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

Location: Hybrid, preferably 1 day per week in the Warsaw or Cracow office, Poland

Company

Build a large-scale fintech platform from the ground up within an international e-commerce and logistics organization, using AI-native engineering practices.

What you will do

• Define and maintain backend architecture for Payments Core, Merchant, or Consumer platform areas, including domain boundaries, event contracts, state machines, consistency models, and cross-service APIs.
• Author ADRs, RFCs, and design documentation while facilitating technical decisions and documenting trade-offs.
• Evaluate databases, cloud services, message broker topologies, and consistency models for financial data.
• Evolve the agentic development harness through instrumentation, adoption and friction measurement, and data-driven improvements.
• Drive organization-wide technical changes across teams without direct authority and contribute to product strategy.
• Mentor Staff-track engineers through design reviews, pairing, and technical writing feedback.

Requirements

• 8+ years of software engineering experience, including 2+ years in cross-team technical leadership or architecture authority.
• 3+ years designing distributed payments or fintech systems.
• Hands-on experience with multiple technology stacks and backend expertise.
• Strong knowledge of distributed systems architecture, including event sourcing, CQRS, domain events, saga patterns, state machines, and financial entity lifecycles.
• Experience designing service-boundary APIs, including REST, asynchronous, and event-based contracts.
• Experience reasoning about relational, time-series, document, and ledger-style databases and evaluating AWS, GCP, or Azure architectures.
• Experience designing or evolving an agentic engineering harness, including instrumentation, adoption measurement, and iteration.
• Working knowledge of LLM tool-use patterns and context management in engineering workflows.
• Excellent technical writing skills for ADRs, RFCs, and design documents; English proficiency at B2 or above.

Nice to have

• 2+ years in platform or internal developer tooling engineering.
• 1+ years of agentic or LLM system design experience.
• 2+ years in BNPL or lending domain architecture.
• PCI DSS or 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.

Culture & Benefits

• Hybrid work with flexible hours and regular office collaboration in Warsaw or Cracow.
• B2B contract offered.
• Diverse, international, and cross-functional environment with experienced engineering and leadership colleagues.
• Training opportunities and career development across locations in Europe.
• Benefits and opportunities to contribute to sustainability, convenient deliveries, and the circular economy.