Stash Learn


Sep 20, 2022

Introducing Stash Core

By Team Stash
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Stash is on a mission to empower everyday Americans to invest and build wealth. Our customers open personal brokerage accounts, earn rewards as they use their debit card for everyday purchases with our Stash Stock-Back® Debit Mastercard®, and open retirement accounts and find options to buy life insurance—all of this starting at just $3/month. We make it affordable and easy for Americans to plan for their long-term financial future.

As we scale and grow, our technology needs to keep pace. We imagined an infrastructure that could serve as a bedrock to allow us to more quickly innovate and introduce new products and services faster to serve our customers and give them the best experience possible.

In 2022, we undertook an enormous project as an organization: to imagine, build, and launch Stash Core, our new world-class infrastructure platform. The tenets of speed, service, and flexibility are at its heart. We’re excited to bring it to millions of Americans, and to share more details on this incredible transformation.

Building with purpose 

“What problem are we trying to solve?” was at the center of our Stash Core innovation journey. A well-designed platform requires the collective brain power of Product, Engineering, and Design sitting together and creating solutions that align with our brand and our mission. We organized ourselves into cross-functional squads focused on “value” streams. Each squad had representation from product, engineering, design, operations, data science and other critical functional areas. No matter what hat a person wore, a product manager or an operations specialist or a technical lead, the first priority was to do right by the customer. 

Value creation 

At Stash, we are here to help our customers build wealth. Banking is a critical part of that, which is why the first product launch built on Stash Core is our new banking experience, complete with a refreshed Stock-Back® Debit Mastercard®.1 The Stock-Back Card has always been an industry differentiator (the tech is covered under U.S. patent 11,443,338) and now it’s even more seamless and powerful. With every purchase, a customer gets rewarded with up to 1% stock back2: for example, go on a shopping trip to Target, get Target stock; fill up at Shell for gas; get Shell stock. The shares don’t expire and become part of our customers’ personal portfolios for the long-term. It’s a financial literacy and diversification tool, and helps people get started on their investing journey.

In addition, customers will have access to more than 55K fee-free ATMs globally (that’s nearly 3x more than what’s available from institutional banks).3 Plus budgeting tools to help them to stay on top of their finances and build savings for certain expenses, like a vacation.

Overcoming challenges

To build this type of platform, we decided to re-evaluate several aspects of how we build things at Stash. We started fresh with our patterns and practices. We had already undergone a larger shift in our engineering patterns and practices—shifts such as moving from Heroku to AWS and thereby needing expertise in infrastructure management; moving from a single monolithic application to containerized services; and moving from a very synchronous system to a larger and scalable asynchronous system. We took these changes and doubled down on their direction. The main tenets always remained the same: speed, reliability, and ownership.


As Stash scaled and this project began in earnest, we focused on how to continue to deliver value at speed.

We first chose technologies that were very easy and fast to learn, and were the standard choice in our industry. No reinventing the wheel. An example of this was the choice of using Go as our primary programming language. Not only is it used to build such large-scale tools such as Terraform or Kubernetes, but it is very easy to pick up and learn. Of the 50+ engineers we hired, only a few had previous professional experience with Go. Yet our average time from start to putting up a substantial PR (pull request; basically the moment new code is integrated) was 3.4 days.

Another example of speed involved rethinking how we build features. The partnership between the engineering and product leaders on each squad is critical to their success. Gone are the days where each member of the team simply executes their specific role and throws tasks over the wall. Nearly every team member at Stash writes tickets, interfaces with vendors, and is actively involved in what is being built.


With Stash Core, Stash now owns the real-time money movement infrastructure. For example: we read and write actual NACHA files in-house for ACH; we make real-time decisions for debit card authorizations and ATM withdrawals; we actually manage the ledgering of every customer account and general ledger in-house across dozens of processes and files everyday; and we are always the final say for a specific customer’s balance and available balance. These changes mean that uptime and reliability became our #1 priority. If our systems go down, then the customer suffers. To avoid this, we added new and specialized roles within the organization: Site Reliability Engineers (SRE) and Network Operations Center (NOC) technicians.

Today, SREs are embedded on each squad and actively engaged in the product development so they have full contextual knowledge of the system and can guide where we need more monitors or alerts. Our new NOC technicians are the frontline defense for any system outages and are also actively engaged with squads to build out remediation processes in the event of system outages. Ideally, we want a system where no engineer is on-call (a radical idea) and all failures are either caught before code reaches production or by a very well established process to be run by the NOC.

Reliability does not stop with the new roles. We also needed to rethink how we build code. To mitigate dependency on external vendors, we looked hard at buy-vs-build for nearly every single aspect of our system and selected partners that are truly top in their field. We built our system to be multi-region from the outset to help mitigate AWS outages. Testing is another process that has gone through a substantial overhaul. We adopt the mentality of deploying anytime anywhere—and this requires an extremely robust testing suite.


The final important change to how we do business within Stash Core entails ownership. As a leadership team, we give individual squads nearly free latitude to identify and solve problems. We believe they are the closest to the work and the problems, and therefore they know the best solution. This extends not only to their individual squad roadmaps, but also to the technical architecture choices and tools they want to use.

