Steering token routing toward an expert centroid controls which expert processes a token

Ternovtsii & Bilak train a custom cosine-routing MoE from scratch (8 layers, 1024 rank-1 experts/layer) and show its expert centroids are a causally-steerable geometric object [ternovtsii-bilak-2026-geometric-routing-causal-control] Biasing a token's routing position toward a temporal expert's centroid increases P(temporal) by a median +321%, while suppressing a geographic expert drops P(geographic) by 23.2% (vs 0% for random) [ternovtsii-bilak-2026-geometric-routing-causal-control] Directly rewriting a geographic expert's up-projection weight vector ("expert surgery") halves P(geographic) [ternovtsii-bilak-2026-geometric-routing-causal-control] Cross-layer composed steering is near-additive while same-layer composition interferes, so the routing-centroid direction behaves like an ordinary composable steering vector [ternovtsii-bilak-2026-geometric-routing-causal-control]