{"slug": "what-is-claude-mythos-and-how-is-if-different-from-claude-fable", "title": "What is Claude Mythos? And how is if different from Claude Fable?", "summary": "Anthropic released Claude Mythos 5.2 and Claude Fable 5.2 as its most capable models, with Fable 5.2 adding guardrails that block cybersecurity, chemistry, biology and distillation queries and fall back to Opus 4.8 or Opus 5, Anthropic said. Anthropic first announced Claude Mythos Preview on April 7, 2026, withholding it from wide release because it had uncovered \"thousands of high-severity vulnerabilities, including some in every major operating system and web browser,\" and instead gave it to Project Glasswing partners including Amazon, Apple, Broadcom, Cisco, CrowdStrike, Google, JPMorganChase, the Linux Foundation, Microsoft, Nvidia and Palo Alto Networks. Anthropic said Fable 5.2 produces about 55% fewer blocks than Fable 5.1 in early testing, and on Zapier's AutomationBench Claude Fable 5.2 ranks #3 overall at max effort, behind two Gemini 4 Carbon settings.", "body_md": "On April 7, 2026, Claude Mythos Preview was officially announced, but it was apparently too dangerous to release. According to Anthropic, Claude Mythos [__represented a unique cybersecurity threat__](https://red.anthropic.com/2026/mythos-preview/) (they claimed that \"the fallout—for economies, public safety, and national security—could be severe.\")\n\nInstead of releasing Mythos to the general public, they spun up Project Glasswing, a cybersecurity initiative that also involved some big-name companies. The idea was that they'd be able to deploy Mythos for defensive cybersecurity purposes [__before an open Chinese model developed the same capabilities__](https://zapier.com/blog/what-is-deepseek/) and threw the whole web wide open. \n\nTwo months later, Anthropic released a guardrailed version of Mythos—called Fable—that was fully available to the public...for about three days. Then the U.S. government told them they needed to [__suspend access to all foreign nationals__](https://www.anthropic.com/news/fable-mythos-access), which realistically meant suspending access for everyone. And on June 30, [that suspension was lifted](https://www.anthropic.com/news/redeploying-fable-5).\n\nSince then, new versions of the models have been released—now Claude Mythos 5.2 and Claude Fable 5.2 are Anthropic's most capable models. They aren't designed for everyday use but for maximum performance in tasks like software engineering, scientific research, computer vision, and automating knowledge work. As [__Anthropic explains it__](https://www.anthropic.com/news/claude-fable-5-mythos-5), the longer and more complex the tasks, the more capable Mythos and Fable are relative to other models. \n\nAs a tech journalist, I've been covering AI and security (separately and together) for well over a decade. My read is that while there's a degree of marketing to Anthropic's claims, Mythos and Fable are some of the most powerful models ever released. When they were first available, they jumped to the top of almost every leaderboard. Now, on Zapier's [__AutomationBench__](https://zapier.com/benchmarks), which tests models on real-world workflows, Claude Fable 5.2 now ranks #3 overall at max effort, behind two Gemini 4 Carbon settings.\n\n**Table of contents:**\n\n- [What are Claude Mythos and Claude Fable?](#what)\n- [How good is Claude Fable 5.2?](#how)\n- [How dangerous is Claude Mythos?](#dangerous)\n- [How to try Claude Fable 5.2](#next)\n\n## What are Claude Mythos and Claude Fable?\n\nClaude Mythos 5.2 and Fable 5.2 are general purpose [__large language models (LLM)__](https://zapier.com/blog/best-llm/) that are particularly good at coding, reasoning, and vision-based tasks. The only meaningful difference between them is that Fable 5.2 has guardrails that prevent it from answering queries about cybersecurity, chemistry and biology, and distillation (or [__or how it works__](https://www.anthropic.com/news/detecting-and-preventing-distillation-attacks), in an attempt to train cheaper models). Anthropic says Fable 5.2 produces about 55% fewer blocks than Fable 5.1 in early testing, and when the guardrails do kick in, it automatically falls back to Opus (Opus 4.8 for cybersecurity, Opus 5 for biology).\n\nMythos has been available since April 7, 2026. At the time, Anthropic claimed it was [__too dangerous for wide release__](https://red.anthropic.com/2026/mythos-preview/) because it had already uncovered \"thousands of high-severity vulnerabilities, including some in every major operating system and web browser.\"\n\nThat's why Mythos Preview was released to Project Glasswing partners. At the time, that included Amazon, Apple, Broadcom, Cisco, CrowdStrike, Google, JPMorganChase, the Linux Foundation, Microsoft, Nvidia, and Palo Alto Networks—though [__that group has now been expanded__](https://www.anthropic.com/news/expanding-project-glasswing) as part of a wider rollout. Initial results suggest the project has been a big success. [__Partners found and patched__](https://www.anthropic.com/research/glasswing-initial-update) more than 10,000 high- or critical-severity security bugs as a result. While things didn't go full Skynet, it seems like Anthropic's slow rollout was the right approach. \n\nMythos 5.2 isn't available to the general public. Anthropic offers it to vetted organizations through its Cyber Verification Program and Life Sciences Verification Program, and Claude Enterprise customers can use it through Claude Security.\n\nIncidentally, in launching Mythos 5 and Fable 5 (the first numbered versions of the two models), Anthropic has made a complete mess of its [model](https://zapier.com/blog/claude-models) numbering convention. Fable and Mythos are now on 5.2, while its other three models are currently Opus 5.5, Sonnet 5.5, and Haiku 5.5.\n\n## How good is Claude Fable 5.2?\n\nThere are two ways of looking at how good Claude Fable 5.1 is:\n\n- The benchmarks and claimed abilities\n- What it's like for real-world applications\n\nFirst, the benchmarks: [__Fable smashes them__](https://artificialanalysis.ai/articles/claude-fable-5-1)—5.2 took the number one spot on Artificial Analysis for intelligence.