The members of Chicago are prepping the release of a new box celebrating their long stage career — and although that set won't arrive in stores until next month, fans can get a sneak peek at the contents with this exclusive premiere of a "25 or 6 to 4" live performance pulled from deep in the vaults.

You can listen to it below.

As previously reported, the new Chicago box — titled VI Decades Live (This Is What We Do) — summarizes the band's lengthy concert history with a five-disc overview that covers 1969-2014. The first two discs are devoted to the band's headlining performance at the 1970 Isle of Wight festival; film footage from another complete set, originally broadcast on Germany's Rockpalast concert series in 1977, takes up the VI Decades Live DVD. In between, the box offers an assortment of cuts from different eras, including the Dec. 8, 1969, performance of "25 or 6 to 4" above.

Due in stores April 6 and available to pre-order now, VI Decades Live (This Is What We Do) arrives ahead of another busy touring year for Chicago. They'll be on the road with a rejiggered lineup in 2018, having recently weathered the departures of drummer Tris Imboden — with the band since founder Danny Seraphine's 1990 exit — and bassist Jeff Coffey, who stepped in after longtime Chicago vet Jason Scheff left in 2016.

With percussionist Walfredo Reyes Jr. moving over to drums, bassist Brett Simons rounding out the rhythm section and new tenor singer Neil Donell helping handle vocal duties, Chicago will embark on a co-headlining tour with REO Speedwagon this summer. Look over those dates here, and check out "25 or 6 to 4" above.

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