Fable

Where the book uses it

• Chapter 3 — The Missing Researcher

  The dated promise of an AI that does its own research, what the laboratories have published, and what the public record can and cannot yet check.

• Chapter 8 — The Arsenal Behind Every Arsenal

  The state as customer: how the Pentagon buys frontier AI, the contract clauses a laboratory fought over, and what the courts said about a company that would not sign.

Where the record uses it

• Person Sacks, David

Sources that use it

• Anthropic, “Claude Fable 5 and Claude Mythos 5,” 9 June 2026 (the launch page prices both models at “$10 per million input tokens and $50 per million output tokens” and stages the top model off the seat: “From today through June 22, Fable 5 is included on Pro, Max, Team, and seat-based Enterprise plans at no extra cost” and “On June 23, we’ll remove Fable 5 from those plans. Using it after that will require usage credits. If capacity allows, we’ll extend the included window”; the 9 June release also sets the retention floor by capability tier — “we’re making a change to the way we handle business customer data for Fable 5, Mythos 5, and future models with similar or higher capability levels. We will require 30-day retention for all traffic on Mythos-class models” — defines Mythos-class in footnote 1 as “a tier of Claude models that sit above our Opus class in capability”, and states that access to Mythos 5 will be widened “In consultation with the US government”; Mythos 5 is “the same model as Claude Fable 5 but with cyber safeguards lifted”; the launch page read from anthropic.com on 19 September 2026, unchanged; the release deploys Mythos 5 “as an upgrade to Claude Mythos Preview”, says users of the Preview “will be able to upgrade to Claude Mythos 5—the same model as Claude Fable 5 but with cyber safeguards lifted”, and its footnote dates the first Mythos-class model, Claude Mythos Preview, to April through Project Glasswing; the system card of the same day calls Mythos 5 and Fable 5 “two configurations of a new large language model” and scores Mythos Preview as a separate model; re-read on the page as archived at 17:32 UTC on release day). In the Sources
• Anthropic, “Introducing Claude Fable 5.1 and Claude Mythos 5.1,” September 2026 (the page dates itself to the month; the Internet Archive’s first capture is 1 September 2026, 18:02 UTC) (Fable 5.1 generally available, Mythos 5.1 “available only through our trusted access programs”; the two “are the same model, but with different levels of safeguards”; Fable 5.1 “can now be used to discover software vulnerabilities—though not to develop exploits for them”; the biology access program “developed in partnership with the US government”; Mythos “only available to a set of US organizations”). In the Sources
• Anthropic, “Pricing,” Claude Platform Docs, retrieved 4 September 2026, with the “Steering thinking” and “Fast mode” pages (base input, cache writes, cache hits and output priced apart; the Steering thinking page’s own Pricing section, “Thinking incurs charges for: Tokens Claude uses while thinking (billed as output tokens)” and “You are billed for the full thinking process, not the thinking content visible in the response”; the model table’s five columns, headed “Base input tokens”, “5m cache writes”, “1h cache writes”, “Cache hits and refreshes” and “Output tokens”; the two retired Opus rows, Claude Opus 4.1 and Claude Opus 4, marked retired except on Bedrock and Google Cloud, at “$15 / MTok” base input and “$75 / MTok” output; fast mode for Opus 5 at “$10 / MTok” in and “$50 / MTok” out, the section reading in full, “Fast mode, in research preview, provides significantly faster output for Claude Opus 5 and Claude Opus 4.8 at premium pricing,” with one table row, “Claude Opus 5 / Claude Opus 4.8 $10 / MTok $50 / MTok”; “This tokenizer produces approximately 30% more tokens for the same text”; the page continues, “The exact increase depends on the content and workload shape”; cache hits on Claude Fable 5.1 and Claude Mythos 5.1 “are priced at 0.025x the base input price. All other models use the standard 0.1x multiplier” — $0.25 per million against Opus 5’s $0.50, on a base input of $10 against $5; the section “Long context pricing”: “Claude 4.6 and later models and Claude Mythos Preview include the full 1M token context window at standard pricing. (A 900k-token