As a Mobile Engineer at American Express, you are at the forefront of the digital customer experience. American Express is not just a legacy financial institution; it is a technology-driven global payments network. The mobile application is the primary touchpoint for millions of Card Members worldwide, allowing them to manage their accounts, redeem rewards, and access exclusive benefits with absolute security and reliability.

Your work directly impacts how users interact with their finances on a daily basis. The engineering culture here prioritizes robust, scalable, and highly secure code. Because the app handles sensitive financial data, the engineering standards are rigorous. You will be expected to build seamless, intuitive interfaces while navigating complex backend systems and strict compliance requirements.

This role is both challenging and rewarding. You will work with modern tech stacks—such as Kotlin and Jetpack Compose for Android, or Swift and SwiftUI for iOS—and collaborate deeply with product managers, designers, and backend engineers. If you are passionate about crafting pixel-perfect UIs, optimizing app performance, and building features that operate flawlessly at a massive scale, this role offers an exceptional platform for your skills.

The questions below represent the types of technical and practical challenges candidates face during the American Express interview process. They are designed to test both your theoretical knowledge and your ability to execute under pressure.

Kotlin and Swift Fundamentals

These questions test your deep understanding of the language syntax, features, and optimal usage.

• How do you handle asynchronous operations in Kotlin using Coroutines, and how does it compare to RxJava?
• Explain the difference between let, run, with, apply, and also in Kotlin. Give examples of when to use each.

Preparation is key to navigating the technical rigor of the American Express interview process. Your interviewers will look for a balance of deep platform expertise and practical problem-solving skills.

Role-Related Technical Knowledge – You must demonstrate a profound understanding of your chosen platform (Android or iOS). Interviewers evaluate your familiarity with modern languages, core SDKs, memory management, and lifecycle events. You can show strength here by discussing recent framework updates and best practices.

Hands-On Problem Solving – American Express heavily indexes on live, time-boxed coding tasks. Rather than purely abstract algorithmic puzzles, you will be evaluated on your ability to write clean, functional code for realistic mobile scenarios. Practicing rapid feature implementation and debugging will set you apart.

Quality and Testing Mindset – Writing code is only half the job; ensuring it works flawlessly is the other. Interviewers will assess your approach to testing, specifically focusing on UI testing and test-driven development. Strong candidates seamlessly integrate testing strategies into their architectural discussions.

Culture Fit and Collaboration – American Express values a collaborative, low-ego environment with a strong emphasis on work-life balance and teamwork. You will be evaluated on how you communicate trade-offs, handle feedback during live coding, and align with the company's customer-first philosophy.

The interview process for a Mobile Engineer at American Express is designed to be efficient, focused, and highly practical. Candidates frequently report a surprisingly swift timeline, often moving from the initial application to the final decision in roughly two weeks. The process is rigorous but fair, focusing heavily on your day-to-day coding abilities rather than abstract computer science trivia.

You will typically begin with a Hiring Manager Round, which serves as both a behavioral screen and a high-level technical alignment check. Following this, the process dives deep into technical assessments. You should expect dedicated rounds focusing on your core language experience (e.g., Kotlin or Swift), immediately followed by time-boxed coding tasks. These tasks are usually 30-minute practical exercises where you must write executable code.

The final technical stages focus on core platform frameworks, UI building, and testing. Interviewers will probe your knowledge of modern UI toolkits like Jetpack Compose or SwiftUI, and they place a significant emphasis on UI testing. You will face another time-boxed coding task specifically targeting these areas. Throughout the process, the emphasis is on clean architecture, testability, and modern mobile development practices.

This visual timeline outlines the typical progression of the interview stages, from the initial Hiring Manager screen through the specialized technical deep dives. Use this to structure your preparation, ensuring you allocate equal time to conversational technical deep-dives and rapid, 30-minute practical coding tasks. Note that while the core structure remains consistent, specific frameworks discussed will vary depending on whether you are applying for an Android or iOS role.

To succeed, you must understand exactly what the engineering team is looking for. The technical rounds are divided into specific domains, each testing a different facet of your mobile engineering expertise.

