"That's ridiculous. California is at-will through and through."

Errr, actually, california has a lot of exceptions to at-will. Here's a random article analyzing it. Note the conclusion: http://www.hullmcguire.com/pdf/Hull%20McGuire%20-%20Californ...

It's pretty common. I believe there is even case law saying that once you've been at a place for some significant amount of time, you have the right to expect to only be terminated for cause.

Paying an equity grant isn't the same as continuing to employ someone and continuing to pay their salary. If someone has an equity grant, that's already a liability to be paid. "At will" refers to ongoing employment, not paying existing liabilities.

I'm not sure what you mean by "paying an equity grant". If you fire someone they no longer receive new equity. And for a company that's been public for 4 years with a constantly dropping stock price I doubt the volume of early employees exercising options could possibly bankrupt the company. I don't understand how that could happen to any reasonably well managed company.

>Even among its Silicon Valley peers, which have drawn closer scrutiny from investors recently because of their generous stock-based compensation practices, Twitter is notable for how much equity it doles out.

>And those grants of restricted stock units or options, which would have to be covered to some degree by any buyer, simply add to the purchase price of any deal.

>According to Twitter’s most recent annual filing, the company racked up $682 million in stock-based compensation last year. By comparison, the company’s adjusted earnings before interest, taxes, depreciation and amortization — which also excludes stock-based compensation — for the year was $557.8 million.

>Factoring in the payouts would have pushed Twitter well into the red for the year.

https://www.nytimes.com/2016/09/27/business/dealbook/twitter...

Is a grant an option? No. A grant is a grant. The employee isn't buying the stock at some price. The employee is being paid in equity with a grant. It's stock that's been issued in lieu of higher salaries. And yes, if an employee gets a grant vested you must fulfill the grant even if the employee leaves after vesting. You can't just hire people and refuse to pay their compensation.