A 19b-4 filing, which is a form used by exchanges to inform the SEC of a proposed rule change. In this case, a rule change is required under the Securities Exchange Act of 1934 because a spot bitcoin ETF is a new product, and the exchanges — NYSE, Nasdaq and Cboe — must provide rules to explain how the product will trade. The SEC must approve the rule changes before the product can trade. This is the filing that is facing a deadline of Jan. 10 for the Ark/21Shares Bitcoin Trust.