Staff Software Engineer, Backend - Fintech Platform (m/f/n)

About this role

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 .