🗺️ Phased is Feasible: Country-by-country SAP S/4HANA migration reduces disruption and addresses local requirements effectively.

🔗 Data Consistency Matters: Ensure robust integration between ECC and S/4HANA to avoid data discrepancies during phased rollouts.

📆 Templates Save Time: Creating a global template first prevents repeated customisations and keeps phased rollouts efficient.

🧩 Hybrid Strategies Work: Combining phased and big-bang approaches lets you tailor the migration to your business priorities.

🗣️ Stakeholders are Crucial: Continuous communication and strong governance help maintain momentum and minimise change fatigue throughout migrations.

Migrating from SAP ECC to SAP S/4HANA is a major undertaking that can be executed via a “big bang” (all-at-once) or a phased “trickle” migration. A trickle migration involves moving to S/4HANA in incremental steps – for example, by geographic region, business unit, or module – rather than a single cutover. This phased approach is increasingly used by large enterprises to reduce risk and downtime, especially given the deadline to transition off ECC.

In this blog post, we explore real-life examples of trickle migrations from ECC to S/4HANA, analyze the feasibility of a country-by-country migration strategy (with benefits and challenges), and examine alternative phased rollout patterns. We also provide project management insights on risk mitigation, stakeholder coordination, and best practices for a successful phased SAP migration.

Trickle Migration versus Big Bang: An Overview

Trickle (Phased) Migration: A phased or “wave-based” migration breaks the S/4HANA transition into multiple smaller go-lives. Each wave might focus on specific business units, regions, or modules, enabling a gradual transition. The primary benefit is minimized disruption – only part of the organization transitions at a time – and greater control, since each phase can be tested and validated before the next. This approach suits complex or global businesses by allowing adaptation to unique local requirements and regulatory compliance one area at a time. However, the timeline is longer and managing a prolonged program introduces challenges. Common risks include data inconsistencies (if old ECC and new S/4 systems need to coexist and interface), user adoption fatigue from continuous change over many months, and the danger of an incomplete transition if momentum is lost or parts of the business resist change.

Big Bang Migration: In a big bang, the entire enterprise switches from ECC to S/4HANA in one coordinated event. This yields a shorter overall project timeline and faster realization of S/4HANA’s benefits, as the new system is live for all business functions at once. It also confines disruption to a single cutover window. Yet, the big bang carries higher immediate risk: any issues during go-live can impact the whole organization. The planning and testing effort is immense, and a fallback plan is crucial since failures would have enterprise-wide repercussions.

Big bang is often chosen by smaller or less complex organizations, or when a company can tolerate a full-stop cutover (for example, during a quiet period in business). In contrast, large multinational companies typically lean towards phased approaches to manage complexity and risk.

Feasibility of Country-by-Country Migration

One common trickle strategy for multinationals is migrating country by country (or region by region). This approach is feasible and in fact supported by SAP’s own recommended methodologies. SAP’s Selective Data Transition (SDT) approach explicitly allows phased S/4HANA go-lives, “for example, by country”. Under this model, a company might move a subset of its legal entities or country operations onto S/4HANA while others remain temporarily on ECC, and then continue in waves until all are migrated.

Benefits of a Country-by-Country Approach

• Reduced Business Disruption: Each country rollout is a smaller project, so local operations face shorter downtime and focused change management. The rest of the business can continue on ECC, avoiding a global shutdown. This isolation of impact makes it easier to maintain business continuity.
• Localized Focus and Compliance: Country-specific requirements (taxes, regulations, languages, local business practices) can be addressed in each rollout. This ensures the S/4HANA solution is fully compliant and optimized for that locale before moving on. Highly regulated industries benefit by focusing on one jurisdiction at a time. For example, Bayer AG prepared “localization projects” to tailor a global template to each country’s needs during its S/4HANA rollout.
• Gradual Skill Building: IT teams and end-users can learn and adapt in waves. Lessons learned in early country deployments (pilot countries) inform improvements for subsequent rollouts. This iterative learning reduces risk in later phases and builds internal expertise progressively.
• Spread Out Investment: Rather than one massive budget spike, costs are distributed over a longer period. This can aid budgeting and resource allocation, and allow adjustment of pace if needed. It also means benefits (e.g. improved processes) start accruing in parts of the business earlier, which can help fund or justify later phases.
• Change Management is More Manageable: From a project manager’s perspective, training and stakeholder engagement can be done in smaller, culturally coherent groups. Each country organization can receive high-touch attention during its migration, which might be more effective than a one-size-fits-all global change program.

