The migration roadmap (0 → ATC-green)
What you'll learn
Measure live usage first, stage the checks from broad to strict, baseline the old debt, retire unused code, and warn the business about any behaviour changes.
- Start by measuring live usage (SCMON) to scope around code people actually run.
- Stage the check variants: DEFAULT, then S4HANA_READINESS, then CLOUD.
- Baseline existing debt and set a decommission policy for unused code.
A move toward Clean Core is a sequenced programme, not a single switch. The first step is to measure what is actually used: SAP's usage logging (SCMON) shows which custom code real users run, so you scope effort around live code instead of a paper inventory. Code that nobody runs may simply be retired.
Next, stage the automated checks from broad to strict. Teams typically run the general DEFAULT rulebook first, then the release-readiness variant (S4HANA_READINESS) to surface what an upgrade will break, then the strictest CLOUD variant for true Clean Core. You baseline the existing debt so the team only chases new issues, and you set a decommission policy so unused code is removed on a schedule rather than carried forever.
Finally, plan the business communications. Some clean-up changes behaviour that end users will notice, so the roadmap must include who tells the business, and when. The destination — often described as 'ATC-green' — is a state where the agreed rulebook passes with no new high-priority findings.
Key points
- Start by measuring live usage (SCMON) to scope around code people actually run.
- Stage the check variants: DEFAULT, then S4HANA_READINESS, then CLOUD.
- Baseline existing debt and set a decommission policy for unused code.
- Plan business communications for any change end users will notice.
Examples
Quarter 1: measure usage and baseline. Quarter 2: clear new DEFAULT findings. Quarter 3: pass S4HANA_READINESS and brief the business on two behavioural changes. Quarter 4: turn on the CLOUD variant for new work.
Source notes: clean-core-curriculum (business synthesis)
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