Up until November 2020, FIX 5.0 Service Pack 2 remained the latest version of FIX Protocol. It was the last of traditional, numbered versions identified in the FIX field ApplVerID(1128) – a field added as follows in FIX 5.0.
Extension Packs (a.k.a. EPs) were introduced after the release of FIX 4.4 as a means to identify each gap analysis proposal that contributed to the enhancements of FIX. In EP260 “FIXLatest” was added as an official “version” label and successor to FIX 5.0 Service Pack 2 (see here for details).
FIX 5.0 Service Pack 2 has now been moved to the list of unsupported versions of the FIX Protocol (see here). This does not mean that implementations can no longer use ApplVerID(1128) = 9 (FIX50SP2); implementations can also still use any of the other unsupported versions. It means that FIX will not analyse reported errors or correct any errors in unsupported versions.
Versions FIX 4.2 and FIX 4.4 are supported versions and have been migrated to the Orchestra Standard v1.0. The repositories for these two versions are available in GitHub where they are maintained and can be visualized with the free tool Orchimate, which was developed and is maintained by a FIX member firm. The FIX 4.2 and FIX 4.4 specification documents define the functional scope of these versions and are not subject to change.
The version FIX Latest is enhanced with every FIX Extension Pack. When an EP is released, the published repository artefacts always include functionality from all previous EPs, i.e. each EP release is cumulative. Therefore it is not necessary to download prior EPs of FIX Latest. Correction of issues found in previous EPs are only made to the latest EP and documented on the download page.
It should be noted that that the value of BeginString(8) does not identify the FIX Protocol version but the FIX Session Layer protocol, a change made as part of FIX 5.0. Prior to FIX 5.0 the value was identical to the FIX Protocol version, e.g. “FIX.4.4”. With the release of FIX 5.0, the BeginString(8) value was changed to “FIXT.1.1” and has not changed since.
Hanno Klein
FIX Technical Director