Senior Software Engineer - London

H Company; Greater London; Hybrid; GBP 90,000 - 130,000; Full time

Job summary

H is hiring to build and operate an evaluation framework that runs benchmarks across web apps, desktop environments and command lines. You will help researchers and forward deployed engineers integrate benchmarks, enforce input standards, and ensure observability so runs are fast, reliable and cost-efficient.

This role emphasizes end-to-end engineering—from cluster tuning to new benchmark integrations—while working closely with researchers, product teams, and a VP of Engineering.

Qualifications

• 5+ years in backend development with production Python at the core.
• Experience building test, QA or evaluation tooling used by other teams.
• Operated distributed systems on Kubernetes in a public cloud (AWS helps).
• Experience building end-to-end systems including APIs (REST/GraphQL) and external integrations.

Responsibilities

• Integration support for researchers and forward deployed engineers bringing benchmarks into the framework.
• Set the standard for how benchmarks enter the framework and build checks to enforce it.
• Schedule and monitor workloads to maximize cluster efficiency without idle time.
• Ensure reproducible results across trials so that releases are data-driven.
• Handle diverse stacks as Benchmarks evolve, from clusters to browser extensions or desktop environments.
• Engage with customers to understand measurement needs and automate results into harnesses.

Skills

Python

Backend development

Distributed systems

Kubernetes

REST/GraphQL

Testing/QA tooling

Observability/Monitoring

Benchmark integration

Tools

Kubernetes

AWS

Docker

PostgreSQL

Grafana

Datadog

Playwright

Selenium

Job description

About H:

When we released Holo4 on 28 September, we published every trajectory behind its public benchmark scores at trajectories.hcompany.ai. For OSWorld that's 369 desktop tasks, each run 3 times, with the steps, tokens and time of every attempt. This role builds and runs the evaluation framework that produces runs like these.

H builds computer-use agents and the models behind them. Developers use them through a managed API, and our forward deployed engineers take them into enterprise workflows.

What this team owns

The evaluation framework: orchestration, runtimes and observability. Researchers and forward deployed engineers bring the benchmarks, across web apps, desktop applications and the command line. Your job is to make the framework that runs them reliable, fast and cheap, and to make adding a new one quick. Research uses the results to choose checkpoints and decide whether a model ships. Product and the forward deployed engineers use them to measure agents on customer workflows. It carries roughly 50 benchmarks now. That number should be between 100 and 200 soon, and the framework has to keep up.

What you'd be doing

• Integration support for researchers and forward deployed engineers bringing in a benchmark, with a shorter path each time.
• Setting the standard for how a benchmark enters the framework, and building the checks that enforce it.
• Scheduling and observability, so cluster capacity isn't left idle while evaluation jobs queue.
• Reproducible results across trials, so a release decision rests on numbers that hold.
• Whatever stack a benchmark calls for. One week that's cluster tuning; the next it's a browser extension or desktop environments.
• Time with customers, from single developers to large companies, to find out what they want measured, then automating it so the results flow back into our harnesses and models.

The first few months

By 3 months you'll have helped researchers or forward deployed engineers integrate 5 benchmarks, and started fixing what slows the framework down. By 6 months one part of it is yours, for example scaling the runs, observability, or a group of related benchmarks, and a release will have gone out on your numbers. By 12 months you'll know the design and trade-offs of the whole evaluation system, and be the person the rest of H asks about evaluations.

Who you'd work with

Ceiran Chapman, our VP Engineering, is hiring for this role. You'd join the evaluation team. The people relying on your work day to day are H's researchers and forward deployed engineers.

What we think it takes

Likely a good fit if you

• Have spent 5+ years in backend development, with production Python at the core, and use coding agents to go faster without letting quality drop.
• Have built test, QA or evaluation tooling that other teams depended on, and care whether a number is right.
• Have operated distributed systems on Kubernetes in a public cloud. AWS experience helps most.
• Have built and shipped systems end to end, including APIs (REST or GraphQL) and integrations with outside services.
• Know relational and non-relational databases, and message queues such as SQS, RabbitMQ or Kafka.
• Instrument what you build, with metrics, tracing and monitoring from the start.

Stronger still if you have

• Measured LLM quality before, or built agents yourself.
• Packaged and run workloads in Docker and on virtual machines.
• Used Temporal, Dask, FastAPI, PostgreSQL, Grafana or Datadog.
• Automated web or desktop software with Playwright, Selenium or a browser extension you wrote.
• Set standards other engineers follow, through code review, design review or mentoring.

You do not need a background in machine learning. We'll work that out with you.

How we hire

A 30 minute call with our Talent team, a 60 minute technical challenge, a 60 minute system design interview, and a 30 minute final conversation with Ceiran. About 3.5 hours in total.

Practicalities

London posting: Hybrid in London. That means 3 office days a week and a Paris trip about once every 4 to 6 weeks. There is a Paris posting for the same role. We offer a competitive package.