Clean Core Extensibility: Future-proof SAP S/4HANA extensions and modern ABAP
Why Clean Core Extensibility is changing the playing field for SAP S/4HANA extensions
Over the years, many SAP landscapes have become too complex: customer-specific logic, direct table access, and undocumented interfaces slow down upgrades and innovations.
With the Clean Core approach, SAP is pursuing a clear strategy; Clean Core means keeping the core of SAP S/4HANA so clean that it remains stable, upgradeable, and maintainable in the long term. At the same time, companies should retain the flexibility they need to continue implementing their specific requirements for SAP S/4HANA in extensions.
Clean Core Extensibility thus creates an opportunity to use modern ABAP and other technologies in a way that accelerates innovation and reduces technical debt.
Why Clean Core is crucial for SAP software
The ERP system is the digital backbone of a company. In many companies, this backbone has been individualized and adjusted to fit the specific requirements of the respective company's business, oftentimes resulting in a system containing many modifications and on-stack customer-specific developments. During upgrades and migrations, this may lead to the following problems:
- Lack of standardization: Departments work with different processes, some of which are not defined.
- Excessive customization: In-house developments have a profound impact on the standard.
- Poor data quality: Different processes lead to inconsistencies and ambiguity in the data.
The Clean Core principle solves these problems by protecting standard processes and, for example, clearly decoupling extensions for SAP S/4HANA from the core. This creates:
The four Clean Core Levels: From "clean" to "problematic"
SAP further developed its previous 3-tier model in the summer of 2025 and is now introducing a four-tier clean core level concept for SAP S/4HANA enhancements. The classification into the 4 clean core levels is based on their update security:
Level A – The premier league: SAP Build Extensions with ABAP Cloud
Only officially approved APIs and modern ABAP Cloud are used here. Level A extensions use ABAP Cloud and can be implemented as on-stack extensions or side-by-side extensions:
Level B – Proven classic APIs
This is where the “old friends” come into play: BAPIs and established frameworks such as ABAP List Viewer (ALV) in Dynpro or WebDynpro. Although these are no longer cutting edge, they are well documented and largely upgrade-stable for Clean Core-compliant SAP S/4HANA enhancements.
Level C – Use of SAP internal objects with risk and changelog
Applications are at Clean Core Level C if they use internal objects that are technically usable but have not been declared by SAP as released, recommended, or cloud-ready. The use of such objects is not officially recommended, and future functionality is not guaranteed. However, company-specific developments can be found in many SAP S/4HANA or SAP ERP systems – SAP will therefore provide a changelog for SAP objects that enables customers to respond early to future incompatibilities after upgrades and to adapt customer-specific developments in their SAP systems that use such objects.
Developments at Clean Core Level C can therefore only be considered clean to a limited extent.
Level D – Not recommended extension options
Modifications, access to “noAPI” objects, implicit enhancements, or direct write access to SAP tables belong in Level D. These enhancements are not recommended. They jeopardize the Clean Core principles and should be collected on a remediation list and revised.
Objects classified as “noAPI” can be identified via the Cloudification Repository.
On-Stack vs. Side-by-Side: When should I use which for SAP S/4HANA extensions?
Clean Core Extensibility recognizes two main paths for SAP S/4HANA extensions:
| Option | On-Stack Extensibility | Side-by-Side Extensibility |
|---|---|---|
| Runtime environment | Running directly on SAP S/4HANA | Running on SAP Business Technology Platform (SAP BTP) |
| Suitable for | Extensions close to the core, such as
|
|
| Technology | modern ABAP with ABAP Cloud | ABAP, CAP, Java, JavaScript, Python |
In a hybrid scenario, a mixture often makes sense: core logic on-stack, user interfaces and additional functions side-by-side.
SAP Build as the central development platform for Clean Core Extensibility
With SAP Build, SAP has created a unified platform for Clean Core-compliant SAP extensions that supports both pro-code and low-code development. Of particular interest is the integration of the AI co-pilot Joule, which helps developers write modern ABAP code and create workflows.
This powerful tool is designed to significantly increase development speed according to Clean Core Extensibility, especially for mixed teams of ABAP cloud developers and key users.
The reality: “Stay Clean” and “Get Clean” for SAP extensions
In practice, companies must tackle two challenges simultaneously for their clean core strategy:
Stay Clean – Keeping new SAP enhancements clean
- Establish clear governance structures for clean core extensibility
- Critically review every extension request
- Introduce automated code quality checks for ABAP Cloud
- Consistently enforce development guidelines for modern ABAP
Get Clean – Reducing existing technical debt in SAP S/4HANA extensions
- Measure current clean core status with KPIs
- Introduce the scout principle: always leave code cleaner than you found it
- Set realistic but ambitious goals for debt reduction
- Migrate legacy code to ABAP Cloud
Measurable KPIs for the success of the clean core strategy
Without measurement, there can be no management. You should keep an eye on the following KPIs for your clean core strategy:
- Clean Core Share: What percentage of your SAP S/4HANA extensions correspond to which level? See SAP Note 3565942
- Technical Debt Score: Quantified assessment of technical debt
- ABAP Cloud Adoption Rate: Proportion of extensions with modern ABAP
- Unused Code Share: How much dead code do you have in your system?
