Callstack

Callstack builds and modernizes cross-platform applications for enterprises using React and React Native. Its services span consulting, prototyping, implementation, performance optimization and team training. Alongside client engineering, it develops tools for mobile teams: Re.Pack brings Module Federation to React Native, allowing applications to load JavaScript modules at runtime; Agent Device lets AI agents run and test applications on devices locally or in the cloud. Its React Native AI SDK lets developers switch between cloud and on-device language models without rewriting application logic.

Founded in Wrocław, Poland, in 2016 by Mike Grabowski and Anna Lankauf, Callstack built its business around React Native engineering and open-source contributions. Grabowski is its current CEO, returning to the role in 2026. The company is a founding member of the React Foundation and a React Native core contributor. It expanded its offering in 2026 to include AI-assisted delivery, agent infrastructure and enterprise AI adoption. Agent Device also converts established mobile workflows into replayable scripts that run without further model calls.

In 2026, Callstack reported 100-plus enterprise clients. Its 2025 revenue reached PLN 151 million, with PLN 57 million in EBITDA. Viking Global Investors acquired a majority stake in 2025 at a reported company valuation of approximately PLN 500 million; Grabowski retained a stake.