Tcl/Tk 9.1.0, the latest development release, was published on September 29, 2026, aiming toward stable releases in September 2026. This version adds new features and interfaces to the foundation of Tcl/Tk 9.0.

Highlights of Tcl 9.1 include new commands like `unicode` for Unicode normalization, `timer` for monotonic clocks with microsecond resolution, and `lfilter` for list selection. New C routines such as `Tcl_UtfToNormalized*` and `Tcl_IsEmpty` are introduced. Applications must now call an initialization routine, either `Tcl_FindExecutable` or `TclZipfs_AppHook`. The update also brings C99 math functions as expr functions, improved list internals for memory efficiency, and extended 64-bit size support.

Tk 9.1 focuses on accessibility with screen reader support and bidirectional text for RTL languages. New widgets like `ttk::toggleswitch` and commands like `tk attrib` are added. The send command is revised on Aqua, and improvements include rotated text on labels, better listbox selection colors, and limiting dialogs to physical screen width. Obsolete Windows XP appearance support is removed.

This release is available for download from the main Tcl Developer Xchange site at www.tcl-lang.org.