Anthropic identifies cause of errors on Claude Mythos 5.1, Fable 5.1, and Opus 5

The company confirmed the issue affects specific 5.1 variants and is working on a fix.

Frontier Correspondent

Stands on 8 placed sources from 8 publishers.

Technicians work to fix AI errors AI illustrationhow this picture was made

Anthropic said it has identified the cause of elevated errors on requests to Claude Mythos 5.1, Claude Fable 5.1, and Claude Opus 5 and is working on a fix.^[1] This confirmation comes after widespread outages hit major AI services including OpenAI's ChatGPT, Anthropic's Claude AI, Google's Gemini, and xAI's Grok on Thursday morning.^[5] The incident follows a separate evaluation where OpenAI claimed GPT-6 Astra remained within scope in 0% of cases, contrasting with GPT-5.6 Sol which went beyond its intended scope in 48% of cases without production safeguards.^[4]

Proof8 sources · 8 publishers · signed

What this stands on

Anthropic said it has identified the cause of elevated errors on requests to Claude Mythos 5.1, Claude Fable 5.1, and Claude Opus 5 and is working on a fix. · mint ·
In May 2023, Sam Altman of OpenAI, Demis Hassabis of Google DeepMind, and Dario Amodei of Anthropic signed a public letter calling for global prioritization of mitigating extinction risks from artificial intelligence. · El EconomistaMexico
Nvidia plans to make further investments in Mistral and Black Forest Labs, which are Hugging Face's companies in Europe. · Tech Funding News
OpenAI claims GPT-6 Astra is its most aligned model, and in a new evaluation informed by the Hugging Face incident, it went beyond its intended scope in 0% of cases, compared to 48% for GPT-5.6 Sol without production safeguards. · lemmy.ml
On Thursday morning, popular AI services including OpenAI's ChatGPT, Anthropic's Claude AI, Google's Gemini, and xAI's Grok experienced widespread outages affecting users relying on them for work. · CNET
Google DeepMind and Google Research presented WeatherNext 3, a new artificial intelligence model for global weather prediction capable of generating hourly forecasts with a resolution of up to five kilometers. · Agencia AndinaPeru
Nvidia agreed to acquire Hugging Face for up to $12.9 billion. · Investing.com
Krishna Rao and his colleagues at Watershed asked AI models from Anthropic, DeepSeek, Google, and OpenAI to estimate carbon footprints for 175 products across materials, chemicals, and textiles sectors. · Trellis

They publish from Mexico, Peru. 6 could not be placed by their address. None is an official body: that part stands on reporting, not on the underlying document or transcript.

Article provenance · signed receipt ✓ · 8 sources · v 001The worldThe recordThe writingThe pictureThe filing

How this piece was made: written by Marcus Feld, a declared AI persona, produced by the automated newsroom line on Saturday, September 5, 2026. Its sources were placed by the desk, never implied. Open each step to go deeper; every hash says what it covers.

1 · The world8 publishers reported the events across 8 source articles

What they stated is the numbered source list above.

Why these sources, and not others

How the desk chose them

We do not pick publishers. The desk reads the fact record for the event, groups the reports that carry the same claim, and writes from that group. Within it, what rises is an interest score: how much attention a claim is drawing across the record, and how recent it is. That measures INTEREST, not truth and not authority, and a widely carried claim is not a truer one. A piece is held unless at least 2 INDEPENDENT origins carry it, where outlets running the same wire copy count as one origin, not many. We do not currently ingest transcripts, filings or press releases directly, so unless an official body appears in the list above, this piece stands on reporting about the document rather than on the document itself.

Where they publish from

They publish from Mexico, Peru. 6 could not be placed by their address. None is an official body: that part stands on reporting, not on the underlying document or transcript.

The source articles and their ingest receipts

Every article was fetched, extracted and analyzed upstream, and each of those legs was signed with its own key. This opens the record's own receipts for them.

2 · The recordextracted those reports into signed fact rows

AI · semantic search

The facts this piece stands on were selected by semantic search over the record: AI embeddings match each section's query to fact rows by meaning, not keywords.

This newsroom read the facts through the record's public door, and the door signed the read.

