The comparison reveals that different AI models excel at specific tasks. Opus 4.5 is a strong front-end designer, while Codex 5.1 might be better for back-end logic. The optimal workflow involves "model switching"—assigning the right AI to the right part of the development process.
The test intentionally used a simple, conversational prompt one might give a colleague ("our blog is not good...make it better"). The models' varying success reveals that a key differentiator is the ability to interpret high-level intent and independently research best practices, rather than requiring meticulously detailed instructions.
The core advantage demonstrated was not just improving a single page, but generating three distinct, high-quality redesigns in under 20 minutes. This fundamentally changes the design process from a linear, iterative one to a parallel exploration of options, allowing teams to instantly compare and select the best path forward.
Unlike models that immediately generate code, Opus 4.5 first created a detailed to-do list within the IDE. This planning phase resulted in a more thoughtful and functional redesign, demonstrating that a model's structured process is as crucial as its raw capability.
Opus 4.5's winning design wasn't just about layout; it actively scanned the project's repository to incorporate existing assets like background images and brand elements ("rings"). This contrasts with other models that used generic gradients, showing a deeper contextual understanding of the brand's visual language.