Microsoft introduced the Team Foundation Server Extension Model in fall 2015, with the release 2015 Update 2. Before that, libraries and interfaces of Team Foundation Server changed frequently. The Extension Model guarantees a stable interface with which to integrate for extension publishers . With 2015 Update 2.1, this interface has been adjusted for the last time.
All releases of 7pace Timetracker marked as "for the Extension Model" are compatible with every release of Team Foundation Server, starting from 2015 Update 2.1 - including TFS 2017, TFS 2018 and Azure DevOps Server 2019 (following the new naming introduced by Microsoft in late 2018).
If you are using a version of Team Foundation Server prior to 2015 Update 2.1, please identify your version of Team Foundation Server from the list below, to see what versions of 7pace Timetracker are available to support this.