\n\nBut it also does well on Zapier's [AutomationBench](https://zapier.com/benchmarks), which tests AI models on end-to-end workflow execution using 47 real tools across six business functions. Each task drops an agent into an isolated environment (CRM records, inbox threads, calendars, and more) with the kind of ambiguity that makes real work hard. That's solid evidence that Fable translates into the real world. \n\n**Did you know?** Every time a new major AI model is released, Zapier runs it through [AutomationBench](https://zapier.com/benchmarks), an open benchmark that tests models on real business workflows.\n\n## How dangerous is Claude Mythos?\n\n[__In an article that coincided__](https://red.anthropic.com/2026/mythos-preview/) with the launch of Glasswing, cybersecurity researchers at Anthropic detailed Mythos's cybersecurity capabilities. \n\nAs I said, I've been [__writing about this stuff for years__](https://www.popsci.com/authors/harry-guinness/), and their summary seems legitimately concerning. In some of the worst exploits, under the right circumstances, a hacker could use Mythos to go from an unauthenticated visitor on a website to having admin access on the server. \n\nThe big takeaways are that Mythos sounds to be very good at finding and exploiting subtle vulnerabilities. It's also able to combine multiple vulnerabilities into more powerful exploits. In testing, it's found \"zero-day\" (or undiscovered) exploits in every major operating system and web browser that have been sitting there unfixed for years. The oldest bug it found was from the '90s in OpenBSD.\n\nThe researchers go into a deep technical explanation of some of the exploits Mythos found, and it's worth reading if you're technically inclined.\n\n__Anthropic__\nThe researchers stress that Mythos wasn't trained to have these capabilities. They emerged as an unintended consequence of its improvements in coding, reasoning, and autonomy. It's better at finding and fixing vulnerabilities too, but it's now good enough to exploit them as well.\n\nWhile this information comes from Mythos Preview rather than Mythos 5.1, it's safe to assume its capabilities are only improving. The [__early project Glasswing results__](https://www.anthropic.com/research/glasswing-initial-update) also back them up, with partners finding more than 10,000 serious security bugs in its first few weeks. \n\nI'm not a biochemist, so I can't assess whether the fears about Mythos being used to develop novel viruses and biochemical weapons are overblown, but AI models have shown a huge amount of promise with drug development, protein folding, and other adjacent fields, so I wouldn't rule it out. There's also the fear that by lowering the barrier for entry, they'd essentially enable bad actors to vibe-compound dangerous chemicals.\n\nI don't think Mythos 5.1 is going to [__bring about the AI apocalypse__](https://www.cnbc.com/2026/04/07/anthropic-claude-mythos-ai-hackers-cyberattacks.html), but there are certainly arguments that it needs stronger guardrails for general use. The U.S. government's temporary export controls made that case pretty clearly. It's also worth noting that Anthropic claims to have deliberately set the guardrails high with a view to reducing the number of false positives in the future after they gather more data. \n\n## How to try Claude Fable 5.2\n\nFable 5.2 is available for Claude Pro, Max, Team, and some Enterprise subscribers in the Claude app, Claude web app, and Claude Code CLI—as well as through the API (where at $8 per million input tokens and $40 per million output tokens, it costs twice as much as Opus 5.5).\n\nIf you use your own API key for Fable 5.2 on Zapier, you can add its power to all your existing workflows. Drop an AI step wherever you need it, and leave the rest to determinstic automation that doesn't burn through tokens. Or you can use AI by Zapier to [__automate other Claude models__](https://zapier.com/apps/anthropic-claude/integrations), like Opus 5.5 and Sonnet 5.5, without an API key or even an Anthropic account.\n\nAnd with [__Zapier MCP__](https://zapier.com/mcp), you can go even further, giving Claude structured access to the tools and context it needs to take action across your stack. That means turning Claude from a smart assistant into an active part of your systems, triggering workflows, updating records, and orchestrating multi-step processes directly from your chat window, securely and at scale. Learn more about [__how to use Zapier MCP with Claude__](https://zapier.com/blog/automate-claude-zapier-mcp/).\n\n**Related reading:**\n\n- [__What is Claude Code? The AI coding tool anyone can use__](https://zapier.com/blog/claude-code/)\n- [__Claude API: How to get a key and use the API__](https://zapier.com/blog/claude-api/)\n- [__Claude Skills: Build repeatable workflows in Claude__](https://zapier.com/blog/claude-skills/)\n\n*This article was originally published in April 2026. The most recent update was in November 2026.*", "url": "https://wpnews.pro/news/what-is-claude-mythos-and-how-is-if-different-from-claude-fable", "canonical_source": "https://zapier.com/blog/claude-mythos", "published_at": "2026-11-10 04:00:00+00:00", "updated_at": "2026-11-10 18:20:35.053297+00:00", "lang": "en", "topics": ["artificial-intelligence", "large-language-models", "ai-safety", "ai-products"], "entities": ["Anthropic", "Claude Mythos 5.2", "Claude Fable 5.2", "Claude Mythos Preview", "Project Glasswing", "Zapier", "Gemini 4 Carbon", "Opus 4.8"], "also_reported_by": [], "alternates": {"html": "https://wpnews.pro/news/what-is-claude-mythos-and-how-is-if-different-from-claude-fable", "markdown": "https://wpnews.pro/news/what-is-claude-mythos-and-how-is-if-different-from-claude-fable.md", "text": "https://wpnews.pro/news/what-is-claude-mythos-and-how-is-if-different-from-claude-fable.txt", "jsonld": "https://wpnews.pro/news/what-is-claude-mythos-and-how-is-if-different-from-claude-fable.jsonld"}}