request is billed at the same per-token rate as a 9k-token request.) Prompt caching and batch processing discounts apply at standard rates across the full context window”; the scope of the tokenizer sentence, stated beside it: “Claude 4.7 and later models and Claude Mythos Preview use a newer tokenizer”, and its closing sentence, “Claude Sonnet 4.6 and earlier models use the previous tokenizer”; the model pricing table as of 20 September 2026: Claude Fable 5.1, Claude Fable 5, Claude Mythos 5.1 and Claude Mythos 5 each at “$10 / MTok” base input and “$50 / MTok” output, and Claude Opus 5 at “$5 / MTok” and “$25 / MTok”; read on 4 September 2026 and re-read on 13, 19, 20 and 21 September 2026, the model table, the long-context section, the tokenizer note and the cache-hit multiplier unchanged on the last reading and the Steering thinking page by then served at platform.claude.com/docs/en/build-with-claude/thinking-steering-and-cost, the live page archived as VERIFY 260913/ch02 fold, VERIFY 260919/T1, VERIFY 260920/FOLD 255 and, with the Steering thinking page, VERIFY 260921/R68 B; re-read 23 September 2026: the model table adds Claude Opus 5.5 at “$4 / MTok” base input and “$20 / MTok” output, its footnote reading “Cache hits and refreshes on Claude Opus 5.5 are priced at 0.05x the base input price”; Claude Opus 5 stays at $5 and $25, Claude Fable 5.1 and Claude Mythos 5.1 at $10 and $50; the fast mode table now reads “Claude Opus 5.5 $8 / MTok $40 / MTok” above the Opus 5 row; archived as VERIFY 260923/FOLD 277; re-read 4 October 2026 for the section “Data residency pricing”: “For Claude 4.6 and later models, specifying US-only inference through the inference_geo parameter incurs a 1.1x multiplier on all token pricing categories, including input tokens, output tokens, cache writes, and cache reads. Global routing (the default) uses standard pricing”; archived as VERIFY 261004/FOLD 552; the model table’s rows: Claude Fable 5.1 and Claude Mythos 5.1 at “$10 / MTok” base input and “$50 / MTok” output, Claude Opus 5 and the Opus 4.5 to 4.8 classes at “$5 / MTok” and “$25 / MTok”). In the Sources
• Anthropic, “Redeploying Fable 5,” 30 June–1 July 2026 (controls lifted; global access restored; dated Jun 30, 2026 on the page: “As of today, June 30, the export controls on Fable 5 and Mythos 5 have been lifted”; Fable 5 available “starting tomorrow, Wednesday, July 1, to users globally”; Mythos 5 restored only “for a set of US organizations, following the US government’s approval on June 26”; the post also states the cause — “The export control directive on June 12 came after the government became aware of a report in which Amazon researchers had found a method of bypassing Fable 5’s safeguards” — and that CAISI researchers tested the old and new safeguards; the post read on 19 September 2026 also settles what became of the seat: “For Pro, Max, Team, and select Enterprise plans, Fable 5 will be included for up to 50% of weekly usage limits through July 7, after which it will be available via usage credits,” with footnote 1, “For standard Enterprise seats, there is no included Fable 5 allowance, although you can get access through usage credits”). In the Sources
• Anthropic, “Statement on the US government directive to suspend access to Fable 5 and Mythos 5,” 12 June 2026 (“an export control directive to suspend all access to Fable 5 and Mythos 5 by any foreign national, whether inside or outside the United States”; “The net effect of this order is that we must abruptly disable Fable 5 and Mythos 5 for all our customers”; received 5:21pm ET; “The letter did not provide specific details of its national security concern”; the directive reached the company’s own staff — “to suspend all access to Fable 5 and Mythos 5 by any foreign national, whether inside or outside the United States, including foreign national Anthropic employees”; the company’s understanding “that the government believes it has become aware of a method of bypassing, or ‘jailbreaking’ Fable 5”, and “we disagree that the finding of a narrow potential jailbreak should be cause for recalling a commercial model deployed to hundreds of millions of people”). In the Sources

And 16 more: search the Sources.

Related terms

• Mythos
• Adoption clock
• Agent
• AGI
• AISI
• Alignment
• Amici
• ARC-AGI-3
• Arsenal behind every arsenal
• Astra
• Automated AI researcher
• Benchmark