Hi @htrumbo2,
Mark to Market trading is generally associated with
Section 1256 Contracts and Straddles from a tax perspective, covering futures and options trading. All open trades in this category, as of the end of the year (December 31), are reported as being sold at fair market value, even if you continue to hold the investment. For tax purposes, every Section 1256 gain or loss is treated as 60% long term and 40% short term, no matter how long it is owned.
This article provides further detail on this topic: https://turbotax.intuit.com/tax-tips/investments-and-taxes/what-is-form-6781-gains-and-losses-from-section-1256-contracts-and-straddles/L2rfcJXT9