Marxists and Anarchists have a different view on what the "state" entails, and what constitutes "class." The former see the state as an instrument of class oppression, while the latter see it as an institution of hierarchy. The former see class as relations to production, the latter see class as relations of hierarchy.

I recommend reading my comment here where I go over why this is the case, and why Marxists see Communism as a fully publicly owned and planned economy, while Anarchists see Communism as a fully decentralized network of communes, and neither recognizes the other as truly "stateless" or "classless" due to these differences.