I am currently working for a company and I'm on an H1B. I know that I cannot accept compensation from any other employer but the company that filed for my visa.
What if another company grants me stock options though? Stock options have no value (I don't even have to pay taxes on them) till I exercise them. Would this be a valid exception that lets me start collaborating part-time with another company?
Would this be a valid exception that lets me start collaboratingOf course not. It would be compensation, and as you said - you're not allowed to have that.
part-time with another company?
But the truth is that what you're not allowed is to work for anyone other than your H1b sponsor. With, or without compensation. Even if you volunteer to work for free, unless its a charity - you'd be breaking the law.
Check with an immigration attorney if you want to be sure, I'm not an attorney.