Is Claude (Anthropic) Down?

CLAUDE FABLE 5.1 AND MYTHOS 5.1 LAUNCH -- AND THE PRICE CUT IS ENTIRELY IN THE CACHE READ, NOT THE HEADLINE RATE (2026-09-01, vendor-primary): Anthropic shipped **Claude Fable 5.1** (generally available) and **Claude Mythos 5.1** (trusted-access only), which it states plainly are '**the same model, but with different levels of safeguards**'. Anthropic calls them 'the world's most advanced models for coding and knowledge work'. **READ THE PRICING CAREFULLY, BECAUSE THE HEADLINE RATE DID NOT MOVE.** Anthropic's claim is that Fable 5.1 'will cost an estimated **25% less than Fable 5** for typical workloads' and 'up to approximately **45%**' for highly agentic work -- but the verified rate card shows **base input unchanged at $10/MTok and output unchanged at $50/MTok**. The entire saving comes from one line: **cache hits drop from $1/MTok to $0.25/MTok**, because Fable 5.1 and Mythos 5.1 are priced at a **0.025x cache-read multiplier instead of the standard 0.1x** -- the only models in the range that are. Cache writes are unchanged ($12.50 5-minute, $20 1-hour); Batch is unchanged at $5/$25. **So the discount is real but conditional: if your workload does not reuse cached context, you pay exactly what Fable 5 cost.** That is why the quoted saving ranges from 25% to 45% -- it scales with cache-hit ratio, not with usage. **BENCHMARKS (vendor-published, Fable 5.1 vs Fable 5 vs Opus 5 vs GPT-5.6 Sol):** Terminal-Bench-Science 0.1 **52.6%** vs 24.7% vs 29.0% vs 22.4% -- more than double its predecessor and the largest single gain on the card; Terminal-Bench 4.0 **55.8%** (60.9% for Mythos 5.1) vs 42.0% vs 52.3% vs 37.3%; GDPval-AA v2 **1853** vs 1723 vs 1824 vs 1711; Humanity's Last Exam **60.9%** no-tools / **65.0%** with tools; AutomationBench **31.4%** vs 17.1% vs 26.9% vs 19.6%; CursorBench 3.2.0 **73.4%** vs 70.5% vs 70.0% vs 67.2%; OSWorld 2.0 **77.9% partial / 41.7% strict**. **A CAVEAT ANTHROPIC PUBLISHES AND MOST COVERAGE WILL DROP:** these were run **with production safeguards enabled**, and on tasks where safeguards intervened Fable 5.1 **scored a zero** -- Anthropic says this 'likely reduces the performance of Fable 5.1 and Fable 5 on these benchmarks'. The Mythos 5.1 gap on Terminal-Bench 4.0 (60.9% vs 55.8%) is **entirely a safeguards artefact between two identical models**, not a capability difference, and Anthropic expects it to shrink. **EFFORT DEFAULTS DIFFER BY SURFACE AND THIS AFFECTS YOUR BILL:** Fable 5.1 defaults to **High effort in Claude Code**, **Medium in Claude Cowork and on Claude.ai**. At Low or Medium it matches or beats Fable 5 at much lower cost. **DATA RETENTION -- THE PART ENTERPRISES SHOULD READ:** Anthropic announced **Enterprise Frontier Safeguards (EFS)**, which stores data in **cloud infrastructure the customer controls, not Anthropic's**, giving zero-data-retention-equivalent privacy while retaining adversarial-use prevention. **EFS is not available yet** -- it rolls out to enterprise customers 'in phases, beginning later this fall'; until then eligible customers get plain zero data retention. **SAFEGUARDS LOOSENED IN ONE SPECIFIC DIRECTION:** cybersecurity safeguards now block **60% fewer false positives**, and Anthropic states Fable 5.1 '**can now be used to discover software vulnerabilities -- though not to develop exploits for them**'. Mythos 5.1's biology access runs through a program built with the US government, enrollment 'soon'.