Challenges and Considerations

• Integration Between Old and New: If one country is live on S/4HANA while others still use ECC, the systems must share data. Companies often need interim interfaces or middleware to sync data (e.g. global finance consolidation, supply chain transactions) between S/4 and ECC. Without careful design, this can lead to data inconsistencies or process breaks. One mitigation is deploying SAP Central Finance as a bridge – feeding financial data from both ECC and S/4 systems into one ledger – to ensure a single source of truth during the transition period.
• Extended Timeline: A country-by-country migration for dozens of countries can take years. During this time, the organization is in flux and must support dual environments. Strong governance is needed to maintain momentum and avoid “project fatigue.” There’s also a risk of external changes (market conditions, new business acquisitions, etc.) intervening mid-program. Companies like Bayer anticipated ~4–5 years to cover ~90 countries, grouping smaller markets into clusters to expedite the rollout. Such a timeline demands sustained executive support and funding.
• Adoption Fatigue: As noted, rolling waves can exhaust teams if not managed well. Employees may have to endure multiple go-lives (especially central teams or IT staff supporting all countries). Clear communication of the vision and incremental wins is crucial to keep morale up. Rotating deployment teams or providing breaks between waves can help.
• Complex Cutover Planning: Each mini go-live still requires careful planning (data migration, cutover, verification) and possibly temporary freezes on changes. Coordinating these activities repeatedly for each country increases overhead. Automation of migration tasks and rehearsals (mock cutovers) for each wave can mitigate errors. Utilizing SAP’s Near-Zero Downtime techniques can also help minimize downtime per wave.
• Cost Overrun Risks: A phased approach can have a higher cumulative cost than a big bang if not managed tightly, due to prolonged project activities and potentially redundant testing efforts. To combat this, successful organizations create a global template at the start – a standardized S/4HANA design that all countries will use with minimal variation. This was Bayer’s strategy: they spent ~1.5 years building a unified global template and only allowed deviations for specific divisions or localizations. A solid template reduces rework and keeps later rollouts efficient and on-schedule.

Case Study: Bayer – Multi-Year Country Rollouts

Bayer AG, a global life sciences company, pursued a country-by-country S/4HANA migration using a template and rollout model. They first established a single global ERP template covering common processes, then handled local requirements via add-on localization projects. After piloting the system in initial countries, Bayer planned a phased global deployment: “around 80% of Bayer’s global sales [migrated] to the new system within three years from template completion,” and roughly 90 countries in total over 4–5 years, with larger countries done individually and smaller countries in clusters. This incremental approach allowed Bayer to carefully manage compliance and change in each market while steadily progressing toward a unified S/4HANA landscape. Key success factors included strong emphasis on using standard SAP processes (to minimize custom development) and shifting any needed custom solutions to side applications integrated with S/4HANA, rather than customizing the core. By adhering to a standard core and leveraging partners for specialized needs (e.g. Trintech Cadency for financial close), Bayer kept the core template clean and easier to roll out globally.

