Isn't it meant to slot somewhere between a strategic and tactical bomber?
Good question! Going by Wikipedia, the B-21 Raider is,
"an American under development for the (USAF)...". Though I am not sure if the term strategic bomber has a defined range and/or payload capacity."
Wikipedia again on strategic bombers states,
"is a medium- to long-range aircraft designed to drop large amounts of onto a distant target for the purposes of debilitating the enemy's capacity to wage war. Unlike , , , and , which are used in operations to attack enemy combatants and military equipment, strategic bombers are designed to fly into enemy territory to destroy strategic targets (e.g., , , , factories, etc.)"
I think based on the above definition that the B-21 would be considered strategic, since it would to attack infrastructure, logistics, military installations, etc as mentioned above. Thought it clearly wouldn't be limited to that role.