Core Modernization in Banking with Sapient Slingshot

For banks, core modernization is never just a technology program. It is a balance-sheet decision, a risk decision and a growth decision all at once. Core platforms still power the products, payments, batch processes and data flows that keep the institution running. But those same systems can also slow change, absorb budget, concentrate knowledge in a shrinking pool of specialists and make every transformation initiative harder to forecast.

That is why the path forward is not simply to replace the core in one leap. For most banks, the smarter approach is progressive migration: understand the legacy estate in detail, define a clear target-state architecture, sequence change around business priorities and move in controlled increments. Publicis Sapient helps banks do exactly that with Sapient Slingshot, our AI-powered software development and modernization platform.

Sapient Slingshot is built to accelerate complex software processes across the lifecycle, from code analysis and specification generation to design, code transformation, testing and deployment readiness. In banking, that means a more predictable way to modernize critical systems without treating them like black boxes and without asking leaders to choose between speed and control.

Why banking modernization demands a different approach

Banking estates are uniquely difficult to modernize. Core logic is often buried in decades-old COBOL environments, spread across main files, subroutines, copybooks and tightly coupled interfaces. Product rules, data mappings and operational dependencies may be poorly documented but still essential to customer outcomes, financial reporting and day-to-day resilience. Payments modules and batch feeds add another layer of complexity because they connect so many downstream processes across the enterprise.

At the same time, the pressure to modernize is rising. Banks need more modular architecture, faster product change, better integration across channels and stronger operational efficiency. They also need modernization programs that can stand up to scrutiny from finance, risk, compliance and architecture stakeholders. When budgets are constrained and risk tolerance is low, traditional approaches often struggle. Manual analysis takes too long. Documentation gaps introduce uncertainty. Large-scale rewrites create too much exposure.

This is where an AI-assisted, human-governed model becomes valuable. Sapient Slingshot helps banks compress the work around modernization, not just the coding itself, so teams can move from legacy understanding to executable transformation plans with more confidence.

From opaque legacy code to executable modernization roadmap

One of the hardest parts of core transformation is understanding what the existing system actually does. Slingshot helps analyze legacy code, surface logic and dependencies, and generate functional specifications, field mappings, flowcharts and other artifacts that make legacy systems explainable again. This code-to-spec capability is especially valuable in banking environments where undocumented business rules and data relationships can turn even small changes into high-risk work.

Once intent is visible, Slingshot helps accelerate the next step: moving from recovered business logic to future-state design. Teams can define target-state architecture, redesign data models and translate validated requirements into structured delivery artifacts. That makes modernization more than a discovery exercise. It becomes an actionable roadmap that product owners, architects and engineering teams can execute in phases.

For banks pursuing a coreless banking strategy, this matters even more. A coreless model depends on decoupling capabilities, reducing reliance on monolithic systems and enabling modular services to evolve at different speeds. But getting there requires a disciplined bridge between the current estate and the desired state. Slingshot helps create that bridge by carrying context from legacy analysis into design and execution, reducing the disconnects that often slow transformation programs.

Built for banking priorities: core transformation, payments and batch feeds

Modernization in banking rarely happens in isolation. A bank may be rethinking its core platform while also modernizing payments, rationalizing batch feeds, redesigning data products or improving integration across finance and operations. These programs are deeply linked, which is why continuity across the software development lifecycle matters.

Sapient Slingshot supports that continuity through intelligent workflows, context binding and an adaptive agent architecture. Rather than producing generic outputs, it helps generate modernization assets grounded in enterprise context and aligned to the work at hand. Specifications can be turned into architecture and design artifacts. Requirements can be translated into user stories and backlog items. Modern code and tests can be generated with approved context carried forward.

In one financial services modernization effort, Publicis Sapient analyzed more than 350 files and nearly half a million lines of code across two critical programs in just eight weeks. The scope included mainframe batch feeds for financial and data products as well as a payments module in a highly complex Unisys COBOL environment. The team produced program overviews, flowcharts, detailed field mappings and fan-out diagrams, then defined a target-state architecture, redesigned the data model and converted the resulting requirements into execution-ready user stories. The impact was significant: a 70% reduction in manual effort for code-to-spec work, 95% accuracy in generating specifications and a 40% to 50% increase in migration speed.

For banking leaders, the lesson is clear. AI can add the greatest value not by bypassing discipline, but by accelerating the most time-consuming and error-prone parts of disciplined modernization.

Progressive migration with humans in control

In banking, no modernization platform should operate as a black box. Decisions must be explainable. Outputs must be reviewable. Delivery must remain traceable from legacy analysis through release readiness. That is why Publicis Sapient combines Slingshot with human-in-the-loop engineering and integrated delivery teams.

Our engineers and banking practitioners review, refine and validate AI-generated outputs at every critical stage. Product owners can confirm business functionality earlier. Architecture teams can assess target-state alignment sooner. Risk and compliance stakeholders gain more visibility into how requirements, designs, code and tests connect. This governed model helps banks move faster while maintaining confidence in quality, accountability and control.

That operating model is especially important when modernization must proceed progressively. Many banks cannot afford a single-step cutover from mainframe to fully modular architecture. They need phased transformation that protects core operations while creating room for modernization release by release. Slingshot supports that reality by helping teams work incrementally: understand the system, define the next modernization slice, generate the necessary artifacts, validate with the business and move forward with greater predictability.

Why this approach helps de-risk the journey

The promise of AI in banking modernization is not just faster code conversion. It is better predictability. With stronger code-to-spec accuracy, generated documentation, workflow visibility and accelerated backlog creation, banks can reduce uncertainty earlier in the program. Teams spend less time reconstructing intent and more time validating outcomes. Leaders gain a clearer view of scope, sequencing and value realization. Engineering capacity shifts away from repetitive manual effort and toward higher-value modernization decisions.

Sapient Slingshot is built to support a broad range of legacy and modern languages and is designed to deliver up to 99% code-to-spec accuracy. It connects the software development lifecycle instead of fragmenting it, helping modernization move from analysis to design, from design to code and from code to test and deployment readiness in a governed flow.

For banks navigating core transformation, that can change the economics of the journey. Instead of treating modernization as a one-time high-risk intervention, institutions can build a repeatable capability for continuous change across core platforms, payments, batch processing and surrounding services. That is the foundation of a more modular, more resilient and more future-ready bank.

Modernize the core without compromising the business

Core transformation does not have to begin with a leap of faith. With the right approach, banks can move from opaque legacy systems to explainable specifications, from fixed-function cores to modular target states and from fragile modernization programs to governed, phased delivery.

Publicis Sapient brings together banking expertise, modernization strategy and Sapient Slingshot’s AI-assisted capabilities to help institutions de-risk this journey. The result is a more practical path from mainframe to modular: one that supports progressive migration, strengthens delivery confidence and helps banks modernize the systems that matter most without losing sight of the business they are there to protect and grow.