somewhere around Marxism in politics.

Shalizi states at least part of his position as follows:

"Market socialism" is a current of ideas [...] for how to make extensive use of markets without thereby creating gross economic and political inequality. [...] On the other hand, modern states are powerful enough as things stand; to turn the economy wholly over to them is a bad idea. To combine markets with socialism seems like an elegant and feasible solution, at least technically, and it's one which I support [...]

and on the same page says these things:

Incredible things were done in the name of [the political control of economic life], some of them noble and heroic (like resistance to Fascism, and the creation of democratic welfare states), others scarcely matched for wickedness (like Stalin's purges and deliberate famines) and stupidity (like Mao's Great Leap Forward and apparently unintentional but highly foreseeable famines).

and

The history of socialist movements is [...] bound up with the histories of organized labour, of economics and left-wing politics and general, and, less honourably, with that of revolutions and totalitarianism. [...] it had become clear [...] that they [sc. the Soviets] were far, far worse than capitalist democracies [...]

I have to say that none of this sounds very Marxist to me. Shalizi apparently finds revolutions dishonourable; the most notable attempts at (nominally) Marxist states, the USSR and the PRC, he criticizes in very strong terms; he wants most prices to be set by markets (at least this is how I interpret what he says on that page and others it links to).

Oh, here's another bit of evidence:

Sometime between [1956] and 1968 [...] he [sc. Kolakowski] stopped considering himself a Marxist, even a revisionist one [...] though still a socialist and (I think) an atheist.

followed in the next paragraph by

I think his views of socialism and Marxism are absolutely on-target

which seems to me to imply, in particular, that Shalizi doesn't consider himself "a Marxist, even a revisionist one".

He's certainly a leftist, certainly considers himself a socialist, but he seems quite some way from Marxism. (And further still from, e.g., any position taken by the USSR or the PRC.)