Screenshot Shows Claude Mythos 5.5 in Anthropic Site Code

A screenshot posted on X on 1 November 2026 shows the name “Claude Claude Mythos 5.5” in the source code of Anthropic’s Mythos page, in a hidden page header and in the logo’s alt text. When we fetched the same page at 17:31 UTC that day, both places read “Claude Mythos 5.1” and the string “Mythos 5.5” appeared 0 times.

A second trace points to Fable 5.5. On 13 October, the open-source LiteLLM project added an entry named azure_ai/claude-fable-5-5, priced at $10 per million input tokens and $50 per million output tokens. It removed the entry on 14 October, “which Azure does not list”. Anthropic’s newsroom names neither model.

Business Pill · The Model and the Harness

A short explainer on the difference between an AI model and the product built around it. It teaches the general idea only and says nothing about the 5.5 traces in this piece.

What the Screenshot Shows

The X user @kimmonismus posted the screenshot at 15:23 UTC, writing that “Mythos 5.5 is already listed HTML source code of Anthropic’s official website” and crediting an anonymous tip sent by email. The image shows a browser view of the page source with the hidden header and alt text reading “Claude Claude Mythos 5.5”.

The doubled “Claude Claude” matches how Anthropic’s Fable page labels its own hidden header today, which reads “Claude Claude Fable 5” in our fetch. The account @testingcatalog quoted the page’s tagline alongside the name: “Our most capable model class for cybersecurity and biology research.” That tagline is on the live page today, next to the 5.1 name.

What Was Posted on X

The post by @kimmonismus on 1 November 2026 that shared the screenshot. It says Mythos 5.5 is listed in the HTML source code of Anthropic’s website and credits an anonymous tip sent by email. We could not verify the screenshot; our own fetch of the page about two hours later showed 5.1.

The @testingcatalog post on 1 November 2026, which quoted the Mythos page tagline next to the 5.5 name and speculated about timing. The speculation is the account’s, not ours.

The @chetaslua post on 1 November 2026 linking the Mythos screenshot to the Fable 5.5 entry that LiteLLM added on 13 October and removed on 14 October. We checked the two LiteLLM commits on GitHub; we did not verify its MLflow claim.

What We Found on the Live Page

We fetched anthropic.com/claude/mythos twice at about 17:31 UTC, once with a cache-busting parameter. Both copies carried “Claude Mythos 5.1” in the hidden header and the logo alt text. By our count the page mentioned “Mythos 5.1” 43 times and “Mythos 5.5” 0 times.

That does not settle whether the screenshot’s version was ever served. It means the 5.5 name was not on the page we retrieved two hours after the post. The Internet Archive’s most recent capture we found is from 31 October, before the post.

The Fable 5.5 Price Entry

LiteLLM, an open-source library for routing calls across AI providers, keeps a public file of model prices. Its 13 October commit, titled “feat(azure): add azure_ai/claude-fable-5-5”, added the entry with a one-million-token context window and a 128,000-token output limit. The entry cited Azure’s own model-list endpoint as its source.

The prices and the 5 December 2027 deprecation date in that entry match LiteLLM’s current entry for Fable 5.1 on Azure. The next day’s commit, “fix(cost-map): remove azure_ai/claude-fable-5-5, which Azure does not list”, deleted it. The account @chetaslua connected both traces in a post on 1 November.

The Business Lever: Where Model Names Surface

As we read it, both traces surfaced in the plumbing around a model rather than in an announcement: a page template and a price file that third-party software syncs from cloud catalogues. We have also reported that GPT-6.2 Astra shows up in Codex usage screenshots on X.

As we read it, matching prices in the Fable entry would mean no price change at the model tier, if the entry reflected a real listing. LiteLLM’s own correction says Azure did not list it.

The Structural Read

As we read the LiteLLM history, the Fable 5.5 entry arrived through an automated price sync from Azure’s model-list endpoint, and the correction came because Azure did not list the model.

As we read our own fetch, the screenshot cannot be confirmed or ruled out from the live page: the 5.5 name was absent about two hours after the post, and the newest archive capture we found predates it.

As we read the timing, the Anthropic traces echo another report of ours: GPT-6.2 Astra shows up in Codex usage screenshots on X.

Three Implications

FOR DEVELOPERS ON AZURE LiteLLM’s current price file lists Fable 5.1 on Azure and no Fable 5.5 entry.

FOR BUYERS COMPARING MODELS The removed Fable 5.5 entry carried the same per-token prices as the Fable 5.1 entry.

FOR READERS TRACKING LAUNCHES Anthropic’s newsroom page named neither Mythos 5.5 nor Fable 5.5 when we checked on 1 November.

The Business Engineer Lens

This story maps onto the Business Engineer framework Inside Anthropic’s Permission Layer.

The framework says “The governance layer sits at the intersection of capability, regulation, national security, access control, and geopolitical alignment.”

The framework predates these traces and does not discuss them.

Related coverage: GPT-6.2 Astra shows up in Codex usage screenshots · Anthropic terms on training rivals · This Week in the AI Supercycle

What Is Not Established

Anthropic has not announced a Mythos 5.5 or a Fable 5.5 model, and its newsroom page names neither. We could not verify the screenshot independently, and the page we fetched showed 5.1. We did not verify a claim on X that an MLflow model list still carries Fable 5.5. Release timing, pricing and capabilities of any 5.5 model are not public.

The Bottom Line

A screenshot posted on X shows “Claude Claude Mythos 5.5” in the source of Anthropic’s Mythos page, but the live page we fetched at 17:31 UTC on 1 November read 5.1. Separately, LiteLLM added an Azure price entry for Fable 5.5 on 13 October and removed it a day later because Azure did not list it.