--- title: 'Backend & Cloud Engineer at Citadel AI' canonical: 'https://feeny.ai/job/backend-cloud-engineer-citadel-ai-tokyo-wyqs46n3prjb' type: 'job' last_seen: '2026-09-13' --- # Backend & Cloud Engineer at Citadel AI - **Company:** Citadel AI - **Location:** Tokyo, Japan - **Employment:** full-time - **Work type:** hybrid - **Posted:** 2026-07-29 - **Last confirmed live:** 2026-09-13 - **Apply:** https://jobs.ashbyhq.com/citadel-ai/fe1c4e76-9ac8-4f30-a48c-713690a3c03b ## Job description ※日本語の募集要項は下部にございます。 ## 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. ---------- 〜AIシステムを支える、堅牢でスケーラブルなプロダクト基盤を構築する〜 役割・ミッション Citadel AIは、AIへの信頼を構築することをミッションに、AIモデルやAIエージェントの品質、安全性、信頼性を継続的に評価・管理するためのソフトウェアを開発しています。 本ポジションでは、少数精鋭のフルスタックチームの一員として、クラウドインフラからプロダクトのバックエンド機能まで、幅広い領域を担当していただきます。インフラ領域では、レイテンシーやコストの最適化、スケーラビリティ、モニタリング、デプロイメントなどに取り組みます。プロダクト領域では、Webサーバーやデータベース、API、LLM・AIライブラリ、GPU、外部サービスとの連携などを通じて、AI システムやエージェントを適切に管理するための機能を開発します。 技術スタック クラウド基盤には主に Google Cloud を利用しており、Compute Engine、Cloud Run、Cloud Build、Artifact Registry、Vertex AI などを活用しています。また、Azure および AWS 上でのセルフホスト型デプロイにも対応しています。 バックエンドは主にPythonで開発しています。現在使用している主な技術は、Docker、Helm、Tilt、OpenTofu、PostgreSQL、Redis、FastAPI、Flaskなどです。 なお、記載されているすべての技術に関する経験は必須ではありません。特定のクラウドプラットフォームや技術スタックにおける専門性と、新しい技術を素早く習得し、実務に適用できる能力を重視しています。 具体的な業務内容 - クラウドインフラの設計・構築・運用および継続的な改善 - システムのレイテンシー、コスト、可用性、スケーラビリティの最適化 - モニタリング、障害対応、デプロイメント基盤の設計・改善 - Webサーバー、API、SQLデータベースを利用したバックエンド機能の開発 - LLM・AI関連ライブラリやGPU推論基盤を活用した機能開発 - Azure および AWS 環境へのセルフホスト型デプロイメントの設計・サポート 必須スキル・経験（Must） - クラウドインフラ及びバックエンドシステムに関する3年以上の実務経験 - ビジネスレベルの日本語および英語でのコミュニケーション能力 - 変化の速い技術や市場環境に適応し、新しい技術を自ら学びながら業務を進める能力 歓迎スキル・経験（Want） - AIプロジェクトの推進経験 - 主要クラウドサービスを利用したインフラの設計・構築・運用経験 - 英語での基礎的なコミュニケーション能力 この仕事で得られるもの - スタートアップでの勤務経験 - AI、機械学習、LLMを利用したプロダクトの開発経験 - 顧客への導入支援の経験 ## About Citadel AI ## Company Overview - **One-liner**: Citadel AI provides a unified platform to evaluate, monitor, and govern AI systems, helping organizations minimize risk and maximize AI performance. - **Entity Type**: Private (Incubator/Accelerator stage, raised $4.63M total funding) - **Headquarters**: Shibuya, Tokyo, Japan (with presence in the United States and France) - **Founded**: 2020 - **Founders**: Hironori "Rick" Kobayashi (Co-Founder, CEO) and Kenny Song (Co-Founder, CTO) ## Core Business - **Primary Industry**: AI Risk Management, AI Evaluation & Monitoring, AI Governance - **Target Customers**: Engineering teams and governance/compliance teams in regulated industries (healthcare, finance, manufacturing, automotive), as well as any organization deploying high-risk AI systems (LLMs, computer vision, tabular AI). Focus is B2B Enterprise. - **Mission Statement**: "Make the world's AI systems more reliable and trustworthy." ## Products & Services - **Citadel Lens**: Their core platform for AI evaluation and monitoring. It automatically identifies weak spots and reliability issues in AI models, generates synthetic test data, and produces detailed "Lens Model Reports." Features include a Bias Finder, data error detection, and global/local explainability for model transparency. Supports LLMs, computer vision, and tabular models. Acts as a bridge between AI development and AI governance. - **Citadel Radar**: An AI firewall and monitoring solution announced in June 2026, designed for real-time protection and oversight of deployed AI systems. - **Lens Governance**: A module launched in May 2026 that specifically connects AI governance workflows with AI deployment, enabling compliance with internal policies and external standards (e.g., ISO). - **LangCheck**: An open-source library for the multilingual evaluation of LLMs. ## Market Standing - **Valuation/Market Cap**: Not publicly disclosed. - **Key Metric**: