When should banks prioritise open finance over a full core replacement?

Banks should prioritise open finance when the business needs faster service innovation, better customer data sharing, and improved interoperability, but the core platform is still stable enough to keep running. Open finance is the better choice when speed and flexibility matter more than a risky transformation programme. It lets institutions deliver value sooner while deferring deeper modernization decisions.

Why open finance can be the better interim choice

Open finance is usually the right priority when the bank needs to move faster than a core replacement programme can realistically deliver. It is a delivery and sequencing decision, not a statement that the core does not matter. The question is whether the institution can create customer value, interoperability, and product reach without taking on the operational drag of replacing the core first.

That makes open finance most attractive when the current core is stable, integration work is manageable, and the bank needs to expose or consume services sooner. In practice, this is often the better path when the business case depends on faster partner connectivity, data portability, and incremental product expansion rather than a wholesale change to processing architecture.

A full core replacement is a different class of programme. It can deliver deeper simplification, but it also brings migration risk, higher coordination cost, and a longer period in which benefit is deferred. When those costs would delay market response or block near-term revenue opportunities, open finance can create a better risk-adjusted path to change.

When the core is stable enough to defer replacement

The key test is whether the existing core still supports reliable operations, regulatory obligations, and material product servicing. If it can do that, the bank may not need to absorb replacement risk simply to enable new customer-facing capabilities. Open finance can sit on top of the existing estate while the institution modernises selectively around it.

This approach works best when the core is not already a source of severe fragility. If the platform is failing frequently, constraining product changes, or making data exposure too hard to govern, then open finance alone will only expose the limits of the back end. In that case, the bank may be postponing a structural problem rather than solving it.

For this reason, leaders should treat open finance as a bridge when it unlocks interoperability without forcing immediate core disruption. The objective is to preserve operational continuity while changing the rate at which the bank can ship new capability.

What open finance changes in the delivery model

Open finance changes the way banks extend value by shifting emphasis from monolithic transformation to controlled exposure of services and data. That can reduce time to market, improve partner integration, and make it easier to test business models before committing to a full replacement. It is especially useful where customer demand is immediate but the institution is not ready to rebuild its core processes.

The practical advantage is flexibility. Banks can add API-based services, data-sharing capabilities, and ecosystem connections in a way that is usually less disruptive than a core migration. That flexibility matters when the organisation needs to respond to competition, regulatory pressure, or partner demand while keeping existing operations stable.

Used well, open finance also creates a cleaner decision point later. Once the bank has learned which products, channels, and integrations generate real demand, it can make a more informed choice about whether a core replacement is still justified, or whether targeted modernization is enough.

Risk and Threat Considerations

Open finance introduces exposure at the integration boundary, especially where data sharing, third-party access, and API dependencies expand faster than governance. The operational risk is not only technical instability, but also the possibility that the bank accumulates a broad set of externally connected services on top of an ageing core without improving the underlying control posture.

Failure mechanism: Banks can create a fragmented architecture where customer data, access control, and service dependencies are spread across multiple layers, but the core remains the single point of truth and failure. If interfaces are added faster than monitoring, entitlement control, and change discipline can keep up, exposure grows faster than resilience.

Impact: The bank may gain speed in the short term, but at the cost of greater third-party risk, weaker visibility, and more complicated incident recovery. If the core is already constrained, open finance can amplify the consequences of misconfiguration or outage instead of reducing them.

Standards & Framework Alignment

This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.

NIST CSF 2.0 sets the technical controls, while DORA and ISO/IEC 27001:2022 define the regulatory obligations.

Framework	Control / Reference	Relevance
NIST CSF 2.0	GV.SC-01 — Cybersecurity Supply Chain Risk Management	Open finance depends on third-party integrations and ecosystem trust.
	PR.AA-05 — Identity Management, Authentication and Access Control	Open finance relies on controlled access to shared customer and service data.
	DE.CM-01 — Monitoring for Unauthorized Personnel, Connections, Devices and Software	Open finance needs visibility across exposed interfaces and partner connections.
Recommendation — Assess third-party dependencies and set governance for external data-sharing relationships. Enforce least-privilege access for API and data-sharing connections. Monitor API and partner activity for abnormal access or misuse.
DORA	ICT Third-Party Risk Management	Open finance increases reliance on external providers and integrations in financial services.
Recommendation — Govern ICT third-party dependencies before expanding open finance connectivity.
ISO/IEC 27001:2022	A.5.23 — Information security for use of cloud services	Open finance often extends services through cloud-hosted platforms and shared interfaces.
Recommendation — Define security requirements for externally hosted integration services.

Practitioner Guidance

What to prioritise: Prioritise open finance when it is tied to a clear commercial or customer outcome that can be delivered without destabilising the core. If the main benefit is speed to market, ecosystem reach, or incremental product innovation, the case is stronger than if the programme is really a disguised core remediation effort.

What to verify: Verify that the core can still support stable processing, auditability, and controlled integration over the period in which open finance will be expanded. If that is uncertain, the bank should treat the architecture as a resilience problem first, not only a product strategy question.

Practitioner takeaway: Choose open finance first when it buys time, flexibility, and measurable customer value, but do not confuse that with avoiding core modernisation forever. The right decision is the one that reduces near-term friction without silently increasing long-term architectural risk.