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LLM FoundationsHard· Mixture of Experts· Ablation Studies

How would you run the ablation to decide whether to inc...

To properly decide on including a shared expert, you should train three 1B-parameter models for 100B tokens each, keeping hyperparameters fixed. The variants are: (a) 0 shared, 64 routed, K=6; (b) 1 shared, 64 routed, K=6 (adding 17% FFN FLOPs); and (c) 0 shared, 64 routed, K=7 (adding 17% FFN FLOPs via an extra routed expert). Comparing held-out perplexity against the FLOP budget determines the winner. If (b) beats (c), the shared expert is justified; if (c) beats (b), adding a routed expert is a more efficient use of compute.

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