The dated evidence
Fable 5.1 released
The version-specific documentation records this release date. It is a Fable 5.1 milestone, not a Fable 5.5 announcement.
Opus 5.5 announced
Anthropic announced Opus 5.5. A 5.5 version in the Opus line does not establish a release date for the Fable line.
Fable 5.5 source review
We reviewed the official model directory, model documentation, announcements and product pages. Fable 5.5 remains unconfirmed in this source set.
Two confirmed dates, two different models
Claude Fable 5.1’s documentation records September 1, 2026 as its release date. The accompanying announcement identifies Fable 5.1 and Mythos 5.1, rather than Fable 5.5.
Claude Opus 5.5’s announcement is dated September 22, 2026. That date agrees with its model documentation. It cannot be reused as the launch date of a Fable model.
Claude Fable 5.1 documentation ↗Fable 5.1 and Mythos 5.1 announcement ↗Opus 5.5 announcement ↗Claude Opus 5.5 documentation ↗
What would confirm a Fable 5.5 release date?
For this tracker, a confirmed date needs an official statement that names the precise model and states what happens on that date. We separately record an announcement, preview access and broader availability.
An announced day without a time zone is still just a day. We would display it as published, rather than inventing a midnight deadline. A countdown would require an explicit future time and time zone, and reaching zero would not prove access had opened.
- Exact version: does the statement name Fable 5.5?
- Event: is it an announcement, an invitation program or usable access?
- Scope: which channel, users and regions does it cover?
- Time: is the source giving a date, a window or a precise timestamp?
What to do while the date is unknown
Keep existing deployment plans tied to models you can verify and use. If a reported launch date matters to your decision, follow its original announcement link and check the version and access conditions before changing your schedule.
We do not turn the gap between earlier releases into a timetable. A release pattern can suggest a question to investigate; it cannot supply a commitment from Anthropic.