diff --git a/crates/ml-alpha/src/rl/isv_slots.rs b/crates/ml-alpha/src/rl/isv_slots.rs
index 51c1b1a53..e46a8c1ca 100644
--- a/crates/ml-alpha/src/rl/isv_slots.rs
+++ b/crates/ml-alpha/src/rl/isv_slots.rs
@@ -1886,6 +1886,24 @@ pub const RL_POLICY_GATE_ENTROPY_MEAN_INDEX: usize = 781;
 /// single action.
 pub const RL_POLICY_PER_HEAD_ENTROPY_MEAN_BASE_INDEX: usize = 782;
 
+/// Multiplier applied to the gate Adam learning rates (W_gate, b_gate) on
+/// top of the shared `RL_LR_PI_INDEX` (slot 411) value. Bootstrap 5.0 per
+/// Phase 2A-D fix B1 (2026-06-03): 3-seed mid-smoke at HEAD 5f10bcde3
+/// (flag-on) showed gate_entropy_mean pinned at MAX log(K) ≈ 1.0983 for
+/// 2000 steps with argmax_mass = 1.000 — the gate gradient
+/// `grad_gate_probs[k] = Σ_a pi_probs_k[k,a]·grad_pi_probs[a]` is
+/// structurally weak near uniform g_k ≈ 1/K because all heads contribute
+/// similarly, so W_gate moves too slowly to escape the uniform basin.
+/// Scaling only the gate Adams (NOT the head Adams) accelerates routing
+/// learning without destabilising head training. Range [0.5, 50.0] for
+/// the ISV controller — outside that we expect either degenerate noise
+/// (too high) or no effect (too low). Slot defaults to 0.0 sentinel when
+/// the multi-head flag is off; the bootstrap write at slot 790 happens
+/// inside the same `if self.use_multi_head_policy { ... }` block as
+/// slots 761-764, so flag-off bit-equality is preserved (0² contributes
+/// 0 to the `isv_state` checksum).
+pub const RL_POLICY_GATE_LR_MULTIPLIER_INDEX: usize = 790;
+
 /// Last RL-allocated slot index (exclusive).
 /// Pre-risk-stack: 662. Post-Fix-B: 685. Post-v9 (warmup boundary): 696.
 /// Post-regime-observer (F1.1): 716. Post-warmed-flag addendum: 717.
@@ -1902,4 +1920,5 @@ pub const RL_POLICY_PER_HEAD_ENTROPY_MEAN_BASE_INDEX: usize = 782;
 /// Post-rollout-buffer+GAE Phase 1B-A (3 PPO control slots): 760.
 /// Post-multi-head-policy Phase 2A-A (4 policy-gating slots): 764.
 /// Post-multi-head-policy Phase 2A-D (25 aggregate diag slots): 789.
-pub const RL_SLOTS_END: usize = 790;
+/// Post-Phase 2A-D fix B1 (gate LR multiplier slot 790): 790.
+pub const RL_SLOTS_END: usize = 791;
diff --git a/crates/ml-alpha/src/trainer/integrated.rs b/crates/ml-alpha/src/trainer/integrated.rs
index 901d5889d..415130405 100644
--- a/crates/ml-alpha/src/trainer/integrated.rs
+++ b/crates/ml-alpha/src/trainer/integrated.rs
@@ -4167,11 +4167,16 @@ impl IntegratedTrainer {
             //   * head_entropy_floor   = log(N_ACTIONS)·0.4 ≈ 0.959
             //   * aux_prior_beta       = 0.05 (5% of policy-loss magnitude)
             if self.use_multi_head_policy {
-                let mhp_isv_constants: [(usize, f32); 4] = [
+                // Phase 2A-D fix B1 (2026-06-03): slot 790 gate-LR multiplier
+                // bootstrap 5.0 — addresses gate-not-learning observed in
+                // 3-seed mid-smoke at HEAD 5f10bcde3 (gate_entropy stayed
+                // pinned at MAX, argmax_mass = 1.0). See slot doc-comment.
+                let mhp_isv_constants: [(usize, f32); 5] = [
                     (crate::rl::isv_slots::RL_POLICY_NUM_HEADS_INDEX,             3.0_f32),
                     (crate::rl::isv_slots::RL_POLICY_GATING_ENTROPY_FLOOR_INDEX,  0.549_f32),
                     (crate::rl::isv_slots::RL_POLICY_HEAD_ENTROPY_FLOOR_INDEX,    0.959_f32),
                     (crate::rl::isv_slots::RL_POLICY_AUX_PRIOR_BETA_INDEX,        0.05_f32),
+                    (crate::rl::isv_slots::RL_POLICY_GATE_LR_MULTIPLIER_INDEX,    5.0_f32),
                 ];
                 for (slot, value) in mhp_isv_constants.iter() {
                     let slot_i32 = *slot as i32;
@@ -5522,11 +5527,21 @@ impl IntegratedTrainer {
         // Phase 2A-C: mirror lr_pi onto the multi-head Adam state when
         // the gate is on. ISV[RL_LR_PI_INDEX] remains the single source
         // of truth — no separate slot for multi-head LR.
+        //
+        // Phase 2A-D fix B1 (2026-06-03): gate Adams use lr_pi × ISV[790]
+        // (RL_POLICY_GATE_LR_MULTIPLIER_INDEX, bootstrap 5.0) so the
+        // routing gradient — structurally weak near uniform g_k ≈ 1/K —
+        // can escape the uniform basin without amplifying head training.
+        // Heads keep raw lr_pi.
         if self.use_multi_head_policy {
+            let gate_lr_mult = self.read_isv_host(
+                crate::rl::isv_slots::RL_POLICY_GATE_LR_MULTIPLIER_INDEX,
+            );
+            let lr_gate = lr_pi * gate_lr_mult;
             if let Some(a) = self.mhp_w_heads_adam.as_mut() { a.lr = lr_pi; }
             if let Some(a) = self.mhp_b_heads_adam.as_mut() { a.lr = lr_pi; }
-            if let Some(a) = self.mhp_w_gate_adam.as_mut() { a.lr = lr_pi; }
-            if let Some(a) = self.mhp_b_gate_adam.as_mut() { a.lr = lr_pi; }
+            if let Some(a) = self.mhp_w_gate_adam.as_mut() { a.lr = lr_gate; }
+            if let Some(a) = self.mhp_b_gate_adam.as_mut() { a.lr = lr_gate; }
         }
         self.value_w_adam.lr  = lr_v;
         self.value_b_adam.lr  = lr_v;