https://www.buildingsmart.org/ifc4-soft ... milestone/
IFC4 certification for ARCHICAD is official, at least according to this press release. But you have to read the text carefully, as the title does not even indicate the software name. If these press-releases are correct, ARCHICAD is second, after Vectorworks, for IFC4 Reference View 1.2 Export Certification (Architectural Reference Exchange)
I have been using the beta several times, with specific focus on IFC and the support for IFC4 is thorough. In the current releases, the internal IFC-structure was Ifc2x3, meaning you could only select classes and predefined types if they were available in Ifc2x3. Now you can choose the main scheme (IFC2x3 or IFC4) and base your mapping on that. You can even organise multiple mappings from the same model. Pretty clever (but also a bit complex if you want to fully configure this).
At the same time, I have been playing with Vectorworks 2019 specifically to test IFC support and they also have a good implementation, with both Ifc2x3 and IFC4 supported properly.
All in all, both provide mature implementations. To do some of the same things in Revit requires editing specific mapping files in text-format and using countless Shared Parameters with specific meanings, such as NameOverride or IfcExportAs. You get there most of the times, though, so for OpenBIM this is a good thing.