Infrastructure
Modular Financial Infrastructure: Replacing the Monolith Gradually
Core replacement programmes are long, expensive and frequently abandoned. This paper argues for an incremental model in which new product lines run on modular infrastructure alongside the existing core, and examines how institutions sequence that migration.
29 pages · Published June 18, 2026
Overview
Most institutions do not fail at core modernisation because of technology choice. They fail because the programme is scoped as a single cutover that must succeed completely to deliver any value.
A modular approach inverts that: new propositions launch on new infrastructure, the legacy core keeps running, and volume migrates by product line rather than by big-bang date.
This paper examines the ledger, orchestration and reconciliation requirements that make parallel operation viable, and the governance model that keeps it from becoming permanent duplication.
Key topics
What the paper covers
Parallel Operation
Running new infrastructure alongside a legacy core without duplicating the record of truth.
Product-Line Migration
Sequencing by proposition rather than by system boundary.
Reconciliation Between Systems
Keeping two platforms provably consistent during migration.
Governance
Deciding when a legacy component is finally retired.
Takeaways
What you'll learn
- Why single-cutover core replacement fails so often
- How to define the boundary between legacy and modular infrastructure
- What reconciliation is required during parallel operation
- How to prevent indefinite dual-running
Authors
jStack Research
Financial Infrastructure Research
The jStack research group studies how payment, wallet and settlement infrastructure evolves across emerging and established markets.