It must have been in the first round [1], but leaves open the question of whether this is still the case:
> Returns for our first round of investors are capped at 100x their investment (commensurate with the risks in front of us), and we expect this multiple to be lower for future rounds as we make further progress.
> Returns for our first round of investors are capped at 100x their investment (commensurate with the risks in front of us), and we expect this multiple to be lower for future rounds as we make further progress.
[1] https://openai.com/blog/openai-lp/