OpenAI chief revenue officer Denise Dresser sent a four-page internal memo to staff on Sunday, signalling a clear shift in the company’s cloud allegiances—Amazon is now the enterprise growth engine, while Microsoft has “limited” its reach. The memo touts “staggering” inbound demand since the $50 billion Amazon partnership was announced in February. Meanwhile, Microsoft insists nothing has changed—and is reportedly weighing legal action to prove it.