Earlier quoted context omitted.
Where is this other $300B coming from? Is OpenAI paying AMD $400B or what? I looked at the article but it seems disjointed and hard to parse for me. And I don't see where it mentions some $400B coming to AMD one way or another. It's implied... how? Sorry, this isn't sarcasm or anything like it. I just don't get it and your answer does not help.
The traditional "efficient market" theory would be: synergies. The market believes that AMDs value increased BECUASE OpenAI now owns it. That is to say, the market believes that OpenAI taking a stake in AMD increases the value of AMD. There are a host of different hypothesis you could pose to explain that. Maybe OpenAI has some secret sauce they'll share with AMD now that they have a stake. Maybe OpenAI will be more…
Imho AMD itself needs to have a theory, which underpins their signing of the deal. For my clueless self, that investors have various theories and we don't know what they are is ok-ish, but that AMD has a theory but keeps it secret yet it gets the result of stock rise... is fishy.
Everyone is going in circles making suppositions and estimations based on who knows what. That can't be healty, can it? There used to be requirements that publicly listed companies act with some level of transparency, and those requirements existed for a reason. I guess. I am certainly no expert in finance.