Introduction
Credit Suisse's CSX was a digital-first account popular with younger Swiss clients. After UBS migrated all former Credit Suisse clients onto its systems in 2026, CSX users moved into the UBS app, and UBS is now decommissioning Credit Suisse's legacy IT, a step it expects to largely finish by the end of 2026. The prompt: should UBS rebuild CSX's most-loved features in the UBS app before fully switching off the legacy platforms, or decommission first and rebuild later? This is a classic trade-off between client retention and cost and risk reduction, with a hard deadline attached.
I'll clarify the context, identify the trade-off type, understand the product, form a hypothesis, define metrics, design an experiment, plan analysis, set a decision framework and give a recommendation.
Step 1
Clarifying Questions (3 minutes)
Why it matters: Rebuilding all features is impossible; we need the top few. Expected answer: Spending insights, savings pots and instant card controls appear most in feedback. Impact on approach: The trade-off is about two or three features, not full parity.
Why it matters: Decommissioning savings are part of UBS's integration cost targets. Expected answer: A meaningful run cost per month plus operational risk of maintaining old systems. Impact on approach: Delay has a real price.
Expected answer: Engagement is about 20% below UBS peers; account closures are slightly elevated. Impact on approach: Retention risk is real but not catastrophic.
Expected answer: Mostly front-end and data features that can be built on UBS platforms. Impact on approach: Rebuilding does not require keeping legacy systems alive.
Expected answer: Partly; decommissioning uses platform teams, rebuilds use app teams, but both compete for testing and release slots.
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