WE ARE HIRING · 採用情報
Infrastructure Engineer
Tokyo & San Francisco
Kotoba develops cutting-edge AI voice-generation technology. We are looking for an Infrastructure Engineer to design and operate the cloud infrastructure across Japan and the United States that supports the rapidly growing Kotoba app and our API/SDK platform.
ABOUT KOTOBA
At the frontier of voice generation AI
Kotoba is a generative AI company on a mission to “become the defacto for voice AI in East Asia,” developing state-of-the-art voice generation AI models. At our core is a low-latency, high-accuracy speech translation model that connects conversations so naturally it feels as though both speakers share the same language. It supports major language pairs — including Japanese, English, Korean, Chinese, and Spanish — breaking down the language barrier. We also develop our own ultra-low-latency speech-to-text and text-to-speech models that run everywhere from the data center to edge devices, and we license this foundational technology, which powers the next generation of voice agents, to Fortune 50 companies and major U.S. tech firms. We create world-class voice AI from our two hubs in Tokyo and San Francisco.
Kotoba brings this technology to the world through its own product, the Kotoba app, available on iOS and Android. Since launch it has won explosive support across countries and regions including Japan and Korea, growing to a steady 2,000–3,000 new downloads per day. In the App Store and Google Play category rankings, it has reached No. 1 in its category, ahead of the likes of Google Translate and Audible. Loved by individual users, it is also seeing accelerating adoption among major enterprises — centered on Japan — and has supported nearly 100 events on the ground, including SusHi Tech Tokyo. It has drawn media attention as well, featured on numerous programs such as TV Asahi, NHK, TV Tokyo, Abema Prime, and PIVOT.
Kotoba was founded in 2023 by two Japanese generative AI researchers who earned their PhDs at top U.S. universities. To date it has raised a cumulative total of more than ¥3 billion (roughly US$23 million) from prominent VCs in Japan and the U.S. (including Kindred Ventures and Globis Capital Partners) and from the corporate venture arms of leading U.S. and Japanese enterprises, and it also receives strong government support in Japan for AI model training. World-class research paired with a product that keeps winning in the market — with both, Kotoba is one of the most exciting generative AI startups today.
Media
— TV Tokyo：https://www.youtube.com/watch?v=17CG6kSv2zs
— TV Asahi：https://tver.jp/episodes/epy340m62i
— PIVOT：https://www.youtube.com/watch?v=N30YYfIqGEg
Kotoba was founded in 2023 by two Japanese generative AI researchers who earned their PhDs at top U.S. universities. To date it has raised a cumulative total of more than ¥3 billion (roughly US$23 million) from prominent VCs in Japan and the U.S. (including Kindred Ventures and Globis Capital Partners) and from the corporate venture arms of leading U.S. and Japanese enterprises, and it also receives strong government support in Japan for AI model training. World-class research paired with a product that keeps winning in the market — with both, Kotoba is one of the most exciting generative AI startups today.
ROLE DESCRIPTION
THE ROLE
As an Infrastructure Engineer, you will be responsible for the maintenance, management, and design of Kotoba’s entire cloud infrastructure. As we expand our infrastructure footprint from Japan to the United States, a key mission of this role will be to design and operate infrastructure across multiple regions and continents. Our infrastructure is managed as code using Terraform and is designed with a cloud-agnostic approach. We are looking for someone who can take a holistic view of the infrastructure supporting both our application and API/SDK platforms. Rather than remaining confined to a traditional infrastructure role, you will be expected to develop a deep understanding of our products and proactively contribute to end-to-end testing and troubleshooting. Your responsibilities will span a broad range of areas, including deploying customer-specific AI models, managing testing endpoints, maintaining real-time communications infrastructure, and ensuring security across the platform.
RESPONSIBILITIES
What you'll do
Maintain, manage, and design Kotoba’s cloud infrastructure, which is managed as code using Terraform.
Design and build cross-regional infrastructure spanning Japan and the United States.
Manage infrastructure across both the application and API/SDK platforms.
Develop a thorough understanding of our applications and proactively contribute to end-to-end testing and troubleshooting, taking responsibility for the overall service rather than limiting your scope to infrastructure alone.
Deploy customer-specific AI models and manage testing endpoints.
Manage the real-time communications infrastructure using technologies such as WebSocket, WebRTC, and gRPC, while meeting the quality and performance requirements of real-time voice communication.
Optimize GPU and CPU resource configurations and manage infrastructure costs.
Build and regularly monitor the infrastructure required to maintain certifications such as ISO, while overseeing security and internal controls, including VPN infrastructure and access management.
QUALIFICATIONS
Who we're looking for
Required
Experience designing infrastructure across multiple continents and regions. This is one of the most technically challenging aspects of the role, and we welcome candidates who are confident in taking on this responsibility.
Experience designing and operating cloud infrastructure, particularly on Azure and AWS.
Ability to look beyond infrastructure in isolation, understand our applications, and take ownership through end-to-end testing. We are seeking a versatile engineer who can maintain a holistic view of the system in a startup environment rather than focusing on a narrowly defined specialty.
Hands-on experience with Kubernetes and Helm.
Knowledge of real-time communication technologies such as WebSocket, WebRTC, and gRPC. Candidates should be capable of supporting real-time systems rather than having expertise limited to HTTP-based infrastructure.
Business-level English proficiency. Native-level fluency is not required, but English is essential for daily communication with the broader team and colleagues responsible for PoC projects.
Substantial hands-on experience and the ability to take ownership of the company’s overall cloud infrastructure.
Ability to thrive in a fast-paced, demanding AI startup environment.
Preferred
Knowledge of infrastructure security, including experience supporting certifications such as ISO.
Experience operating infrastructure for AI model–based services.
Experience managing and optimizing GPU resources.
Infrastructure experience with high-traffic, API-based systems.
Experience implementing and managing logging systems required for effective service monitoring, maintenance, and operations.
HOW TO APPLY
If you’re interested, please apply Kotoba’s hiring team directly
at hiring@kotoba.tech with your resume attached.
