IFC 2x3 vs IFC 4: what changed and which one to deliver

Many BIM briefs still ask for IFC 2x3, others for IFC 4, and most authoring tools export both. This page compares the two versions using buildingSMART's release database and other public sources, and points out what matters when you check a model.

By Julian Bringold · Updated on October 21, 2026

Quick answer

IFC 2x3 dates from 2005; its TC1 corrigendum, in 2007, was published as ISO/PAS 16739:2005. IFC 4 followed in 2013, and its ADD2 TC1 release became ISO 16739-1:2018. buildingSMART lists both as official, alongside IFC 4.3 ADD2 (ISO 16739-1:2024). The brief or the receiving software decides which one to deliver.

IFC 2x3 and IFC 4 releases, according to buildingSMART

Release	Published	ISO publication	buildingSMART status
IFC 2x3	December 2005	None	Retired
IFC 2x3 TC1	July 2007	ISO/PAS 16739:2005	Official
IFC 4	February 2013	ISO 16739:2013	Retired
IFC 4 ADD1	June 2015	None	Retired
IFC 4 ADD2	July 2016	None	Retired
IFC 4 ADD2 TC1	October 2017	ISO 16739-1:2018	Official
IFC 4.3 ADD2	April 2024	ISO 16739-1:2024	Official

Two versions, several releases

buildingSMART numbers IFC releases as Major.Minor.Addendum.Corrigendum. IFC 2x3 TC1 is release 2.3.0.1 and IFC 4 ADD2 TC1 is release 4.0.2.1. A corrigendum improves the documentation without changing the schema; an addendum may change the schema but guarantees upward compatibility.

So when a brief asks for "IFC 4", the release buildingSMART lists as official is IFC 4 ADD2 TC1, published as ISO 16739-1:2018. IFC 4.1 (2018) and IFC 4.2 (2019) were withdrawn. The current line is IFC 4.3, whose ADD2 release was published as ISO 16739-1:2024.

What IFC 4 changed

Moving from 2x3 to 4 is a change of major version. In buildingSMART's notation, a major version expands or cuts the scope of the schema and may break compatibility. An IFC 2x3 file does not become an IFC 4 file by editing its header: the software has to export it in the target schema.

Wikipedia lists several classes introduced with IFC 4: IfcPropertySetTemplate, for defining property sets in the file itself, IfcMaterialProfileSet and IfcMaterialConstituentSet, for describing materials, and IfcProjectLibrary, for object libraries attached to a project. buildingSMART's documentation remains the reference for the full list.

Telling which version a file uses

An .ifc file is a text file. Its header contains a FILE_SCHEMA line naming the schema, for example IFC2X3, IFC4 or IFC4X3_ADD2. A text editor is enough to read it; an .ifczip file has to be unzipped first.

SeveUp App opens IFC2X3, IFC4 and IFC4X3 models, as .ifc or .ifczip files, in its online IFC viewer.

Which version to deliver

The answer is in the project documents: the BIM brief, or the exchange information requirements in ISO 19650 terms, usually states the IFC version and sometimes the export settings. Our page on the French BIM charter, brief and protocol explains where to look.

If nothing is specified, agree on the version with whoever receives the files, and check that their software reads it. Our ISO 19650 overview explains the requirements chain, from the client down to the delivery team.

Checking requirements across versions

With IDS 1.0, each specification states the IFC versions it targets, among IFC2X3, IFC4 and IFC4X3_ADD2. A requirement can therefore target a single version or several.

Watch inheritance: in an IFC2X3 file, targeting IFCWALL does not cover IFCWALLSTANDARDCASE, you have to list both. Our page on BIM requirements and IDS covers these traps, and the guide on checking BIM requirements with IDS shows the steps in SeveUp App.

Frequently asked questions

Is IFC 4 compatible with IFC 2x3?

Not fully. In buildingSMART's notation, moving from 2x3 to 4 is a change of major version, which may break compatibility. A file has to be exported in the target schema.

Is IFC 2x3 still valid?

buildingSMART lists IFC 2x3 TC1 as an official release in its release database, last modified in May 2026. It was published as ISO/PAS 16739:2005.

What is the ISO number of IFC 4?

IFC 4 was published as ISO 16739:2013. Its ADD2 TC1 release was published as ISO 16739-1:2018, and IFC 4.3 ADD2 as ISO 16739-1:2024.

How do I know which IFC version a file uses?

Open the .ifc file in a text editor and read the FILE_SCHEMA line in its header, for example IFC2X3 or IFC4.

Does SeveUp App read both versions?

Yes. SeveUp App opens and checks IFC2X3, IFC4 and IFC4X3 models, as .ifc or .ifczip files.

Sources

Sources checked on October 21, 2026.

IFC Schema Specifications (IFC release database), buildingSMART International, table last modified 27 May 2026.
Industry Foundation Classes, Wikipedia, last edited 23 December 2025.
Information Delivery Specification (IDS), ids.xsd schema, buildingSMART International (GitHub), checked on 21 October 2026.
ISO 16739-1:2024, Industry Foundation Classes (paid standard), ISO, 2024.

Check your models, whatever their version

Upload IFC2X3, IFC4 or IFC4X3 models and check each one against your IDS requirements.

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