Case Study: E.ON – Regional Waves in a Global Utilities Company

E.ON, one of Europe’s largest energy companies, chose a wave-based trickle migration to S/4HANA to accommodate its hundreds of legal entities across many countries. Instead of one big go-live, E.ON opted to migrate groups of companies in multiple phases. In the first three-year tranche, over 150 E.ON companies were migrated to S/4HANA, with a roadmap to reach a total of 550 companies by 2027. This indicates E.ON’s migration is segmented likely by country or business unit, spreading the effort over roughly 5+ years. The phased approach enabled continuous process optimization between waves, and helped E.ON simultaneously move from on-premise infrastructure to S/4HANA Cloud without disrupting all operations at once. E.ON’s example highlights the feasibility of breaking a massive global conversion into manageable waves. It also underscores the need for robust central program management – coordinating 150+ entity migrations – and maintaining a high level of standardization to ensure all those entities can align on common processes as they converge on one S/4HANA system.

Alternative Trickle Migration Strategies

Besides organizing by country, organizations have employed other phased migration strategies. The “trickle” concept can be applied by module, business unit, or even a hybrid of approaches. Below we explore a few alternatives and examples:

Phased Module Rollouts (Functional Trickle Migration)

Instead of migrating geographically, some companies migrate by functional scope, rolling out S/4HANA module by module. For example, a company might implement S/4HANA Finance first, then later migrate Sales, Procurement, or other processes. This often involves standing up an S/4HANA system to handle specific processes while the rest remain on ECC. A common scenario is deploying Central Finance (CFIN) on S/4HANA as an initial phase. In a Central Finance approach, financial accounting is replicated in real-time from legacy ECC (and even non-SAP systems) into a new S/4HANA instance. This gives an organization a consolidated financial platform on S/4HANA without disturbing operational ECC systems, essentially “focusing the first SAP S/4HANA phase on finance-related processes”.

Case Example – Kyndryl (Finance-First Hybrid): Kyndryl, the IT services company spun off from IBM, undertook a multi-step S/4HANA implementation that illustrates a phased module rollout. Kyndryl opted for a clean-slate (greenfield) S/4HANA implementation, but staggered the deployment across its 66 countries by process. They started with Central Finance on S/4HANA as a unified reporting layer, then expanded to a full Finance and Quote-to-Cash implementation, and finally integrated Procurement processes using SAP Ariba and Fieldglass. This sequence allowed Kyndryl to achieve early wins (e.g. central financial reporting) and build on that foundation. After the finance-centric phases, Kyndryl executed two major country rollout waves – first transitioning 24 countries that were already on SAP ECC, and later 42 countries that had non-SAP legacy systems. By phasing by module/process first and then by country waves, they combined the advantages of both functional and regional trickle strategies. Kyndryl’s approach demonstrates that a phased module rollout can be part of a broader hybrid migration plan, providing flexibility to address high-priority processes first (finance) while pacing out the rest of the transition.

Benefits of module-based phasing include giving specific departments (e.g. Finance) an improved system early, and reducing the complexity of each cutover by limiting scope. However, this approach demands robust integration between the new S/4 module and remaining ECC functions. For instance, if only Finance is on S/4HANA initially, data from ECC modules (like sales orders, invoices, etc.) must flow correctly into S/4 Finance for financial postings. This is why Central Finance (which is designed to pull data from ECC) is a popular tool – it provides built-in integration for finance data. Companies must also ensure that users understand which system to use for which tasks during the interim period to avoid confusion. Clear process maps and possibly interim “bridging” user interfaces can help during a phased module rollout.

Business Unit or Division-Based Migration

Another trickle migration variant is to proceed by business unit, product line, or division. In conglomerates or firms with semi-autonomous divisions, each unit might have its own ERP or at least loosely coupled processes. This lends itself to migrating one division at a time into S/4HANA. The approach is similar to country-by-country, except the segmentation is organizational rather than geographic. The benefits are comparable – contained risk per go-live and ability to tailor to each unit’s needs. For example, a manufacturing company might first migrate its Consumer Products division to S/4HANA, while the Industrial division remains on ECC until a later phase. This could be driven by differing timelines (perhaps one division is more ready or has a stronger business case for earlier migration).

