diff --git a/src/h3_blackwell_runtime/qwen3vl_vision.py b/src/h3_blackwell_runtime/qwen3vl_vision.py
index e4b5a9b..1391f01 100644
--- a/src/h3_blackwell_runtime/qwen3vl_vision.py
+++ b/src/h3_blackwell_runtime/qwen3vl_vision.py
@@ -674,12 +674,14 @@ class Qwen3VL32BVision(nn.Module):
     @staticmethod
     def _merge_tokens(x: torch.Tensor, grid_thw: torch.Tensor) -> torch.Tensor:
         """Flatten 2x2 spatial-merge blocks (the reference's pre-merge flatten)."""
-        # grid_thw is a 2D long tensor [[t, h, w], ...]; take the first image.
         first = grid_thw[0]
         t = int(first[0].item())
         h = int(first[1].item())
         w = int(first[2].item())
         merge = 2
+        print(f"[merge_tokens] x.shape={tuple(x.shape)}, t={t}, h={h}, w={w}, "
+              f"target=({t}, {h//merge}, {merge}, {w//merge}, {merge}, {x.shape[-1]}), "
+              f"prod={t*(h//merge)*merge*(w//merge)*merge*x.shape[-1]}", flush=True)
         return x.view((t, h // merge, merge, w // merge, merge, x.shape[-1])).permute(0, 1, 3, 2, 4, 5).reshape(-1, -1)
 
     def forward(self, flatten_patches: torch.Tensor, grid_thw: torch.Tensor) -> tuple[torch.Tensor, list[torch.Tensor]]: