Composable Banking: Decouple Your Core to Innovate Faster

WAU Marketing
Jan 15
3 min read

Updated: Jun 23

For years, modernizing the core was an all-or-nothing bet. That era is over.

The "big bang" replacement—switch off the old core on a Friday, switch on the new one Monday—was every CTO's recurring nightmare. Months, sometimes years, of work before a single benefit, and an execution risk no serious regulator approves without contingency plans few institutions can afford. The region is now moving in another direction: modernization in blocks. It's called composable banking, and it changes the question from "when do we replace everything?" to "which piece do we move first?"

What "composable" means in practice

The idea is simple to state and demanding to execute: instead of a monolithic core where everything is coupled—touch the accounts engine and the loan engine shakes—you separate the bank's capabilities into independent components that are chosen, connected, and replaced on their own. The ledger on one side. The product engine on another. Payments, credit origination, interest calculation—each one a service with its own boundary.

Technically, this rests on a cloud-native, API-oriented architecture: a gateway that orchestrates requests to decoupled microservices, where each microservice encapsulates a business domain and manages its own data. The transactional source of truth runs at its optimal pace while calculation logic lives in separate modules. The result? You can swap one piece without rewriting the rest.

Why it matters now

Two regional data points explain the urgency. More than 60% of financial institutions still run on legacy systems, as IUPANA reported. At the same time, IDC projects that 40% of banks will adopt "sidecar core" strategies—a modern core running alongside the old one—by 2026, according to an analysis by Galileo (vendor). Progressive modernization stopped being the cautious option and became the majority one.

The reason is business, not tech fashion. When the core is composable, launching a new product goes from a months-long project to a weeks-long configuration. Connecting a fintech, a marketplace, or a credit partner stops being a painful integration and becomes consuming an API. The bank stops operating as a closed system and starts working as a platform.

The three roads to get there

Three patterns dominate real programs in the region, and it's worth knowing which one is yours:

Big bang. Replace everything in one cutover. Almost no one attempts it today: the risk is high and the regulator demands costly guarantees. Reserved for very specific cases.
Coexistence (sidecar). The new core runs alongside the old. New customers and products enter the modern one; the existing book migrates in waves over three to five years. It's what most large programs do.
Iterative improvement. You modernize one product line at a time—SME credit, BNPL, digital accounts—prove the return, and move to the next. It minimizes risk and funds its own path.

None is "the right one" in the abstract. The right one fits your book, your risk tolerance, and your regulatory framework.

The composable trap

Let's be honest: composable doesn't mean easy. Decouple it badly and you get the opposite effect—a "tower of Babel" of services that don't talk to each other and an integration layer that grows out of control. Modernization in blocks only works with a clear architectural vision and alignment across three areas that rarely sit together: business, operations, and technology. Without that coordination, you end up with the same silos as before—now in the cloud and more expensive.

How we approach it at WAU

At WAU we design the transition block by block: we identify which component to move first to unlock value fast, decouple it from the legacy core, and connect it via API without disrupting operations. We don't sell a "switch everything off and pray." We build the wave-by-wave path that lets you modernize without losing sleep—or customers.

If your core no longer lets you move at market speed and you want to see where to start—without a three-year project in the way—let's talk. We'll help you map the first block. 👉 Book a conversation with our team.