It sounds very out of line of what you'd expect.
OpenAI continues to develop core AI offered over API. Microsoft builds the developer ecosystem around it -- that's Sam's expertise anyway. Microsoft has made a bunch of investment in the developer ecosystem in GitHub and that fits the theme. Assuming Sam sticks around.
Also, the way the tweet is worded (looking forward to working with OpenAI), seems like its a truce negotiated by Satya?
Either there in house team wins out and Microsoft wins.
Or OpenAI wins out and Microsoft wins with there exclusive deal and 75% of OpenAI profits.
Better to have two horses in the race in something so important, makes it much harder than one of the other companies will be the one to come out top.