OpenAI's ad experiment did not begin in strength. The $60 CPM it charged at launch in February was a premium rate that assumed ChatGPT's audience was uniquely valuable to advertisers — more targeted, more intentional, more conversion-ready than a generic search audience. That assumption was tested and disproved in ten weeks. The CPM erosion from $60 to $25 is not a blip in a new market finding its floor; it is advertisers communicating that ChatGPT's inventory is closer in value to a mid-tier display network than to Google's intent-capture apparatus.…