Version 2026.4

Upstream version 2026d released 2026-09-11T22:21:07+00:00

Briefly:

Canada’s Northwest Territories moved to permanent -06 on 2026-08-21. Obsolescent
settings like TZ="EST5EDT" now conform better to POSIX. Fix security,
performance and porting bugs in zic and localtime.

Changes to future timestamps

Canada’s Northwest Territories will not fall back on 2026-11-01 and will stay on
-06 year-round, matching Alberta’s recent change. Model this with its
traditional abbreviation CST. Although the change to permanent -06 legally took
place on 2026-08-21, temporarily model the change to occur on 2026-11-01 at
02:00 for the same reason as other recent temporary hacks. (Caution: see “NOTE
FOR 2026b TEMPORARY HACK FOR CLDR AND CANADA” below.) This affects only
America/Inuvik as the rest of the territory is covered by America/Edmonton, for
which the equivalent change was released in 2026c.

Changes to past timestamps

Colombia’s 1992-05-02 spring forward was at 00:00, not 24:00.

Iran’s 1979-05-26 spring forward was at 00:00, not 24:00. (Thanks to N.F. Hase.)

The backward-compatibility names EST5EDT, CST6CDT, MST7MDT, and PST8PDT now
conform better to POSIX. For example, EST5EDT now always uses the abbreviation
"EST" for standard time (now always 5 hours behind UT) and "EDT" for daylight
saving time, whereas it formerly had different UT offsets before standard time
was introduced and sometimes used abbreviations like "LMT", "EWT" and "EPT", all
contrary to POSIX. Also, though not required by POSIX these names now use US
federal rules rather than rules of places like New York, reverting to 2024a
behavior. This change affects only timestamps before 1966-10-30 at 01:00
standard time.

Other data changes

The temporary hacks used for North American timekeeping changes now work around
a libstdc++ std::chrono bug in GCC 14.1-14.4, 15.1-15.2, and 16.1; see GCC bug
124851. This data change does not affect TZif files or timestamps. The change
does not work around the related but less serious GCC bugs 116110 and 124513.
These GCC bugs are all fixed in GCC 16.2.

Changes to documentation

URLs for release tarballs in tz-link.html have been updated to reflect their new
canonical URLs on data.iana.org.