Module 3.1 established that an IFC file is a data schema, not a shape container. What that lesson left out is that the schema itself is not fixed. Like any standard, IFC has changed over time, and each change is released as a new schema version. Three versions show up constantly in real projects today, IFC2x3, IFC4, and IFC4.3, and the actual reasons teams choose one over another turn out to be far more practical than "newer is better."
A schema version defines what kinds of information an IFC file can represent, and how that information is organised. A newer version does not retire an older one the way a software update replaces the last release. Versions coexist for years, sometimes decades, because a file only works if the software receiving it can actually read what was used to write it. That single fact, whether the receiving software can read it, turns out to explain almost everything in this lesson.
IFC2x3 arrived in 2006 and has been the industry's default for nearly two decades. The reason has less to do with age than with what happens when software vendors try to move past it.
Getting software certified by buildingSMART is not free. Certifying a single application for a single exchange type has cost vendors on the order of fifty to a hundred thousand US dollars, and that cost applies separately for import and for export, and separately again for each specific workflow the certification covers. Faced with that cost, vendors picked up IFC4 certification slowly and piece by piece. Autodesk began working toward it for Revit in 2017, Graphisoft for ArchiCAD in 2018, and Nemetschek for Allplan in 2020, roughly four to seven years after IFC4 itself was finished. Even then, certification often arrived in fragments. ArchiCAD reached certification for IFC4 import specifically in 2023, with export following separately, so "certified for IFC4" never meant the whole picture was solved at once.
Those gaps are not just administrative. They show up as real data loss. Allplan users have reported IFC4 files where entire categories of elements, columns, beams, and others, get silently placed into an "ignored elements" list on import, with the same file opening correctly in other IFC viewers. The problem runs in both directions, with Revit also reported to struggle loading IFC4 models generated by Allplan. When two applications interpret the same schema version differently, the safest choice is whichever version both of them have already proven they handle the same way, and that has kept IFC2x3 the practical default even now.
Two real examples show this decision being made deliberately. A technical report on exchanging models between Revit and Allplan, produced through a BIM4INFRA research project at TUM, states plainly that the newer IFC4 Design Transfer View would have been the more appropriate choice for the work, but Allplan did not support importing IFC4 at the time, so IFC2x3 Coordination View 2.0 was the version actually used. Graphisoft's own current interoperability add-in for Revit and ArchiCAD makes the identical call today, exporting only IFC2x3 because, in their words, it is currently the latest worldwide-certified IFC standard and the recommended version for model sharing across disciplines and systems. Neither decision reflects a preference for older technology. Both reflect a refusal to risk a newer version that could not yet be trusted to arrive intact.
IFC4 became an ISO standard in 2013, built as an extension of IFC2x3 rather than a replacement for it. The technical improvements are real: better geometry handling, richer property sets, and smaller file sizes, with one direct comparison finding pure geometry files around 30 percent smaller under IFC4 than the equivalent IFC2x3 export.
IFC4 also changed how certification itself works, and this is part of why adoption took so long. Earlier certification had allowed one broad exchange definition to cover both coordination and full model handover, which led to inconsistent results, since nothing forced software to handle every part of it correctly. IFC4 split this into two separate, stricter certifications, one for Reference View, used for viewing and coordination, and one for Design Transfer View, used when a model actually needs to be edited further downstream. A vendor can only apply for Design Transfer View certification after already passing Reference View, and each requires full compliance rather than partial credit. That stricter process improved consistency once achieved, but made the certificate itself considerably harder to earn, which slowed how quickly it spread across the industry.
The result is a gap between the official schema and what is actually produced day to day. Most Revit and ArchiCAD installations exporting "IFC4" today are still producing IFC4 Add2 TC1, the 2018 edition, because tool adoption of a new schema release tends to lag the official ISO standard by one to three years. IFC4's story is less about one headline project and more about the ordinary, uneven way software vendors caught up to a standard that had already been finished for years.
IFC4.3 is a larger jump than IFC4 was. Earlier versions refined how buildings were described. IFC4.3 extends the schema into infrastructure for the first time, adding proper support for roads, railways, bridges, ports, and tunnels, domains the schema had no real classes for before.
Certification for IFC4.3 also works differently than it did for IFC4. Rather than one central process and price, domain and jurisdiction-specific certification, such as separate criteria for bridges in the United States versus bridges in Norway, is being left to accredited third parties, with requirements varying by jurisdiction and use case. It is worth being direct about a genuine gap here: buildingSMART's own public list of IFC4.3 software implementations is explicitly self-reported by vendors and is not a list of certified tools, so a vendor claiming IFC4.3 support there is not the same thing as that support being independently verified.
HS2 shows what adopting IFC4.3 early actually looks like in practice. As the main works civil contractor for HS2 Area North, Balfour Beatty VINCI's BIM team was tasked with delivering several thousand digital infrastructure assets as IFC4.3, at a time when the schema was newly released and industry software support was still catching up, which pushed the team to build much of its own process in-house to meet the requirement. That work saw the team shortlisted for Digital Team of the Year at the Digital Construction Awards 2026. Several countries, including the UK, Germany, and the Nordic countries, are also moving toward mandating IFC4.3 specifically for infrastructure work.
That last point matters for how this section should be read. IFC4.3 is not simply replacing IFC4 the way IFC4 slowly replaced IFC2x3. Most Revit and ArchiCAD installations still default to IFC4 Add2 TC1 for ordinary building projects, and IFC4.3 becomes genuinely necessary specifically where infrastructure entities are involved, since it is the only version that defines them at all.
Not every application supports every version, or every exchange within a version, equally. Import and export behaviour can vary noticeably even between two applications that both claim support for the same schema. Project requirements often specify a version outright, and two IFC files can look identical in a viewer while behaving very differently underneath, depending on which version, and which certified exchange, actually produced them.
That leads to the one habit worth taking from this lesson. It is tempting to assume newer is always better, IFC4.3 over IFC4 over IFC2x3, and to therefore always export the newest version available. In practice, the right version depends entirely on context, and on what has actually been proven to work reliably between the two applications involved. A client may specifically require IFC2x3 because it is the version guaranteed to arrive intact. A coordination platform may only fully support one particular exchange within IFC4. An infrastructure project may specifically require IFC4.3, as HS2 does, because it is the only version with the entity types that work needs. Choosing an IFC version is a decision shaped by what the recipient's software can actually handle, not a straightforward upgrade path.
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