On April 7, 2026, the Claude Mythos Preview was officially announced, but apparently it was too risky. According to Anthropic, Claude Mythos Represents a unique cybersecurity risk. (He claimed that “the consequences—for economies, public safety, and national security—could be dire.”)

Instead of releasing Mythos to the general public, they launched Project Glasswing, a cybersecurity initiative involving some big-name companies. The idea was that they would be able to deploy Mythos for defensive cybersecurity purposes. Before an open Chinese model developed the same capabilities And threw the whole web open.

Two months later, we now have a protected version of Mythos — called Fable — fully available to the public.

Claude Mythos 5 and Claude Fable 5 are Anthropic’s most capable models. They are designed not for everyday use but for maximum performance in tasks such as software engineering, scientific research, computer vision, and automated cognitive work. As Anthropic explains it.The longer and more complex the tasks, the more capable Mythos and Fable are compared to other models.

Mythos 5 and Fable 5 are actually the same model. Fable 5 just added security guardrails to prevent bad actors from using it to launch cyberattacks or develop new bioweapons (seriously). As a result, Mythos 5 is only available to security researchers and other approved partners, while Fable 5 is available to paid subscribers via the Claude app, Claude Code, and API—though with some caveats.

As a tech journalist, I’ve been covering AI and security (separately and together) for over a decade. My reading is that while Anthropic’s claims have a degree of marketing, the Mythos and Fable are the most powerful models ever released. They have jumped. At the top of almost every leaderboardIncluding Zapier’s Automation Benchwhich tests the models on real-world workflows.

Table of Contents:

What are Claude Mythos and Claude Fable?

Claude Mythos 5 and Fable 5 are general purpose. Large Language Model (LLM) who are particularly good at coding, reasoning, and vision-based tasks. The only meaningful difference between them is that Fable 5 has guards that prevent him from answering questions about cybersecurity, chemistry and biology, and distillation.Or how it worksin an attempt to train cheap models). Entropic estimates that Guardrails is triggered in about 5 percent of queries, and in those cases, it automatically falls back to Opus 4.8.

Mythos is available from April 7, 2026. At the time, Anthropic claimed that it Too dangerous for wide release Because it had already uncovered “thousands of more serious vulnerabilities, some of which are embedded in every major operating system and web browser.”

That’s why the Mythos Preview was released to Project Glasswing partners. At the time, it included Amazon, Apple, Broadcom, Cisco, CrowdStrike, Google, JPMorgan Chase, The Linux Foundation, Microsoft, Nvidia, and Palo Alto Networks. This group has now been expanded. As part of a wider rollout. Initial results indicate that the project is a great success. The partners were found and chased. This resulted in more than 10,000 high- or critical-severity security bugs. While things didn’t go full Skynet, it looks like Anthropic’s slow rollout was the right approach.

Anthropic also plans to release a version with biology and chemistry considerations for scientists as part of its Trusted Access program in the coming months.

How good is Claude Fable 5? (since you can’t try Claude Mathos 5)

There are two ways to see how good CloudFable 5 is:

First, the standards: Myth 5 breaks them down.. In addition to ranking first on synthetic analysis, it established the highest scores on 5 out of 10 core benchmarks. It’s a solid step up from Opus 4.8, which ranks second.

As for claims, Anthropic says that Fable 5 (or Mythos 5) was able to migrate a 50 million line Ruby codebase to compress “months of engineering into days” for Stripe. It specializes in both drug design and developing novel hypotheses in molecular biology, and successfully conducted a genomics project where it designed and trained a machine learning model that identified cells with the same role across animal species. Most impressively, he beat. Pokemon Fire Red With its built-in vision capabilities and was three times better. Kill the spire As of Opus 4.8.

All of this is to say that Fable 5 and Mythos 5 are legitimately setting new frontiers for AI models. But how does this translate into the real world?

For starters, Fable 5 topped Zapier’s AutomationBench, which tests AI models on end-to-end workflow execution using 47 real tools across six business functions. Each task leaves an agent in an isolated environment (CRM records, inbox threads, calendars, and more) with the kind of ambiguity that makes real work hard. This is solid proof that fiction translates into the real world.

I also tested Fable 5 myself with a moderated code audit and refactor. I won’t bore you with the details, but basically, I’m building a WhatsApp pipeline that I’ve coded to work reliably in 99% of cases — not just the easy 80%. With two pointers, he created a solid plan, implemented the first phase of the three-phase plan, and covered my entire session usage and over 10% of my weekly limit.

