Staff Backend Engineer, Voices in London

Synthesia is the world’s leading AI video platform for business, used by over 90% of the Fortune 100. Founded in 2017, the company is headquartered in London, with offices and teams across Europe and the US. As AI continues to shape the way we live and work, Synthesia develops products to enhance visual communication and enterprise skill development, helping people work better and stay at the center of successful organizations.

Following our recent Series E funding round, where we raised $200 million, our valuation stands at $4 billion. Our total funding exceeds $530 million from premier investors including Accel, NVentures (Nvidia's VC arm), Kleiner Perkins, GV, and Evantic Capital, alongside the founders and operators of Stripe, Datadog, Miro, and Webflow.

About the role:

• You will work on the core systems powering Synthesia’s script preview and voice generation experience, ensuring users can reliably generate high-quality voiceovers across a wide range of languages, providers, and use cases.
• You will build and operate backend services that orchestrate multiple text-to-speech (TTS) providers, alongside Synthesia’s in-house models, delivering a seamless and consistent experience to end users despite underlying system complexity.
• You will be responsible for designing and evolving systems that handle provider reliability, request routing, and output consistency, ensuring users can generate and regenerate voice content with predictable, high-quality results.
• You will contribute to user-facing product problems from a backend perspective, working closely with frontend engineers to ensure APIs and workflows integrate cleanly into the product experience.
• You will own projects that span multiple systems and domains, such as:
• Building robustness layers (retries, throttling, failover) to handle unreliable third-party providers
• Designing persistence systems to ensure consistent voice outputs across generations
• Improving how voice data is stored, retrieved, and reused
• You will also work on newer initiatives around voice discovery and recommendations, helping users find the best voices by building evaluation systems, improving recommendation logic, and adding observability to monitor quality.
• You will evaluate your work through system performance and user experience metrics, using observability to debug and continuously improve reliability.
• You will collaborate closely with product, frontend, and R&D teams, ensuring backend systems support both current product needs and future innovation.

What we’re looking for:

• You have several years of experience building and operating backend systems in production.
• You’re a strong backend engineer (we use Python/FastAPI) with experience designing reliable, observable services, ideally working with third-party APIs or distributed systems.
• You have a product mindset and focus on solving user-facing problems, not just backend architecture.
• You’re comfortable working close to the client, understanding how APIs are consumed and how backend decisions impact the end-user experience.
• You’re willing to step outside your comfort zone — including jumping into frontend code when needed to debug and understand end-to-end flows.
• You work well in an iterative, experiment-driven environment, shipping quickly and improving based on data and feedback.
• Experience with observability tools (e.g. Datadog), workflow systems (e.g. Temporal), or evaluation/recommendation systems is a plus, but not required.
• Comfortable with touching the frontend in any language and/or framework.

Why join us?

We’re living the golden age of AI. The next decade will yield the next iconic companies, and we dare to say we have what it takes to become one.

Our culture:

At Synthesia we’re passionate about building, not talking, planning or politicising. We strive to hire the smartest, kindest and most unrelenting people and let them do their best work without distractions. Our work principles serve as our charter for how we make decisions, give feedback and structure our work to empower everyone to go as fast as possible.

Serving 50,000+ customers (and 50% of the Fortune 500). We’re trusted by leading brands such as Heineken, Zoom, Xerox, McDonald’s and more.

Proprietary AI technology:

Since 2017, we’ve been pioneering advancements in Generative AI. Our AI technology is built in-house, by a team of world-class AI researchers and engineers.

AI Safety, Ethics and Security:

AI safety, ethics, and security are fundamental to our mission. While the full scope of Artificial Intelligence's impact on our society is still unfolding, our position is clear: People first. Always.

The hiring process:

• 30-40min call with our Technical Recruiter
• 45min call with an Engineering Manager about your past projects
• 90min Live Coding interview, a collaboration exercise with our Engineer (not Leetcode style)
• 60min System Design, technical discussion usually about a real problem we had in production
• 45min call with leadership, focus on examples of collaboration, growth and going through details of your future team

The process does not need to take long - we can be done in seven working days.

This is a remote role from an EU country, UK or Switzerland. The salary starts at EUR/GBP/CHF 130,000 base + stock option plan. This is full-time employment only - no contractors possible - usually through OysterHR. Everyone at Synthesia gets 25 days of leave + local holidays (no extra paid or unpaid leave possible). We only sponsor VISA if you are in the UK/EU country already and need support.