SWE-bench Pro 89.9% in Anthropic's launch table, ahead of Claude Fable 5.1 (81.2%) and Opus 5 (79.2%)
Cheaper than the model it replaces: $4/$20 per 1M against Opus 5's $5/$25, and cache reads at $0.20/1M
1M context and 128K output at standard rates, with effort levels up to max
Weaknesses
Not ahead everywhere: Anthropic's own table has Opus 5 higher on Toolathlon Verified (80.6% vs 77.8%)
Fast mode doubles the price to $8/$40
Terminal-Bench 4.0 differs by effort setting (66.4% at xhigh, 64.8% at max), so single-digit gaps against rivals are directional
Real-world use cases
What people actually use Claude Opus 5.5 for.
Repository-scale changes and PR work — Anthropic reports 89.9% on SWE-bench Pro, up from 79.2% for Opus 5
Long unattended agent runs where per-task token spend matters as much as the per-token price
Reports, analysis and briefs that need to state findings and next steps plainly
How Claude Opus 5.5 compares
The nearest models people weigh against it, and what actually separates them.
vs Claude Sonnet 5.5 — Against Claude Sonnet 5.5 (Anthropic), Claude Opus 5.5 costs about 50% more per token and answers slower. Claude Sonnet 5.5 is the one to check first if the price difference matters more than the ceiling.
vs Claude Fable 5.1 — Against Claude Fable 5.1 (Anthropic), Claude Opus 5.5 runs about 60% cheaper per token. Take Claude Opus 5.5 unless you specifically need what Claude Fable 5.1 does better.
vs Claude Fable 5 — Against Claude Fable 5 (Anthropic), Claude Opus 5.5 runs about 60% cheaper per token. Take Claude Opus 5.5 unless you specifically need what Claude Fable 5 does better.
Ready to try it?
Start using Claude Opus 5.5
Agentic coding, long-running agents and knowledge work where Opus 5 was the bar. Start free — no card required.
Anthropic's September 28, 2026 Sonnet — built for well-scoped everyday work like features, bug fixes, documents, slides and spreadsheets, priced at $2/$10 and close to Opus 5.5 on most of Anthropic's launch rows.
Verdict
Near-Opus 5.5 quality on scoped work at half the price.
Quality score
96%
Pricing
$2.00/1M in
$10.00/1M out
Speed
Fast
4/5 speed
Context
1M tokens
Released September 28, 2026. Gateway id anthropic/claude-sonnet-5.5. $2/$10 per 1M (cache read $0.10, cache write $2.50). 1,000,000 context, 128,000 max output, knowledge cutoff June 2026. Launch figures as reported by Anthropic (Sonnet 5.5 / Opus 5.5): Terminal-Bench 4.0 70.6 / 66.4; OSWorld 2.1 80.1 / 81.8; Humanity's Last Exam 64.5 / 67.7; GDPval-AA v2.1 1,844 / 1,846. Verified October 10, 2026.
CodingWritingFast1M contextValueNew
Best for
Everyday feature work, bug fixing and polished documents at mid-tier pricing
Anthropic's September 1, 2026 frontier release and the new capability ceiling for coding, agents, and scientific work. Base pricing is unchanged at $10/$50, but cache reads dropped 75% to $0.25/1M — roughly 25% cheaper on typical workloads and up to 45% cheaper on agentic ones. 1M context, 128K output, adaptive thinking always on.
Verdict
Anthropic's highest-ceiling model — strongest on open-ended research; Opus 5.5 now leads coding.
Quality score
98%
Pricing
$10.00/1M in
$50.00/1M out
Speed
Deliberate
2/5 speed
Context
1M tokens
Released September 1, 2026 alongside Claude Mythos 5.1, the first update to the Mythos-class line since Fable 5 on June 9. API ID claude-fable-5-1; generally available on the Claude API, Amazon Bedrock, Google Cloud, and Microsoft Foundry. Published launch numbers (Fable 5.1 / Fable 5 / Opus 5 / GPT-5.6 Sol): Terminal-Bench-Science 0.1 52.6 / 24.7 / 29.0 / 22.4; Terminal-Bench 4.0 55.8 / 42.0 / 52.3 / 37.3; CursorBench 3.2.0 73.4 / 70.5 / 70.0 / 67.2; AutomationBench 31.4 / 17.1 / 26.9 / 19.6; OSWorld 2.0 strict 41.7 / 36.1 / 39.6; Humanity's Last Exam (no tools) 60.9 / 57.8 / 56.6; GDPval-AA v2 1853 / 1723 / 1824 / 1711. GDPval-AA v2 is rescaled from the v1 numbers quoted on the Fable 5 page and is not directly comparable to them.
