Currently there is no preview release which is newer than the latest stable release.
The current stable version is: 2.17.0
Here you can find our preview releases which are built from the latest code that represents the cutting edge of the TortoiseGit development. These versions are used by the TortoiseGit developers for their daily work (in the past these also were of good quality). Preview releases are provided on an irregular basis, however, without translations.
Right now, there are no preview releases available for download.Preview releases also use the automatic update checker to retrieve new preview and stable releases. However, if you upgraded to a new stable version you won't be notified for new preview releases. This default can be changed by setting VersionCheckPreview to true in TortoiseGit advanced settings.