Regina has always offered British English spelling throughout its API. See for example Triangulation<3>::minimiseVertices(), or GroupPresentation::recogniseGroup().

There are some cases where Regina will continue to offer both British and American English spellings for the same functions:

when referring to the name of another software package that uses American English, such as in Triangulation<3>::recognizer();
when mirroring functions in another software package that uses American English, such as in SnapPeaTriangulation::randomize().

In all other cases, Regina will offer the British English spelling only (since one consistent convention is easier for the developers to maintain). Any legacy aliases that used to offer American alternatives (such as Triangulation<3>::minimizeVertices()) are now deprecated, and will eventually be removed.