The decision most sponsors cannot defend
Ask a program sponsor which S/4HANA path their organization is taking and you will usually get a confident answer. Ask why that path beats the other two and the room goes quiet. The path was often chosen for you — by an implementation partner with a preferred playbook, by a tooling vendor, or by inertia. That is a problem, because the clock on this decision is a board-level risk item: SAP’s mainstream maintenance for SAP Business Suite 7 core applications runs until the end of 2027, with optional extended maintenance available for three years from the beginning of 2028 until the end of 2030 at a premium of two percentage points on the maintenance basis. On the other side of the move, SAP has stated an innovation commitment for S/4HANA until the end of 2040. The runway is finite and the destination is durable; what remains is choosing the road.
SAP’s three official roads — not the marketing names
Strip away the vendor synonyms and SAP defines exactly three transition scenarios: new implementation (what the market calls greenfield), system conversion (brownfield), and selective data transition (often sold as “bluefield” — a label SAP itself does not use as a scenario name). Every hybrid a vendor pitches you is one of these three wearing a different jacket, and mapping the pitch back to SAP’s terminology is the first act of diligence.
Brownfield: conversion in place, with real mechanics underneath
A system conversion turns your existing SAP ERP system into an S/4HANA system in place, executed by the Software Update Manager (SUM). The mechanics matter more than the label. SAP’s Database Migration Option (DMO) combines the software update with the database migration into a single tool run; standard DMO is an in-place procedure that changes only the database, while “DMO with system move” relocates the system to a different environment in the same pass. For organizations where the downtime window is the binding constraint, downtime-optimized DMO migrates selected large application tables while the system is still up, shrinking the business-downtime phase — and DMO keeps the source database intact as a fallback, so a SUM reset remains available if the run goes wrong.
Brownfield’s honest profile: lowest process-redesign effort, full retention of historical data, fastest transition of the three in SAP’s own comparison — and full retention of your custom-code estate and process debt, which is either an asset or a liability depending on how disciplined the last fifteen years were.
Greenfield: the reset, priced honestly
A new implementation builds a fresh S/4HANA system and adopts SAP Best Practices through a fit-to-standard approach under the SAP Activate methodology. You get the clean core, the standard processes, and the chance to shed every workaround that no longer earns its keep. You pay for it in the highest process-redesign effort of the three paths, and — in SAP’s own framing of the scenario — you do not carry historical transactional data into the new system. Any partner selling greenfield as painless is selling; the redesign effort is the point.
Selective data transition: the middle road, with a caveat nobody quotes
Selective data transition (SDT) combines redesign with retained history: SAP describes it as covering the migration of relevant business data from SAP ERP to SAP S/4HANA, enabled by SAP Landscape Transformation tooling, with “shell conversion” and “mix-and-match” approaches that let you selectively carry configuration, ABAP repository objects, master data, and chosen slices of historical transactions.
Two facts about SDT rarely make it into vendor decks. First, it is an official SAP support engagement, established in 2020 as an expert group of four named companies: cbs, Natuvion, SAP, and SNP. Second — and this is the caveat sponsors are almost never shown — SAP explicitly does not certify, qualify, or endorse partner tools, and issues arising from non-SAP tools are not covered by SAP Support Agreements. SDT can be exactly the right road. It should be chosen with that support-coverage boundary written into the risk register, not discovered during an incident.
The four criteria that make the choice defensible
In our delivery practice at IOTEK, we force the path decision through four questions before any partner preference enters the room. (This rubric is IOTEK’s method for structuring the decision, not an SAP-published standard — though the ordering it produces aligns with SAP’s own scenario comparison.)
- Customization level. How much of your custom code still earns its keep? A heavily customized system with living, valuable differentiation argues for brownfield or SDT; a system encrusted with dead code argues for a reset.
- Data volume and quality. Clean, trusted history is worth carrying; polluted history carried into a new system is debt with a new address.
- Downtime tolerance. What can the business actually absorb? Downtime-optimized DMO changes this calculus for brownfield — but note that specific downtime hours are landscape-dependent, and any number quoted before your own rehearsals is illustrative at best.
- Process-redesign appetite. Fit-to-standard is an organizational commitment, not an IT setting. If the business will not show up for redesign, greenfield’s core benefit evaporates.
Score the paths against those four honestly and the recommendation usually writes itself — and, more importantly, survives cross-examination.
The diligence gate before any path is committed
Whatever the scoring says, two SAP tools belong in front of the final decision. SAP’s conversion guidance positions the Maintenance Planner as a required step in a system conversion — it generates the stack file that SUM consumes — and SAP Readiness Check as the analysis of an ECC system’s conversion readiness across simplification items, custom code, add-on compatibility, and sizing. Run both before the business case is signed, not after: they convert assumptions about your landscape into evidence, and they regularly move the path recommendation.
The board-defensible one-pager
The output of all of this is short: the three paths named in SAP’s terms, the four criteria scored with evidence, the tooling findings attached, and the residual risks (downtime range, support-coverage boundaries, redesign commitment) stated without varnish. A sponsor holding that page can defend the recommendation to a board — and, just as usefully, can detect when a partner’s pitch is a preference dressed up as an inevitability.
There is no universally right road to S/4HANA — there is only the road you can defend. The three scenarios are SAP’s; the discipline of choosing between them on evidence, with the caveats left in, is where a consulting partner either earns trust or spends it.