Update 4/21 11:28AM ET: A Twitter spokesperson tells Engadget the company has received Musk's updated proposal, but that it's still conducting a "careful, comprehensive and deliberate review" of the offer. You can read the full statement below.
"We are in receipt of the updated, non-binding proposal from Elon Musk, which provides additional information regarding the original proposal and new information on potential financing. As previously announced and communicated to Mr. Musk directly, the Board is committed to conducting a careful, comprehensive and deliberate review to determine the course of action that it believes is in the best interest of the Company and all Twitter stockholders."