- Start
- Sep 21, 202650% CONFIDENCEfrom the source
Anthropic Expected to Release Its Next Claude Opus Model
- Polymarket's per-day market "Next Claude Opus released on...?" (opened Sep 16, 2026, 6:24 PM ET, End Date Oct 1, 2026, $45,044 volume) makes September 21 the single likeliest day at 35% - the summary strip gives 34.6% - ahead of September 22 at 32%, September 23 at 8% (strip: 13.5%) and September 24 at 12%; "No release by September 30" trades at 9%.[2]
- Its companion deadline market "Next Claude Opus released by...?" ($236,245 volume, End Date Jan 1, 2027) prices a release by September 24 at 80%, by September 27 at 88%, by September 30 at 90%, by October 31 at 96% and by December 31 at 97%.[1]
- Both markets resolve only on a model "explicitly named Opus" - Opus 5.1, Opus 5.5, Opus 6 or other Opus variants qualify, while Sonnet, Haiku, Fable or Mythos do not - and the model must be "launched and publicly accessible, including via open beta or open rolling waitlist signups", with closed or private access, labeling errors and placeholder version names not counting; "Claude Opus 5, released on July 24, 2026", and any snapshot, rollout or re-release of it is explicitly excluded. Resolution comes from official Anthropic information plus a consensus of credible reporting.[1][2]
- Anthropic has announced nothing: as of late August 2026 there was no announcement, model card, API identifier, pricing page or benchmark for Opus 5.1, with Anthropic's docs listing claude-opus-5, claude-sonnet-5 and claude-fable-5 as current.[3][4]
- "Opus 5.1" is a community name traced to two test strings, claude-marshmallow-eap and claude-melon-eap, circulating in screenshots and Discord from August 21 to 24, 2026; the strings "never contained 'opus', 'sonnet' or '5.1'" and commentators inferred the names on August 24. Readings are contested - most take Marshmallow as the Opus successor and Melon as Sonnet, others read Melon as a new Haiku - and testers claim neither reaches Fable 5.[3][4]
- The expected window comes from cadence: Opus 4.8 in late May, Fable/Mythos 5 and Sonnet 5 in June, Opus 5 on July 24, 2026, and Fable 5.1 and Mythos 5.1 on September 1[1][4]; a claude-honeycomb-eap string reportedly surfaced roughly two to three weeks before Opus 5 shipped, implying a late-August-into-September window.[3][4]
- Earlier predicted dates have slipped: a rumored "late August" window and a circulated August 28 date passed, and one widely circulated but unverified view placed Fable 5.1 around August 31 and Opus 5.1 around September 5. A September 14 update notes one X account claiming Opus 5 in Claude Code is being served by a newer model it calls "Opus 5.2", with no identifier or traffic report backing it.[3][4]
- What a release would be measured against: Opus 5 is priced at $5 per million input and $25 per million output tokens (the same as Opus 4.8), with a 1-million-token context, up to 128k output tokens, adaptive thinking and effort controls, and reported Frontier-Bench v0.1 of about 43.3%; point releases have historically held tier pricing, so continuity at $5/$25 is expected.[3][4]
References 465% CONFIDENCE
The first entry is always the pin's source. Overall confidence is a weighted average of how firmly each reference supports the start and end times used above; a reference counts half as much for every 180 days older than the newest.
- [1]50%polymarket.com/event/next-claude-opus-released-byptptpt-20260727142323912polymarket.com· Posted Sep 19, 2026· Starts Sep 21, 2026 ✓· 26% of score
No official date: September 21 is the day Polymarket's[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.
- [2]70%Polymarket: Next Claude Opus released on...?polymarket.com· Added Sep 19, 2026· 26% of score
Polymarket's[1] daily market is where the September 21 date comes from: it priced that day at about 45%, ahead of September 22 (18%) and September 24 (14%), with 24.5% on no release by September 30.
- [3]70%Claude Opus 5.1 Release Date: Leaks vs What Shippedcellcog.ai· Published Sep 14, 2026· 25% of score
CellCog traces the "Opus 5.1" name to the claude-marshmallow-eap and claude-melon-eap strings seen around August 21-24, and notes "there is no announcement, model card, API identifier, pricing page, or benchmark."
- [4]70%Claude Opus 5.1 Is Coming Soon: What Developers Should Expectcometapi.com· Published Sep 3, 2026· 24% of score
CometAPI applies the roughly 2-3 week gap from the Honeycomb early-access build to Opus 5 and says "a public release could arrive in the coming weeks," while stressing the dates remain unverified.
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