Experts are organized into groups; the router first picks groups, then experts inside them - friendlier to multi-GPU serving.
With hundreds of experts spread across devices, letting a token pick any k experts scatters traffic everywhere. Grouped routing first selects the best expert groups (which map to devices), then the best experts within those groups. DeepSeek introduced this 'node-limited' routing to cap cross-device communication; you will see it in graphs as a two-stage top-k.
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