Quick Take

Claude Sonnet 5 (released June 30, 2026) and GPT-5.5 (xhigh) (released April 23, 2026) are the latest iterations from Anthropic and OpenAI. Claude Sonnet 5 focuses on adaptive reasoning with a medium-effort profile, while GPT-5.5 (xhigh) is positioned as a high-performance model with extensive documentation and benchmark validation.

Benchmark Read

GPT-5.5 (xhigh) provides a comprehensive look at its capabilities through a variety of standardized tests. It holds an Intelligence index of 54.8 and a Coding index of 74.9. Specific benchmark results include:

• GPQA: 0.935
• HLE: 0.443
• SciCode: 0.561
• IFBench: 0.758
• LCR: 0.743
• TerminalBench Hard: 0.606
• TAU2: 0.938

Conversely, Claude Sonnet 5 currently has no benchmark rows available for comparison, making its performance profile more opaque compared to the data-rich GPT-5.5.

Cost and Speed

There is a significant difference in both pricing and latency between the two models:

• Pricing: Claude Sonnet 5 is more affordable, with a blended cost of $6.00/1M tokens (Input: $3.00/1M, Output: $15.00/1M). GPT-5.5 (xhigh) is priced at a blended $11.25/1M (Input: $5.00/1M, Output: $30.00/1M).
• Performance: Claude Sonnet 5 offers a faster time to first token at 2.069s, compared to 18.464s for GPT-5.5. However, GPT-5.5 (xhigh) maintains a higher output speed of 76.599 tok/s versus Claude’s 69.618 tok/s.

Best Fit

Claude Sonnet 5 is best suited for developers and businesses looking to minimize costs while maintaining low-latency interactions. Its adaptive reasoning capabilities make it a strong candidate for general-purpose tasks. GPT-5.5 (xhigh) is the superior choice for research, complex coding, and scientific applications where the model's performance must be verified against rigorous benchmarks like the newly introduced LifeSciBench.