diff --git a/src/art/megatron/flex_attention.py b/src/art/megatron/flex_attention.py
index 2e4ab5a0..e5f583d3 100644
--- a/src/art/megatron/flex_attention.py
+++ b/src/art/megatron/flex_attention.py
@@ -77,14 +77,16 @@ def forward(
         )
 
 
-_compiled_create_block_mask = torch.compile(create_block_mask)
+# Sequence-length churn can break the Inductor backend here. Keep this
+# on aot_eager instead.
+_compiled_create_block_mask = torch.compile(create_block_mask, backend="aot_eager")
 
 
 def create_shared_prefix_attention_state(
     group_ids: Tensor,
     parent_ids: Tensor,
 ) -> SharedPrefixAttentionState:
-    """Build a compiled block mask for ART shared-prefix packing.
+    """Build a block mask for ART shared-prefix packing.
 
     Initialized on the device of the group_ids tensor.