Quick Take

Claude Sonnet 5 (released June 30, 2026) and GPT-5.5 (xhigh) (released April 23, 2026) represent two distinct approaches to AI deployment. Claude Sonnet 5 focuses on adaptive, low-effort reasoning with a high emphasis on speed. In contrast, GPT-5.5 (xhigh) is a high-performance model backed by extensive benchmark data, positioning it as a tool for complex, technical, and scientific applications.

Benchmark Read

GPT-5.5 (xhigh) provides a transparent look at its capabilities through a wide range of benchmarks. It records an Intelligence index of 54.8 and a Coding index of 74.9. Its performance on specific evaluations includes:

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

Claude Sonnet 5 currently has no benchmark rows available, making direct quantitative comparison against GPT-5.5 impossible. Users should rely on the model's design focus on adaptive reasoning for their specific use cases.

Cost and Speed

There is a significant difference in the economic and latency profiles of these models:

• Claude Sonnet 5: Offers a blended cost of $6.00/1M tokens (Input: $3.00, Output: $15.00). It is highly responsive, featuring a time-to-first-token of 2.445s and an output speed of 55.073 tok/s.
• GPT-5.5 (xhigh): Commands a premium price with a blended cost of $11.25/1M tokens (Input: $5.00, Output: $30.00). It is faster in raw output speed at 76.599 tok/s, but experiences a much slower time-to-first-token of 18.464s.

Best Fit

Claude Sonnet 5 is best suited for applications where latency is critical and cost-efficiency is a priority. GPT-5.5 (xhigh) is the superior choice for users requiring verified performance in coding and complex logic, particularly where the initial wait time for the first token is secondary to the model's overall output speed and reasoning depth.