About Osmosis

At Osmosis, we help companies use cutting-edge reinforcement learning techniques to fine-tune open-source language models that beat foundation models on performance, latency, and cost.

We’ve raised $7M in funding from Y Combinator, top institutional investors like CRV and Audacious Ventures, as well as angel investors including Paul Graham (Y Combinator), Erik Bernhardsson (Modal Labs), Misha Laskin (Reflection AI), and Guillermo Rauch (Vercel).

About the Role

We're looking for a Machine Learning Engineer to contribute to high-performance distributed training infrastructure for RL at scale. You'll work directly with our founding team and design partners to push the boundaries of what's possible with post-training and continual learning systems.

This role requires expertise in RL algorithms, distributed training, and low-level optimization. You'll have exceptional agency to make impactful decisions while working in a fast-paced, customer-driven environment.

Responsibilities

You’ll contribute to work in areas like:

Distributed Training Infrastructure: implement new RL algorithms and build scalable post-training pipelines
Resource Management & Optimization: design infrastructure systems for efficient GPU utilization and dynamic resource allocation
Customer-Facing Work: work directly with customers on production deployments and custom model development

Technology

Backend: Python FastAPI, Golang
Frontend: React, TypeScript, Next.js
Cloud Infrastructure: AWS Fargate, Docker, Kubernetes, AWS SageMaker
ML Frameworks: Verl / slime / Megatron-LM / SkyRL, PyTorch (FSDP experience is a plus), vLLM / SGLang
Databases: DynamoDB, S3

About the company

We're building an end-to-end platform for reinforcement fine-tuning. We help the fastest growing AI companies fine-tune OSS models that outperform foundation models.

We bring a combination of deep startup and technical expertise:

Kasey (CEO) - Previously co-founded and sold a gaming startup, most recently worked in early-stage VC focusing on AI investments. In a past life, he competed in classical piano competitions and performed at Carnegie Hall.

Andy (CTO) - Real-time data/ML expert who was the youngest tech lead at TikTok, where he led their real-time recommendations & data infrastructure team. Hacked Gradescope during COVID.

We've raised $7M from leading institutional investors like YC & CRV, as well as angels like Paul Graham and Guillermo Rauch.

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