SAP experts note that large enterprises with complex operations often use wave-based migrations to handle different business units separately. By doing so, they can “manage complexity and adapt to unique requirements” of each unit. Highly diversified companies sometimes treat each business unit as a mini-project under a program umbrella. The key challenge here is if the business units share one ECC system instance; in that case, carving out one unit’s data and processes to move to S/4 while others remain can be technically complex (it might involve a landscape transformation to split the system). Tools and services under SAP’s Selective Data Transition can facilitate this by extracting specific company codes or data sets into a new S/4 system.

Case Example – E.ON and JBS: E.ON’s earlier mentioned approach can be viewed through a business-unit lens as well – each regional company (or group of companies) was treated as a wave to migrate. Another example is JBS USA, a global food processing firm, which embarked on a multi-year S/4HANA migration in waves. JBS leveraged a wave-based approach with Selective Data Transition, using specialized tools to migrate only relevant data and transform their structures (like a new global chart of accounts) as they went. Their roadmap included seven waves from 2022 to 2025, each involving preparation, build, test, and deployment phases. By phasing the migration, JBS was able to implement over 50 key innovations and eliminate a lot of historical custom code (“back to standard”) gradually, rather than trying to do it all in one go. This highlights how a division or wave-oriented strategy not only phases the technical migration, but also allows stepwise process improvements and data cleansing.

Business unit migrations require careful consideration of any cross-division processes. If divisions share customers, products, or supply chains, the first unit moved to S/4 might still need data from those on ECC. Mitigation can include interim data replication or the temporary use of separate instances with consolidation at a higher level (similar to the Central Finance concept but for other data domains). If divisions are fairly independent, this strategy can work very smoothly.

Hybrid Strategies (Mixed Approach)

In practice, many large SAP programs use a hybrid migration strategy, combining elements of phased and big bang approaches to balance risk and speed. A hybrid might mean doing several phased rollouts for less critical or less integrated parts of the business, and then executing a final big bang for the remaining core. For example, one global manufacturer decided to “start with a wave-based migration for its subsidiaries in less critical regions… to fine-tune the process and address issues gradually,” then later perform a big bang migration for its main production facilities and headquarters. This way, the most critical business areas experienced only one cutover (reducing their risk), whereas smaller areas helped pilot the approach and did not hold up the overall timeline.

Another hybrid approach is selective data migration combined with reimplementation. Also known as the Bluefield approach (blending greenfield and brownfield), this involves standing up a new S/4HANA system (like in a reimplementation) but migrating selective data from ECC into it, possibly in multiple waves. The SAP SDT Engagement is essentially enabling this kind of hybrid: you can consolidate or split systems, “introduce new business processes… while protecting prior investments,” and either do one big go-live or multiple phased rollouts under the same project. Many consulting firms also offer methodologies under various names that boil down to hybrid migration – keeping what’s valuable from the old system (master data, open items, transactional history as needed) but redesigning processes where beneficial, and phasing the migration to manage risk.

Case Example – Large Retail (Coop) Hybrid: Coop Group (a major Swiss retailer) pursued what could be described as a hybrid strategy: they had two large ECC systems (retail and trading) that needed to move to S/4HANA. They opted to migrate both systems together (effectively a big bang for scope), but used a Near-Zero Downtime technique to achieve the go-live within an 18-hour cutover window. While this was more big bang than trickle, it shows how hybrid thinking (combining new technology to reduce downtime risk within a big cutover) can be applied. On the other end, we have examples like Kyndryl (mentioned above) which combined a greenfield implementation with phased deployments – effectively a hybrid of new implementation and phased rollout.

Hybrid strategies are tailored to an organization’s specific landscape. They often require more up-front planning to decide which parts will follow which approach. Key to success is “picking the right components of your business for each method” – for instance, stable parts of the business could be moved in waves, whereas time-sensitive or highly integrated processes might be deferred to a carefully orchestrated final cutover. The hybrid approach aims to get the best of both worlds: the lower risk of phased transitions in some areas and the speed/clean-slate benefits of a targeted big bang in others.

