João Birk
Senior Staff Software Engineer
@ Cash App · Block Inc.
A 22-year journey through mobile platforms, from J2ME on feature phones in Porto Alegre to building the future of finance for millions at Cash App.
Years
Platforms
Java Certs
Languages
Chapter One
The Origins
Porto Alegre, Brazil · 2002–2011
It started with curiosity. A computer science student at PUCRS who couldn't stop building things. By the time mobile phones could run Java, João was already writing apps for them.
Engineering Track
Teaching & Thought Leadership
PUCRS
B.S. Information Technology · Concluded 2007
Pontifícia Universidade Católica do Rio Grande do Sul
Chapter Two
The Rise
New York City · 2012–2021
A move to the United States. From senior engineer to team lead, to principal, to engineering manager. Six platforms, two continents, and the realization that the best code is the code that empowers others.
TriPlay Inc.
Senior Team Lead
Five years building eMusic and eStories across every mobile platform: iOS, Android, Tizen, BlackBerry, Windows Phone, J2ME. Grew from senior engineer to managing the entire mobile team.
Meetup
Senior Android Developer & Eng. Lead
Discovery Team. The bridge between PM, design, product and engineering. Building features that helped millions find their people.
Yahoo Finance
Principal → Manager → Sr. Engineering Manager
Three promotions in three years. Took a struggling app and transformed it into a best-in-class product.
90%
↓
99.8%
Crash-free sessions
5s
↓
400ms
Cold start time
3.8
↓
4.7
Play Store rating
400K
New users in 6 months via Instant App
Rewrote the entire app in Kotlin — from a monolith to 20 reusable modules. That architecture enabled 2 new apps (TV & Instant App) built purely by reusing code. Became the reference for Yahoo Mail, Sports, and Weather teams. Improved the company-wide Ads SDK, fixing revenue metrics used across all products.
Chapter Three
Cash App
Block Inc. · 2021–Present
The current chapter. Senior Staff engineer at one of the most impactful fintech products on the planet. Not just writing code — building tools, leading migrations, and making the entire engineering organization faster.
RxJava → Coroutines Migration
Led the entire org through the migration. Created a prize program with support from Jack Dorsey and a handwritten letter from the CEO. Taught a Coroutines course Block-wide.
Deeplink Workflow Automation
Built code-generation tools from YML files. Eliminated manual steps for adding new deeplinks across mobile. Reduced bugs and SEVs.
Feature Flag CLI
Created a CLI tool for engineers to create, update and manipulate feature flags. Generates code for both iOS and Android. Removed complexity, improved speed, reduced SEVs.
First Full Compose Feature
Developed the P2P (send/receive money) flow — the first feature built entirely in Jetpack Compose. Then helped multiple teams migrate from XML views.
The $12K/Month Bug Fix
Found and fixed a contact-sync issue that had persisted for nearly 3 years. Cloud costs dropped by $12,000/month overnight.
Android Studio Plugin
Built an IDE plugin for creating module, presenter, view, and test skeletons. Engineers can now drag-and-drop UI elements using the correct design system.
Open Source Contributions
Active contributor to open source projects maintained by Block, helping improve tools used by the broader Android community.
Interlude
What colleagues say
From peer feedback
João has completely transformed how we handle feature flag management, and the impact of his tools is probably bigger than we realize. The whole process is straightforward now and handles everything automatically. It’s been incredible not having to juggle multiple windows just to make sure all the settings are right.
I also want to recognize João for eliminating exposure tracking on Android. When I contacted him, he acted incredibly fast. Within 24 hours, he had already reached out to the right people to confirm the change and had it implemented — eliminating a major source of problems that caused multiple CCBs just within the past few months.
— Cash App colleague
João is one of the best people at Cash at shipping early and rapidly iterating on feedback. Instead of trying to ship a perfect product on day 1, he built an MVP, solicited feedback, and quickly incorporated it. The end result was a viable tool a lot faster than we otherwise might have.
He was able to cut through the noise and find creative solutions — hiding the complexity of flag ownership and code generation so that certain classes of mistakes are impossible.
— Cash App colleague
João is an awesome engineer and mentor. His automation work across feature flags, client routes, and deployment workflows saves weeks of engineering time. He pairs with others, shares resources, and supports the team. He builds tools for us, shares knowledge, and makes the team and teammates better.
One day I would love to work directly with João.
— Cash App colleague
I want to recognise João’s continuous contributions to improving the codebase and the community. He’s one of the most active members in our Slack channels, consistently helping others. He proactively messaged me about incorrect feature flag setup, pointed me to the CLI tool, and made time to answer my questions — it’s a tool I’ve relied on ever since.
When I asked about push notifications not being received in debug builds, João was the only person who responded. He offered practical solutions with clear reasoning, and even when I pushed back, he used it as a teaching moment. Thanks for making Cash a better place to work.
— Cash App colleague
Teaching people new ideas and making them question things that they have been rather complacent about.
— Yahoo colleague
Team is more engaged, the code is smaller and leveraging modern tools.
— Yahoo colleague
Interlude
The Toolkit
Core Skills
Sun/Oracle Certified — All 7
Platforms
Current Stack
Historical
Speaking & Publishing
Conference Talks