Senior Backend Engineer

About the role

We are looking for a Senior Backend Engineer to design and build core platform capabilities that underpin real-time control, security, and observability for agentic systems.

This is not a narrowly scoped feature role. This is for someone who can:

• Design and implement high-performance backend services that sit in critical execution paths
• Build systems that handle request/response flows, enforcement logic, and real-time decisioning
• Work with authentication and authorisation protocols (e.g. OAuth) to securely manage identity and access
• Develop integrations with external systems, including identity providers and third-party platforms
• Write efficient, reliable code that performs under load and supports low-latency requirements
• Contribute to system design across multiple parts of the platform as the product evolves
• Ensure security, correctness, and observability are built into all layers of the system

This role is built for a strong mid-level engineer who is ready to make the step up to senior. You will contribute directly to core product capabilities and architectural direction, take growing ownership of system design, and be supported to become a senior technical voice in the team. Working as part of a high-calibre engineering team, you will thrive in a fast-paced environment where performance, reliability, and clean design are critical.

What you’ll bring

Experience

• 5+ years' professional software engineering experience, including building production-grade backend systems
• At least one tenure of 2+ years at a relatively large or established technology company
• Currently a strong mid-level engineer with a clear track record of owning features end to end, now looking to step up to senior
• Experience working on systems in the request path (e.g. APIs, gateways, middleware, or similar)
• Strong ownership mentality and ability to operate with incomplete requirements
• Pragmatic decision-maker who balances speed with long-term maintainability
• Willingness to support and mentor other engineers as you grow into a senior role
• A BSc in Computer Science is preferred; degrees in Mathematics, Physics or Engineering are also welcome

Backend Systems & Architecture

• Experience designing and building scalable backend services
• Strong understanding of distributed systems concepts such as latency, throughput, and fault tolerance
• Familiarity with handling high-throughput or low-latency systems
• Experience building systems that are observable, reliable, and secure

Authentication & Integrations

• Strong understanding of authentication and authorisation protocols (OAuth, OIDC, etc.)
• Experience integrating with identity providers (e.g. Okta, Azure AD, Auth0) or similar external systems
• Understanding of secure session handling, token validation, and access control

Programming

• Strong commercial experience with .NET (C#) and SQL, using modern engineering practices
• Hands-on experience building and running services on Azure or AWS
• Experience writing performant, production-quality code
• Understanding of testing, CI/CD, and software engineering best practices

Reliability & Security

• Experience building systems that operate reliably under load
• Strong understanding of secure coding practices and backend security principles
• Awareness of common vulnerabilities in authentication flows and API systems

Nice to have

AI tools

• Experience with Copilot, Cursor, Claude, or similar AI-assisted development tools

AI systems

• Exposure to LLM-powered systems, agent frameworks, or tool orchestration patterns
• Interest in how agent actions and execution context can be structured for analysis

How we work

• Small, dynamic, high-calibre team
• Incomplete requirements are normal; shaping solutions is part of the job
• Code quality, consistency, and architecture are considered at the earliest phase of design to avoid accumulation of technical debt
• Close collaboration between frontend, backend, ML, DevOps and platform engineers

This is a role for someone who wants impact, ownership and intellectual challenge.

About us

Every generational shift in computing requires a new layer of security infrastructure. In today's agentic era, Outerlimit provides the world's first decentralised security and authorisation layer designed specifically for securing Agentic AI.

We are backed by Evolution Equity Partners, AlbionVC and Crane Venture Partners, and our founding team has a proven track record of defining AI security landscapes, building market-leading security products and scaling businesses from startup to scale-up to exit.

Our values

Seek the truth: We're deeply curious, and we don't settle for the easy answer. Clarity beats comfort.

We own it: No job too small, no job too big. If it needs doing, we don't wait to be asked.

Never complacent: Good enough today isn't good enough tomorrow. We aspire to relentless improvement.

Do the right thing: Especially when it's hard, when no one's watching, and under pressure.

Why join Outerlimit

Real ownership: meaningful equity for everyone. When Outerlimit wins, you win.

Top-of-market pay, matched by benefits built to attract the best.

Flagship offices in London King's Cross and New York City, with flexibility in how you work.

The whole team together in one room at least quarterly.

A real budget for conferences, courses, books and gear.