Project Management Insights for Trickle Migrations

Executing a trickle migration in an SAP ERP environment is a complex program management exercise. Project managers need to coordinate across technical teams, business users in various units or countries, and executive stakeholders for an extended period. Below are key considerations and best practices for managing such a project successfully:

Risk Mitigation Strategies

Managing risk is paramount since a phased SAP migration introduces ongoing operational risk (during each go-live and between them). Some mitigation strategies include:

• Ensure Data Consistency: Mitigate the risk of data discrepancies between ECC and S/4HANA by implementing robust integration and reconciliation processes. For a country-by-country or module rollout, plan how data will flow between legacy and new systems. Options include using SAP Central Finance for financial data alignment, real-time replication tools for master data, or temporary interfaces for cross-system transactions. Thorough data validation after each wave is critical. As one best practice, only migrate necessary historical data and leave obsolete data behind – this reduces complexity and potential errors. For example, JBS (in its wave migration) migrated only the last 2 years of transactional history into S/4HANA to reduce data volume and complexity.
• Minimize Downtime: Each migration cutover should employ techniques to reduce business downtime. SAP’s Near-Zero Downtime (NZDT) or similar tools can synchronize data while the system is live and then apply delta changes in a short final cutover. This was crucial for cases like Coop’s 15-hour migration, and it can be applied in trickle migrations as well to make each country or module go-live almost seamless to end-users. Dry-run cutovers (repeated rehearsals) are recommended to fine-tune timing and catch issues.
• Strong Governance and Monitoring: Treat the program as a series of mini-projects with a centralized governance structure. Establish a Transformation Management Office that tracks progress, issues, and risks across all waves. Regular risk assessments should be conducted at the end of each phase and ahead of the next. If one rollout uncovers issues (e.g., data quality problems or a custom code gap), allocate time to resolve these globally before they affect the next wave. This iterative risk management ensures the later deployments run smoother thanks to lessons learned.
• Scope Control & Template Discipline: One risk in multi-phase projects is scope creep – each local unit may request new features or deviations. A clear global template and strong change control board can mitigate this. As seen in Bayer’s case, sticking to standard processes in S/4HANA was a guiding principle. Only truly critical variations were allowed, and even those were handled by ancillary solutions rather than core modifications. This discipline reduces the risk that the project overruns time or budget due to custom development in each phase.
• Parallel Operations and Fallbacks: During transition, some processes might temporarily run in parallel on old and new systems (for example, running financial ledgers in both ECC and S/4 until a full cutover). Have clear criteria for when to switch off the old process and ensure a fallback plan if something goes wrong. For each wave, define a “no-go” decision checkpoint — if critical issues are found, the wave can be deferred without impacting the overall business (other countries still on ECC can carry on). This flexibility in scheduling is a benefit of trickle migrations, but it requires pre-planned contingency windows.
• Testing and Quality Assurance: With trickle migrations, testing is an ongoing activity. Establish an automated testing regimen to repeatedly test end-to-end processes that span old and new systems. Before each go-live, conduct integration testing between ECC and S/4 (if they will co-exist) and full user acceptance testing for the scope of that wave. Consider a dedicated testing team that moves from wave to wave, carrying knowledge forward. Also, after each go-live, institute a hypercare phase where the project team closely monitors system performance and user issues, ready to resolve any post-migration hiccups. This “hypercare” support ensures each rollout stabilizes before the team moves on.

Stakeholder Coordination and Change Management

Successful phased migrations hinge on excellent stakeholder management. Unlike a one-off project, you must keep stakeholders engaged over a longer timeline and through multiple go-live events.

