The 83(b) informs the IRS that you will pay taxes, for the tax year you received the grant, on an entire stock grant (RSUs, or early-exercised stock options) up front, at its current valuation. This also starts the clock on long-term capital gain, even though your stock isn't fully vested yet. 🎉
When do I file the 83(b) election?
You must mail the election to the IRS within 30 days of receiving a stock grant or purchasing your stock options.