Latest Release: Tcl/Tk 9.1.0 (Sep 29, 2026) Tcl/Tk 9.1.0 is the current development work on Tcl and Tk, aiming toward stable releases in September 2026. They add new features and interfaces to the foundation of Tcl/Tk 9.0. Download Tcl/Tk 9.1.0 Source Releases Highlights of Tcl 9.1 New command unicode : Unicode normalization New C routines Tcl_UtfToNormalized* : Unicode normalization New command timer : monotonic clock; microsecond resolution New command lfilter : select items from list New command interp set : variable access in child interpreter New subst options: -backslashes , -commands , -variables . New switch options: -integer . Many C99 math routines now available as expr functions. Applications now required to call an initialization routine, either Tcl_FindExecutable or TclZipfs_AppHook . New C routine Tcl_IsEmpty . New C routine Tcl_GetEncodingNameForUser . New C routine Tcl_AttemptCreateHashEntry . New C routines Tcl_ListObjRange , Tcl_ListObjRepeat , Tcl_ListObjReverse .…