Callosum

Agent Runtime & Systems - Member of Technical Staff

Callosum
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16 days ago
London, United KingdomSenior
H1B sponsor

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.

Categories

Callosum

About Callosum

11-50 employees
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