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.

Who this role is for

You are probably senior at a scale-up or a larger company today. You may have recently moved into a management track and found that you miss building, or you may be at the point where the next step is leading people and you want that step to come with code still attached.

This is that role. You lead, you set direction, you own the relationship with the rest of the business, and you stay hands-on. If you want to run a large organisation, we are too small for you. If you want to stop being interrupted, this is the wrong role. If you want the scope of a lead without giving up the work, this is a good fit.

You are not being hired to stop writing code. The split is roughly 60% hands-on engineering, 40% leading technically and aligning.

What you'll do

Build (approximately 60%)

• Implement, maintain, and continuously improve a robust, scalable, 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.

• Lead the reduction of technical debt and the consolidation of our platform.
  
  

Lead and align (approximately 40%)

• Translate commercial and product priorities from the leadership team and internal stakeholders into technical work, and give an honest read on cost, risk, and sequencing before anything is committed. Write these down. Decisions here are made in short documents, not in meetings, and this bullet is most of what you will be writing.

• Contribute to what we build, not only how. Product direction here is shaped by the people closest to the system, and you will be one of them.

• Grow the team. You will define what we need, run technical interviews, make the call on candidates, and own whether people ramp up well.
  
  

The position

You report to the CTO (Aaron) and work alongside two senior software engineers (Sylvain and Tim). You are the technical authority on the platform and the day-to-day lead for the team.

We have no dedicated ops team, so running your own services in production is part of the job. There is no on-call rotation.

This is a hybrid position based in Central Paris, 1-2 days per week on site. The alignment part of this role works better in person, and the people you will be translating for are here.

What you bring

• Professional fluency in English (C1/C2).

• Product judgment. You can tell the difference between a request and a requirement, and you have opinions about what should be built that you are willing to defend and to drop.

• Senior-level experience building and operating back-end systems in critical production environments, including a period as tech lead, lead developer, or the de facto technical owner of a small team.

• Working frontend experience. You do not need to be a frontend specialist, but you need to be able to ship a feature end to end without waiting for someone else, and to review frontend work credibly.

• Ability to explain technical subjects clearly to non-technical audiences

• Advanced programming skills in Python 3.12+.

• Real experience with GCP or an equivalent (AWS, Azure), or a clear willingness to get there fast.

• Analytical and critical thinking, the ability to take responsibility for quality from prototype to production, and the 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 and retry philosophy: fail fast in development, rigour in production.

• A genuine interest in producing battle-tested, production-grade code within a distributed environment, and in staying current on software engineering and security.

• Entrepreneurial mindset: you find solutions, take initiative, and accept that at our size responsibilities do not come in neat boxes.
  
  

Bonus points

• Familiarity with IoT, MQTT, or building automation (HVAC).

• Networking knowledge: routers, VLANs.

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

• True fullstack experience (from prototype to production, any framework, any language) and the ability to maintain a production fleet.

• Infrastructure as code with Terraform.
  
  

You are curious and willing to learn. So are we. Even if you do not tick every box, 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 or Tim • 1-1.5 hour

• Interview on culture fit or tech interview • 1 hour

• Final interview with our CEO, Nico • 1 hour