I don't know the answer, but considering Meta (known for 100m+ offers) was in the rumors, and he mentions multiple labs (and many investors), and all the hype around openclaw ... I can easily see 9 figure, and would not be surprised by 1b+ "signing bonus", perhaps in the equivalent number of OpenAI shares.
... Why would they pay 9 figures? It's not like Openclaw required specialized PhD-level knowledge held by <1000 people in the world to build, and that's what Meta and the other AI labs are paying ludicrous salaries for. Openclaw is a cool project and demonstrates good product design in the AI world, but by no means is a great product manager worth 1 billion dollars.