- Business Modifications: Number of modifications to the SAP standard
What does Clean Core mean for your SAP S/4HANA system?
The Clean Core is becoming more and more a necessity for future-proof SAP S/4HANA extensions. The good news is that the switch to Clean Core Extensibility is feasible, but it requires a clear strategy and consistent implementation. Companies that do not switch to ABAP Cloud and modern Clean Core practices now will encounter problems with system updates in the medium term.
For companies that currently still rely on SAP ECC and are planning to make the leap to SAP S/4HANA, this is a particularly exciting challenge and opportunity at the same time. This offers the opportunity to start with Clean Core-compliant extensions in SAP S/4HANA and modern ABAP right away and avoid carrying over old technical debt.
Conclusion: Clean Core Extensibility – Act now, reap the benefits later
Clean Core Extensibility with ABAP Cloud is more than just a technical trend – it is the foundation for the digital future of your S/4HANA system. Companies that consistently switch to modern ABAP and Clean Core principles now will be able to operate more agilely and cost-effectively in a few years' time.
Therefore, the question is not whether you will implement Clean Core principles for your SAP S/4HANA extensions, but how quickly you will start using ABAP Cloud and Clean Core principles. Because one thing is certain: the pressure on companies with “unclean” extensions will increase in the future.
Fundamentals and Clean Core Extensibility
Does Clean Core mean that I can no longer do any individual SAP developments?
No. Clean Core simply means that customizations must be developed in a clean and upgrade-stable manner. You can still implement all necessary customizations – just with approved APIs instead of modifications.
Can I already apply clean core principles in SAP ECC?
Yes, partially. Side-by-side extensions on SAP BTP already work with SAP ECC today. For on-stack developments, you should at least prefer classic APIs (Level B) and avoid modifications (Level D). This will give you a better starting point for the later switch to SAP S/4HANA.
How can I determine the Clean Core level of my existing extensions?
Use the ABAP Test Cockpit with the appropriate check variants (see SAP Note 3565942). These automatically analyze your custom code and assign it to the appropriate levels. It's even easier with the RISE with SAP Methodology Dashboard.
ABAP Cloud and modern development
What is the difference between ABAP Cloud and “normal” ABAP?
ABAP Cloud is a restricted but more secure version of ABAP. The compiler only allows access to approved APIs, thereby preventing “unclean” developments. In return, you get upgrade stability and cloud readiness. Classic ABAP remains available, but is only partially Clean Core-compliant.
Can I migrate my existing ABAP developments to ABAP Cloud?
That depends on the code. Clean developments with approved APIs can often be ported with little effort. Coding using SAP-internal objects or modifications requires more extensive modifications, such as the creation of wrapper function modules, which are then classified as cloud-ready.
Do I have to pay extra for ABAP Cloud?
No. Separate costs are only incurred for SAP BTP for Side-by-Side Extensions (Level A).
Practical implementation
How long will the transition to Clean Core Extensibility take?
That depends on your current code base. You can implement the governance structures immediately for new developments in your SAP system landscape. Existing code should be gradually reworked; plan for this to take 2-3 years, depending on the scope of your extensions.
Which extensions should I renovate first?
Prioritize Level D extensions (modifications, noAPI), as these pose the highest risk and quickly become cost drivers during upgrades. Next come Level C extensions, which are frequently used or business-critical.
What will happen to my extensions during the next SAP upgrade if they are not Clean Core-compliant?
Level D extensions can cause errors during updates and upgrades. Level C extensions receive advance warning of incompatible changes via the SAP change log. Levels A and B are upgrade-stable.
What should I do if there is no approved API for my use case?
You have three options:
1. Request release of the object from SAP
2. Develop a temporary Level C extension and monitor the changelog for SAP objects
3. Solve the use case with side-by-side extensions
Clean Core strategy
How much does the switch to Clean Core cost, and when does it pay off?
The initial costs for governance development and code remediation typically pay for themselves within a few years through reduced upgrade costs and faster development cycles. New projects are often even cheaper with Clean Core.
Can I also introduce the Clean Core principles gradually?
Yes, that is actually the recommended approach. The Clean Core principles are intended as guidelines to help you implement your SAP enhancements. Start with new developments based on Clean Core principles and gradually refactor existing code. This will allow you to gradually gain experience.
