top-2 expert routing

**Top-2 expert routing** is the **MoE policy that sends each token to the two highest-scoring experts and combines their outputs with learned weights** - it improves routing smoothness and representation flexibility compared with top-1 assignment. **What Is Top-2 expert routing?** - **Definition**: Router selects the best two experts per token based on gating logits or probabilities. - **Combination Rule**: Final token output is weighted sum of the two expert outputs. - **Capacity Dynamics**: Doubles potential expert traffic relative to top-1 and increases communication volume. - **Modeling Effect**: Allows tokens with mixed semantics to benefit from multiple expert functions. **Why Top-2 expert routing Matters** - **Quality Improvement**: Often yields better accuracy due to richer token processing paths. - **Gradient Flow**: Two-expert participation provides smoother optimization signals. - **Specialization Flexibility**: Supports overlap between expert competencies where useful. - **Systems Cost**: Higher compute and routing overhead require careful capacity planning. - **Deployment Choice**: Tradeoff between model quality and throughput is architecture-dependent. **How It Is Used in Practice** - **Policy Benchmarking**: Compare top-1 and top-2 on validation quality and cost-per-token. - **Capacity Tuning**: Increase expert capacity factor and communication budget for top-2 workloads. - **Inference Decisions**: Use top-2 where quality gains justify added latency or compute spend. Top-2 expert routing is **a quality-oriented MoE routing strategy with measurable systems tradeoffs** - it can improve modeling performance when infrastructure budget supports the extra work.