Research Engineer

Built Different; Paris; Hybride; EUR 102 000 - 138 000; Plein temps

Avantages offerts par ce poste

Founding equity

Résumé du poste

Built Different is seeking a Founding Junior RL Engineer/Researcher for a hybrid role in Paris, Amsterdam, or London, with some remote options. The position offers €120,000 plus founding equity and the chance to work with frontier AI labs and paying clients from day one.

You’ve built or explored RL environments or training infrastructure at a serious AI company, think in first principles, and move fast. Join a founding team shaping long-horizon AI tasks.

Qualifications

• Experience building RL environments or training infrastructure.
• Familiarity with RL experiments and evaluation frameworks.
• Ability to work in a fast-paced, founding-team setting.

Connaissances

RL environments

Training infrastructure

Experiment design

Description du poste

Founding Junior RL Engineer/Researcher (Mediors welcome also)

Hybrid | Amsterdam / London / Paris | €120,000 + Founding Equity

The best AI engineers aren't waiting for a job ad. They're waiting for the right moment. This might be it.

Anthropic leadership has discussed spending over $1 billion on RL environments in the next year alone. The market is moving - fast and at scale. One pre-seed company just closed a round at a valuation most Series A companies would envy, with frontier AI labs already as paying clients and acquisition interest already on the table (x2).

The reason? They cracked something the rest of the market hasn't.

Most teams build RL environments from synthetic data - easy to demo, easy to commoditise, brittle. This team mines real human behavioural data - how domain experts actually reason, decide, and solve complex tasks over long-horizon workflows. 10-100+ step environments. Closed-loop systems where environments, data, training, and evaluation are tightly integrated. Not proxies. Not short cuts.

25-30% uplift in model task success rates. 50-65% more training signals. Evals that reflect how humans actually work.

The funding just landed. Second time founders. The founding team is being built right now. There are very few seats. Are you going to be in one of them?

£100,000 + founding equity at a ~$40M seed valuation

Frontier AI labs as paying clients from day one

Environment design treated as a first-class problem - not an after thought

London / Paris hybrid with some remote options

You'll love this if...

• You've built or have explored RL environments, gyms, or training infrastructure at a serious RL or AI company
• You think environment design & the lack of data available are the most underrated problems in AI right now
• You move fast, think in first principles, and thrive without a playbook
• You want to work at the forefront of innovation with frontier labs

Because great teams are Built Different.