Senior Java Engineer

Cosmose AI develops smartphone integrations used by eight phone makers, capturing first-party data to drive over 2 billion daily user interactions in 60+ countries. The company builds a core product called KaiKai Lock Screen used by millions of users daily.

• Strong experience in Java backend development
• Experience building scalable and high-performance backend systems
• Familiarity with event-driven systems (Kafka) and modern architectures
• Knowledge of relational databases and SQL
• Ability to take ownership and drive solutions
• Good communication skills in Polish and English
• Experience with high-traffic systems is a plus

• Design, develop, and maintain backend services for KaiKai Lock Screen and CMS
• Build scalable systems for large-scale data processing and real-time content delivery
• Contribute to architecture and system design improvements
• Maintain high code quality through testing, code reviews, and engineering best practices
• Work with distributed and event-driven systems
• Improve system performance, reliability, and efficiency
• Support integrations with external services and third-party systems
• Collaborate with Product, Content, and Data teams
• Share knowledge and contribute to continuous team improvement