100+ Enterprise Clients

7B+ active clients users

$1.8T Clients Revenue

From startups to Fortune 500.

From React Native migrations to AI-native delivery infrastructure, these are the products, platforms, and engineering systems we helped teams move forward.

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Case Study CoverCase Study Cover
Architecture & Performance
AI-Driven QA & Testing
Self-Hosted CI/CD Infrastructure
Finance
Android
iOS

Enhancing Application's Performance for Expensify

Discover how we revamped the Expensify app for lightning-fast experiences, guided by a systematic DMAIC approach.

5x

faster message sending time

4.5x

faster search screen loading time

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Self-Hosted CI/CD Infrastructure
Architecture & Performance
Finance
iOS
Android

Building Scalable Observability for a High-Growth React Native App

3→1

analytics systems unified into a single interface

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End-to-End Product Development
Self-Hosted CI/CD Infrastructure
Architecture & Performance
Media & Streaming
TV
Tizen

Launching a High-Performance React Native App on Samsung TV

5

platforms under one RN codebase: tvOS, FireTV, Tizen, LG, Vizio

28.6%

lower TTI compared to the inherited RN app (15.27s → 10.9s)

0

extra hires needed to support new platform

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End-to-End Product Development
Feature Development
Software Development
iOS
Android

Launching White-Label Super App for Zephyr Cloud With Re.Pack

We integrated ZephyrCloud with React Native and developed a white-label application to showcase Zephyr features as well as provide easy getting started story.

Short heading goes here

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Architecture & Performance
End-to-End Product Development
Media & Streaming
TV

Optimizing Android TV Startup for Global Streaming Platform

5%

faster startup time on FireTV and FireHD devices

1 line

to improve startup performance

0 rewrites

required, change applied at build level

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AI-Assisted Migrations
End-to-End Product Development
Self-Hosted CI/CD Infrastructure
Automotive
iOS
Android

Migrating iOS and Android Apps to React Native for AutoZone

AutoZone partnered with Callstack to replace its aging native apps with a single cross-platform codebase, keeping its biweekly release cycle while migrating core app functionality to React Native.

2x

growth in mobile user base during the migration period

4.2 -> 4.7

app rating increase after migrating to React Native

0

missed releases during the transition to React Native

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Feature Development
End-to-End Product Development
Software Development
Web
iOS

Building a browser-based React Native playground for Expo

We partnered with Expo to enable instant prototyping, real-device preview, and easy sharing of React Native projects, all without local setup.

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Team Training
AI-Assisted Migrations
Architecture & Performance
Retail & E-commerce
Android
iOS

Training HelloFresh Engineers to Build Production Apps With React Native

2.8x

increase in knowledge over 8 weeks (25% → 71% assessment scores)

15

developers trained across web and native backgrounds

86%

of devs self-rated their knowledge as 3/5 or higher after training (up from 0%)

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Architecture & Performance
Feature Development
Software Development
iOS
Android

Creating React Native SDK Wrapper for Rive

100k

weekly downloads on npm

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End-to-End Product Development
Feature Development
Team Training
Finance
iOS
Android

Enhancing Performance of Momo's Super App With Re.Pack

MoMo successfully migrated its platform and mini apps to a new architecture using Re.Pack, boosting performance and scalability.

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Architecture & Performance
End-to-End Product Development
Sports & Entertainment
iOS
Android

Improving Chat Performance and Creating a Custom UI Library for Dream11

We enhanced the performance of the Dream11 platform by optimizing chat functionality for low- and medium-end devices, and creating a custom UI component library.

78%

bundle size reduction (from 50 MB to 11 MB)

30%

faster component mount time after render optimization

60%

faster initial load time enabled by switching to Hermes

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AI-Assisted Migrations
Self-Hosted CI/CD Infrastructure
Retail & E-commerce
Android
iOS

Migrating a Legacy React Native App to Expo for Faster Builds and Simplified Releases

6x

faster builds after replacing Jenkins with EAS

1.5x

more reliable builds with EAS

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Architecture & Performance
AI-Assisted Migrations
AI-Driven QA & Testing
Finance
Android
iOS

Migrating Questrade Edge Mobile to a Faster, More Scalable Architecture

33%

fewer re-renders across most features

18%

faster time-to-interactive

-28%

CPU usage in critical trading flows

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End-to-End Product Development
Feature Development
Software Development
iOS
Android

React Universe App: Networking Evolved with Liquid Glass

63%

adoption rate; majority of attendees registered in the app

67%

of attendees connected through QR badge sharing

45%

created personalized badges to showcase identity and goals

49%

of attendees onboarded before day one, arriving ready to network

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Feature Development
Architecture & Performance
Automotive
Web

Migrating AutoZone’s Storefront to Next.js for Better Performance and SEO

#1

SEO rank, recovering from 3-9

260kB

less in blocking JS payload

2–5x

faster feedback loop

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AI-Assisted Migrations
Feature Development
End-to-End Product Development
Healthcare
iOS
Android

Modernizing 7Cup's React Native Codebase and Adding Platform Features

130%

increase in users post-upgrade

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Clients

Trusted by enterprise teams at scale

I appreciate their attention to detail, flexible approach and a high degree of expertise.

Glen Moriarty

Founder and CEO

I recommend them as a trusted tech partner for running complex projects.

Jin Chung

Co-Founder, CTO

We had been struggling with React Native application performance until we met Callstack.

Huỳnh Chí Hùng

Associate Director

The trainers are always very helpful and supportive. It really makes a difference!

Artem Musiienko

Staff Eng

Their engineers proved to be a crucial part of our mobile app relaunch project.

Brian Aznar

Engineering Director

Not only does Callstack have tremendously talented engineers, but I know they care about the success of the project as much as I do.

TC Davis

Product

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