Senior Full Stack Developer

About Thermosphr

Thermosphr is a ClimateTech startup optimising energy management for commercial buildings across Europe. Our software combines thermal modelling, model predictive control, AI, and real-time energy management, delivering over 30% energy savings for offices, shopping centres, and universities. Over 1 million square metres operated across Europe, with more than 3,000 tons of CO2 avoided to date.

We are an international team based in Paris and Berlin, in a phase of rapid growth. We value ownership, continuous learning, and close collaboration. This role offers direct, measurable impact on how we operate and scale.

What you'll do

You will work in close collaboration with the CTO, energy managers, customer success team, thermal and controls engineers, and building automation engineers to build and maintain the infrastructure underpinning our SaaS platform. Concretely, you will:

• Implement, maintain, and continuously improve a robust, scalable, and high-performance backend and cloud infrastructure;

• Take full ownership of architecture and software development across the full cycle, from prototype to production;

• Ensure stable and reliable real-time data flow between buildings and the cloud, including monitoring and alerting;

The position

• We're looking for a fullstack software engineer, with an interest towards DevOps, as we get increasingly growing needs in this aspect.

• You'll take full ownership across the full cycle, from prototype to production. Since we have no dedicated ops team, running your own services in production is part of the job. No on-call, though.

• You'll join a team of two people (Sylvain & Tim) in close collaboration with the CTO (Aaron).

• Yes, this is a full remote position. :)

What you bring

• Professional fluency in English (C1/C2);

• Senior-level mindset & experience developing back-end solutions in critical production environments;

• Advanced programming skills in Python 3.12+;

• Genuine experience with GCP or equivalent (AWS, Azure); or you're willing to learn and/or improve;

• Knowledge of IoT, or a strong will to learn it;

• Analytical and critical thinking; ability to take responsibility and ensure quality from prototype to production; ability to say no;

• Fluency with AI-assisted coding tools (Claude Code and similar), including the ability to critically evaluate AI-generated code and continuously improve internal procedures;

• Comfort with a die & retry philosophy: you try often, fail fast, and learn quickly (fail fast in dev, rigor in production);

• You stay ahead of the curve in software engineering and security, with a genuine interest in producing battle-tested, production-grade code;

• Entrepreneurial mindset: you find solutions, take initiative, and want to directly shape Thermosphr's product and direction (because you will).

Bonus points

• Familiarity with IoT, MQTT and/or building automation (HVAC);

• Networking knowledge: routers, VLANs;

• Ability to challenge existing architectures, including ones that have worked for years;

• (True) fullstack development experience (any framework, any language, ability to maintain a production fleet);

• Infrastructure as code with Terraform.

• You're curious. You're willing to learn. I've already said that. But we're all lifelong learners, after all.

Even if you don't tick all the boxes, we encourage you to apply!

We're committed to making the recruitment process as fast and transparent as possible. It goes as follows:

• A first phone call with our CTO, Aaron • 10-15 min

• Tech Interview with Sylvain & Tim • 1-1.5 hour

• Final interview with our CEO, Nico • 1 hour

For the tech interview: expect an in-depth technical conversation where we ask each other questions; no live coding, no homework, no pointless platform test, and nothing to prepare beforehand!

We really value your real-world experience with the tools, languages, and processes you work with every day, and how you reason as a software engineer. :)