Summary Are you a mobile engineer who thrives on building exceptional user experiences, bringing a new product to life, and raising the technical bar for the team around you? As a Senior Mobile Engineer at Topstep, you'll play a foundational role in building our mobile trading platform with React Native and TypeScript. Mobile is new for Topstep, and the product is at an early MVP stage—an opportunity to shape both the trader experience and the engineering foundations behind it. You'll help build out the MVP, establish reusable patterns and components, and own mobile features from design through iOS and Android release. The challenge is to turn high volumes of real-time trading data into a mobile experience that stays responsive, clear, and trustworthy as market activity and app usage grow. You'll work closely with product, design, backend engineers, and quality engineering, bringing mobile expertise into cross-functional feature teams as the product grows. This role combines deep React Native expertise with a product mindset and pragmatic engineering judgment. You'll balance immediate delivery with a foundation other engineers can build on, mentor through reviews and pairing, and help define what mobile excellence looks like at Topstep. Key Responsibilities • Help build out Topstep's mobile MVP in React Native and TypeScript, integrating with GraphQL APIs across our trader and trading experiences. • Establish mobile architecture patterns, reusable components, and engineering practices that other engineers and feature teams can adopt. • Own mobile features end-to-end, from technical design through App Store and Play Store releases, monitoring, and iteration. • Partner with product and design to translate trader needs into intuitive, accessible experiences that balance user experience with technical constraints and platform capabilities. • Design for high volumes of real-time updates while keeping screens responsive, information current, and user actions clear across devices and network conditions. • Build quality into the product from the start through testing, monitoring, performance optimization, and secure handling of trader information. • Bring mobile expertise into cross-functional feature teams as the product grows, helping teams deliver mobile features confidently. • Mentor engineers through reviews and pairing, sharing practical approaches to React Native development, architectural decisions, and production ownership. • Champion mobile-first thinking across the organization, helping backend and frontend partners understand mobile constraints and opportunities. • Support the mobile experience in production, investigate issues, and improve reliability. Participate in the team's agreed support or on-call responsibilities after onboarding. Required Qualifications and Key Competencies • 5 + years of professional experience building and shipping production mobile applications, including several years of hands-on React Native development. • Deep React Native expertise and a strong TypeScript and modern JavaScript foundation, including navigation, state management, hooks, and component design. • Experience shipping applications to both iOS and Android, including platform-specific differences, mobile build and release pipelines, and app-store distribution. • Experience integrating GraphQL APIs, including client caching, mutations, and error handling. • Experience improving mobile performance and reliability through profiling, secure session handling, and debugging production issues. • A strong testing mindset with practical experience writing unit, integration, and end-to-end tests for mobile applications. • A track record of owning features end-to-end and helping other engineers through technical decisions, code reviews, reusable components, and mentoring. • Clear communication and pragmatic engineering judgment, including the ability to explain mobile constraints, build consensus, and balance long-term architecture with MVP delivery. Preferred experience • Experience with real-time data integration using WebSockets or similar streaming connections. • Native iOS or Android development, including work at the React Native/native boundary. • Experience with complex mobile interfaces such as charts, animations, or gesture handling. • Familiarity with Expo or comparable React Native tooling. • Experience building trading, financial, or fintech products. Company Culture & Perks • Topstep is an engaging working environment that ranges from fully remote to hybrid. We foster a culture of collaboration by keeping cameras on during meetings and maintaining a robust Slack environment for communication. • Seven Company-paid Holidays and generous Family Leave. Paid time off is front-loaded. • Competitive 401(k) matching, health, dental, and vision insurance are offered for full-time employees. • Vacations are encouraged with a bonus for taking 5 consecutive days. Topstep offers a food and groceries budget and contributes towards health and wellness. New Hire Base Salary Range • $155,000 - $200,000 annually. • The compensation offered will take into account the internal compensation structure and may vary depending on the candidate's geographic region, job-related knowledge, skills, and experience, among other factors. • This position is eligible for a performance-based bonus as provided by the plan terms and governing documents. Equal Opportunity Employer Topstep is an Equal Opportunity Employer. We are committed to fostering an inclusive environment where all employees and applicants are valued. All qualified candidates will receive consideration for employment without regard to race, color, religion, gender, gender identity or expression, sexual orientation, national origin, age, disability, or veteran status, in compliance with applicable federal, state, and local laws. Interested in the role? Apply today with your resume! The collection, use, and handling of your data provided in response to this job posting is described further in our Privacy Policy. If you are a California resident, please review our California Notice at Collection. Notice of Use of Artificial Intelligence in Recruitment and Hiring: Notice Pursuant to 775 ILCS 5/2-102(L). Topstep LLC uses artificial intelligence ("AI") in connection with its recruitment and hiring process. Examples include, but are not limited to, AI tools used to improve job descriptions, generate interview questions, draft communications, assist with scheduling, and source candidates, as well as AI features built into third-party platforms such as LinkedIn, Indeed, and Glassdoor. Topstep will not use AI that has the effect of subjecting employees or applicants to discrimination on the basis of any protected class under the Illinois Human Rights Act. The collection, use, and handling of your data provided in response to this job posting is described further in our Privacy Policy. If you are a California resident, please review our California Notice at Collection.