The Heroes of the Inner Sphere DLC is now available for MechWarrior 5: Mercenaries for PC and consoles. Piranha Games' single-player, BattleTech action game (and the new DLC) can also now be purchased for Windows through GOG.com or Steam, and the Xbox Series X|S edition is also now available. There's an added incentive on GOG.com, where you'll get a free copy of The Surge with your purchase. The PC version of Mercenaries had been exclusive on the Epic Games Store since late 2019 (updated to remove some erroneous date math, thank you Joshua for the heads-up). Here's a DLC Launch Trailer and some details:

MechWarrior 5: Mercenaries finds players in the battlefields of the future, dominated by BattleMechs, hulking machines of war capable of leveling entire cities. As the inheritor of a once-glorious Mercenary company, the quest for glory and revenge will stretch light years, chasing the threads of interstellar intrigue on the journey to become an elite MechWarrior and mercenary commander.

The merc life of a MechWarrior BattleMech pilot continues in the Heroes of the Inner Sphere DLC. Follow your chosen career path from War Dog to Treasure Hunter in the new Career Mode. Explore new warzones, new quests, and new missions that span the full scope of the Inner Sphere. Hunt the Heroes with special quests that tell the story of seven new heroes and their lostech mechs. Find new mech chassis and variants, weapons, equipment, as well as blueprints to quirk your prized mechs.