Claude Sonnet 5 achieves 53 on the Artificial Analysis Intelligence Index, but without promotional pricing will cost more per task than Opus 4.8

We supported Anthropic to evaluate Claude Sonnet 5 ahead of release: with max effort it improves 6 points over Sonnet 4.6 to achieve the same Intelligence Index as GPT-5.5 with high reasoning, but remains behind Opus 4.7 and 4.8

➤ Claude Sonnet 5 is the #5 model on the Artificial Analysis Intelligence Index, only 2-3 points behind GPT-5.5 (xhigh) and Opus 4.8 (max)

➤ With max effort, Sonnet 5 works harder than previous Anthropic models: it used ~40% more output tokens per Intelligence Index task than Sonnet 4.6, and ~3x the agentic turns for our knowledge work evaluations AA-Briefcase and GDPval-AA. This behavior scales well with the ‘effort’ setting, with the max effort using around 6x more turns than low effort on GDPval-AA

➤ Claude Sonnet 5 costs more per task than Opus 4.8 before accounting for promotional pricing: Claude Sonnet 5 costs $2.29 per task on the Intelligence Index, a ~2x increase compared to Sonnet 4.6 and ~15% more than Claude Opus 4.8. This is driven entirely by increased token usage. Sonnet 5 retains the same $3/$15 per 1M input/output token pricing as Sonnet 4.6 (compared to $5/$25 for Opus 4.8), however Anthropic is offering a one-third reduction to $2/$10 until September 1. Our results use standard $3/$15 pricing

➤ Sonnet 5 matches or outperforms Opus 4.8 on agentic knowledge work tasks: on both AA-Briefcase and GDPval-AA, Claude Sonnet 5 sits just ahead of Opus 4.8, trailing only Claude Fable 5 (which is not currently generally available). These benchmarks test the ability of models to produce accurate and well-presented professional outputs using our open source reference agent harness, Stirrup

➤ For reasoning and knowledge-heavy tasks, Sonnet still sits behind its larger siblings: despite substantial gains across many evaluations, heavy reasoning and knowledge benchmarks still show Opus 4.8 ahead of Sonnet 5. On CritPt, a frontier physics reasoning benchmark developed by researchers at Argonne and UIUC, Sonnet 5 scores 17% - this is 14 points higher than its predecessor, but behind GLM-5.2, Claude Opus and Fable, and GPT-5.5 (xhigh and Pro)

➤ Sonnet 5 also showed significant improvements over Sonnet 4.6 on Terminal-Bench v2.1 (+9 points), Humanity’s Last Exam (+10 points), and SciCode (+7 points), with relatively flat scores elsewhere

➤ Context window of 1 million tokens (equivalent to Sonnet 4.6)

➤ Pricing of $3/$15 per 1M tokens of input/output (reduced to $2/$10 until September 1); cache pricing remains at a 25% premium for cache writes ($3.75 per million tokens) with 5-minute time to live, and 90% discount for cache hits ($0.3 per million tokens)

➤ Effort remains the recommended way of configuring model performance and latency. Sonnet 5 adds an additional ‘xhigh’ effort setting relative to Sonnet 4.6, matching the 5 effort levels available on Opus 4.8 (max, xhigh, high, medium, low)