Anthropic's new Mythos-class flagship and the most capable coding model anyone can use — 80.3% SWE-Bench Pro, an 11-point jump over Opus 4.8. 1M context, 128K output, native parallel subagents. Released June 9, 2026.
Verdict
Superseded by Fable 5.1 — still 80.3% SWE-Bench Pro, but 5.1 is better and cheaper to run.
Quality score
97%
Pricing
$10.00/1M in
$50.00/1M out
Speed
Deliberate
2/5 speed
Context
1M tokens
Launched June 9, 2026 as the public, Mythos-class release. Available on the Claude API, Microsoft Foundry, and Google Vertex AI. Free for all users until June 22, 2026. Same underlying model as Claude Mythos 5, with safeguards that block specific high-risk cyber responses. Superseded by Claude Fable 5.1 on September 1, 2026 — same $10/$50 base pricing, cache reads cut from $1.00 to $0.25 per 1M tokens.
SWE-Bench Pro 80.3%Mythos-classParallel subagentsAgenticLong contextPremiumSuperseded
Best for
The hardest coding tasks, autonomous multi-step agents, and frontier-grade reasoning
Pricing moves, ranking shifts, and capability updates.
New ModelSep 22, 2026
Claude Opus 5.5 released — new SWE-bench Pro leader, and cheaper than Opus 5
Anthropic released Claude Opus 5.5 on September 22, 2026. Its launch table reports 89.9% on SWE-bench Pro, ahead of Claude Fable 5.1 (81.2%) and Opus 5 (79.2%), and 93.9% on SWE-bench Multilingual. The price fell from Opus 5's $5/$25 to $4/$20 per million tokens, with cache reads at $0.20, and Anthropic says it spends fewer tokens per finished task. It is not ahead on every row: Opus 5 still scores higher on Toolathlon Verified (80.6% vs 77.8%), and its Terminal-Bench 4.0 result depends on the effort setting (66.4% at xhigh, 64.8% at max). Context is 1M tokens with 128K output; Fast mode costs $8/$40. Opus 5.5 is now the top coding pick across the directory. Verified October 10, 2026.
Claude Opus 5.5 costs $4 per million input tokens and $20 per million output tokens on the API, with cached input at $0.2 per million. A month of 10M input and 2M output tokens runs about $80.00 at list price, before any batch or caching discounts.
What is the context window of Claude Opus 5.5?
Claude Opus 5.5 has a 1M tokens context window, with up to 128k tokens of output per response. That is the total of prompt plus response the model can hold in one request.
What is the knowledge cutoff of Claude Opus 5.5?
Claude Opus 5.5's training data runs through June 2026, and the model was released on September 22, 2026. For anything after that date it needs web search or documents in the prompt.
What is Claude Opus 5.5 best for?
Claude Opus 5.5 is best for agentic coding, long-running agents and knowledge work where opus 5 was the bar. It is a strong fit when that workflow matters more than the tradeoffs around premium pricing and deliberate speed.
When should I avoid Claude Opus 5.5?
Your tasks are well-scoped and latency-sensitive — Sonnet 5.5 is half the price and Anthropic says it is the fastest Sonnet yet.
What is a cheaper alternative to Claude Opus 5.5?
Claude Sonnet 5.5 (Anthropic) at $2.00/1M/1M input against Claude Opus 5.5's $4.00/1M/1M — roughly 50% less per token all in. Near-Opus 5.5 quality on scoped work at half the price. Compare it first if Claude Opus 5.5's pricing is the thing stopping you.
What is a faster alternative to Claude Opus 5.5?
Claude Fable 5.1 — deliberate against Claude Opus 5.5's deliberate, with 1M tokens of context. Worth the swap when response time is what your users notice rather than the last few points of reasoning depth.
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