Senior Java Engineer: Scale Real-Time AI Backend

Cosmose, Inc.

Warszawa

On-site

PLN 180,000 - 300,000

Full time

14 days+

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Job summary

Cosmose AI is seeking a strong Mid or Senior Java Engineer to scale the backend of our KaiKai Lock Screen and CMS, processing content for millions of users daily. You will design and maintain backend services, build scalable data pipelines, and collaborate with Product, Content, and Data teams to deliver meaningful features.

We value ownership, proactive problem solving, and fluency in English and Polish as we push the boundaries of AI-powered mobile content.

Qualifications

Strong experience in Java backend development.
Experience building scalable and high-perf 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 within the team (Polish and English required).
Experience with high-traffic systems is a plus.

Responsibilities

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 to build scalable backend solutions.
Improve system performance, reliability, and efficiency for a high-traffic product.
Support integrations with external services and third-party systems.
Collaborate closely with Product, Content, and Data teams to deliver meaningful features.
Share knowledge and contribute to continuous team improvement.