The thesis is blunt: AI models are now the medium, and designing how they behave is the new design practice. This piece from Sidebar argues that the discipline is not shrinking, it is relocating upstream, into the systems, prompts, and behavioral constraints that shape model output before any visual layer exists.
The interesting tension is what 'shifting left' actually demands from designers. It is not Figma. It is not user flows. It is an understanding of model behavior, evaluation criteria, and the humanistic values baked into system-level decisions. That is a different skill set, and the piece does not pretend otherwise.
Worth reading in full for the argument it makes about professional identity: if designers do not claim this upstream territory, engineers and product managers will, by default. The question is not whether this work gets done. The question is who does it.
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