Senior Engineer

Halcy is an AI-powered group travel platform. We help people plan trips with the people they care about: generating itineraries, co-editing them in real time as a group, handling reservations, and guiding travellers through the journey. Halcy AB is based in Stockholm and the role is location-flexible.

As Senior Engineer you will be the most senior technical person outside the founding team. You will own the architectural decisions that determine whether the platform works at its next order of magnitude, while continuing to write production code yourself.

Success in the first year means three things: the platform holds under launch load without emergency intervention, an operational foundation exists and is trusted by the team, and the engineers who join after you are hired and onboarded through a process you designed. This role sets the technical standard for the engineering organisation as it grows from three people.

Responsibilities:

• Own the architectural decisions that determine performance at scale, including concurrency, AI inference cost, collaborative state, and content delivery on mobile.
• Translate product direction into the technical bets that deliver it, and determine which problems to solve first.
• Establish and maintain the operational foundation: observability, error tracking, end-to-end coverage of critical user journeys, structured logging, alerting, and runbooks.
• Build the infrastructure that keeps delivery fast as the team grows, including continuous integration, preview environments, and automated database migrations.
• Write and ship production code every week alongside the founding team.
• Define the engineering hiring standard, including role descriptions, interview process, and onboarding for the next ten engineers.
• Identify decisions that are expensive to reverse and surface them while they are still open.
• Increase the capability of the engineers around you through code review, pairing, and technical mentorship.

Required:

• At least five years building production systems, including a period as the most senior engineer in a small team.
• Deep TypeScript across the stack (React with Node or Deno), and the judgement to make architectural decisions without a senior peer to consult.
• A demonstrated track record of improving the engineers around you.
• Direct experience in at least one of the following: real-time multiplayer systems at scale; payments and bookings, for example Stripe combined with a travel or marketplace stack; or Postgres with extensive row-level security across hundreds of tables.

Preferred:

• Mobile delivery experience with Capacitor, React Native, or native, including App Store and Google Play releases.
• A pragmatic approach to observability and security, with the ability to identify gaps before they cause incidents.
• Experience shipping AI-heavy products, including tool-use orchestration, multi-model gateways, prompt evaluation, and the cost mechanics of running LLMs in production. We run Anthropic and Gemini alongside each other.

Compensation:

• €100,000 to €180,000, calibrated to experience
• Meaningful equity