Opus 5, Fable 5.1 and Mythos 5.1 — what the Claude 5 family means for Australians

Posted: 19 September 2026 · Updated: 20 September 2026 · Category: AI Assistants & Chatbots

TL;DR: Anthropic's top tier is now three models. Australians can buy two of them. The 30-day retention rule attached to the third and to Fable 5.1 is an API rule. If you pay for Claude Pro, Max or Team, it does not apply to you, and changing model does not change your position.

What changed

Anthropic released Claude Opus 5 on 24 July 2026, then Claude Fable 5.1 and Claude Mythos 5.1 together on 1 September 2026. Opus 5 is the everyday flagship. It costs US$5 per million input tokens and US$25 per million output, with a 1M-token context window as standard. Fable 5.1 sits above it at US$10 / US$50, and its cache reads now cost a quarter of Fable 5's. Mythos 5.1 offers the same capabilities as Fable 5.1, by invitation only. Sonnet 5 (US$2 / US$10) and Haiku 4.5 (US$1 / US$5) complete the line-up.

At the current rate (1 USD ≈ 1.40 AUD, verified 20 September 2026), Opus 5 runs about A$7 / A$35 per million tokens ex-GST. Fable 5.1 runs about A$14 / A$70. GST-registered businesses quoting an ABN are not charged GST; other buyers add ~10%.

You cannot get Mythos 5.1

There are two vendor statements about why, at two different levels of the product.

Anthropic's developer docs list Mythos 5.1's availability as "Project Glasswing participants only", with no geography attached. Its product page is narrower: "Currently, we're only able to make it available to a set of US organizations, though we're working to expand access."

Those are not in conflict. The docs describe the programme gate. The product page describes where Anthropic can serve that programme today. The product page is the one a prospective Australian buyer actually lands on, and it is the one to plan around: the answer is no.

The programme itself is not US-only. Anthropic said on 2 June it was extending Project Glasswing to about 150 new organisations in more than fifteen countries. Access runs through two trusted-access programmes. The Life Sciences Verification Program is an invite-only beta. The Cyber Verification Program will include Mythos access "in the near future".

The 30-day rule is not about your subscription

This is where most coverage of the launch has gone wrong, including our first version of this post.

What the rule is. Anthropic designates Fable 5.1, Mythos 5.1, Fable 5 and Mythos 5 as Covered Models. They require 30-day data retention, and zero data retention "is therefore not available for any of them unless expressly authorized by Anthropic". Opus 5 is not on that list. No retention requirement attaches to it.

Who it binds. Zero data retention is an arrangement on a Claude API organisation, not a feature of a subscription. Anthropic's data-retention page is explicit about what it does not cover. Listed first: "Claude Free, Pro, and Max plans", including the web, desktop and mobile apps and Claude Code. Team and Enterprise product interfaces are "not ZDR-eligible" either.

So if you pay for Pro, Max or Team, the model you choose changes nothing here. You never had zero data retention to lose. Your chat, file and project content follows your organisation's retention policy, set in claude.ai under Organization settings, unless you delete it sooner. Moving sensitive work from Fable 5.1 to Opus 5 buys you exactly nothing on retention. Anyone telling you otherwise has read an API page and applied it to a consumer plan.

If your business builds on the Claude API, it is a live decision. Calling Fable 5.1 from an organisation that holds a ZDR arrangement means switching 30-day retention on. You can do that organisation-wide, or for a single workspace with the rest left at zero. Enterprise customers eligible for Enterprise Frontier Safeguards can hold the data on their own cloud instead. Until that ships, Anthropic says eligible customers can use Fable 5.1 with zero data retention. Ask your account team which of those you are.

Under the Privacy Act the question is the same either way. APP 11 requires reasonable steps to protect personal information, and destruction or de-identification once you no longer need it. Where your prompts sit, and for how long, is a decision somebody has to make. For most Australian readers that decision lives in your retention setting, not in a model name. None of this is legal advice — check your own obligations with a privacy professional.

One restriction carried over, and one didn't

Anthropic suspended access to Fable 5 and Mythos 5 on 12 June 2026, under a US export-control directive covering all foreign nationals. Australians were caught by it. Its own product pages now record the reversal. Fable 5 access "has been restored" on 1 July 2026. Mythos 5's export controls "have been lifted" the same day, following US government approval.

Fable 5.1 is a different model, released in September and listed as available to all customers. The June restriction does not carry across to it.

One note on price

Since 16 September, claude.com/pricing renders native AUD to Australian visitors. Pro is A$28 a month on annual billing (A$340 up front) or A$34 monthly, and Max starts at A$170.01. Team Standard is A$34 a seat on annual billing and A$43 monthly. The page states "Prices include 10% GST". Enterprise is the one tier Anthropic still quotes in US dollars. Our Claude review carries the full table.

Does it change our recommendation?

No. Our Claude review holds at 21/25 and the Claude Code review at 20/25. Opus 5 is a better model at the same price — good news, but not a point's worth. The retention rule sits in the API column, not the subscription column, so it does not move Australian Fit either. For the wider picture on where each assistant keeps your data, see our data-residency explainer.