THE SONNET 5 PRICE RISE WAS CANCELLED -- $2/$10 IS NOW THE STANDARD PRICE, NOT AN INTRO RATE (confirmed 2026-08-31 on Anthropic's own pricing doc): every version of this page since 2026-06-30, and effectively all coverage of the Sonnet 5 launch, said the $2/$10 per 1M rate ran as **introductory pricing through August 31, 2026** and then rose to **$3/$15 on September 1**. **It will not.** Anthropic's pricing documentation now carries an explicit note: '**The $2/$10 per million input/output token pricing for Claude Sonnet 5, announced at launch as introductory pricing through August 31, 2026, is now the standard price. The previously scheduled increase to $3/$15 per million input/output tokens on September 1, 2026 will not occur.**' **This is a 33% cheaper input and output rate than anyone budgeting off the launch announcement would have planned for**, and it lands the day before the increase was due. **The full verified rate card, from the same table:** base input **$2/MTok**, 5-minute cache writes **$2.50/MTok**, 1-hour cache writes **$4/MTok**, cache hits and refreshes **$0.20/MTok**, output **$10/MTok**. **Read the competitive position, because it is the real story:** Sonnet 5 now permanently undercuts **Sonnet 4.6 and Sonnet 4.5, which both remain at $3/$15** -- so Anthropic's newer, more capable Sonnet is now cheaper than the two it replaced, rather than converging on their price. **The one caveat that has NOT changed:** Sonnet 5's updated tokenizer maps input to roughly **1.0-1.35x more tokens** than the older models depending on content type, so a like-for-like workload can still cost more per request than the headline rate implies. **If you deferred a Sonnet 5 migration because of the September increase, the reason is gone.**

ANTHROPIC OPENS A RESEARCH PREVIEW OF THE MODEL HARDWARE STANDARD (2026-08-27, vendor-primary): Anthropic announced **MHS**, a shared specification letting AI agents **safely operate physical devices** -- microscopes, liquid handlers, robotic arms -- in parallel, opened as a research preview to selected scientific labs and advanced manufacturers and built originally with **HHMI Janelia Research Campus**. It standardizes a device driver around `read`/`write` primitives plus network discoverability, cutting integration work Anthropic says normally takes weeks or months down to **hours or minutes**. **The relevant fact for this page is the strategy, not the lab equipment: MHS is explicitly model-agnostic and reachable by any agent harness over standard protocols including MCP.** This is the second time Anthropic has published an open interoperability standard it does not control the demand side of -- MCP for software context, MHS for physical hardware -- and it is a deliberate pattern of standard-setting rather than feature-shipping. **Not generally available: early version, application-gated access, partners recruited to co-develop safety evaluations, and explicitly not open source yet.** See the Claude Science page for the full detail.

FABLE 5 IS EXCLUDED BY DEFAULT FROM GITHUB COPILOT ENTERPRISE ENABLEMENT -- ON DATA RETENTION, NOT CAPABILITY (2026-08-26, vendor-primary): When GitHub's **global model policy** went GA on 2026-08-26 (gradual rollout through 2026-09-01), it carved out two classes of model from default enablement on Copilot Business/Enterprise: **open-weight models (GitHub names DeepSeek and Kimi K2), and any model 'not covered by GitHub's data retention agreement' -- for which the named example is Fable 5**. Those exclusions hold **regardless of what an enterprise admin's default policy is set to**; an admin must enable Fable 5 explicitly. **THIS IS A DISTRIBUTION FACT WORTH TRACKING PRECISELY BECAUSE IT IS NOT A QUALITY JUDGEMENT.** Fable 5 is excluded on the same mechanical grounds as an open-weight Chinese model, for an unrelated reason -- the absence of a data-retention agreement between GitHub and the vendor -- and it means the default-on path into a large enterprise distribution channel is closed to Anthropic's model until that agreement exists. **Contract posture, not benchmarks, is now a gate on enterprise reach.** Watch for a GitHub/Anthropic data-retention agreement as the thing that would flip it.

