Opus 5
A reportedly forthcoming flagship large language model from Anthropic, rumored to succeed the Fable model and representing the fifth generation of the Claude family's Opus series.
Core Facts
Opus 5.5 reaches the level of Fable 5.1 on most tasks, but with approximately 40% lower operating costs and faster speed.
Anthropic states that Opus 5.5 can reduce total costs for typical tasks by approximately 40% and improve output speed by more than 30%.
Claude Opus 5.5 generates output more than 30% faster than Opus 5.
Timeline (last 90 days)
Anthropic's three steep jumps in merge volume correspond respectively to the releases of Fable 5 and Mythos 5 (June 9), Opus 5 (July 24), and Fable 5.1 and Mythos 5.1 (September 1).
The author speculates that when using Opus 5 as a coding agent in experiments, it confidently gave incorrect conclusions about correlations, which may be the result of the combined effect of RLVR and RLHF.
Across 14 tests covering approximately 145 skills, Jev found the correct skill in under 5 seconds on average, while using Opus 5 by default required approximately 30 seconds.
The Box team applied Opus 5.5 to enterprise knowledge work, achieving 63% token savings, 42% reduction in redundancy, and 30% speed improvement compared to Opus 5, with accuracy gains of 39% on financial services tasks and 65% on cloud cost analysis.
Reasoning models exhibit overthinking at excessively high effort levels, causing them to overturn originally correct answers, and a similar pattern has been observed in Anthropic's Opus 5.
After being criticized by the author, Opus 5.5 offered only a brief apology and a one-sentence summary, whereas Opus 5 wrote an entire paragraph of self-examination and used phrases such as "this is the honest version."
In a comparison using the same codebase, same prompt, and same high reasoning intensity, Opus 5.5 delivered the core information in a single paragraph, while Opus 5 produced an overly lengthy final answer after laying out its reasoning steps.
According to data from Artificial Analysis, the number of reasoning tokens per task doubled from approximately 42,000 in Opus 5 to 84,000 in Opus 5.5, while output tokens only increased from 30,000 to 35,000.
Compared to the previous-generation Opus 5, the typical usage cost of Opus 5.5 has decreased by approximately 40% and output speed has improved by more than 30%.
Anthropic launched Claude Opus 5.5, with capabilities close to the flagship Fable 5.1, costs reduced by 40%, and output speed improved by more than 30% compared to Opus 5.
40 more timeline events
All Facts (20)
Opus 5.5 reaches the level of Fable 5.1 on most tasks, but with approximately 40% lower operating costs and faster speed.
80%VerifiedAnthropic states that Opus 5.5 can reduce total costs for typical tasks by approximately 40% and improve output speed by more than 30%.
70%VerifiedClaude Opus 5.5 generates output more than 30% faster than Opus 5.
70%VerifiedV4.1 Flash surpassed Opus 5 on the DeepSWE benchmark by a narrow margin of 0.2 points.
70%VerifiedAccounting for real usage scenarios, the actual cost advantage of Opus 5 over Fable is approximately 20% to 25%, with Fable costing about $2.75 per task and Opus 5 about $2.03.
65%VerifiedOpus 5's pass rate at Low Effort is approximately 60%, surpassing Opus 4.8's 59% at the Max level, for which the per-task cost is as high as $13.
65%VerifiedClaude Opus 5's capabilities are close to the level of the previous-generation flagship Opus, but with significantly reduced inference costs.
65%UnverifiedThe release party claimed that the cost of DeepSeek-V4.1-Flash is only 1/40 that of Opus 5 and GPT-5.6 Sol.
70%Partially VerifiedThe per-task cost of GPT-6 Sol High on Automation Bench is only one-tenth that of Opus 5.
65%UnverifiedOpus 5 can handle multiple technical layers in a single generation, including 3D scene construction, collision detection, user input response, and audio triggering.
60%UnverifiedOpus 5 is the flagship model of Anthropic's Claude series, known for its longer context window (capable of handling codebases of hundreds of thousands of tokens) and more cautious output style.
60%UnverifiedClaude Opus 5 scored 30.2% on ARC-AGI-3, compared to only 1.5% for the previous generation.
60%UnverifiedClaude Opus 5 scored 1861 on the knowledge work benchmark GDPval, above the human average.
60%UnverifiedAnthropic's three steep jumps in merge volume correspond respectively to the releases of Fable 5 and Mythos 5 (June 9), Opus 5 (July 24), and Fable 5.1 and Mythos 5.1 (September 1).
50%UnverifiedThe author speculates that when using Opus 5 as a coding agent in experiments, it confidently gave incorrect conclusions about correlations, which may be the result of the combined effect of RLVR and RLHF.
50%UnverifiedAcross 14 tests covering approximately 145 skills, Jev found the correct skill in under 5 seconds on average, while using Opus 5 by default required approximately 30 seconds.
50%UnverifiedThe Box team applied Opus 5.5 to enterprise knowledge work, achieving 63% token savings, 42% reduction in redundancy, and 30% speed improvement compared to Opus 5, with accuracy gains of 39% on financial services tasks and 65% on cloud cost analysis.
50%UnverifiedReasoning models exhibit overthinking at excessively high effort levels, causing them to overturn originally correct answers, and a similar pattern has been observed in Anthropic's Opus 5.
50%UnverifiedIn a comparison using the same codebase, same prompt, and same high reasoning intensity, Opus 5.5 delivered the core information in a single paragraph, while Opus 5 produced an overly lengthy final answer after laying out its reasoning steps.
50%UnverifiedAfter being criticized by the author, Opus 5.5 offered only a brief apology and a one-sentence summary, whereas Opus 5 wrote an entire paragraph of self-examination and used phrases such as "this is the honest version."
50%