Fable, Opus, Mythos. Anthropic’s model names, explained in plain English.

A year ago, knowing your Claude from your Copilot was enough. Now the model names matter commercially: which one your subscription includes, which one is gated behind a trusted-access programme, and which one your team should build workflows on are different questions with different answers. Here is the whole naming system on one page, in plain English, with the prices in pounds.

Two naming quirks worth knowing. First, the version numbers do not line up across tiers: Opus is on 4.8 while the Mythos class launched at 5. Second, Fable and Mythos are the same model; Anthropic chose two names precisely because the difference is the safeguards, not the intelligence. Fable comes from the Latin fabula, “that which is told”, a sibling of the Greek mythos.

Launched 9 June 2026, Fable 5 is the first Mythos-class model anyone can use. It ships wrapped in safety classifiers: separate AI systems that watch for queries about cybersecurity, biology and chemistry, or attempts to distil the model into competing systems. Flagged queries are answered by Opus 4.8 instead, and the user is told; Anthropic reports this touches fewer than 5% of sessions. Early evidence of the capability jump is striking: Stripe compressed a two-month, 50-million-line code migration into a day, and Simon Willison called it “something of a beast”. Our full breakdown, including the until-June-22 inclusion window on paid plans, is in the Fable 5 employer post.

Mythos 5 is the same model with some safeguards lifted, which gives it what Anthropic calls the strongest cybersecurity capabilities of any model in the world. It is restricted to vetted organisations, most visibly the Project Glasswing cyberdefence consortium (AWS, Apple, Cisco, CrowdStrike, Google, JPMorganChase, Microsoft, NVIDIA and others), which has used Mythos-class models to surface more than 10,000 high or critical severity vulnerabilities in production software. Anthropic plans a broader trusted-access programme for cybersecurity organisations, and a separate one for biology researchers. The governance story, and what it means for UK security teams, is covered in our Mythos and Glasswing post.

On the API, Fable 5 and Mythos 5 cost around £7.50 per million input tokens and £37 per million output tokens (converted from dollar pricing at the June 2026 rate), roughly twice Opus 4.8 and less than half what Mythos Preview cost. On subscriptions, Fable 5 is included on Pro, Max, Team and seat-based Enterprise plans at no extra cost until June 22; from June 23 it needs usage credits until capacity lets Anthropic restore it as standard. CNBC reported the commercial logic from Anthropic’s product lead: customers buy accuracy and return per task, not cheap tokens, and the more intelligent model wins on ROI.

The names will keep changing; the release cadence is roughly every two months and Anthropic says more capable models arrive in the coming months. What does not change is the work around the model: spotting the process, commissioning the task, wiring the tools, checking the output, governing the result. That is the skill the Claude Apprenticeship builds in your doers (a live automation by month 3, a working agent by month 4), and that the free AI Leadership taster days introduce to your leaders. Train for the discipline, and every name on this page becomes an upgrade rather than a disruption.

Sources & further reading

Anthropic: Claude Fable 5 and Claude Mythos 5. CNBC: Anthropic releases Mythos-like AI model to the public. Simon Willison: Initial impressions of Claude Fable 5. TESS: the Opus 4.8 launch post.