Bring your next engineering challenge.

Work with engineers behind widely used open-source tools. We build and scale products across platforms, and help your teams deliver more with AI.

Highlights

• 

  3.7×

  Lower React Native task cost vs Claude Opus 5.5

  $0.50

  1M input tokens

  $3.00

  1M output tokens

  

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  import { generateText } from "ai"
   
  const { text } = await generateText({
    model: "apex",
    prompt: "Ship this React Native screen.",
  })

  Check Apex

  Apex: 3.7× lower React Native task cost.

  Scored 87.8% versus Claude Opus 5.5’s 88.6% on React Native evals. Run Apex inside your existing coding tools.

• 

  

  

  5x

  Faster message sending time

  Read case study

  5x faster message sending for Expensify.

  Search screens loaded 4.5× faster, too. We added continuous performance checks to catch regressions.

• 

  3x

  Delivery acceleration

  70

  Pages in 3 weeks

  80%

  Effort executed by agents

  Read case study

  Agentic delivery: up to 3x estimated acceleration.

  Agents executed an estimated 80% of development effort. Engineers owned architecture, review and release.

• 

  Built on Agent Device.

  • 
  • 
  • 

  Check Agent Device

  Let agents verify the apps they build.

  Our open-source tool lets agents inspect, control and verify apps on real devices. 4,900+ GitHub stars.

• 

  ~6x

  Faster prototyping

  60+

  Components mapped with full coverage

  Read case study

  ~6x faster screen prototyping with AI.

  From about an hour to around 10 minutes for a typical enterprise screen, using a shared design system across web and mobile.

• 

  

  10 min

  From code change to mini-app release

  

  Read case study

  Teamworks: mini-app releases in ~10 min.

  Re.Pack helped seven mini-apps ship independently. Their previous delivery process took 1–2 days for even small updates.

• Check results

  Expert Engineering·Finance

  Enhancing Expensify app performance

  5x

  faster message sending time

• Check results

  Expert Engineering·Finance

  Migrating Questrade Edge Mobile to a Faster, More Scalable Architecture

  33%

  fewer re-renders across most features

• Check results

  Expert Engineering·Sports & Entertainment

  Teamworks cut mobile change lead time from days to minutes

  10

  min from code change to mini-app release

• Check results

  Agentic Delivery·Software Development

  Building an Agentic SDLC for a Web Launch in Under One Month

  3x

  estimated delivery acceleration

• 

  The team at Callstack are the most experienced engineers in the React Native community.

  

  Nader Dabit

  Senior Developer Advocate / AWS

• 

  If you're looking for skilled and trusted React Native developers, Callstack is definitely the way to go.

  

  Tom Occhino

  Director of Engineering / Meta

• 

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

  

  Brian Aznar

  Engineering Director / MLS

• 

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

  

  Artem Musiienko

  Staff Eng / Hello Fresh

• 

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

  

  Glen Moriarty

  Founder and CEO / 7cups

• 

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

  

  Huỳnh Chí Hùng

  Associate Director / MoMo

• 

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

  

  Jin Chung

  Co-Founder, CTO / Rainbow

• 

  Teamworks needed Module Federation, we helped make it real

  

  Michael Song

  Head of Platform / Teamworks

• 

  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 / Expo