How SaaS is quietly rebuilding the banking stack, one API at a time

By Nikhil Mangal, Senior Vice President, Zeta

For much of modern banking history, institutions built and owned everything themselves, from ledgers and loan systems to fraud checks and customer channels. Banks were vertically integrated ecosystems, with tightly coupled systems designed for robustness, not agility.

That model worked in an era of physical branches and predictable demand. But as digital-first banking emerged, the same architecture that once delivered stability began to constrain innovation. Building new products meant rewriting decades-old code. Integrating new partners required multi-year projects. And regulatory changes tok forever to implement. Legacy stacks weren’t just technical debt; they became strategic debt.

The Great Unbundling: FinTech Take the Stage

Over the past decade, the balance shifted as fintech innovators began unbundling the bank, one service at a time.
Payments, lending, savings, and cards, once owned by a single institution, became independent, API-powered categories. For instance, digital ...