![\"Anthropic](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2026\/06\/1781363569_571_ImageResizer.ashx.jpeg\")
<\/p>\nAfter initially holding back its state-of-the-art large language model (LLM) Claude Mythos Preview from public consumption, artificial intelligence company Anthropic has released a new AI with similar capabilities, in versions with different safeguard layers.<\/p>\n
<\/p>\n
Claude Fable 5 and Mythos 5 use the same underlying model, but the former comes with stricter classifiers that trigger when it encounters prompts on biology, chemistry and cyber security.<\/p>\n
If that happens, Fable 5 drops down to the less capable Opus 4.8.<\/p>\n
The classifiers will trigger in less than five percent of usage sessions, Anthropic claimed, while conceding it has tuned the safeguards conservatively, meaning they will catch some harmless prompts.<\/p>\n
Fable 5 also has a classifier to detect large-scale attempts to distil its capabilities into competing models, and a separate, covert intervention that limits the model’s usefulness when it detects someone trying to build a competing frontier AI.<\/p>\n
Unlike the other classifiers, the latter does not trigger a fallback or notify the user.<\/p>\n
Anthropic said the Fable 5 classifiers are robust enough to enable a release of the model to the public, and is is available at no additional cost until June 22 US time for paid subscribers.<\/p>\n
After that date, Claude subscribers will have to stump up usage credits for Fable 5, billed in advance with a daily redemption limit of US$2000.<\/p>\n
Anthropic said that it intends to restore Fable 5 to its subscription plans as quickly as it can, when “sufficient capacity allows us to do so”<\/p>\n
The model is fully available over Claude’s application programming interface (API) and Anthropic’s consumption based Enterprise plans.<\/p>\n
Fable 5 consumes double the amount of tokens (the mathematical representations of input to the AI) as Opus 4.8; it costs US$10 per million input tokens, and US$50 per million output tokens to use.<\/p>\n
Whether or not Anthropic charges the same amount when the Mythos-class Fable 5 drops down to Opus 4.8 for certain prompts is unclear.<\/p>\n
A potentially controversial condition for accessing Claude Fable 5 and Mythos 5 is that they come with a 30-day data retention policy.\u00a0<\/p>\n
For its earlier models such as Claude Opus and Sonnet, paid users can opt out of data retention, which is a requirement for regulated industries.<\/p>\n
Anthropic said it will not use the retained data for model training, and that the data will be deleted after the 30-day period.<\/p>\n
It said the reason for the data retention is to help the company detect novel attacks and to reduce false positives.<\/p>\n
Claude Mythos 5 available under Project Glasswing<\/p>\n
The Mythos 5 branded model meanwhile has had some of the Fable 5 included safeguards lifted, Anthropic said.<\/p>\n
Mythos 5 will be deployed through Anthropic’s Project Glasswing<\/a> with select participants such as the US government, and potentially Australian organisations using the prior Claude Mythos Preview<\/a> as per June this year.<\/p>\n iTnews\u00a0has asked Anthropic if Australian government and other organisations will have access to Mythos 5.<\/p>\n In terms of performance, Anthropic published a software exploitation pipeline benchmark score obtained with ExploitBench that the company claimed shows Mythos 5 capturing 10.75 capability flags for Chrome V8 Javascript engine vulnerabilities.<\/p>\n That number compares to 5.56 for Opus 4.8 and 4.44 for competing AI vendor OpenAI’s GPT-5.5.<\/p>\n