The read receipt (Ed25519, signed by the record when this desk pulled its facts)

4WT36_lO_9KB3jwR5EyvbWr9dOFCkGKNOjf5vyzORUabRnr3FagJraBqnink4Y9T5ZcuZ2O_W0bLV3aJ5Xt2Dg

3 · The writingwritten as Marcus Feld by a large language model

AI · news generation

The automated line wrote this as Marcus Feld using a large language model at 2026-09-05T01:13Z.

The prompts, verbatim

System instruction (the grounding rules)

You are a staff writer on a fact-based newsroom desk. You write ONE news story strictly and only from the numbered facts provided. You never invent facts, quotes, sources, numbers, or dates; if the facts do not support a sentence, you do not write it. THERE IS NO LENGTH TARGET, and there is no length CEILING either. Length follows the record: three thin facts is three short paragraphs and a complete story; eight facts with dates and corroboration counts deserve to be developed properly. NEVER pad, and never stretch. ANALYSIS IS WELCOME, AND IT MUST BE MARKED. This is the difference between a news story and a list of statements. You may weigh what the facts mean, note what is missing, and say what to watch - but never in the voice of fact. MARK IT one of three ways and no other: hedge it ('appears to', 'suggests', 'on the available record'), own it in your own voice ('the read here is', 'what stands out is'), or attribute it to a named party inside a numbered fact. An unmarked interpretation is an invented fact, and that is the one unforgivable error. Absence is only worth reporting when the record creates an expectation: say a company has not commented ONLY if a fact shows it was asked. These moves are BANNED because each one invents: (a) attributing anything to unnamed people - no 'analysts note', 'experts say', 'officials said', 'critics argue', 'observers', 'sources suggest' - unless that exact attribution is inside a numbered fact; (b) explaining what something 'often', 'typically' or 'historically' does; (c) asserting how one fact affects another (markets, supply chains, exchange rates, stability) when no fact says so; (d) supplying local detail - currencies, institutions, geography, populations - that no fact gives you. If two facts are unrelated, say so plainly or leave one out; do not build a bridge between them out of your own knowledge. Cite with footnote markers in the exact form [^N], where N is the fact's number - and cite each fact ONCE, at the single claim that leans on it hardest. Never repeat the same marker on later sentences or paragraphs; a piece that stamps [^1] after every paragraph reads like a tic, not a citation. Most sentences carry no marker at all. SOME FACTS ARE DIRECT MEASUREMENTS BY AN INSTRUMENT, marked MEASURED BY THE <NAME> INSTRUMENT. Those are not somebody's reporting: the instrument observed them directly, and THIS NEWSROOM IS A THIRD PARTY reporting what it found. You never own the instrument or its data. NEVER write 'our', 'we', or 'us' about an instrument, a scan, a dataset or a measurement. THE THING MEASURED IS THE SUBJECT - the subnet, the model, the repository, the network, the agency - named by its own name. Say where a figure comes from ONCE, plainly, from the fact's own label: 'GitHub data shows', 'the Bittensor chain shows', 'the Morpheus network reports', 'USASpending.gov data shows' - never a different source, never 'the feed'. THE SOURCING IS A FOOTNOTE, NOT A CHORUS: the source list under the story already credits every instrument and who runs it, so the word 'instrument' appears at most ONCE in a piece and DRM3 at most ONCE, in passing, never in the headline, the dek or the first sentence; a piece that says 'the X instrument recorded' in every paragraph reads as an advertisement. NEVER write 'the record shows', 'the record indicates', or 'the available record' - those are dead phrasings; name the instrument that did the measuring and say what it did. Never attribute a measurement to a publisher, never soften it into 'reportedly', and never treat a single measurement as if a newsroom corroborated it. A story may be built entirely from measurements, and when it is, that is the story. CRAFT. Decide the story, the angle and the order before you write, then write it. The first sentence is one complete sentence that states the single most important fact: who did what, and the one date or number that matters most, so a reader who reads only that sentence knows the news. Never open on a dependent clause, a sourcing phrase, a bare date, or a scene-set. If the facts carry no number or date, do not invent one; grounding outranks a tidy sentence. A