Principal Software Engineer - Fintech Platform (m/f/n)

InPost is building its own fintech platform from the ground up. It’s a large-scale, international initiative where engineers will have the opportunity to shape the architecture, build core fintech components, and create solutions designed to operate at InPost’s scale. We’re building a lean, highly effective engineering organization in Poland, with AI-native engineering at its core. We’re looking for strong engineers who are comfortable with agentic engineering, from experienced professionals building complex systems and engineering tooling to a new generation of engineers who have embraced AI-driven development from the start of their careers. As Principal Software Engineer, you'll work directly with the Head of FinTech Engineering and business leadership, translating critical business goals - new product lines, regulatory deadlines, growth targets - into architecture decisions and roadmap input. You'll be the final word on cross-domain technical questions that no single team or Staff Engineer can resolve alone. → Hybrid working model: preferably 1 day per week in the Warsaw or Cracow office.   Responsibilities: - Serve as the single cross-domain technical authority, arbitrating architecture decisions across Payments Core, Merchant, and Consumer platform areas - Partner directly with the Head of Engineering and business leadership to turn business strategy into technical roadmap input - Author Architecture Decision Records (ADRs) and RFCs for organisation-wide decisions, with reasoning accessible to both engineers and business stakeholders - Own the agentic engineering harness at an organisational level — design, instrument, and continuously improve AI-assisted engineering workflows based on real production data - Identify and drive the adoption or deprecation of patterns across all teams, building the case and sequencing change without direct authority - Mentor Staff Engineers and Engineering Managers on architecture craft, technical communication, and agentic tooling - 10+ years in software engineering, including 5+ years in cross-team technical leadership or architecture authority - 5+ years designing distributed payments or fintech systems - 3+ years of agentic/LLM engineering in production — shipped systems, not theoretical patterns - Deep knowledge of distributed systems architecture: event sourcing, CQRS, domain events, saga pattern - Experience designing APIs at an organisational boundary level — REST, async, and event-based contracts - Strong grasp of database trade-offs (relational, time-series, document, ledger-style) and cloud architecture evaluation (AWS/GCP/Azure) at organisation scale - Hands-on experience with multi-agent orchestration, tool-use patterns, context management, and evaluation harnesses for AI-assisted engineering workflows - Excellent technical writing for mixed audiences — ADRs and RFCs that work for engineers and business leadership alike - English proficiency at B2 or above - University degree in Computer Science, IT, or a related fieldNice to have:  - 3+ years in platform or internal developer tooling engineering - 1+ years of agentic/LLM system design experience - PCI DSS / PSD2 architecture compliance experience from the design phase - BNPL or lending domain architecture experience - Open-source contributions or external technical publishing - Experience building or scaling an internal developer platform - Formal mentorship of Staff-level or EM-track engineers - Polish language skills - Opportunity to work in a diverse, international, and cross-functional environment, along with leading experts.  - You work and learn from a senior leader and their leadership team, expanding your experience and exposure in the e-commerce and logistics industries.  -  InPost is a growing company that offers its people an increasing number of opportunities in several locations in Europe.  - Fulfilling careers with a range of benefits for people and investing in providing training opportunities for their development.  - You will feel a part of the InPost community that makes an impact on sustainability, convenient deliveries, and the circular economy every day.  - Excellent working environment and flexible hours - We offer B2B type of contract