Interoperability

Interoperability is the property that lets separate systems work as one. The CPMI’s glossary defines it as the technical or legal compatibility that enables a system or mechanism to be used in conjunction with other systems or mechanisms. Email is the canonical success: users on different providers reach each other without thinking about it. Payments are the canonical failure: the world’s settlement systems, domestic rails, consortium ledgers, stablecoin networks, largely cannot.

The consequences are familiar to anyone who moves money across borders. A participant in one system that needs to pay a participant in another must find a chain of intermediaries that belong to both, which is correspondent banking in a sentence. Where new settlement networks have emerged, each has solved the problem inside its own membership and reproduced it at its edges: value moves instantly within the network and hands off to slower rails at the boundary. The result is liquidity fragmentation, balances parked in every venue an institution touches.

Why the gaps persist

The barriers are structural rather than accidental. First, different systems settle different assets. One settles commercial bank money, another central bank money, a third a stablecoin, and a claim on one is not a claim on another; converting between them is itself a settlement problem, which is why the singleness of money features so heavily in central bank writing. Second, for private networks, membership is the product. A network’s value to its members comes partly from exclusivity and control of the rulebook; full openness is rarely in the operator’s interest. Third, legal and technical standards differ: message formats, operating hours, finality rules, liability. A technical bridge between two systems still leaves a lawyer’s question unanswered: when is the linked transaction final, and under whose law?

The three answers

The serious efforts fall into three shapes. Interlinking keeps systems separate and connects them, bilaterally or through a hub; Project Nexus, which would link national instant payment systems through one multilateral scheme, is the flagship example. Common platforms dissolve the boundary by putting everyone on shared infrastructure, the logic of the BIS’s unified ledger vision and of consortium ledgers. And a coordination layer above the systems accepts that venues will stay separate and routes each payment across whichever one fits, treating the fragmented landscape as something to be spanned rather than merged. Each shape trades away something different: interlinking preserves sovereignty but multiplies agreements, common platforms are clean but slow to assemble, and a routing layer inherits the reach of the venues beneath it.