you must select 1256 contracts marked to market. this includes any 1256 contracts closed out during the year. if you have open 1256 contracts at year-end they are deemed sold at FMV on 12/31 (that's where the M-T-M comes from). of course if you have no open contracts at year-end think as you in effect have marked to market just that the amount is $0
you may want to read the instructions for form 6781 (below the form) because that's where 1256 contract reporting is done. and despite the true holding period 60% are treated as long term and 40% are treated as short-term.
https://www.irs.gov/pub/irs-pdf/f6781.pdf
