In the Pre-Agentic Web, “Mobile First” was the undisputed law. For over a decade, SEOs and developers optimized for the thumb, the swipe, and the 375px viewport. But as we transition into the era of Agentic Traversal, the “Inference Window” is shifting the architecture back toward the desktop.

The bottom line for 2026: Every major AI agent uses a desktop browser. If you want your site to be navigable by autonomous agents, you must prioritize your desktop layout—specifically at widths between 1024px and 1440px.