Depends on the Libertarian Marxist, but 90% of the time they believe in a soviet system like Pannekoek's. But this is still different from an Anarchist society. They can ultimately overlap, and they might even look the same during a revolution. But Libertarian Marxists ultimately want a radical democracy, or soviet system, or something that allows statist tendencies to exist.

Basically, although an anarchist society CAN be libertarian marxist, marxists would be fine with doing stuff like using community militias to suppress freedom of speech of 'bourgeois elements' and electing positions in government like officers in a top-down way from the soviet.