Staff Engineer, Backend Developer

at WEX Inc. in South Portland South Portland, Maine, United States

About the team / Role:
As a Staff Software Engineer, you will be the primary architect and execution lead for leading the platform changes for the Digital Credit Application.

We are pivoting from a legacy monolith to a high-performance, pluggable API ecosystem. Your mission is to decouple core adjudication logic, enable rapid A/B testing of the customer journey, and lay the technical foundation for future AI-driven chat and automated decisioning experiences.

This is a high-impact role designed for a true "builder" who thrives on the duality of supporting a live production environment while aggressively migrating mission-critical services to a modern, microservices-based backbone. You will encounter varied customer scenarios where your out-of-the-box approach is a better fit than standard industry practices. We expect you to make a true difference for the customer, leveraging technology and AI to best serve and solve for good.

The AI Edge:
We are a forward-thinking engineering org. You are expected to be an expert in leveraging AI Software Development Lifecycle (ADLC) tools (e.g., Git Hub Copilot, Cursor, Amazon Q, LLM-based code gen and architecture agents) to accelerate migration, write bulletproof tests, and automate documentation.
How you'll make an impact:
Architectural Migration & Strategy:
Strangler Fig Migration:
Lead the decoupling of core credit application logic out of the legacy monolith and into a scalable, cloud-native Java/Spring Boot micro services environment.
Migration with Zero Downtime:
Design and execute high-volume traffic migration strategies from legacy systems to new stacks seamlessly without disrupting live customers.
Salesforce Proficiency: A significant portion of existing systems is embedded within various Salesforce capabilities throughout the application lifecycle. Proficiency in Salesforce is a strong advantage, as different integrations will require the new stack to support bidirectional data and state synchronization within the Salesforce ecosystem.
Pluggable Adjudication & API Ecosystem:
Modular Architecture:
Design and implement a modular adjudication layer allowing the business to swap or update credit rules and third-party data providers without impacting core application flows.
API-First Design:
Build and maintain robust, versioned REST/gRPC APIs that support a multi-channel experience (Mobile, Web, and future AI Chat interfaces).
A/B Strategy Enablement:
Engineer backend infrastructure for dynamic routing and experimentation, allowing real-time testing of various application flows.
AI Readiness & Process Acceleration:
AI DLC Mastery:
Champion the use of AI tools across the development lifecycle to write code faster, refactor legacy code into modern Java, and generate robust test suites.
Data Science Partnership:
Partner with Data Science teams to ensure data pipelines and backend schemas are optimized for LLM integration and real-time credit decisioning models.

Operational Excellence & Leadership:
Observability & CI/CD:
Establish rigorous standards for CI/CD, observability (Open Telemetry), and automated contract testing.
Technical Mentorship:
Provide guidance to mid-level and senior engineers, fostering a culture of high engineering standards, clean code, and AI-assisted productivity.

Experience you will bring:
Technical Architecture & Stack:
10+ Years of Engineering Excellence:
Proven track record in backend architecture, specifically within Fintech, Lending, or Credit systems.
Modern Java Stack:
Expert-level proficiency in Java 17/21, Spring Boot 3.x, and Spring Cloud.
Monolith-to-Distributed Migration:
Significant experience extracting tightly coupled business logic from legacy…