active parameters
How much of a model actually runs to produce one token, as opposed to how much of it sits in memory. In a name like qwen3.6-35b-a3b the a3b is this number: 35 billion parameters stored, 3 billion of them used per token. It predicts speed, where the total predicts memory.
A dense model has no such number, because the answer is always all of them. The a-number only appears on a mixture of experts, and its absence is itself information: no a-number means dense.
The two numbers pull in opposite directions when you shop. Total parameters decide whether the file fits. Active parameters decide whether waiting for it is bearable.