With ownership comes accountability. Squads revamped how they ticket and track work to become much more predictable. Timeline slips are identified much sooner and solutioned. This allows freedom to explore new paths and ideas over feature shipping. Hyper focus is a huge added benefit. Features no longer span 5+ squads and need to be discussed in meetings of 40+ people. Instead, generally no more than 3 different departments are involved at any one time and meeting sizes are reduced to about 4-6 people.

With Stash Core built and launched, we have the opportunity to more completely address the needs of our customers—who trust us to help them build their wealth—and also better serve our internal teams, including our CX and operations agents. 

Establish trust

Our goal at launch was for customers and agents to experience a seamless transition. To start, we’re asking our customers to open a new banking account with Stride Bank, N.A.. Our design, content, and compliance teams have been diligently working together to provide customers with more self-service options and minimize the number of interactions–making the process seamless and easy, just like we strive to do for all Stash touchpoints. 

We also revamped all of our backend customer service agent experiences. From now and into the future, we can offer step-function improvements in our customer-service experiences that results in faster resolution times.

What’s next? Innovate with care

With the accomplishment of building and launching Stash Core in the rear-view mirror, we’re dreaming even bigger. In the future, the open system unlocks the ability for us to launch new features, such as enhanced debit offerings, new credit capabilities, lending and much more to meet our customers’ needs at every point in their life. We can innovate faster, pivot, and adjust our strategies all while keeping our platform costs manageable.

Stash Core has inspired new ways of working and thinking at Stash. We’re now considering: How can we help our customers achieve key wealth management goals with new personalized experiences? How can banking further empower investing? There’s an incredible opportunity ahead of us to serve our customers’ needs. 

The millions of people who rely on Stash to invest and bank care about the benefits. That’s why we are now designing experiences like personalization and financial mentorship across the entire product experience, all built on Stash Core and with the product, design, engineering, and operations skills we’ve expertly honed in the process.

About Stash

Stash is an investing and banking app with more than 2 million customers and nearly $3B in assets under management. Stash’s plans—starting at just $3 a month—provide easy and affordable access to a suite of products including investing, banking, education, and advice. Regular, long-term investing is the foundation of the Stash platform—in direct response to the fact that only 56% of Americans invest in stocks; more than 30% don’t have a retirement account; and 34% can’t save any money. Stash members are 18% more financially literate than the average American and grow their financial literacy over time.

About Stash Core

Stash Core, its custom-built backend technology, allows Stash to own the ledger, the money movement infrastructure, and every customer touchpoint for the millions of Americans who rely on Stash to bank like an investor and build wealth. Stash’s banking solutions, including its new banking account and refreshed Stock-Back® Debit Mastercard®, integrate with Stash personal brokerage accounts by design, empowering customers to follow The Stash Way: regularly invest into a diversified portfolio, over the long-term. The Stash Stock-Back patent, U.S. Patent number 11,443,338, applies to the back-end technology that allows customers to earn specific securities and ETFs that are directly invested into their portfolio when they shop at thousands of retailers, in-person and online. To learn more and sign up for Stash’s new banking product, visit

About Stride Bank N.A.

Originally chartered in 1913 as Central National Bank of Enid, Stride Bank N.A. has grown rapidly. OCC regulated and Oklahoma based, Stride Bank N.A. is a long-time innovator and has developed highly specialized payment solutions for some of the nation’s largest corporations, including real-time payments; consumer and commercial lending; third-party issuer services for debit, prepaid, and credit; and network sponsorship to Visa, MasterCard, and Discover. Also offering broad spectrum mobile banking, wealth management, and treasury services to numerous industries. Stride Bank has branches throughout Oklahoma in Enid, Tulsa, Oklahoma City, Bartlesville, Blackwell, Woodward, and Mooreland, as well as Salt Lake City, Utah. Member FDIC. Equal Housing Lender. Learn more at


Written by

Team Stash

1 Stash Banking services provided by Stride Bank, N.A., Member FDIC. The Stash Stock-Back® Debit Mastercard® is issued by Stride Bank pursuant to license from Mastercard International. Mastercard and the circles design are registered trademarks of Mastercard International Incorporated. Any earned stock rewards will be held in your Stash Invest account. Investment products and services provided by Stash Investments LLC and are Not FDIC Insured, Not Bank Guaranteed, and May Lose Value.
2 1% Stock-Back® rewards available only on Stash+ ($9/mo) and only for client’s first $1,000 of Qualifying Purchases in each calendar month program. All rewards earned through use of the Stash Stock-Back® Debit Mastercard® will be fulfilled by Stash Investments LLC and are subject to Terms and Conditions. You will bear the standard fees and expenses reflected in the pricing of the investments that you earn, plus fees for various ancillary services charged by Stash. In order to earn stock in the program, the Stash Stock-Back® Debit Mastercard must be used to make a qualifying purchase. Stock rewards that are paid to participating customers via the Stash Stock Back program, are Not FDIC Insured, Not Bank Guaranteed, and May Lose Value. 
3 Get fee-free transactions at any Allpoint ATM, see the app for location details, otherwise out-of-network ATM fees may apply. For a complete list of fees please see the Deposit Account Agreement for details.

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