Quick Take

Claude Sonnet 5 (Anthropic) and GPT-5.5 (xhigh) (OpenAI) represent the latest high-effort models in the competitive AI market. Released in mid-2026, these models target different segments: OpenAI focuses on peak intelligence and complex reasoning, while Anthropic provides a balanced, high-speed alternative at a lower price point.

Benchmark Read

GPT-5.5 (xhigh) outperforms Claude Sonnet 5 across all shared metrics. In the Intelligence index, GPT-5.5 scores 54.8 compared to Sonnet 5’s 41.7. Coding performance follows a similar trend, with GPT-5.5 at 74.9 and Sonnet 5 at 66.4.

Detailed benchmark comparisons show a clear lead for OpenAI’s model:

• GPQA: 0.935 (GPT-5.5) vs 0.8 (Sonnet 5)
• HLE: 0.443 (GPT-5.5) vs 0.178 (Sonnet 5)
• SciCode: 0.561 (GPT-5.5) vs 0.486 (Sonnet 5)
• LCR: 0.743 (GPT-5.5) vs 0.587 (Sonnet 5)

GPT-5.5 also demonstrates strong performance in specialized benchmarks like TAU2 (0.939) and TerminalBench Hard (0.606).

Cost and Speed

Cost efficiency is a primary differentiator. Claude Sonnet 5 is significantly cheaper, with a blended cost of $6.00/1M tokens, compared to $11.25/1M for GPT-5.5.

Performance metrics reveal a trade-off:

• Latency: Claude Sonnet 5 is much faster to initiate, with a time to first token of 1.338s, whereas GPT-5.5 takes 16.257s.
• Throughput: GPT-5.5 offers a higher output speed of 81.747 tok/s, compared to 71.116 tok/s for Sonnet 5.

Best Fit

Claude Sonnet 5 is best suited for high-volume, latency-sensitive applications where cost management is a priority. GPT-5.5 (xhigh) is the superior choice for complex, compute-heavy tasks that require the highest possible intelligence and coding accuracy, provided the user can accommodate the higher latency and pricing.