No, it simply means that it can better utilize multiple cores to do the GC work faster, so pauses will be proportionally shorter. With the current SBCL collector (or the old one, since this one is already released), even if you ran on a 16-core system, the GC would still only use a single core to reclaim memory (in practice, to move some of/all your live objects to a different address, as it was a copying collector).