• Executive Alignment and Vision: Ensure top executives understand the phased strategy and the end-state vision. Remind them (and the organization) of the business drivers for the migration. Tying each phase’s outcomes to tangible business value keeps leadership committed. For example, if the goal is to enable faster financial close or better analytics, report improvements from the first migrated units to demonstrate progress. Kyndryl noted that aligning the technical project with preferred business outcomes (like streamlined IT landscape, data centralization) helped “increase buy-in from leaders across the organization”. Continuously communicate how the migration supports strategic objectives.
• Local Stakeholder Engagement: In a country-by-country rollout, involve local business leaders early. Each country or unit should have a sponsor and a change champion on the ground. These stakeholders help tailor the change approach to local culture and business practices. They also facilitate training and can proactively identify local business quirks that need attention (e.g. specific reports or integrations used only in that location). Local involvement mitigates resistance and smooths the cutover since local teams feel ownership.
• Clear Communication Plan: Maintain transparent communication with all stakeholder groups throughout the program. Different audiences have different concerns – business users care about minimal disruption and ease of use, IT staff focus on technical issues and integration, executives watch timeline, costs, ROI, etc. Craft communications appropriate to each: for example, periodic executive briefings on overall progress and value achieved, detailed technical updates for IT, and simple, jargon-free notices to end-users about upcoming changes. One best practice is to provide regular status updates (e.g. a monthly newsletter or dashboard) to keep everyone informed. Salesforce did this for a large data migration, sending weekly update emails which resulted in “95% of stakeholders felt well-informed”. Frequent, honest communication builds trust and helps preempt rumors or misinformation that can derail change efforts.
• Training and Change Readiness: With a phased approach, training is not a one-time event but a rolling wave as well. Develop a comprehensive training plan for each phase, leveraging a “train-the-trainer” model if possible. As each country or unit goes live, ensure users are comfortable with S/4HANA (and new Fiori interfaces, etc.) through hands-on workshops and e-learning. Also prepare support materials like quick reference guides specific to any process changes. It’s wise to pilot the training in the first rollout and refine it for subsequent groups. Additionally, consider organizational change management (OCM) initiatives: readiness surveys, super-user networks, and feedback channels. JBS, for instance, listed OCM as a crucial element in their lessons learned for multi-wave S/4HANA migration. Managing the human side of change at each step helps maintain productivity and morale.
• Stakeholder Support Structure: Establish governance that involves key stakeholders. A steering committee with executive sponsors, and regional or functional leaders can meet regularly to review progress and issues. This ensures continued stakeholder alignment. Also, celebrate milestones – when a wave is successfully delivered, acknowledge the work of teams involved and share success stories. Recognizing achievements (e.g. “Asia region successfully on S/4HANA – zero disruption to customers and 10% faster order processing recorded!”) boosts confidence in the upcoming phases and keeps stakeholders invested in the outcome.

Best Practices for Successful Trickle Migration

For project managers overseeing SAP trickle migrations, the following best practices can serve as actionable guidance:

