When a central bank decides to issue a digital currency, its biggest challenge isn't just the technology. It's the architecture. The fundamental question is: how will this new form of money reach the public, and who will manage the relationship with the end-user? This choice determines the entire structure of the financial system.

The two main paths are the one-tier (or direct) model and the two-tier (or indirect) model. Each comes with significant trade-offs in terms of risk, efficiency, and the role of the central bank itself.

In a one-tier system, the central bank does everything. It would issue the CBDC, manage all individual accounts, process every transaction, and handle all customer service. Essentially, the central bank would become the sole commercial bank for every person and business in the country.

This approach offers maximum control. The central bank would have a real-time view of the entire economy and could implement monetary policy directly. However, the operational burden would be astronomical. Central banks are not equipped to handle millions of customer support calls, manage retail fraud detection, or perform the Know Your Customer (KYC) checks required for every citizen.

This model could also lead to disintermediation of the commercial banking sector. If everyone can hold their money directly with the risk-free central bank, why would they keep deposits at commercial banks? This could drain the funding that banks use to provide loans for mortgages and businesses, fundamentally altering the credit creation process in the economy.

The two-tier model is a public-private partnership and the overwhelming preference of most central banks exploring CBDCs. In this structure, the roles are clearly divided. The central bank issues the CBDC and oversees the core system's integrity. Commercial banks and other licensed payment service providers (PSPs) manage all customer-facing aspects.

This means private companies would handle onboarding, wallet provision, customer support, and compliance. The central bank provides the foundational layer of trust and settlement, while the private sector innovates on the services and user experience built on top of it. This preserves the existing financial structure and leverages the expertise and infrastructure that commercial banks already have.

Even within the two-tier model, there are crucial design choices to make. The most important one is about who the CBDC is a claim against. This leads to two main variants: the hybrid model and the indirect model.

The distinction between hybrid and indirect models is subtle but vital. It all comes down to liability.

In an indirect model (sometimes called a synthetic CBDC), the digital currency you hold would be a liability of your commercial bank, not the central bank. Your bank would hold reserves at the central bank to fully back the CBDC it issues to its customers. This is very similar to how bank deposits work today, but with the funds potentially being 'ring-fenced' and not used for lending.

In a hybrid model, the CBDC is a direct liability of the central bank. The money in your wallet is a direct claim on the central bank, representing the safest form of money available. However, the private sector still manages the payments infrastructure and all user interaction. The central bank would maintain a central ledger of all transactions, but would not have personal data linking those transactions to individuals. Intermediaries would be responsible for that layer.

This hybrid approach is often seen as the best of both worlds. It maintains the absolute safety of a direct central bank claim and promotes the singleness of money—the idea that all forms of money (cash, bank deposits, CBDC) should be interchangeable at par value without question. At the same time, it prevents the central bank from becoming an unwieldy, monopolistic commercial operator and encourages private sector competition and innovation in payment services.

Choosing the right architecture is a balancing act. It involves weighing the need for safety, control, and efficiency against the importance of innovation, privacy, and maintaining a dynamic private financial sector. For most nations, a two-tier hybrid model appears to offer the most promising path forward.