Backend Engineer (Billing & Control Plane) @ AI startup

Backend Engineer  (Billing & Control Plane)

Role overview

As a Backend Engineer, you will be responsible for the control-plane and gateway layer that connects the customer to our compute serving infrastructure. You will build and power the customer request lifecycle end to end, including handling requests via Cloudflare worker nodes, managing authentication and tenancy, validating requests, routing to the correct model endpoints, enforcing quotas and rate limits, and implementing reliability mechanisms to ensure platform stability under load. This layer is also key to achieving significant service performance latency through optimization. The goal is to build a backend that is fast, secure by default, abuse-resistant, and highly operable at scale.

You will collaborate with the application and platform teams on developing the backend architecture. We expect you to be a central, hands-on contributor to the code stack, driving both the building and technical decision-making as an expert from the ground up. You will work closely with the President and engineering leadership on backend routing decisions that accurately reflect real capacity and failure domains, and ensure the system provides the necessary telemetry for rapid debugging.

Responsibilities

• Architect Authentication & Billing: Build the OAuth/Billing layer, ensuring seamless tenancy management. You are responsible for Metrics & Billing Database, ensuring that every token is logged and billed.
• Manage the Control Plane: Engineer the backend services that handle user flows, API key generation, and workspace management. You ensure this layer remains highly available and decoupled from the high-traffic data plane.
• Data Persistence & Integrity: Manage the storage of data and design schemas that can ingest high-velocity telemetry from the edge without becoming a bottleneck.
• System Observability: Build the telemetry pipelines that aggregate logs from the Edge Gateway. Provide the tools that allow the team to debug why a specific routing decision was made or why a specific rate limit was triggered.
• Business Logic Implementation: Translate complex business requirements (customer tiers) into technical configurations that the Edge Traffic Engineer can enforce.
• API Design: Design and maintain the internal and external APIs that allow customers to programmatically interact with their accounts and settings.

[Employment Type]
Full-time employee
*Probationary period: 3 months

[Salary]
Annual Salary: ¥8,000,000 - ¥14,000,000
Monthly Salary: ¥666,667 - ¥1,166,667 (Monthly Base Salary: ¥666,667 - ¥1,166,667)
■Salary Increases: Available

[Working Hours]
9:00 AM - 6:00 PM (60-minute break)

[Work Location]
Queen's Tower A, 10th Floor, 2-3-1 Minatomirai, Nishi-ku, Yokohama, Kanagawa Prefecture, 220-6010
■Access: 7-minute walk from Sakuragicho Station (all lines), direct access from Minatomirai Station (Toyoko Line, Minatomirai Line)
■Non-smoking workplace
■Changes to work location: Company-designated offices
■Transfers/Secondments: None

[Holidays and Leave]

120 days off per year Days
Full two-day weekend
Annual paid vacation (minimum 10 days after the seventh month of employment)

[Benefits]
Partial transportation allowance (up to ¥15,000 per month)
Social insurance (health insurance, employee pension insurance, employment insurance, workers' compensation insurance)
Overtime pay: Standard overtime pay

You may be a fit if you have the following skills:

• Robust Backend Architecture: extensive experience with AWS ecosystems and server-side languages (Go, Python, or Java). You excel at building services that require high data integrity.
• Database Expertise: Strong proficiency in SQL and NoSQL database design, specifically for time-series data (metrics) and transactional data (billing/ledgers).
• Auth & Identity: Deep understanding of OAuth2, OIDC, and secure API key management lifecycles. Scalable API Development: Experience building REST or GraphQL APIs that serve as the control interface for complex infrastructure.
• FinOps/Billing Systems: Prior experience building usage-based billing systems or credit ledger systems.