Claude Opus 5.5

Claude Opus 5.5 is the first model in Anthropic\u2019s Claude 5.5 family, released on 22 September 2026. The official API id is claude-opus-5-5. Anthropic says it performs at Fable 5.1 level on most work and costs 40% less to run than Opus 5.

Specs from the docs overview: 1M context, 128K max output, default effort medium. Adaptive thinking is always on — thinking cannot be disabled. Knowledge cutoff is June 2026 (docs comparison table). Zero data retention. Preserved thinking for API accounts created on or after 31 August 2026.

Safeguards Anthropic published with the launch: most cybersecurity tasks are re-routed to Opus 4.8 (cyber fallback). Biology safeguards are described as like Fable 5.1. Breaking API notes: thinking cannot be disabled; forced tool use errors; thinking blocks are tied to model + conversation; computer_20251124 is not accepted on Claude API and Google Cloud.

Anthropic\u2019s product claim versus Opus 5 is cheaper typical runs, a lower token list, faster output, and the bench table below. These are Anthropic\u2019s numbers from the announcement — not independent verification. Unless noted, Anthropic says Opus 5.5 uses adaptive thinking at max effort; Terminal-Bench 4.0 is Opus 5.5 at xhigh versus GPT-6 Astra at high.

Missing cells are missing in Anthropic\u2019s table. This page does not fill them. The practical read of that table versus Opus 5: every published row moves up, with the largest published gaps on Terminal-Bench 4.0 and Terminal-Bench-Science 0.1.

Anthropic\u2019s list: $4 per million input tokens and $20 per million output tokens. Cache reads are $0.20 (Anthropic: 60% less than Opus 5). Cache writes are $5 on the Sonnet 5.5 announcement comparison table.

Anthropic\u2019s cost claims on top of the rate card: the token list is 20% less than Opus 5; typical work costs 40% less to run; output is 30%+ faster than Opus 5. Those are vendor claims about list, token use, and speed — not a relay invoice.

Prices are Anthropic\u2019s published list. A 2026-10-04 nini kiro probe completed as claude-opus-5-5. Listed on llmrelay 2026-10-04 at $2/$10 (half Anthropic list). The previous Claude flagship we can call today is Claude Opus 5.

Yes on Anthropic\u2019s own platforms. Yes on llmrelay as of 4 October 2026, id claude-opus-5-5, $2/$10.

• +Claude Platform, AWS, GCP, Azure — official API id claude-opus-5-5, per anthropic.com/claude-opus-5-5 and the platform.claude.com overview.
• +llmrelay — listed 2026-10-04. Id claude-opus-5-5, $2 input / $10 output per million tokens (half Anthropic list). Prepaid credit.

If you call it on Anthropic or cloud platforms, the breaking notes above matter: thinking cannot be turned off; forced tool use errors; thinking blocks stay tied to the model and conversation; computer_20251124 is rejected on Claude API and Google Cloud.

Request claude-opus-5-5 on llmrelay the same way you request claude-opus-5. Prepaid credit, no subscription.

Anthropic\u2019s positioning is that Opus 5.5 performs at Fable 5.1 level on most work, at a lower Opus-class list than Opus 5. The announcement table is the published scorecard for that claim.

On every row Anthropic published for both models, Opus 5.5 is ahead: Terminal-Bench 4.0 66.4% vs 55.8%, FrontierCode v1.1 Main 54.4% vs 50.3%, CursorBench 4.0 57.8% vs 51.8%, GDPval-AA v2.1 1846 vs 1735, AutomationBench 40.0% vs 31.4%, HLE with tools 67.7% vs 65.6%, Terminal-Bench-Science 0.1 58.7% vs 52.6%, OSWorld 2.1 partial 81.8% vs 80.7%, Chartography with tools 89.0% vs 88.4%. Biology safeguards are described as like Fable 5.1.

That is Anthropic\u2019s table, not a third-party bake-off. This page does not claim llmrelay can call Fable 5.1 or Opus 5.5.

On Anthropic platforms the model id is claude-opus-5-5. Default effort is medium. Adaptive thinking is always on. If Claude Code or Cursor is pointed at Anthropic, AWS, GCP, or Azure and that product accepts the new id, that is Anthropic\u2019s path.

That is also llmrelay\u2019s path now. Point Claude Code or Cursor at llmrelay and request claude-opus-5-5. Listed 2026-10-04. Previous generation claude-opus-5 stays listed; 5.5 is listed and callable.

Previous generation remains listed: Claude Opus 5 (id claude-opus-5) at $2.50/$12.50.

Anthropic\u2019s docs: 1,000,000 input tokens and 128,000 max output tokens.

Default effort is medium. Adaptive thinking cannot be disabled, so long-context calls always run with thinking on. Knowledge cutoff in the docs comparison table is June 2026.

The GPT-6 Astra column below is Anthropic\u2019s announcement table only. Empty cells stay empty. Terminal-Bench 4.0 on that table is Opus 5.5 at xhigh versus GPT-6 Astra at high.

On Anthropic\u2019s table Opus 5.5 leads Terminal-Bench 4.0, FrontierCode v1.1 Main, GDPval-AA v2.1, and HLE with tools. GPT-6 Astra leads AutomationBench (41.4% vs 40.0%) and Terminal-Bench-Science 0.1 (64.6% vs 58.7%). Anthropic did not publish Astra scores for CursorBench 4.0, OSWorld 2.1 partial, or Chartography with tools in that table.

Vendor table, vendor numbers. Independent verification is a separate question, and this page does not claim it. Both GPT-6 Astra and Opus 5.5 are listed on llmrelay as of 4 October 2026.

Anthropic launch docs do not describe a post-release quality cut. What showed up in the last two days on Reddit is a different claim: users saying the first week was exceptional and that quality then dropped — bugs after one-shots, ignored instructions, writing that suddenly felt like Opus 5.

Highest-traffic threads pulled with rdt-cli (authenticated search, 29 Sep–2 Oct 2026):

• +r/ClaudeAI — “Is Opus 5.5 entering a nerfed phase? LiveNerf baseline update” (score 2585, 443 comments). OP is running day-by-day SWE-bench / SciCode. Auto-summary after 400 comments: community consensus was “yes, nerfed.” That is a thread summary, not a lab result.
• +r/ClaudeCode — “something is suddenly off with Opus 5.5” (score 1008, 466 comments). OP tied the change to a monthly limit reset after six days of 12-hour Claude Code use.
• +r/ClaudeAI — “nerfing — how to measure, how to spot, how to sue” (score 1788, 361 comments). OP: custom C++ / Blender MCP work was clean for 5–6 days, then a simple task failed plus an odd “Written for: you…” line.

Comment theories in those threads (quantization, load-based quality, sentiment-driven dials) are user theories. This page does not confirm them. If you need a model llmrelay can actually call today, that is still Claude Opus 5.

No. Anthropic’s Opus 5.5 overview: adaptive thinking is always on. Thinking cannot be disabled. Default effort is medium. That is a documented breaking change, not a Reddit rumor.

Related API notes from the same docs: forced tool use errors; thinking blocks stay tied to the model and conversation; computer_20251124 is not accepted on Claude API and Google Cloud. Cybersecurity tasks are mostly re-routed to Opus 4.8.

Reddit’s last-two-day “it got dumber” threads are about perceived quality, not about a new thinking-off switch. If a client still sends thinking-off, Anthropic’s migration notes say that path does not work on 5.5.