CLAUDE'S TEXT OUTPUT IS BEING WATERMARKED -- GLOBALLY, NOT JUST IN THE EU (2026-08-14, vendor-primary): Anthropic published a detailed explainer confirming that '**future Claude models will generate text that contains a watermark**.' **THE SCOPE IS THE PART TO GET RIGHT: Anthropic is applying it worldwide, not region-scoping it.** Verbatim: '**We're applying watermarking globally at launch because we don't yet have a durable way to scope it by region.**' So this is not an EU-only behaviour you can opt out of by being elsewhere. **The method:** a version of **SynthID-Text**, the approach Google DeepMind published in Nature in 2024 (itself descended from a 2022 Scott Aaronson proposal). It works by changing the *source of randomness* used to break ties between equally-good next words -- instead of an arbitrary RNG, the choice is settled by a key plus the preceding words, leaving a statistical pattern that a key-holder can detect. **WHAT IT DOES NOT DO, because this is where coverage tends to go wrong:** nothing is added to the text, there are **no hidden characters**, it consumes **no extra tokens**, it is **not more expensive**, it has 'a negligible impact on the speed of models,' and it '**carries no identifying information and can't be traced to a specific person, organization, or chat**.' Anthropic reports no measurable quality impact in internal testing, and cites DeepMind's own A/B test on live Gemini traffic finding no statistically significant difference in thumbs-up/down ratings. **WHERE IT IS WEAK -- these are real, vendor-stated limits.** Detection '**doesn't work well on small samples**' and gets more confident as passages lengthen. It is **sparser on factual passages** where there is only one right next word ('Isaac Newton's most famous work was called Principia ___'). **Code carries generally less watermarking than prose**, because exactness leaves no tie to break -- Anthropic says it can attach to arbitrary choices like comments within code but has 'a negligible effect on the actual code produced.' **Proofreading and light editing of human text may not be detectable at all**, since 'the watermark only applies to words Claude chooses.' And a complete rewrite removes it. **What it proves is narrow:** it answers 'what is the likelihood this was partly written by Claude?' -- it **cannot** confirm text was human-written, **cannot** distinguish 'Claude wrote this' from 'Claude heavily edited this,' and **cannot** detect other vendors' AI. Translations DO carry it (every word is Claude's). **STATUS OF THE DETECTOR: there is no public one yet.** Anthropic says 'we will soon be offering a watermark detection API' and is 'in the process of working out the details' -- so as of today you cannot actually check a document. **FILES ARE HANDLED DIFFERENTLY:** generated .png/.jpg/.svg files get a **C2PA content credential** in metadata -- a signed note, not a watermark; nothing in the file changes and it can be stripped like any metadata. **OLDER MODELS ARE NOT COVERED YET:** the EU law grants a transition period for models launched before 2026-08-02, and Anthropic is rolling watermarking out to those 'over the coming months.' **WHY:** compliance with the **EU AI Act**; Anthropic signed the **EU Code of Practice on Transparency of AI-Generated Content** in July 2026 alongside ~190 total signatories, and the marking obligation became effective **2026-08-02**. Anthropic explicitly says other major providers 'will be implementing their own watermarks' -- so expect this across the field, with per-vendor keys and possibly different methods. **PRACTICAL READ:** if you use Claude to draft text you intend to present as unassisted, assume a detector will eventually exist and that long-form prose is the most detectable case. If you use it for code, editing, or short snippets, detectability is materially lower -- by design, not by loophole

LEGACY WORKBENCH + THE EXPERIMENTAL PROMPT-TOOLS APIs RETIRE TODAY, 2026-08-17 -- EXPORT YOUR SAVED PROMPTS (vendor-primary, date arrived): two separate but linked retirements land on the same day. **(1) The legacy Workbench** at `platform.claude.com/workbench` is sunset, verbatim '**being sunset with access ending on August 17, 2026**.' The replacement is the updated Workbench at **`platform.claude.com/playground`** -- and the migration is **lossy in a way that matters**: '**Saved prompts, variables, and evals are not supported in the updated Workbench.**' Anthropic's instruction is to export anything you want to keep 'from the banner and under your **Organizational Settings**.' If you had prompt libraries or eval sets parked in the old Workbench and did not export them before today, that is the data at risk. **(2) The experimental prompt tools APIs** for generating, improving, and templatizing prompts -- **`/v1/experimental/generate_prompt`, `/v1/experimental/improve_prompt`, and `/v1/experimental/templatize_prompt`** -- are '**being retired along with the Workbench on August 17, 2026**,' and '**after removal, requests to these endpoints will return an error**.' These were experimental endpoints, so they were never covered by a stability guarantee, but anything wired into a prompt-optimisation pipeline breaks rather than degrades. No replacement endpoint is named. **Practical read:** the Workbench half is a UI migration with an export deadline; the API half is a hard break with no successor, so if you built tooling on the prompt-improvement endpoints you are writing that logic yourself now