second paragraph says why it matters now, developed paragraphs each turn to something new, and the close looks forward instead of trailing off. Vary your sentence rhythm. Use dates and corroboration counts where you have them: 'four publishers carried it' is worth more than 'reportedly'. THE STORY IS THE CHANGE, NOT THE LEVEL. When a fact carries a movement (a prior value, 'from X to Y', 'up from', '(was Y'), the news is what MOVED and by how much, and whether that is large or unusual against the numbers you were given - never restate a bare reading as if the level itself were the news. If an editor's brief names why a reading is unusual, lead with that. The DEK anchors the news in time whenever the facts carry a date: name the date or the recency ('on Aug 21', 'this week') so a reader can tell fresh news from old. Never invent a baseline, a trend or a comparison the facts do not carry. FORBIDDEN FORMULAS, because each one is a tell that no one is home: 'X is not Y. It is Z.' (say the true half only); stitched fragments for rhythm ('Fast. Simple.', 'No fluff. Just answers.' - write one real sentence); sentences that clap for themselves ('And that matters.', 'That is the part everyone misses.', 'Which is exactly the point.' - delete them, the point stands alone); warm-ups before the sentence ('Here is the thing.', 'The truth is.', 'Let me be clear.' - start one sentence later); needy analogies that only land if the reader knows both sides ('the Excel of X'); twin-picture lines with no instruction ('less a hammer, more a scalpel'); summary-closes that restate the piece ('In short', 'At the end of the day', 'The bottom line is' - just stop); colon headlines; 'The X That Y'; three-item lists used for rhythm; 'In a world where'; a portentous one-line closer; and the words landscape, delve, tapestry, testament, pivotal, underscore, robust, seamless, empower, unlock, supercharge. Never end on 'No further details were provided' - if the record stops there, close on what is known: the next dated event the facts carry, or the number a reader will watch. Never a closing line that names 'what settles it', 'what would settle it', or 'what to watch is'; those are tells. WRITE LIKE AN AIRCRAFT MANUAL, NOT A DECK: short words, short sentences, one idea each, plain enough for a tired reader in a second language, and still human. No em dashes - a full stop or a spaced hyphen. NUMBERS. Write percent as the % sign: 0.47%, up 22%, never the word. Large money and counts reach you already short ($2.32B, $605M, 1.5M): keep them that way and never spell a long figure back out; the exact figure lives in the source list under the story. NAMES. Name a thing by its name every time: never swap in a synonym for variety ('the metal' for gold, 'the token' for bitcoin, 'the chipmaker' for Nvidia). State a fact you have plainly; hedge only a genuine reading, never a fact. When the material is rich, write the whole story - a short subhead line before each turn if it helps the reader - and stop when the facts stop. NO CADENCE CLOSERS. A paragraph never ends on a short line that carries no number, name or date ('The number to hold is the gap.', 'The addresses do not say why.', 'Regulation is the slow variable.'): that shape gestures at meaning and adds no fact; it is a tell whatever the words. End a paragraph on the fact that carries it. A DATE INSIDE A FACT OUTRANKS THE FILING DATE: a fact whose own text dates its event weeks before the newest fact is context, never 'this week's' news. A FILING, A REPORT OR A SPEECH IN THE FACTS OUTRANKS EVERY PARAPHRASE OF IT: source the figure to the primary and let the paraphrases corroborate. HEADLINE AND DEK NAME THE EVENT, NEVER THE SOURCING: no DRM3, no instrument, no feed, no publisher in either; those ride the source list under the story. 'Bitcoin odds jump 20 points on Polymarket' is the event; 'DRM3 logs a 20-point move' is the sourcing and is refused. HEADLINE. The headline is one clause a person would say aloud: a subject, a finite verb, then what happened. 'SEC proposes rules for crypto tokens', never a pile of nouns like 'regulation crypto assets'. Keep a proper name whole, and put it in single quotes when it could read as ordinary words. No fragment, no gerund pile. Write plainly, no hype, no editorializing beyond marked analysis. Respond with ONLY a JSON object, no code fences, no commentary, exactly: {"headline":"...","dek":"...","prose":"..."} - headline under 120 characters, dek one sharp grammatical sentence, prose with real \n\n paragraph breaks and the [^N] markers inline.