Total funding raised is **$4.63M**. The company has **17 employees** (as of mid-2026). - **Notable Investors/Partners**: The University of Tokyo, Coral Capital, ANRI, Mitsubishi UFJ Capital, Plug and Play Japan, Global Startup Acceleration Program, Suntory. Key partners include **BSI** (The British Standards Institution). - **Growth Signals**: Headcount grew **31.2% YoY** (reaching 17 employees). The company has secured notable customers like **Suntory** and **DeepEyeVision**. It has joined the **Coalition for Health AI** as a Certified Assurance Resource Provider, signaling a push into the healthcare vertical. The launch of two major new products (Radar and Lens Governance) in mid-2026 indicates rapid product expansion. ## Competitive Advantages - **Regulatory Alignment**: The platform is built to be fully aligned with international standards (ISO) and internal policies, a critical moat for selling into regulated industries like healthcare and finance. - **Partnership with BSI**: A strategic partnership with a globally recognized standards and certification body (BSI) provides immense credibility and a distribution channel for governance-focused solutions. - **Unified Platform**: Bridges the gap between technical AI teams (who need to iterate and debug) and governance/compliance teams (who need documentation and risk reports), solving a key organizational friction point. - **Strong Founding Team**: CTO Kenny Song is a former Google Brain PM (worked on TensorFlow and AutoML) and a research scholar in adversarial machine learning, giving deep technical credibility. CEO Rick Kobayashi brings leadership experience. ## Strategic Focus - **Healthcare Expansion**: The partnership with the Coalition for Health AI and the testimonial from DeepEyeVision indicate a strong strategic focus on the healthcare sector, which has strict risk management needs. - **Governance as a Product**: The launch of "Lens Governance" and "Citadel Radar" shows a shift from being just a testing tool to a comprehensive governance and security platform. - **Global Market**: While based in Tokyo, the company has a global customer base and an international team. They are actively building a "world-class engineering team" to serve a global market from Japan. ## Why Work Here - **High Impact, Early Stage**: As a small team (~17 people), early engineers will have significant ownership and influence over the product and company trajectory. - **World-Class Peers**: The team includes alumni from Google, Waymo, PayPal, Stripe, Apple, and Toyota. The engineering culture is described as aiming to be "world-class." - **Mission-Driven**: The work directly contributes to making AI safer and more trustworthy, which is a highly relevant and meaningful mission in the current AI landscape. - **Tokyo Location**: Based in Tokyo, offering a unique opportunity to build a global product from Japan. The team is international (English is likely the working language) with members in the US and France. - **Remote/Hybrid Policy**: Not explicitly stated, but the presence of employees in the US and France suggests a flexible, remote-friendly culture. The headquarters is in Tokyo. - **Funding & Stability**: Well-funded by top-tier Japanese investors (The University of Tokyo, Coral Capital, ANRI), providing a strong financial runway. ## Sources 1. [citadel-ai.com](https://citadel-ai.com/) 2. [citadel-ai.com/about](https://citadel-ai.com/about/) 3. [citadel-ai.com/careers](https://citadel-ai.com/careers/) 4. [linkedin.com](https://www.linkedin.com/company/citadel-ai/) 5. [cbinsights.com](https://www.cbinsights.com/company/citadel-ai) ## Other roles at Citadel AI - [AI ソリューション・コンサルタント](https://feeny.ai/job/ai-citadel-ai-tokyo-effp2wwrmggt) — Tokyo, Japan