Anthropic, PBC (stylized as ANTHROP\C) is an American artificial intelligence (AI) public benefit corporation headquartered in San Francisco, California. Its flagship product is Claude, a series of proprietary large language models (LLMs).
Anthropic makes Claude Opus 4.7 generally available, a notable improvement on Opus 4.6 in advanced software engineering, especially on the hardest tasks.
Anthropic releases Claude Opus 4.8, stronger across coding, agentic tasks and professional work, with the consistency to keep working on long-running tasks.
CONFIRMED90% CONFIDENCEThe announcement page does not date itself - it says only “September 2026” and “available today”, and the one ISO timestamp in its HTML is a page build time. The date comes from Anthropic's[1][3] own news index, whose card for this article carries <time>Sep 1, 2026</time>, and is confirmed independently by MacRumors[5]' article:published_time of 2026-09-01T19:15:16Z (“Anthropic today introduced Claude[2] Fable 5.1”) and by Wikipedia's[4] Claude Mythos infobox, “Claude Mythos 5.1 / September 1, 2026”.
Anthropic releases Claude Fable 5.1 and Claude Mythos 5.1 - the same model behind different safeguards - and cuts cache reads by 75%, making typical workloads about 25% cheaper to run than Fable 5.
CONFIRMED93% CONFIDENCEThe source[1] page carries its own date of 22 September 2026 and is a write-up of earlier reporting, so the event's date comes from the two reports it is built on: Reuters[2] published the exclusive at 3:02 AM PDT on 18 September 2026 and TechCrunch[3] the confirmation at 4:13 PM PDT the same day - "Anthropic[4][5][6] has a wet biology lab in the Bay Area where it can use its AI models to run physical experiments, it has confirmed to TechCrunch". The pin is the day the lab was disclosed: Anthropic gave no date for when it opened and declined to say where it is beyond the Bay Area, so the pin sits on San Francisco, the city of its own headquarters.
Anthropic confirmed it operates a wet biology lab in the Bay Area where its models can run physical experiments, its head of life sciences Eric Kauderer-Abrams saying the company is doing real lab work today. Anthropic says the facility's focus is fundamental biology rather than drug discovery, where it partners with pharma customers including Novo Nordisk.
Anthropic, 500 Howard Street, San Francisco, CAAnthropic
ESTIMATED65% CONFIDENCENo official date: September 21 is the day Polymarket's[1][2] per-day market prices highest, at 31% on its outcome row (the page header reads 30.5%), with September 22 at 25% and September 24 at 15%, and “No release by September 30” at 22%. The figures are the chance on each row, not the Buy Yes or Buy No prices in cents beside them.
Polymarket
Polymarket
Prediction-market traders expected Anthropic to ship the successor to Claude Opus 5 (released July 24, 2026) within days. On 19 September 2026 Polymarket's per-day market made September 21 the single likeliest day at 31%, ahead of September 22 at 25%, and its deadline market gave a release by September 30 an 83% chance and by October 31 98%. Anthropic had not announced the model; the “Opus 5.1” name comes from leaked early-access identifiers and early tester reports.
CONFIRMED90% CONFIDENCEUnlike the Fable 5.1 announcement, this page dates itself: the header reads “Claude[2] Opus 5.5 September 22, 2026”. TechCrunch's[3] byline (“9:30 AM PDT · September 22, 2026”, “released on Tuesday”) and XDA's 2026-09-22T16:44Z timestamp agree, so the source[1] keeps the claim and the two reports corroborate it.
Anthropic releases Claude Opus 5.5, the first model in a new Claude 5.5 family, which it says matches Claude Fable 5.1 on most work while costing 40% less to run than Opus 5.
Anthropic, 500 Howard St, San Francisco, CAAnthropic
ESTIMATED67% CONFIDENCENothing has been scheduled: this is a "by when" market. November 2026 is the month it prices highest — the ladder rises from 9% before November 1 to 50% before December 1, a 41-point month against 24 for December — and a month-only date takes its last day.[1]
Kalshi
Kalshi
On 20 September 2026 Kalshi’s Anthropic IPO ladder went from a 9% chance of an announcement before November 1 to 50% before December 1, putting 41 points of probability on November 2026 alone — by far the single likeliest month. By April 2027 the market had the announcement at 91%.
