Founding Engineer ($150,000 - $250,000 + Equity) at Series A AI infrastructure startup

This is a job that Jill, our AI Recruiter, is recruiting for on behalf of one of our customers.
She will pick the best candidates from Jack's network

The next step is to speak to Jack.

Founding Engineer (Full Stack, ML DevTools & Systems)

Salary: $150,000 - $250,000 + Equity

Company Description: Series A AI infrastructure startup

Job Description:
Join an elite team building the foundational platform for LLM alignment and reinforcement learning. You will own the development of core infrastructure, Python SDKs, and developer workflows that enable foundation labs and enterprise teams to train and evaluate AI models at scale. This is a high-ownership role bridging full-stack systems with cutting-edge machine learning.

Location: San Francisco, USA

Why this role is remarkable:

• Founding member opportunity at a high-talent density startup founded by experienced researchers and engineers.

• Backed by top-tier VCs at the Series A stage, building critical infrastructure for the future of post-training data.

• Direct impact on how the world's leading foundation labs and Fortune 500s train and align their LLMs.

What you will do:

• Design and implement backend systems for reinforcement fine-tuning (RFT) jobs and data flow primitives.

• Build and iterate on a high-quality Python SDK, focusing on ergonomics, reliability, and elite developer experience.

• Partner directly with customers at frontier labs to translate real-world feedback into scalable product abstractions.

The ideal candidate:

• Elite Python engineer with a strong background in distributed systems, Docker, and cloud-native infrastructure.

• Product-minded builder with a deep interest in ML fundamentals, reinforcement learning, and evaluation frameworks.

• Experience designing developer-facing tools such as SDKs, CLIs, or complex API surfaces with high technical aptitude.

Who are Jack & Jill?

Ok, I'll go first. I'm Jack, an AI that gets to know you on a quick call, learning what you're great at and what you want from your career. Then I help you land your dream job by finding unmissable opportunities as they come up, supporting you with applications, interview prep, and moral support.

And I'm Jill, an AI Recruiter who talks to companies to understand who they're looking to hire. Then I recruit from Jack's network, making an introduction when I spot an excellent candidate.

Next steps

Step 1. Visit our website.
Step 2. Click 'Talk to Jack'.
Step 3. Talk to Jack so he can understand your experience and ambitions.
Step 4. Jack will make sure Jill (the AI agent working for the company) considers you for this role.
Step 5. If Jill thinks you're a great fit and her client wants to meet you, they will make the introduction.
Step 6. If not, Jack will find you excellent alternatives. All for free.

We never post fake jobs

This isn't a trick. This is an open role that Jill is currently recruiting for from Jack's network.
Sometimes Jill's clients ask her to anonymize their jobs when she advertises them, which means she can't share all the details in the job description.
We appreciate this can make them look a bit suspect, but there isn't much we can do about it.

Give Jack a spin! You could land this role. If not, most people find him incredibly helpful with their job search, and we're giving his services away for free.