diff --git a/crates/ml/src/cuda_pipeline/gpu_dqn_trainer.rs b/crates/ml/src/cuda_pipeline/gpu_dqn_trainer.rs
index 66f777332..dbd098e61 100644
--- a/crates/ml/src/cuda_pipeline/gpu_dqn_trainer.rs
+++ b/crates/ml/src/cuda_pipeline/gpu_dqn_trainer.rs
@@ -629,8 +629,12 @@ pub struct GpuDqnTrainer {
 
     /// CUDA event for async scalar readback (replaces per-step stream.synchronize)
     readback_event: Option<CudaEvent>,
-    /// Pinned host buffer [3 × f32] for async DtoH scalar readback.
-    /// Layout: [0]=loss, [1]=mse_loss, [2]=grad_norm_sq.
+    /// Pinned host buffer [16 × f32] for async DtoH scalar readback.
+    /// Layout:
+    ///   [0]=loss, [1]=mse_loss, [2]=grad_norm_sq          (per-step, from graph_adam)
+    ///   [3]=avg_max_q, [4]=q_min, [5]=q_max, [6]=q_mean, [7]=q_var  (every 50 steps)
+    ///   [8]=causal_mean_sens                               (every N steps)
+    ///   [9..16]=reserved                                   (nan_flags, future use)
     /// Pinned memory enables true async cuMemcpyDtoHAsync without CPU blocking.
     readback_pinned: *mut f32,
     /// Whether there's an in-flight readback to collect
@@ -859,8 +863,6 @@ pub struct GpuDqnTrainer {
 
     /// CUDA event for async Q-stats readback (avoids per-call stream sync)
     q_stats_event: Option<CudaEvent>,
-    /// Host-side buffer for deferred Q-stats from previous reduction
-    q_stats_pending: [f32; 5],
     /// Whether there's an in-flight Q-stats readback to collect
     q_stats_ready: bool,
 
@@ -2794,7 +2796,7 @@ impl GpuDqnTrainer {
             readback_pinned: {
                 let flags = cudarc::driver::sys::CU_MEMHOSTALLOC_DEVICEMAP;
                 unsafe {
-                    cudarc::driver::result::malloc_host(3 * std::mem::size_of::<f32>(), flags)
+                    cudarc::driver::result::malloc_host(16 * std::mem::size_of::<f32>(), flags)
                         .map_err(|e| MLError::ModelError(format!("pinned readback alloc: {e}")))?
                         as *mut f32
                 }
@@ -2846,7 +2848,6 @@ impl GpuDqnTrainer {
             q_stats_kernel,
             q_stats_buf,
             q_stats_event: None,
-            q_stats_pending: [0.0; 5],
             q_stats_ready: false,
             cql_logit_grad_kernel,
             cql_d_value_logits,
@@ -3984,12 +3985,14 @@ impl GpuDqnTrainer {
                 }
             }
             self.q_stats_ready = false;
-            QValueStatsResult {
-                avg_max_q: self.q_stats_pending[0] as f64,
-                q_min: self.q_stats_pending[1],
-                q_max: self.q_stats_pending[2],
-                q_mean: self.q_stats_pending[3],
-                q_variance: self.q_stats_pending[4],
+            unsafe {
+                QValueStatsResult {
+                    avg_max_q: *self.readback_pinned.add(3) as f64,
+                    q_min: *self.readback_pinned.add(4),
+                    q_max: *self.readback_pinned.add(5),
+                    q_mean: *self.readback_pinned.add(6),
+                    q_variance: *self.readback_pinned.add(7),
+                }
             }
         } else {
             // First call — no previous data
@@ -4023,10 +4026,10 @@ impl GpuDqnTrainer {
                 .map_err(|e| MLError::ModelError(format!("q_stats_kernel: {e}")))?;
         }
 
-        // 3. Issue async DtoH for 5 f32s from q_stats_buf
+        // 3. Issue async DtoH for 5 f32s from q_stats_buf into pinned buffer at offset 3
         unsafe {
             cudarc::driver::sys::cuMemcpyDtoHAsync_v2(
-                self.q_stats_pending.as_mut_ptr().cast(),
+                self.readback_pinned.add(3).cast(),
                 self.q_stats_buf.raw_ptr(),
                 5 * std::mem::size_of::<f32>(),
                 self.stream.cu_stream(),
@@ -4064,12 +4067,14 @@ impl GpuDqnTrainer {
             }
         }
         self.q_stats_ready = false;
-        Ok(QValueStatsResult {
-            avg_max_q: self.q_stats_pending[0] as f64,
-            q_min: self.q_stats_pending[1],
-            q_max: self.q_stats_pending[2],
-            q_mean: self.q_stats_pending[3],
-            q_variance: self.q_stats_pending[4],
+        Ok(unsafe {
+            QValueStatsResult {
+                avg_max_q: *self.readback_pinned.add(3) as f64,
+                q_min: *self.readback_pinned.add(4),
+                q_max: *self.readback_pinned.add(5),
+                q_mean: *self.readback_pinned.add(6),
+                q_variance: *self.readback_pinned.add(7),
+            }
         })
     }