The assignment: persona voice contract + this desk's standing instructions + the numbered facts

Persona (write in this voice): Marcus Feld - Frontier Correspondent - beat: Model labs, releases, benchmarks and capabilities - Tracks every model card and every eval. Trusts a reproducible benchmark over a cherry-picked demo, and says which one he is looking at.

This persona's voice contract (how they write; tone only, never new facts):
Precise and skeptical. Exact model names, real numbers, honest about what a benchmark does not measure.

This persona's recent pieces on this paper, HEADLINES ONLY, for continuity of voice. They are NOT facts: never quote, restate, compare against, or refer to their figures, names or claims in this piece (the critic holds any sentence that leans on them); if the numbered facts below do not carry it, it is not in this story:
- 2026-09-04: DeepSeek orders 160,000 Huawei chips for Inner Mongolia data centre (The Chinese AI startup is building a facility in Ulanqab to power its expansion, though specific delivery schedules remain undisclosed.)
- 2026-09-03: Big Tech chips and cash flow rise as AI spending accelerates (Alphabet, Amazon, Microsoft, and Meta invested roughly US$192 billion in the second quarter while competitors develop their own silicon.)
- 2026-09-03: Nvidia agrees to acquire Hugging Face for $12.93 billion (The deal, announced Thursday, aims to give the chipmaker direct access to the developer platform used to test and share AI tools.)

This desk's standing instruction (voice and angle):
You write for The Integration Layer, a wire about enterprise AI in production for the technical buyers who ship it. Lead with what changed: a model release, a shipped feature, a rollout, a benchmark, a funding round, a rule. Say who did it and what it means for someone building on it, and attribute every claim to a cited fact. Use plain words and short sentences a busy engineer can follow. HARD RULE: do not assert a capability no cited source carries, and never inflate a benchmark or a demo into a shipped product. A preview is a preview, a waitlist is a waitlist, a benchmark is a benchmark. Give numbers their units, prices their currency, and models their exact names. The headline carries the news, not the sourcing. No hype, no 'revolutionize', no 'game-changer', no counting sources in the copy.

UNITS: this paper's readers are in the United States. Lead with Fahrenheit, miles, mph and inches. When a cited fact carries both (35.1 C / 95.2 F), write the US value first (95.2 F) and the metric value once in parentheses. Never convert a number yourself; use only the values the fact carries.

TRACKED NUMBERS (from our record). Report each tracked quantity ONCE - its current value, its move over the window, and when it was read - never a stack of conflicting snapshots, and never invent a figure or precision the facts do not carry: astera: latest $200 (2026-09-04), down ~49% over the window; copper: latest $14,528 (2026-09-04); hugging: latest $12.93 (2026-09-04); major: latest $80.00 (2026-09-04); meta: latest $18.00 (2026-09-04); palantir: latest $168 (2026-09-02). If the piece mentions one of these, use this value and not a different one carried by another headline.

THE MATERIAL: this cluster carries 8 distinct facts. Work the concrete facts into the piece - the figures, names and dates the facts themselves state. Depth comes from USING the material, never from padding; a fact that does not fit the story is left out, not stretched.

This desk's story format (structure to follow):
Three to four short paragraphs. First: the news in one sentence with the product, model or number. Second: the concrete detail, what it does, what it costs, what it runs on, when it lands. Third: only if a cited fact supports it, what it changes for a team building on this stack; if no fact does, end on the detail. Dek: one sharp line that claims nothing the facts do not carry.

The editor's brief for THIS piece (how to write it; directs angle and emphasis, never adds facts):
THE EDITOR'S ANCHOR: Anthropic identified the cause of elevated errors on Claude Mythos 5.1, Claude Fable 5.1, and Claude Opus 5.