Frequently asked questions

Can an Australian business use Claude Mythos 5.1?

No. Anthropic's docs restrict it to "Project Glasswing participants only". Its product page says it can currently be offered only "to a set of US organizations". Australians get Fable 5.1, which Anthropic describes as the same underlying model with safeguards added.

Does the 30-day retention rule affect my Claude Pro subscription?

No. Zero data retention is an arrangement on a Claude API organisation, and Anthropic states it does not cover Free, Pro or Max plans. A Pro subscriber never had it, so switching models changes nothing. Your claude.ai content follows your organisation's retention setting instead.

Should I move to Opus 5 or Fable 5.1?

Opus 5 for almost everyone: the same price as Opus 4.8, a 1M-token context window, and no Covered-Model retention requirement. Choose Fable 5.1 for long agentic or research work where Opus 5 falls short, and only after your organisation has settled its retention position.

Sources

A note on snapshots. Save Page Now was unavailable on 20 and 21 September 2026. It returned HTTP 500 on every attempt, and the availability API returned HTTP 429. No same-day capture was possible. Every source below is nonetheless archived. We located existing captures from 9–20 September on 21 September, and cite each at its real date. None is presented as same-day. The one exception is the pricing page. Anthropic serves its Australian render client-side by geolocation, so every archive.org snapshot of claude.com/pricing shows the US dollar version. We checked the 20 September capture and it does. It is cited for page structure only, and the Australian figures rest on the dated live read.

1. Primary — Anthropic, Claude Mythos product page — https://www.anthropic.com/claude/mythos — read 20 September 2026 ("only able to make it available to a set of US organizations"; trusted-access programmes; 30-day retention; "Claude Fable 5.1 is the same underlying model as Claude Mythos 5.1 with safeguards"; 2 June Project Glasswing expansion to ~150 organisations in more than fifteen countries; 1 July export-controls-lifted notice) · Wayback, captured 9 September 2026
2. Primary — Anthropic, Claude Fable product page — https://www.anthropic.com/claude/fable — read 20 September 2026 (Pro / Max / Team / Enterprise availability; 30-day retention by default; Enterprise Frontier Safeguards and the eligible-customer ZDR wording; 1 July "access has been restored" notice) · Wayback, captured 20 September 2026
3. Primary — Anthropic, "API and data retention" — https://platform.claude.com/docs/en/manage-claude/api-and-data-retention — read 20 September 2026 (page scope: Claude API, Claude Platform on AWS, Microsoft Foundry; Covered Models and the 30-day requirement; ZDR excludes Free, Pro and Max plans; Team and Enterprise interfaces "not ZDR-eligible"; claude.ai content follows the organisation's retention policy) · Wayback, captured 20 September 2026
4. Primary — Anthropic, "What's new in Claude Fable 5.1" — https://platform.claude.com/docs/en/models/fable-5-1/whats-new-fable-5-1 — read 20 September 2026 (Fable 5.1 "All customers, on the Claude API and partner platforms"; Mythos 5.1 "same capabilities", "Project Glasswing participants only"; cache-read cut) · Wayback, captured 19 September 2026
5. Primary — Anthropic, Models overview — https://platform.claude.com/docs/en/about-claude/models/overview — read 20 September 2026 (line-up, per-MTok rates, 1M context) · Wayback, captured 17 September 2026
6. Primary — Anthropic, "Introducing Claude Opus 5" — https://www.anthropic.com/news/claude-opus-5 — read 20 September 2026 (24 July release; "the same cost as its predecessor, Opus 4.8"). This page carries no data-retention statement; the Opus 5 retention position above is sourced to item 3, which does not list Opus 5 as a Covered Model. · Wayback, captured 18 September 2026
7. Primary — Anthropic, Claude pricing page — https://claude.com/pricing — read in an Australian browser 20 September 2026 (Pro A$28 annual / A$34 monthly, Max from A$170.01, "Prices include 10% GST", Enterprise quoted in USD). Team seat pricing is taken from our own Claude review, verified against the same page on 19 September 2026. Wayback, captured 20 September 2026 — US dollar render; cited for page structure, not for the Australian figures.
8. Primary (law) — OAIC, APP Guidelines Chapter 11 — https://www.oaic.gov.au/privacy/australian-privacy-principles/australian-privacy-principles-guidelines/chapter-11-app-11-security-of-personal-information — read 19 September 2026 (APP 11.1 and 11.2 wording) · Wayback, captured 17 September 2026
9. FX — open.er-api.com USD→AUD 1.4049, last updated 20 September 2026 00:02 UTC. Corpus basis 1.40 gives the same rounded figures.

Prices are Anthropic's and change; confirm current pricing, your plan's access and your organisation's data-retention arrangement with Anthropic before relying on any of this.

The AI Directory Australia is independent. We review and score AI tools for Australian users — AUD pricing, AU availability, data residency, GST. We don't write ads; affiliate links are disclosed and sponsored content is labelled. Edited by Adam.

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