I think where MoE is misleading is that the experts aren't what we would call "experts" in the normal world but rather they are experts for a specific token. that concept feels difficult to grasp.
It's more of a performance optimization than anything else, improving memory liquidity. Except it's not an optimization for running the model locally (where you only run a single query at a time, and it would be nice to keep the weights on the disk until they are relevant).
It's a performance optimization for large deployments with thousands of GPUs answering tens of thousands of queries per second. They put thousands of queries into a single batch and run them in parallel. After each layer, the queries are re-routed to the GPU holding the correct subset of weights. Individual queries will bounce across dozens of GPUs per token, distributing load.
Even though the name "expert" implies they should experts in a given topic, it's really not true. During training, they optimize for making the load distribute evenly, nothing else.
While current MoE implementations are tuned for load-balancing over large pools of GPUs, there is nothing stopping you tuning them to only switch expert once or twice per token, and ideally keep the same weights across multiple tokens.
Well, nothing stopping you, but there is the question of if it will actually produce a worthwhile model.
so you mean a "load balancer" for neural nets … well, why don't they call it that then?
Even in the single GPU case, this still saves compute over the non-MoE case.
I believe it's also possible to split experts across regions of heterogeneous memory, in which case this task really would be something like load balancing (but still based on "expertise", not instantaneous expert availability, so "router" still seems more correct in that regard.)
They don't really "bounce around" though do they (during inference)? That implies the token could bounce back from eg. layer 4 -> layer 3 -> back to layer 4.
that was AFAIK (not an expert! lol) the traditional approach
but judging by the chart on LLaMa4 blog post, now they're interleaving MoE models and dense Attention layers; so I guess this means that even a single token could be routed through different experts at every single MoE layer!