I think autonomia certainly came from a huge wave of working class struggles, but many of the intellectuals around it were far from Marxism before those struggles and have moved away since. Negri's Multitude book doesn't really see the working class as revolutionary but rather the whole "multitude" of "people" which i think neglects what is specifically revolutionary about the social position of the working class in the process of production, and also dissipates the struggle of the united international proletariat into sectional struggles of parts of the proletariat and other oppressed people who may or may not be working class (racial minorities, women, etc.). It's possible that what I've read about Autonomism was misrepresenting it (I mostly refer to what has been published in the last 20 years under this term), but to me it has gotten tangled into the whole anti-globalization movement which doesn't actually look for a real way to fight capitalism at its heart and a class with an interest in destroying capitalism--the anti-globalization movement celebrates anything that it thinks contradicts what they see as the logic of "globalization" from third worldist statesmen, to tariff demands, to land reclamation movements, etc.