Software Engineer

Supersonik, Inc.; Barcelona; Hybrid; EUR 90,000 - 130,000; Full time

Benefits offered by this job

Significant equity in a company backed

Full ownership, real impact

Fast learning cycles

A tight-knit team

Job summary

Supersonik, Inc. in Barcelona is looking for Senior Engineers to join the core team. You will solve complex, technical problems and shape the product and architecture from day one, thriving in a high-growth startup.

Fluent in modern Python and async programming, you will build scalable, event-driven systems and work at the intersection of performance, AI and great user experience. If you love solving first-principles problems, navigating ambiguity and want to build a product people love you’ll

Responsibilities

• Scale a real-time, event-driven backend architecture where milliseconds matter
• Design and implement low-latency APIs using FastAPI and Asyncio
• Solve engineering challenges in performance optimization, observability, and resilience
• End to end contributions from frontend to infrastructure
• Collaborate on prompt engineering, LLM behaviors, LLM fine-tuning and UX
• Build and maintain infrastructure-as-code with Terraform and AWS
• Contribute to 0→1 product development with a small, fast-moving team

Tools

FastAPI

Asyncio

Redis

PostgreSQL

AWS

Terraform

React

GitHub

Datadog

Linear

Job description

About Supersonik

Supersonik helps B2B SaaS companies sell faster with AI-powered product demos. On a live video call, our AI Agent shares the screen to walk buyers through a personalized, interactive demo in any language. This lets teams skip long sales calls and focus on closing deals.

We’re backed by Andreessen Horowitz (a16z) and work with leading SaaS companies worldwide.

About the Role

We’re hiring Senior Engineers to join our core team in Barcelona.

You’ll be solving complex, technical problems and shaping the product and architecture from day one. You should thrive in high-growth startup environments, be fluent in modern Python and async programming and know how to build scalable, event-driven systems. You care about fast, real-time systems and enjoy working at the intersection of performance, AI and great user experience.

If you love solving first-principles problems, navigating ambiguity and want to build a product people love you’ll fit right in.

What You’ll Work On

• Scale a real-time, event-driven backend architecture where milliseconds matter


• Design and implement low-latency APIs using FastAPI and Asyncio


• Solve engineering challenges in performance optimization, observability, and resilience


• End to end contributions from frontend to infrastructure.


• Collaborate on prompt engineering, LLM behaviors, LLM fine-tuning and UX


• Build and maintain infrastructure-as-code with Terraform and AWS


• Contribute to 0→1 product development with a small, fast-moving team

Our Stack

• Backend: Python, FastAPI, Asyncio, Redis, PostgreSQL


• Infra: AWS, Terraform, CI/CD


• Frontend: React


• Tooling: GitHub, Datadog, Linear

Bonus Points

• Experience with LLMs (prompting, training, alignment)


• Experience with TTS, STT and real-time voice


• Experience with browser automations


• Deep knowledge of AWS, Terraform, and distributed systems


• Experience shipping 0→1 products in a startup

What You’ll Get

• Significant equity in a company backed by A16z


• Full ownership, real impact, and fast learning cycles


• A tight-knit team that values clarity, speed, and smart execution