare.
- Visa sponsorship and relocation benefits.
- In-person work at the company’s London office with provided tools, workspace, and setup.
About Callosum
Callosum builds AI infrastructure that unifies heterogeneous compute—software and systems to orchestrate diverse accelerators and the physical clusters they run on—for organizations training and serving models. The privately held company was founded in 2025 and is headquartered in London. It focuses on designing, deploying, and operating mixed-hardware compute fleets across sites and vendors, and raised a seed round in 2026.