# What changed in tzdata

> 13 changes in tzdata 2026 from its official release notes, upgrade guides and advisories: 1 breaking. Each one cited. Sources checked 2026-10-19. HTML: https://unstale.sh/pypi/tzdata/

To see which of these apply to a repository, run `npx @unstale/cli init` in it.

## tzdata 2026

### Breaking changes

- Alberta is modeled as permanently -06 using CST, with the change temporarily occurring on 2026-11-01 at 02:00. (2026.3) — [release notes](https://github.com/python/tzdata/releases/tag/2026.3)

### Behavior and default changes

- Manitoba is modeled with permanent -05 and the abbreviation EST from 2026-11-01 at 02:00. (2026.5) — [release notes](https://github.com/python/tzdata/releases/tag/2026.5)
- The backward compatibility link now uses the abbreviation EST for affected timestamps. (2026.5) — [release notes](https://github.com/python/tzdata/releases/tag/2026.5)
- Northwest Territories time will stay at -06 year-round, using the abbreviation CST; the change is modeled from 2026-11-01 at 02:00. (2026.4) — [release notes](https://github.com/python/tzdata/releases/tag/2026.4)
- Morocco moves to permanent UTC without daylight saving time transitions on 2026-09-20 at 02:00. (2026.3) — [release notes](https://github.com/python/tzdata/releases/tag/2026.3)
- Western Sahara is affected by Morocco's move to permanent UTC without daylight saving time transitions on 2026-09-20 at 02:00. (2026.3) — [release notes](https://github.com/python/tzdata/releases/tag/2026.3)

### Fixes and other changes

- The historical fallback in Ireland is corrected to 1925-09-20. (2026.5) — [release notes](https://github.com/python/tzdata/releases/tag/2026.5)
- Corrects Colombia’s 1992 spring-forward time to 00:00 instead of 24:00. (2026.4) — [release notes](https://github.com/python/tzdata/releases/tag/2026.4)
- Corrects Iran’s 1979 spring-forward time to 00:00 instead of 24:00. (2026.4) — [release notes](https://github.com/python/tzdata/releases/tag/2026.4)
- The backward-compatibility name now conforms better to POSIX, using US federal rules rather than rules of places like New York for timestamps before 1966-10-30 at 01:00 standard time. (2026.4) — [release notes](https://github.com/python/tzdata/releases/tag/2026.4)
- The backward-compatibility name now conforms better to POSIX, using EST and EDT abbreviations and US federal rules for timestamps before 1966-10-30 at 01:00 standard time. (2026.4) — [release notes](https://github.com/python/tzdata/releases/tag/2026.4)
- The backward-compatibility name now conforms better to POSIX, using US federal rules rather than rules of places like New York for timestamps before 1966-10-30 at 01:00 standard time. (2026.4) — [release notes](https://github.com/python/tzdata/releases/tag/2026.4)
- The backward-compatibility name now conforms better to POSIX, using US federal rules rather than rules of places like New York for timestamps before 1966-10-30 at 01:00 standard time. (2026.4) — [release notes](https://github.com/python/tzdata/releases/tag/2026.4)