Founding Engineer Full Stack, ML DevTools & Systems
Jack & Jill
Job Overview
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Job Description
Founding Engineer Full Stack, ML DevTools & Systems at Jack & Jill (for a 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.
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.
Company Description
We are a Series A AI infrastructure startup, backed by top-tier VCs, building critical infrastructure for the future of post-training data. We are focused on providing a foundational platform for LLM alignment and reinforcement learning.
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.
Key skills/competency:
- Python
- Distributed Systems
- Docker
- Cloud-Native Infrastructure
- Machine Learning Fundamentals
- Reinforcement Learning
- Evaluation Frameworks
- SDK Development
- API Design
- Developer Tools
How to Get Hired at Jack & Jill
- Engage with Jack's AI: Start by visiting the Jack & Jill website and talking to Jack to articulate your experience and career goals.
- Showcase relevant expertise: Highlight your strong background in Python, distributed systems, and ML DevTools to align with this Founding Engineer role.
- Prepare for ML and Systems: Be ready to discuss your experience in reinforcement learning, evaluation frameworks, and cloud-native infrastructure.
- Emphasize product-minded development: Demonstrate your ability to translate customer feedback into scalable product abstractions and developer-facing tools.
- Research AI infrastructure trends: Stay updated on LLM alignment, reinforcement fine-tuning (RFT), and foundational AI platform challenges.
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