Staff Software Engineer, Backend - 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. InPost Pay is looking for a Staff Engineer to define the technical direction for one of our platform areas - Payments Core, Merchant, or Consumer. You'll multiply team output through architecture clarity, engineering standards, and cross-team technical leadership, while helping evolve our agentic engineering harness in a data-driven way. You'll own the evolution of fundamental technology decisions across your area - ensuring they're sound, defensible, and viable for the long term - and act as the technical throughline between engineering teams, product strategy, and the organisation's wider architecture standards. → Hybrid working model: preferably 1 day per week in the Warsaw or Cracow office. Responsibilities:  - Define and maintain the backend technical architecture for your area: domain boundaries, event contracts, state machine patterns, data consistency models, and cross-service API design across multiple teams - Author Architecture Decision Records (ADRs) and RFCs, facilitating technical decision-making across teams with documented reasoning and clear trade-off analysis - Evaluate and decide on fundamental technology trade-offs: database selection, cloud services, message broker topology, and consistency models appropriate for financial data - Own the evolution of the agentic development harness - instrument it, measure adoption and friction, and drive improvements with data - Drive org-wide technical change: identify patterns to adopt or deprecate broadly, build the case, and see adoption through across teams without direct authority - Provide technical input into product strategy; mentor Staff-track engineers through design reviews, pairing, and technical writing feedback - 8+ years in software engineering, including 2+ years in cross-team technical leadership or architecture authority - 3+ years designing distributed payments or fintech systems - Hands-on experience with multiple tech stacks and expertise in backend - Solid grounding in distributed systems architecture - event sourcing, CQRS, domain events, saga pattern - and state machine / financial entity lifecycle design - Experience designing APIs at service-boundary level - REST, async, and event-based contracts - Comfort with database trade-off reasoning (relational, time-series, document, ledger-style) and cloud architecture evaluation (AWS/GCP/Azure) - Experience designing or evolving an agentic engineering harness — instrumentation, adoption measurement, iteration - Working knowledge of LLM tool-use patterns and context management in engineering workflows - Excellent technical writing - ADRs, RFCs, and design docs for multiple audiences - English proficiency at B2 or above  Nice to have: - 2+ years in platform or internal developer tooling engineering - 1+ years of agentic/LLM system design experience - 2+ years in BNPL or lending domain architecture - PCI DSS / PSD2 architecture compliance experience from the design phase - Kafka or equivalent streaming architecture experience at scale - Open-source contributions or technical publishing - 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