RL Environment Engineer

Why join Replay now:

• We've scaled from $0 to a multi-eight figures run rate in a matter of months
• We've raised from top-tier investors (Floodgate, Afore, Ludlow, Hustle Fund, etc.)
• We're small enough that you'll carry outsized responsibility and grow as fast as the company does
• You'll partner and build for the fastest and most important companies in the world
• You'll be a part of building a massive, category-defining business from the ground floor

The Role

Replay is hiring RL Environment Engineers who are looking to take real-world, enterprise data and convert it into model progression. You’ll recreate the entire world of businesses across industries — crafting the highest quality environments and evals while working directly with researchers to understand the capabilities they’re looking to hillclimb.

What You'll Do

• Design and build production-grade RL environments grounded in real enterprise workflows, from task spec through to a stable, versioned release
• Write reward functions and programmatic verifiers that score outcomes reliably, and harden them against reward hacking and shortcut solutions
• Build high-fidelity evaluation environments with seeded failure modes that expose subtle regressions, and reliable model and agent harnesses with bounded behaviour and explicit output verification
• Work directly with frontier lab researchers to understand the capability gaps they want to close, and design task suites that expose and train against them
• Measure task difficulty and solvability by running frontier models against environments, then tune them until they give a usable training signal
• Ship quickly, and help set the standards and patterns for how Replay builds tasks and environments

Required aptitude

• 3-5+ years of ML / software engineering experience shipping production systems
• Personally built production-grade RL environments that were used in real training or evaluation, not only prototypes or research demos
• Ability to turn ambiguous goals from researchers into well-scoped, working systems
• A high-ownership, action-oriented mindset: you take problems from idea to shipped.
• Startup experience, a taste for broad ownership and the ability to do well when requirements are evolving
• Clear written and verbal communication with researchers, engineers, and non-technical partners

Bonus

• Background at or working with a frontier AI lab, or in research-adjacent engineering
• Experience in forward-deployed or customer-facing engineering roles
• Experience with sensitive enterprise data or other high-trust production systems
• Previously a founder or early employee at a startup

Compensation & Benefits

• $200K-350K base salary
• Meaningful equity
• 100% covered medical, dental, and vision
• Unlimited PTO
• Free gym + workout class memberships (via Wellhub)
• $500 desk allowance
• Up to $15,000 relocation bonus where applicable

How We Hire

• Intro Chat (20 min): mutual fit and interests
• Technical Screen (45 min): technical discussion & systems design challenge
• Take-home project (4 hours): work through a technical take-home asynchronously with our team
• Onsite (~3 hrs): meet the team, have snacks
• References -> Offer