It is a four year contract. OpenAI is hoping they'll be able to suppress their competitors long enough to regain their lead and firmly establishe a dominant position in the market.

I'm not too worried though for two reasons. First, I'm confident they'll eventually be in breech of their memory contracts for being unable to pay - as the whole AI market is a house of cards, and has no real path to profitability beyond hopes and dreams. Banks and angel investors will eventually start asking 'where are the profits' and begin pulling out the rug. Second, the chip suppliers began ramping up production (as you suggest) some time back, so the current crazy price increase should only be temporary once they have increased supply output in a year or so. They would have to sign new contracts to get their '40% deal' again, and the memory giants will have much higher price demands for any such deals in future, and I don't think OpenAI will have the money.