Near-Opus 5.5 quality on scoped work at half the price.
98
Coding
98
Writing
95
Research
88
Images
60
Value
95
Long Context
Use this when
Everyday feature work, bug fixing and polished documents at mid-tier pricing
Skip this if
The work is long, ambiguous and multi-step — Anthropic positions Opus 5.5 for exactly that — or you need the lowest possible price, where Haiku 5.5 costs a twentieth as much.
Pricing
$2.00/1M in
$10.00/1M out
Context
1M tokens
Speed
Fast
Claude Sonnet 5.5specs & pricing
Verified Oct 10, 2026 against the AI Gateway catalog
Terminal-Bench 4.0 70.6% in Anthropic's table — above Opus 5.5's 66.4% on that row
Half the price of Opus 5.5 at $2/$10, with cache reads cut to $0.10/1M
Anthropic says it generates more than 30% faster than Sonnet 5
Weaknesses
Anthropic itself says Opus 5.5 is better on loosely defined tasks that need longer reasoning
Trails Opus 5.5 on Humanity's Last Exam (64.5% vs 67.7%)
Real-world use cases
What people actually use Claude Sonnet 5.5 for.
Day-to-day feature and bug-fix work in an IDE or coding agent, where speed matters more than ceiling
Drafting documents, slide decks and spreadsheets that need to be presentable on the first pass
Computer-use tasks — Anthropic reports 80.1% on OSWorld 2.1, within two points of Opus 5.5
How Claude Sonnet 5.5 compares
The nearest models people weigh against it, and what actually separates them.
vs Claude Opus 5.5 — Against Claude Opus 5.5 (Anthropic), Claude Sonnet 5.5 runs about 50% cheaper per token and answers faster. Take Claude Sonnet 5.5 unless you specifically need what Claude Opus 5.5 does better.
vs Claude Fable 5.1 — Against Claude Fable 5.1 (Anthropic), Claude Sonnet 5.5 runs about 80% cheaper per token and answers faster. Take Claude Sonnet 5.5 unless you specifically need what Claude Fable 5.1 does better.
vs Claude Fable 5 — Against Claude Fable 5 (Anthropic), Claude Sonnet 5.5 runs about 80% cheaper per token and answers faster. Take Claude Sonnet 5.5 unless you specifically need what Claude Fable 5 does better.
Ready to try it?
Start using Claude Sonnet 5.5
Everyday feature work, bug fixing and polished documents at mid-tier pricing. Start free — no card required.
Anthropic's September 22, 2026 Opus — a step up from Opus 5 on agentic coding, long-running agent work and vision, at a lower $4/$20 list price and with fewer tokens spent per finished task.
Verdict
Anthropic's new coding default — top SWE-bench Pro score at a lower price than Opus 5.
Quality score
98%
Pricing
$4.00/1M in
$20.00/1M out
Speed
Deliberate
2/5 speed
Context
1M tokens
Released September 22, 2026. Gateway id anthropic/claude-opus-5.5. $4/$20 per 1M (cache read $0.20, cache write $5); Fast mode $8/$40. 1,000,000 context, 128,000 max output, knowledge cutoff June 2026, effort levels low to max. Launch figures as reported by Anthropic: SWE-bench Pro 89.9 (Fable 5.1 81.2, Opus 5 79.2); SWE-bench Multilingual 93.9; Terminal-Bench 4.0 66.4 (xhigh); OSWorld 2.1 81.8; Humanity's Last Exam 67.7; Toolathlon Verified 77.8 (Opus 5 80.6). Verified October 10, 2026.
CodingAgenticFlagship1M contextPremiumNew
Best for
Agentic coding, long-running agents and knowledge work where Opus 5 was the bar
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 28, 2026
Claude Sonnet 5.5 released — near-Opus 5.5 on scoped work, at $2/$10
Anthropic released Claude Sonnet 5.5 on September 28, 2026, positioned for well-scoped everyday work such as building features, fixing bugs and producing documents, slides and spreadsheets. It costs $2/$10 per million tokens — less than Sonnet 5's $3/$15 — with cache reads halved to $0.10, a 1M-token context and 128K output. In Anthropic's launch table it scores 70.6% on Terminal-Bench 4.0 (Opus 5.5: 66.4%), 80.1% on OSWorld 2.1 (81.8%) and 64.5% on Humanity's Last Exam (67.7%). Anthropic says it generates more than 30% faster than Sonnet 5 and still recommends Opus 5.5 for long, loosely defined tasks. Verified October 10, 2026.
Claude Sonnet 5.5 costs $2 per million input tokens and $10 per million output tokens on the API, with cached input at $0.1 per million. A month of 10M input and 2M output tokens runs about $40.00 at list price, before any batch or caching discounts.
What is the context window of Claude Sonnet 5.5?
Claude Sonnet 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 Sonnet 5.5?
Claude Sonnet 5.5's training data runs through June 2026, and the model was released on September 28, 2026. For anything after that date it needs web search or documents in the prompt.
What is Claude Sonnet 5.5 best for?
Claude Sonnet 5.5 is best for everyday feature work, bug fixing and polished documents at mid-tier pricing. It is a strong fit when that workflow matters more than the tradeoffs around balanced pricing and fast speed.
When should I avoid Claude Sonnet 5.5?
The work is long, ambiguous and multi-step — Anthropic positions Opus 5.5 for exactly that — or you need the lowest possible price, where Haiku 5.5 costs a twentieth as much.
What is a cheaper alternative to Claude Sonnet 5.5?
Claude Opus 5.5 (Anthropic) at $4.00/1M/1M input against Claude Sonnet 5.5's $2.00/1M/1M. Anthropic's new coding default — top SWE-bench Pro score at a lower price than Opus 5. Compare it first if Claude Sonnet 5.5's pricing is the thing stopping you.
What is a faster alternative to Claude Sonnet 5.5?
Claude Fable 5.1 — deliberate against Claude Sonnet 5.5's fast, 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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