Callstack Begins a New Chapter to Building the Next Big Tech Stories
Callstack Valued at Half a Billion PLN: Karwatka Brothers Exit as Viking Global Takes the Lead
Tags: Callstack, React Native, Polish Startups, Tech Exit, Viking Global, Tomasz Karwatka, Piotr Karwatka, Open Source, Cross-Platform Development, Venture Capital, Defguard, Wordware, Startup M&A, Wrocław Tech Scene
In a landmark deal for the Polish tech ecosystem, Callstack, a Wrocław-based software consultancy specializing in React Native and cross-platform development, has been valued at approximately 500 million PLN (~€115 million) following a majority investment by American hedge fund Viking Global Investors. The move marks both the company’s graduation to the global tech big leagues and the strategic exit of founding investors Tomasz and Piotr Karwatka, two of the most influential figures in Poland’s startup scene. The transaction doesn’t just mark a financial milestone. It signals a generational shift in Polish tech—from homegrown founders scaling companies to international exits backed by U.S. capital, while those same founders begin reinvesting in the next wave of innovation.
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From Wrocław Café to Global Open Source Powerhouse
Callstack began humbly in Wrocław’s Tutti Frutti café, where Mike Grabowski, a React Native evangelist, and Anna Lankauf, an experienced tech leader, joined forces with the Karwatka brothers after an early conversation about building an open source-first consultancy. The original proposition was simple: a little seed funding, a lot of trust, and an experimental approach to shaping a different kind of tech company. Unlike many service agencies, Callstack focused on developing its own IP through contributions to open-source—establishing itself as a thought leader in the global React Native community. The firm not only helped enterprises build mobile apps from a shared codebase but also contributed to libraries used by thousands of developers worldwide. This hybrid approach made Callstack more than a consultancy; it became a tech enabler at the heart of digital transformation across industries.
Steady Growth and Smart Succession
Callstack’s early decision to prioritize professional governance proved pivotal. As the company scaled, it appointed Krzysztof Lis as CEO—freeing co-founders to step into supervisory roles and allowing operations to mature. By the time Mike Grabowski returned to active leadership, Callstack had grown to generate 50 million PLN in annual EBITDA. This operational maturity made Callstack a prime target for international investors. The deal with Viking Global, which manages over $50 billion in assets, is seen as both a validation of Polish software quality and a strategic expansion opportunity. Callstack is expected to accelerate its international client acquisition and product innovation with fresh capital and a reinforced global structure.
A New Chapter for the Karwatka Brothers
For Tomasz and Piotr Karwatka, the Callstack exit is just one chapter in a broader vision. Both have redefined themselves as serial entrepreneurs and prolific angel investors in Poland’s deep-tech and AI sectors. They recently co-invested in:
Defguard, a cybersecurity startup developing open-source identity and access management tools for public institutions in the EU. The venture raised 5.2 million PLN, supported by Hard2beat VC, Smok Ventures, and others.
Wordware, one of Europe’s most talked-about AI startups, raised $30 million in seed funding with backing from Y Combinator. Wordware enables AI agent creation through natural language prompts, bringing software creation to the next 500 million users without needing to write code.
The Karwatkas also support Rigby, a hardware-scaleup logistics platform, and advise on the development of Medusa, a headless commerce solution disrupting the eCommerce developer stack.
“Our strength is in building from scratch,” says Tomasz Karwatka. “With Callstack, we proved that Polish teams can lead the world in open source and engineering excellence. Now it’s time to empower the next wave.”
What’s Next for Callstack?
Callstack’s post-acquisition phase is just beginning. With Viking Global’s backing, the company is likely to:
Expand its consulting footprint in the U.S. and Western Europe
Double down on proprietary tooling for React Native engineering
Launch new open-source initiatives under Grabowski’s technical leadership
Invest in developer education and community engagement, one of its strongest assets
As React Native continues to dominate mobile development, Callstack is now poised to become a global hub for cross-platform product engineering—serving Fortune 500 clients while staying deeply embedded in the open-source world.
A Symbol of What’s Possible in Polish Tech
The Callstack story is a blueprint for Poland’s new generation of tech companies: start small, build real developer value, stay open-source-native, and execute succession early. With the Karwatka brothers’ exit and Viking Global’s entry, Poland has proven once again that it’s not just capable of launching world-class software—but of scaling, exiting, and reinvesting at the highest level.
This is not just a liquidity event. It’s a proof point: Polish software talent, when paired with long-term vision and open-source leadership, can build global category leaders. And now, Callstack has the backing to do just that.