Core Language and Platform Expertise

This area evaluates your mastery of the fundamental building blocks of mobile development. American Express requires engineers to write highly optimized, secure code, which means you need a deep understanding of your primary language. Strong performance here means writing idiomatic code and clearly explaining the "under the hood" mechanics of the platform.

Be ready to go over:

• Language Fundamentals – Deep dive into Kotlin (coroutines, flow, extension functions) or Swift (optionals, closures, protocols).
• Memory Management & Concurrency – How to handle background tasks, avoid memory leaks, and manage thread safety without blocking the main UI thread.
• App Lifecycle & State – Handling configuration changes, backgrounding, and preserving user state securely.
• Advanced concepts (less common) – Custom view rendering, low-level networking protocols, and platform-specific security measures like biometric authentication and keychain/keystore management.

Example questions or scenarios:

• "Explain how Kotlin Coroutines differ from traditional threading, and demonstrate how you would handle a network timeout."
• "Walk me through the iOS app lifecycle. How do you ensure sensitive financial data is cleared when the app goes into the background?"
• "Describe a time you had to track down and fix a complex memory leak in a production application."

Modern UI Frameworks and Testing

American Express is actively modernizing its app architecture, meaning legacy UI knowledge is not enough. You must be proficient in declarative UI frameworks. Furthermore, testing is not an afterthought; it is a core requirement evaluated explicitly during live tasks.

Be ready to go over:

• Declarative UI (Compose/SwiftUI) – Managing state hoisting, recomposition/rendering lifecycles, and building reusable UI components.
• UI Testing – Writing robust automated UI tests using frameworks like Espresso, Compose Test Rule, or XCUITest.
• Accessibility – Ensuring UI components meet strict accessibility standards (VoiceOver/TalkBack, dynamic text sizing), which is critical for a global financial app.

Example questions or scenarios:

• "Build a custom button component in Jetpack Compose that changes state when clicked, and write a UI test to verify its behavior."
• "How do you manage state in a complex SwiftUI view hierarchy to prevent unnecessary re-rendering?"
• "Implement a 30-minute coding task to create a scrollable list of transactions, complete with basic UI tests."

Architecture and System Design

While you may not be designing backend distributed systems, you are expected to architect robust mobile applications. Interviewers want to see how you structure your code for scalability, testability, and maintainability.

Be ready to go over:

• Design Patterns – Deep understanding of MVVM, MVI, or Clean Architecture, and knowing when to apply them.
• Dependency Injection – Using tools like Hilt, Dagger, or Swinject to decouple components and facilitate testing.
• Networking and Error Handling – Designing resilient API consumption layers that gracefully handle poor connectivity and unexpected backend errors.

Example questions or scenarios:

• "Design the architecture for a new 'Transfer Funds' feature. How do the data, domain, and presentation layers interact?"
• "How do you structure your dependency injection graph to ensure your ViewModels are easily testable?"
• "Explain how you would implement a caching strategy for a user's transaction history to improve offline support."

As a Mobile Engineer at American Express, your day-to-day work revolves around building, refining, and maintaining the features that power the mobile banking and credit card experience. You will spend a significant portion of your time writing clean, modular code using modern languages like Kotlin or Swift. You are not just taking tickets; you are expected to take ownership of feature pods, driving technical decisions from inception to deployment.

Collaboration is a massive part of the role. You will work in cross-functional Agile teams, partnering closely with Product Managers to define feature requirements and with UI/UX Designers to ensure those features meet strict brand and accessibility guidelines. You will also collaborate with backend engineering teams to define API contracts, ensuring that the data payloads are optimized for mobile consumption and adhere to strict security protocols.

Beyond feature development, a major responsibility is maintaining app health. This involves actively monitoring crashlytics, optimizing app launch times, and refactoring legacy code into modern frameworks like Jetpack Compose or SwiftUI. You will also be deeply involved in the code review process, mentoring junior engineers, and contributing to the team's automated testing suites to maintain a high bar for release quality.