• Develop a Global Template Early: As demonstrated by Bayer’s approach, invest time upfront in designing a global S/4HANA template that covers common business processes. This template acts as the blueprint for all phases, ensuring consistency. Define which elements are global vs. local. By locking down the core design, you prevent each country or unit from reinventing the wheel (or worse, diverging in processes). Adjustments for local laws or business models can be configured as extensions to the template, not a full rewrite. A solid template significantly accelerates later rollouts and reduces retrofits.
• Start with a Pilot (or Least Complex) Scope: Kick off the migration with a pilot wave that is representative but manageable – for instance, a smaller country or a non-critical business unit. This pilot is where you fine-tune your migration approach, tools, and cutover runbook. The lessons and confidence gained will inform all subsequent deployments. Many companies choose their home country or a single division as a pilot before global rollout, or they might select one module (like Finance) as the pilot phase. Ensure the pilot has enough importance to test the system rigorously, but enough flexibility that if issues occur, they won’t be catastrophic.
• Use Automated Tools and Accelerators: Leverage SAP and third-party tools designed for migration. The SAP S/4HANA Migration Cockpit can assist in migrating data from ECC to S/4 for each wave. Selective Data Transition tools (often provided by expert partners) help carve out specific data (company codes, etc.) for phased migrations. Test automation tools can greatly speed up repeated testing cycles. Using a proven toolset reduces manual effort and errors. For example, JBS utilized an “Enterprise Transformer” tool to execute their SDT-based data migration in waves, and automated custom code adaptation which saved weeks of effort.
• Parallel Run and Cutover Rehearsals: In phased migrations, you may sometimes run old and new systems in parallel (for verification) or maintain a read-only legacy instance for reference after a wave. Plan how long to keep legacy accessible and how to gradually decommission it. Conduct multiple cutover simulations in a sandbox or staging system for each wave – this ensures your team knows the sequence of activities down to the minute. Rehearse with production-sized data if possible to catch any performance bottlenecks. A detailed cutover plan (hour by hour) and a clearly defined “go/no-go” checkpoint before final cutover are must-haves.
• Focus on Data Cleansing and Master Data Harmonization: Use the phased project timeline as an opportunity to improve data quality. Before migrating each wave, cleanse the data (remove duplicates, correct errors) and harmonize master data across sources. If, for example, you are consolidating multiple ECC systems into one S/4, ensure customer and material masters are aligned. Schütz Group’s preparatory project for S/4HANA is a good example – they harmonized finance and controlling data (merging 28 controlling areas, introducing a group currency, standardizing charts of accounts) prior to migration, to “reduce the complexity of the upcoming migration”. Clean, uniform master data will make the migration smoother and the resulting S/4 system more reliable for analytics and reporting.
• Maintain Flexibility in Plans: While structure and templates are important, retain some flexibility in your rollout schedule. Unexpected challenges may arise (e.g., a country’s deployment needs to slip due to a regulatory project, or business priorities shift). Design your transformation roadmap to accommodate change – for instance, you might have planned “contingency waves” or buffer periods. According to Kyndryl’s experience, a transformation strategy should be “structured enough to keep… on track yet flexible enough to accommodate unforeseen obstacles and opportunities”. In practice, this could mean being ready to adjust wave content or sequence based on interim findings. Continually revisit the roadmap at major milestones and tweak as needed with stakeholder agreement. A phased approach’s advantage is you can pivot the later phases if something isn’t working – just ensure you have the governance to do so intentionally, rather than ad hoc.
• Robust Change Management Program: Don’t treat the migration as just a technical upgrade. Each phase is a business change event. Implement a continuous change management program: conduct impact assessments for each wave, update training materials, communicate upcoming changes to users well ahead of time, and provide ample support post-go-live. Establish two-way feedback loops – for example, after each rollout, survey the end-users and key stakeholders about what went well or what pain points remain. Use that feedback to improve both the solution and the approach for subsequent waves. Keeping the organization engaged and heard throughout the journey greatly increases the likelihood of adoption and project success.

Conclusion

Trickle migrations – whether executed country-by-country, by business unit, or by module – offer a viable path for large organizations to transition from SAP ECC to S/4HANA with controlled risk. Real-world case studies (Bayer, E.ON, Kyndryl, JBS, and others) demonstrate that with careful planning, multi-year phased migrations can succeed and even provide interim benefits along the way. The key is to balance the granularity of phases with the complexity of managing them. If done right, a phased approach minimizes disruption, caters to local needs, and builds momentum through incremental victories. However, it requires diligent project management: robust risk mitigation (to handle data consistency, integration, and timeline risks), proactive stakeholder coordination (to maintain alignment and morale), and strict adherence to best practices (template governance, thorough testing, and change management).

For project managers, overseeing a trickle migration is akin to running a marathon in sprints – each phase must be executed with discipline and energy, while keeping eyes on the finish line of full S/4HANA adoption. By learning from those who have gone before and by applying these structured insights, project leaders can confidently guide their organizations through a phased SAP migration that delivers value at each step and ultimately achieves a smooth, successful transformation to S/4HANA.