Backend & Cloud Engineer

About Citadel AI

Citadel AI builds software products to evaluate, monitor, and govern AI systems. Our mission is to build trust in AI.

We’re located in Tokyo, but we have an international team and global customers. Our goal is to build a world-class startup from Japan, and our team members have previously worked at leading companies such as Google, Paidy, Apple, Stripe, and Meta.

This is a unique opportunity to join a team in Tokyo building new products for a global market. As an early employee at Citadel AI, you’ll have significant impact and ownership over the growth of our startup. We’re supported by Japan’s best investors and a top-tier enterprise customer base, and are currently scaling our business in the 1 → 10 stage.

About the role

We’re hiring a backend engineer to work with our small, full-stack team to build cloud infrastructure and products to evaluate, monitor, and govern AI systems.

You’ll have a wide range of responsibilities across our cloud infrastructure and product backend. On the cloud infrastructure side, you’ll work on latency and cost optimization, scalability, monitoring, and deployments. On the product side, you’ll work with web servers, SQL databases, LLM/AI libraries, GPU inference, API design, integrating with external services (e.g. SSO), and general product functionality to govern AI models and agents.

We primarily run on Google Cloud for our hosted products (mostly Compute Engine, Cloud Run, Cloud Build, Artifact Registry, Vertex AI), but also support self-hosted deployments on Azure and AWS. Our backend is primarily in Python. Some technologies we use are: Docker, Helm, Tilt, OpenTofu, PostgreSQL, Redis, FastAPI, Flask.

Job requirements

Our company, technology, and market are new and changing rapidly, so a large part of the job is to adapt and learn new things. We value learning fast over pre-existing knowledge (“slope is more important than y-intercept”).

You should have at least 3 years of experience in cloud infrastructure and/or backend engineering. We don’t require experience in GCP or Python specifically, but we expect you to be an expert in the cloud platform or technical stack of your choice.

Business-level English and Japanese are required. We prioritize candidates in Tokyo, but may consider remote for exceptional candidates.

Nice-to-have: you've worked at a startup before, or you have AI/ML/LLM experience.