But it's also important to note that only $300K of that is in cash. The other $600K is in profit participation, which could take years (maybe even a decade!) to be realized. It could also be worth $6M a year when it's realized.
But ultimately it's an investment of your time. Or to think of it another way, you're getting paid $900K a year but you're also investing $600K a year in OpenAI, which may end up being an amazing return or nothing at all, just like any startup investment.
Although with Sam at the helm, my guess is it will probably be worth more than $600K a year.
There's a whole class of engineers were completely invisible to most companies, even if they are in the same "local market" [0][1] (Some use the term "dark matter devs" but I know it has another meaning [2]). These guys tend to fly under the radar quite a bit. If you are in a tier 2 market or company, your chances of attracting one are close to nil. Because they are extremely valuable, they don't interview a lot and tend to hop between companies where they know people (or get fast tracked internally).
FAANG companies have internship pipelines, with bonus for returning interns. These guys are off the market years before they even graduate.
[0] https://blog.pragmaticengineer.com/software-engineering-sala...
[1] http://danluu.com/bimodal-compensation/
[2] https://www.hanselman.com/blog/dark-matter-developers-the-un...