Keep in mind, I’m on the $100/month Claude Max (5x) plan, and the same thing happened with two indicators. I can’t say the job wasn’t good — and it does work successfully with a degree of autonomy that no other model has yet matched — but using it for anything but the most complex tasks is a huge waste of money.

Myth 5 took about an hour to burn through my session allowance. Creating your own plan was quite slow compared to Opus 4.8. It can be a little darker on things, but not so much that it made a difference for my work.

My experience tracks with what I’ve seen from other AI experts. Simon Wilson Turns out it was slow, expensive, and “happily dispersed through everything” he threw at it. Every team It smashed their engineering benchmarks and “accomplished ambitious projects with little oversight,” even though testers burned through tokens and hit usability limits.

(For what it’s worth, the synthetic analysis also found that it was the most expensive model they tested on some of their benchmarks. In Humanity’s final test, the Fable 5 scored 53.3% and cost $2,174 to run; the third-place Gemini 3.1 Pro scored 44.7% and cost just $406.)

How dangerous is the Claude Mythos?

In an article that agreed. With the launch of Glasswing, Anthropic’s cybersecurity researchers detailed Mythos’ cybersecurity capabilities.

Like I said, I’ve been. Been writing about this stuff for years.and their summary seems legally relevant. In some worst-case scenarios, under the right circumstances, a hacker can use Mythos to gain admin access to a server from an unauthenticated visitor to a website.

The big thing is that Mythos seems to be very good at finding and exploiting subtle vulnerabilities. It is also able to combine multiple weaknesses into more powerful feats. In testing, it finds “zero-day” (or undiscovered) exploits in every major operating system and web browser that have been sitting there undetected for years. The oldest bug he found was in OpenBSD from the 90s.

Mythos is significantly better at this than Opus 4.8 or Sonnet 4.6. The researchers go into a deep technical explanation of some of the Mythos feats found, and it’s worth a read if you’re technically inclined.

The researchers emphasize that Mythos was not trained for these abilities. They emerged as an unintended consequence of his improvements in coding, reasoning, and autonomy. It’s also better at finding and fixing vulnerabilities, but now it’s also much better at exploiting them.

Although this information comes from the Mythos Preview rather than Mythos 5, it’s safe to assume that its capabilities are only getting better. gave Initial Project Glasswing results Back them up, too, with partners finding more than 10,000 serious security bugs in its first few weeks.

I’m not a biochemist, so I can’t judge whether concerns about Mythos being used to develop novel viruses and biochemical weapons are overblown, but AI models have shown a lot of promise with drug development, protein folding and other related fields, so I wouldn’t rule it out. There is also concern that by lowering the barrier to entry, they will essentially enable bad actors to compound dangerous chemicals.

I don’t think Mythos 5 is going. Bring on the AI ​​apocalypse.but there are certainly arguments that it needs stronger rails for general use. It’s also worth noting that Anthropic claims that they deliberately set the thresholds higher in order to reduce the number of false positives in the future after collecting more data.

How to test CloudFable 5

For Claude Pro, Max, Team, and some Enterprise subscribers, Claude Fable 5 is available now in the Claude App, Claude Web App, and Claude Code CLI. It is also available via API, although at $10 per million input tokens and $50 per million output tokens, it costs twice as much as Opus 4.8.

Anthropic says it’s going to reduce access to Fable 5 on those subscription plans on June 23, but then restore it at a future date. It’s all part of its broader rollout strategy and doesn’t make much sense. My guess is that they are expanding the capacity, and while it is still limited, they are making it available to regular paid subscribers as a teaser. Once they build enough capacity to make Fable 5 and Mythos 5 available to all of their enterprise clients, regular users will lose access for a while.

Regardless, you can access it however you want. Automate Claude Fable 5 with ZapierAdding the power of cloud models to all your existing workflows. And with Zapier MCPyou can go even further by giving Claude structured access to the tools and context it needs to process your stack. This means turning Cloud from a smart assistant into an active part of your system, triggering workflows, updating records, and orchestrating multi-step processes securely and at scale directly from your chat window. Learn more about How to use Zapier MCP with Claude.

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This article was originally published in April 2026. The latest update was done in June 2026.