What I'm confused about though is what makes current AI evaluations a bubble.

Bubbles usually exists when future speculation outpaces productivity: eventually some realization leads the market to no longer believe in that future speculation, causing devaluation which triggers a mass sell-off.

However, AI companies currently have very high revenues and are growing extremely fast. Their valuation is backed by actual commerce. I can't imagine that there is any room for a bubble, as it is very clear where the market is at, and why demand for AI is so high.

Now, certain specific companies I can imagine losing a lot of valuation, but only contingent on the fact that they serve a middle-man role in the market that improvements in the underlying AI models will solve, which would likely only mean more revenue for the frontier labs, and thus less reason for a bubble.