We Asked GPT-5.5 and Claude Opus 4.7 to Design 5 UIs

A head-to-head comparison of GPT-5.5 and Claude Opus 4.7 on five UI design tasks (SaaS landing page, analytics dashboard, settings page, sign-up screen, pricing page), each producing a single self-contained HTML file using Tailwind CSS. Claude Opus 4.7 demonstrated a wider design vocabulary with context-specific typography, color choices, and density, while GPT-5.5 applied a consistent modern-SaaS template across all tasks. GPT-5.5 also missed three explicit prompt requirements. Opus had one visually broken output (pricing card overflow). Both models still require a designer-engineer pass before shipping. Claude Opus 4.7 is recommended as a faster starting point for real product surfaces, while GPT-5.5 suffices for greenfield mockups. GPT-5.5 output tokens are 20% more expensive ($30/M vs $25/M).