This excerpt taken from the ATVI DEFA14A filed Dec 11, 2007.
1. How will this transaction affect Activision vested stock options?
If you have vested stock options at the time the tender offer closes, you will be able to participate in the tender offer with respect to the shares underlying those vested options. The company plans to develop and will provide additional information on a mechanism to simply your participation in the tender offer.
It is anticipated that you will be able to advise the company, at the time of the tender offer, how many vested options you are willing to exercise if your shares are purchased in the tender offer. You will not be required to exercise options until you are advised how many shares the company purchases in the tender offer under the proration features in the tender offer. For example, if all currently outstanding shares were tendered, approximately 50% of these shares would be purchased for cash and 50% would be returned to shareholders.