According to the release notes published on the Tcl Language website, Tcl/Tk 9.1.0 was made available on September 29, 2026 as the current development work toward a stable release later that year. The update builds on Tcl/Tk 9.0 and introduces a series of new commands, C routines, and platform‑specific changes. In the Tcl portion, the release adds a new unicode command that performs Unicode normalization, complemented by new C routines named Tcl_UtfToNormalized* for the same purpose. A timer command provides a monotonic clock with microsecond resolution, and the lfilter command allows users to select items from a list based on a condition. The interp set command enables variable access in a child interpreter, while the subst command gains new options for controlling backslash, command, and variable substitution. The switch command now accepts an -integer option, and many C99 math routines become available as expr functions. Applications are now required to call an initialization routine such as Tcl_FindExecutable or TclZipfs_AppHook. Additional C‑level helpers include Tcl_IsEmpty, Tcl_GetEncodingNameForUser, Tcl_AttemptCreateHashEntry, and list‑manipulation routines Tcl_ListObjRange, Tcl_ListObjRepeat, and Tcl_ListObjReverse. The time API switches to using long long instead of the older Tcl_Time structure. On macOS, file‑system paths are treated case‑insensitively, and on Windows the auto_execok and exec search mechanisms have been revised. The release also improves the search for script libraries and encodings, enhances the internal representation of large lists for better memory efficiency, and extends support for 64‑bit sizes. Tk 9.1 brings accessibility improvements, including initial screen‑reader support and early handling of bidirectional text and right‑to‑left languages. A new ttk::toggleswitch widget is introduced, along with a tk attribtable command. The send command has been revised and improved on Aqua (macOS), and negative screen distances are now handled correctly. Extended states are added to ttk::treeview and ttk::notebook widgets, and the Tk_CanvasTextInfo API receives improvements. Labels can display rotated text, and message boxes and dialogs are limited to the physical width of the screen. Listbox selection colors have been refined, and support for Windows XP appearance themes has been removed. According to the source, these changes collectively aim to modernize the toolkit while maintaining backward compatibility with existing Tcl/Tk 9.0 applications.
