Artificial Analysis scores Claude Sonnet 5.5 at 56, two points behind Opus 5.5
Artificial Analysis says Anthropic has launched Claude Sonnet 5.5 with a score of 56 on its Intelligence Index at max effort. That is 18 points above Sonnet 5 and two points behind Opus 5.5 (max), placing it second on the index.
At max effort, Sonnet 5.5 reaches 64% on Terminal-Bench 4.0, compared with 60% for both Opus 5.5 and GPT-6 Astra. Artificial Analysis also reports near parity with Opus 5.5 on AA-Briefcase (1811 versus 1822 Elo), GDPval-AA (1844 versus 1846 Elo), and AutomationBench-AA (71% versus 70%), with much higher token use. It used about 193,000 output tokens per Intelligence Index task, the highest volume Artificial Analysis has measured—roughly 60% more than Opus 5.5 (max) or Sonnet 5 (max) and about seven times GPT-6 Astra (max).
On AA-Omniscience, Sonnet 5.5 scores 54% factual accuracy against 66% for Opus 5.5, with a lower hallucination rate of 47% versus 59%. It also sits about six points lower on Humanity’s Last Exam and SciCode. Token prices match Sonnet 5 at $2 per million input tokens and $10 per million output tokens, with cache writes at $2.50 and cache reads at $0.20. Artificial Analysis estimates the cost at $7.60 per task, about 50% higher than Sonnet 5, and says the model sits off its intelligence-versus-cost frontier; at lower effort, GPT-6 Astra or Sol configurations deliver equivalent performance for less, while the high-effort setting is narrowly behind GPT-6 Sol at effectively the same cost per task.
The 1 million-token context window, with image and text input, is unchanged. Five effort settings were tested, and Sonnet 5.5 fell back to Sonnet 5 in about 0.1% of Intelligence Index tasks, mainly on Terminal-Bench 4.0. The results are from a pre-release deployment that Anthropic found had a bug degrading structured-output requests. Anthropic says that bug is fixed for the public release and expects minimal change or slightly understated performance. Artificial Analysis plans to re-run the relevant evaluations.