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Anthropic's Mythos page carried the name 'Claude Mythos 5.5' in an October 31 capture. A capture the next day shows Mythos 5.1, and Anthropic has announced no such model.

6 min read

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This record was prepared on the date shown and recovered after a publishing interruption.

An Internet Archive capture of anthropic.com/claude/mythos from October 31, 2026 at 21:49 UTC names the page 'Claude Claude Mythos 5.5' in its hidden header and logo alt text. The November 1 capture at 20:05 UTC reads 'Claude Mythos 5.1', as does the live page. That supports the existence of the name and nothing else: no Anthropic page read announces Mythos 5.5, Fable 5.5 or Opus 5.6, and Claude Code refused all three guessed model IDs on this desk's account. Codex refused gpt-6.2-astra the same way, though OpenAI has not said whether users reporting that name in their usage records are in a test.

aianthropicopenaigooglemodel-releasesusage-limits
source receipts
14
source hosts
10
read time
6min
primary source
Linked

Anthropic's own Mythos product page named a model it has not announced.

An Internet Archive capture of anthropic.com/claude/mythos from October 31, 2026 at 21:49 UTC gives the page's hidden header and logo alt text as "Claude Claude Mythos 5.5". A capture from November 1 at 20:05 UTC reads "Claude Mythos 5.1" in the same place, and so does the live page read this afternoon.

The archive's previous capture, from October 23 at 02:24 UTC, reads "Claude Claude Mythos 5". So the field was already out of step with the page, which described Mythos 5.1, and the doubled word was there before the 5.5 appeared. The name arrived some time after October 23 and was gone by November 1.

The name is the whole of the finding. The body of the October 31 capture still describes Mythos 5.1, and it gives no 5.5 date, price, score or access terms. A page field can hold a planned name that later changes or never ships. Anthropic has not commented in any source read for this record.

What today's claims rest on

Claim Status Basis
"Mythos 5.5" appeared on Anthropic's page Established for one page, between October 23 and November 1 Three archive captures
Anthropic has released Mythos 5.5, Fable 5.5 or Opus 5.6 No record Anthropic's news list, model overview and sitemap name none of them
Opus 5.6 scores 61 on the Artificial Analysis index, 90% on SWE and 81% on RiemannBench, and costs 20% less Unverified A Reddit post attributing them to an unnamed insider. The post's two links do not carry those figures in any text this desk could read
Some Opus 5.5 requests are served by a newer model Unverified X posts from October 11. None shows a model id or API response, according to CellCog's collection of them
gpt-6.2-astra is in a limited OpenAI test Reported, not confirmed Usage screenshots, one showing 19.8% of requests. Others report no such records, according to PANews. OpenAI's Codex model page does not list it

The Reddit post, by u/ThePrimeNumbers in r/Anthropic and read from a screenshot, offered two links as its leak. The "Announcement" tag on it is a community flair and Anthropic did not post it. The first, from X account @kimmonismus, was posted November 1 at 15:23 UTC and says Mythos 5.5 "is already listed" in the HTML source of Anthropic's website, crediting an anonymous email tip. Its text says nothing about Opus 5.6, benchmarks or prices. The second link's status id decodes to January 9, 2026, ten months before the claim it was cited for, and X would not show the post to this desk.

What this desk's accounts could do

These results come from one operator's accounts on one afternoon.

Requested Client Result
gpt-6-astra (control) Codex 0.166.0-alpha.5.1 Answered
gpt-6.2-astra Same "The 'gpt-6.2-astra' model is not supported when using Codex with a ChatGPT account."
claude-opus-5-5 (control) Claude Code 2.1.316 Answered
claude-opus-5-6, claude-fable-5-5, claude-mythos-5-5 Same "It may not exist or you may not have access to it."

The 6.2 reports describe something different from a selectable model: a name in usage records while the picker shows GPT-6 Astra. A refusal does not rule that out. This desk's local Codex logs contain no gpt-6.2 string, but those logs record the model requested, so they would not show a substitution made by the server.

The October ledger

Date Event Checked against
Oct 5 OpenAI's Tibo Sottiaux begins a 28-day pledge of one clear improvement or a full reset per day; thirteen days through Day 27 had a reset The tracker's daily log and his "Day" posts
Oct 7 Claude Haiku 5.5 at $0.10 input and $0.50 output per million tokens, for prompts up to 100k Anthropic
Oct 13 Gemini 4 Argon generally available; its price doubles December 1 Google, in this desk's October 19 record
Oct 26 GPT-6.1 Terra at $1 input and $5 output per million tokens OpenAI
Oct 26 Anthropic publicly files its S-1 Anthropic's news list. Financial figures in press accounts conflict and were not checked against the filing, so none is repeated here
Week of Oct 26 Gemini 4 Carbon goes first to selected cyber defenders; $2 and $10 during an introductory period of unstated length, then $4 and $20 The Register's October 29 report of Google's announcement. Google's own post was not read
Oct 29 OpenAI doubles "all usage limits" for Pro 100/200/500 and Business Premium; a Pro 200 reduction is dropped Sottiaux on X
Nov 1 OpenAI's help page says Plus, Pro and Business allowances will be shared across ChatGPT and Codex "starting in December", measured in tokens OpenAI

The Register reports that Google said Carbon would go to select cyber defenders that week, and that it aims to widen access "as soon as possible", without a date.

If you pay for these tools

  • Opus 5.6, Fable 5.5, Mythos 5.5 and GPT-6.2 have no published price. None has a model id these accounts could select.
  • December changes how usage is measured for Plus, Pro and Business subscribers. OpenAI says usage will depend on the model and the task, and that "Instant chat will not draw from your usage." The page read today gives no token figure per plan and no exact date. It says OpenAI expects most users won't need to wait for resets more often than they do now.
  • Gemini 4 Argon's December 1 doubling is still on Google's price list as of this desk's October 19 record. It was not re-read today.

What the record does not say

  • Why the Mythos name changed. The captures show that it did, between the two capture times, and nothing about who changed it or why.
  • Whether any of these models exists as described. A name in a page field and a name in a usage screenshot are both only names.
  • Who is in OpenAI's test, if there is one. OpenAI has made no statement in anything read here.

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