What Clean Core is, and why it became a priority
SAP's concept for keeping the S/4HANA core close to the standard, the five dimensions it covers, Levels A to D, what it is not, and where SAP itself recommends starting.
"Clean Core" has become one of the most repeated expressions in SAP projects, in RISE with SAP proposals, in upgrade plans and in SAP Cloud ALM dashboards. As with every buzzword, it is used in different ways. It is worth going back to what SAP means by it.
The idea in one sentence
Clean Core means keeping the ERP core as close as possible to the SAP standard, and building everything that is specific to the company in a way that does not break when SAP updates the system.
The "core" is S/4HANA as SAP delivers it. "Clean" does not mean empty: it means no modifications to SAP code, with extensions connected to it only through points that SAP considers stable.
The five dimensions
SAP describes Clean Core in five dimensions, and makes it clear that the concept is not only about code:
| Dimension | What being "clean" means |
|---|---|
| Processes | Business processes close to standard best practices, without unnecessary customization |
| Extensions | Custom functionality built without modifying SAP, connected to the core only through stable points |
| Data | Consistent master, configuration and transactional data, without accumulated clutter |
| Integrations | Communication with other systems through standard scenarios and APIs (OData, SOAP, events) |
| Operations | Ongoing governance and monitoring, so the core stays clean after the project |
The articles in this series cover the extensions dimension, where Z code lives, because it is the one currently measured in SAP Cloud ALM.
Levels A to D
Since August 2025, SAP classifies each extension into four levels. They replaced the former three-tier model (tier 1, 2 and 3), and SAP itself compares them to an energy efficiency label:
| Level | What it is | Status |
|---|---|---|
| A | Only interfaces released by SAP, with a stability contract: code in ABAP Cloud or applications on SAP BTP | Clean Core |
| B | Classic APIs, such as BAPIs, that SAP experts have identified as stable, even without a formal contract | Clean Core |
| C | SAP internal objects, such as direct table reads. SAP can reclassify them at any time, up or down | Conditionally clean |
| D | Usage outside the extension rules: objects marked as not-to-be-released (no API), modifications, implicit enhancements and direct writes to SAP tables | Not Clean Core |
An extension gets the worst level among the ones it uses. The points calculation that SAP Cloud ALM derives from this is described in How SAP Cloud ALM calculates Clean Core debt.
Why it became a priority
- More frequent updates. S/4HANA receives updates regularly, and each one requires testing and fixing the custom code that depends on what changed. The cleaner the core, the lower that cost each time.
- SAP started measuring it. Since the end of 2025, the RISE with SAP dashboard in SAP Cloud ALM shows, system by system, how objects are distributed across levels and a debt score in points. The topic moved out of technical discussions and onto the management dashboard.
- The path to the cloud. Code in ABAP Cloud, Level A, already follows the rules of SAP's cloud editions. Classic code, even at Level B, has to be redone before it goes to Public Edition or to SAP BTP.
How to extend without polluting the core
SAP offers three paths, which can be combined:
| Path | What for | Example |
|---|---|---|
| Key user (in the system itself) | Adjustments made by key users through Fiori apps, without classic programming | Fields and simple logic added to a process |
| Development in S/4HANA itself (on-stack) | Custom code in the same system, in ABAP Cloud, using only released APIs | A company business rule in a standard business object |
| Side-by-side | Separate applications on SAP BTP that talk to S/4HANA through APIs | An app for suppliers or an integration with another system |
What falls outside Clean Core is the uncontrolled classic path: modifying SAP code, writing directly to SAP tables and using internal objects that SAP can change in any update.
What Clean Core is not
- It is not "zero Z code". It is custom code connected to the core through stable points. A Z object in ABAP Cloud, which uses only released APIs, is at Level A; a classic program with no findings at all stays at B (see Why a program with a classic screen stops at Level B).
- It is not all or nothing. A classic program that uses BAPIs and other classic APIs is at Level B, and B counts as Clean Core.
- It is not only for those moving to the cloud. An on-premise system with a clean core upgrades faster, with less testing and less risk.
- It is not a project with an end date. Without governance, new code pollutes the core again. That is why operations is one of the five dimensions.
Where SAP recommends starting
SAP's Clean Core white paper proposes an order of priority for custom code:
- Level D first. SAP calls for immediately fixing what is outside Clean Core.
- Code nobody uses. SAP estimates that about 60% of customers' Z code is not used. The SCMON and SUSG tools show what does not run; deleting it is the cheapest fix there is, starting with what is at D.
- Reduce Level C as much as possible, replacing internal objects with released or classic APIs.
- "Stay clean" for new code: nothing new may enter C or D. ABAP Cloud for new development and an ATC check before each transport ensure this. Organizing code into software components helps avoid hidden dependencies (see Software components in ABAP Cloud: who can call whom).
- "Get clean" for legacy code: reduce the debt gradually, with a target of around 10% per year, using every change to an object to leave it cleaner than it was.
For progress to show up where management looks, SAP recommends importing the ATC result into SAP Cloud ALM every week.
Sources
- SAP, Clean core extensibility (white paper), August 2026 edition.
- SAP, Extend SAP S/4HANA in the cloud and on premise with ABAP based extensions (ABAP Extensibility Guide), version 2.3, August 2025.
- SAP Help, SAP Cloud ALM, Extensibility (RISE with SAP Methodology dashboard).
- SAP Learning, Discovering the Clean Core Concept.