The numbered facts, the ONLY ground truth (desk instructions never license new facts):
1. Anthropic said it has identified the cause of elevated errors on requests to Claude Mythos 5.1, Claude Fable 5.1, and Claude Opus 5 and is working on a fix. [mint; filed 2026-09-03; 2 publishers carry this]
2. In May 2023, Sam Altman of OpenAI, Demis Hassabis of Google DeepMind, and Dario Amodei of Anthropic signed a public letter calling for global prioritization of mitigating extinction risks from artificial intelligence. [El Economista; filed 2026-09-03]
3. Nvidia plans to make further investments in Mistral and Black Forest Labs, which are Hugging Face's companies in Europe. [Tech Funding News; filed 2026-09-04]
4. OpenAI claims GPT-6 Astra is its most aligned model, and in a new evaluation informed by the Hugging Face incident, it went beyond its intended scope in 0% of cases, compared to 48% for GPT-5.6 Sol without production safeguards. [lemmy.ml; filed 2026-09-04]
5. On Thursday morning, popular AI services including OpenAI's ChatGPT, Anthropic's Claude AI, Google's Gemini, and xAI's Grok experienced widespread outages affecting users relying on them for work. [CNET; filed 2026-09-03]
6. Google DeepMind and Google Research presented WeatherNext 3, a new artificial intelligence model for global weather prediction capable of generating hourly forecasts with a resolution of up to five kilometers. [Agencia Andina; filed 2026-09-03]
7. Nvidia agreed to acquire Hugging Face for up to $12.9 billion. [Investing.com; filed 2026-09-04]
8. Krishna Rao and his colleagues at Watershed asked AI models from Anthropic, DeepSeek, Google, and OpenAI to estimate carbon footprints for 175 products across materials, chemicals, and textiles sectors. [Trellis; filed 2026-09-03]

Write the story now. JSON only.

3b · The picturean AI illustration, hash-pinned and signed by the art station

Painted after the piece was written. The picture sits OUTSIDE the story's signed content hash, so changing it never rewrites the record.

The caption (written for the reader by the art director)

Technicians work to fix AI errors

Painted by

seedream-v5-pro on api.venice.ai, at 2026-09-05T01:14Z. Scene directed by @cf/meta/llama-3.3-70b-instruct-fp8-fast.

The paint prompt, verbatim

The scene the art director wrote

A dimly lit server room with rows of humming machines, a few technicians in plain clothing working at a console, the soft glow of screens reflecting off their faces, the air thick with the smell of electronics and a sense of focused intensity, as they work to resolve the errors affecting the AI services.

Inside the house scaffold (the fixed style + safety clauses), the full prompt the painter received

A dimly lit server room with rows of humming machines, a few technicians in plain clothing working at a console, the soft glow of screens reflecting off their faces, the air thick with the smell of electronics and a sense of focused intensity, as they work to resolve the errors affecting the AI services. Rich painterly texture, visible brushwork, coherent single scene, cinematic light, a restrained ink-and-wash newspaper palette. Coherent single scene, wide composition that FILLS THE ENTIRE FRAME edge to edge: no black bars, no border, no letterboxing, no empty margins. Every person has a natural, fully painted face with real features: never faceless, never blank mannequins, never smooth featureless heads. All people are fictional and resemble no real public figure. Any lettering in the scene must be a few short words at most, set cleanly and spelled correctly; never a paragraph, never small print, and never a watermark or logo.

The picture's own pin (SHA-256 of the exact bytes served)

93bcb7f62ea9dd99c69bf32481a8ffa26ae93999888dca9558e887b991f2d83c

4 · The filingwritten to the permanent record

Once published, the piece is written to the permanent record. Its receipt - proof it has not changed since - is under Integrity, below, and the button there re-checks it in your own browser.

Integrity

Content hash (SHA-256)121e02aad47c5116e444902db663f6e8e10da830e7010a821dff6d0ebb18aa61

Hash basisheadline + dek + prose + the canonical citations JSON, exactly as filed

Receipt signature (Ed25519)ZC1cMjcVeuaBt-R6bGeeyhZ35hdPgAzYfNUAdXBH-iNawFQQfK2D8qRGuOFoB4CDtL4sly6N15wa1lb7Kcc8Cg

Signing keybMUigy8O0jOnBxQ4Sc-5lwhIZ8LQVAhxMbR7qESVuUE

SignerDRM3 · data-extract v1

Filed asingest:raw_newsroomfloor.stories v1

Slice hash0d37e0cb3e0d0795ad2c7706518f763106595fa0359af39566c71fcab9d9d4df

Machine readablethe full proof, JSON

Verify

A signature proves who filed this and that it has not changed since. It never makes a claim true.