Quick Take

Anthropic’s Claude Sonnet 5 and OpenAI’s GPT-5.5 (xhigh) are top-tier models released in the spring and summer of 2026. GPT-5.5 (xhigh) establishes a lead in core intelligence and coding metrics, while Claude Sonnet 5 positions itself as a competitive, cost-effective alternative for high-volume tasks.

Benchmark Read

GPT-5.5 (xhigh) consistently outperforms Claude Sonnet 5 across available benchmarks. In general intelligence, GPT-5.5 holds an index of 54.8 compared to Claude’s 53.4. This trend continues in coding, where GPT-5.5 scores 74.9 against Claude’s 71.5.

Specific performance metrics further highlight the gap:

• GPQA: GPT-5.5 (0.935) vs. Claude Sonnet 5 (0.911)
• HLE: GPT-5.5 (0.443) vs. Claude Sonnet 5 (0.396)
• SciCode: GPT-5.5 (0.561) vs. Claude Sonnet 5 (0.536)
• LCR: GPT-5.5 (0.743) vs. Claude Sonnet 5 (0.707)

GPT-5.5 also demonstrates superior performance in specialized testing, including IFBench (0.759), TerminalBench Hard (0.606), and TAU2 (0.939).

Cost and Speed

Cost is a significant differentiator. Claude Sonnet 5 is priced at a blended rate of $6.00/1M tokens, significantly lower than GPT-5.5’s $11.25/1M.

Regarding performance, the models trade blows. Claude Sonnet 5 features a higher output speed of 88.576 tokens per second. However, GPT-5.5 (xhigh) is substantially faster in terms of responsiveness, boasting a time-to-first-token of 18.464 seconds, compared to the 72.504 seconds required by Claude Sonnet 5.

Best Fit

Claude Sonnet 5 is best suited for cost-sensitive applications that require high-throughput text generation. GPT-5.5 (xhigh) is the superior choice for latency-sensitive applications and complex tasks where the highest possible reasoning and coding accuracy is required.