Callstack vs Thoughtworks

Apex Is Now Generally Available: Agentic Coding Model for Mobile and Web, Specialized in React

Apex is now publicly available. Built by Callstack, it brings React Native expertise to feature development, code reviews, debugging, and testing, with strong performance on Next.js tasks too.

Callstack Acquires Margelo for Over $20M

Polish software company Callstack is acquiring Vienna-based engineering firm Margelo in a deal valuing the latter at more than €20 million. Both companies specialize in React Native, a cross-platform framework for building mobile apps. Margelo is known for its open-source libraries (VisionCamera, react-native-mmkv, Nitro Modules) and contract development for clients like Discord, Coinbase, and Expensify. Callstack, founded in 2016, employs over 200 people and serves enterprise clients. The acquisition aims to expand Callstack's technology portfolio and support international growth. Founder Marc Rousavy will stay on and retain a significant stake. The deal follows a recent growth investment from Viking Global Investors that valued Callstack at around €120 million.

• Callstack is acquiring Margelo for a valuation exceeding €20 million.
• Margelo is known for open-source React Native libraries with over 420 million total npm downloads.
• Marc Rousavy will remain with the combined company as a significant shareholder.

Polish Callstack Acquires Vienna-Based React Native Firm Margelo

Polish software consultancy Callstack has acquired Vienna-based engineering firm Margelo in a transaction valuing Margelo at more than €20 million. Margelo is known for open-source React Native libraries such as Nitro Modules, VisionCamera, and react-native-mmkv, and lists Discord, Coinbase, Expensify, and VSCO as clients. Callstack, founded in 2016 in Wrocław, employs more than 200 people and serves over 100 enterprise customers. Margelo founder Marc Rousavy will remain on board and continue developing the libraries. The companies say AI is shifting software development toward architecture, performance, and secure releases. Callstack previously received a growth investment from Viking Global Investors in summer 2025, which valued the company at roughly €120 million. No closing date or regulatory approval details were disclosed.

• Callstack is acquiring Margelo, valuing the Vienna-based firm at over €20 million.
• Margelo's open-source libraries include Nitro Modules, VisionCamera, and react-native-mmkv.
• Margelo has about 39 senior developers and lists Discord, Coinbase, Expensify, and VSCO as clients.

ThoughtWorks Flags AI-Accelerated Shadow IT; Structural Fix Proposed

The ThoughtWorks Technology Radar (April 2026) called out "AI-accelerated shadow IT" under Caution. The article argues this is one visible instance of a broader cloud resource lifecycle governance problem (create, use, modify, abandon, delete) that predates AI tooling but is accelerated by it. HackerOne triage revealed S3 bucket takeover patterns where deleted resources left ghost references that attackers could exploit. The author describes a structural fix: a mechanical "specification gate" that snapshots cloud provider state and evaluates it against a catalog of safety invariants (3,000+ invariants), blocking violations across all lifecycle phases. An open-source engine (Stave) implements this approach and the author frames it as necessary to remove a two-tier system of reviewed core workflows and ungoverned shadow workflows.

• The ThoughtWorks Technology Radar (April 2026) listed "AI-accelerated shadow IT" under Caution.
• HackerOne triage found S3 bucket takeover patterns where deleted buckets left surviving references (DNS, CloudFront, application code) that attackers could claim.
• The lifecycle governance problem spans five phases: Create, Use, Modify, Abandon, Delete and predates AI tooling; AI accelerates creation but not the underlying governance gap.