Senior Android Developer (f/m/d)

adjoe builds the technologies behind mobile apps growth and monetization. adjoe Ads is our programmatic in-app advertising platform that seamlessly connects advertisers and publishers through direct integration of our Android and iOS SDKs. Every ad decision happens in under 200ms across 10 million daily users, powered by real-time bidding algorithms and user quality prediction models that match the right ad to the right user at the right moment. Where 10 Billion Daily Predictions Begin The User Experience team is the origin point of adjoe Ads. Everything the system knows about a user, every prediction the ML models make, every bid placed in an auction. It all starts with code this team ships. The team owns two responsibilities. On the SDK side, a native Kotlin and Swift code runs inside hundreds of publisher apps. It participates in 120 million daily auctions , renders ad creatives across multiple formats, and captures the behavioral signals that power 10 billion predictions per day . The constraint that defines this work: you're executing inside someone else's app, on someone else's device, with zero tolerance for instability. Every ad impression has to feel native and fast to the user. On the analytics side, the dashboards, investigation tools, and data frameworks that turn raw data into decisions: real-time revenue performance across active campaigns, infrastructure cost visibility, and data quality assessments. If a number matters to the business or to engineering, this team makes it accessible. Your Mission & Who We Are Looking For: Kotlin & Android Internals Expertise: You will own the core development and optimization of the adjoe Ads SDK, which runs inside hundreds of publisher apps. We are looking for someone with 5+ years of Android experience (or 3+ years specifically in SDK/library development) who works primarily with Kotlin and has a deep understanding of Android lifecycles, ProGuard/R8, and multithreading to ensure zero tolerance for instability on millions of devices. High-Performance Network Design: You will collaborate with backend teams to design APIs and capture behavioral signals that power 10 billion daily ML predictions. You need a strong track record in API design, maintaining strict backward compatibility for thousands of external integrators, and working with high-performance networking protocols like gRPC, Protobuf, Wire, and OkHTTP. Resource-Constrained Optimization: You will ensure every ad impression feels native and fast while participating in 120 million daily auctions. You must know how to design for minimal footprint, optimizing battery impact and memory usage, as your code executes directly inside someone else’s app and device. Data-Driven Observability: You will monitor, debug, and maintain SDK reliability at scale across millions of global users. You will leverage observability and data tools—including Sentry, Kibana, and AWS (S3, QuickSight, Athena)—to track errors, investigate SDK behavior, and turn raw data into clear engineering decisions. Build Automation & Delivery: You will maintain and improve our CI/CD pipelines to guarantee efficient, reliable SDK delivery. This requires hands-on experience with Gradle and GitLab CI to automate the testing, building, and packaging of our mobile libraries. Plus – AdTech & Low-Level Systems: It is a major plus if you bring experience in ad-tech or programmatic advertising (aligning products with IAB specifications). Additionally, experience with NDK/JNI (C/C++ interop on Android) or parallel iOS development experience is highly valued to help support our cross-platform ecosystem. 🌎 We welcome applications from talent worldwide and provide relocation support to Hamburg, Germany for those ready to join our team. What’s in It for You? At adjoe, you’re not here to just close JIRA tickets, you’re helping build the infrastructure behind one of the most impactful platforms in adtech. The systems you work on will reach hundreds of millions of users and power billions of decisions every day. Go Big. Own projects with impact on 770M users and push adtech boundaries. Move Fast. Ship solutions multiple times a day, learn from results, and keep momentum. Be Direct. Solve problems openly and collaborate across teams. Thrive Together. Grow with a diverse, global team of people from over 40 different countries that learn from each other. Have Fun. Celebrate wins, enjoy daily victories, and bring your energy. We welcome applications from people who will contribute to the diversity of our company.