diff --git a/third_party/vllm/vllm/v1/core/sched/scheduler.py b/third_party/vllm/vllm/v1/core/sched/scheduler.py
index 6f931ad..9a0319d 100644
--- a/third_party/vllm/vllm/v1/core/sched/scheduler.py
+++ b/third_party/vllm/vllm/v1/core/sched/scheduler.py
@@ -2218,7 +2218,12 @@ class Scheduler(SchedulerInterface):
             for group in self.kv_cache_manager.get_block_ids(req_id):
                 sent_block_ids.update(group)
             self._free_blocks(self.requests[req_id])
-            if sent_block_ids:
+            # e13391e: evict sent blocks from the prefix cache. Intended ONLY for
+            # session MIGRATION (the source worker won't see the session again).
+            # For plain PD-disagg producer->consumer transfers this destroys
+            # cross-turn producer reuse, so it is gated OFF by default and enabled
+            # only for migration experiments via VLLM_EVICT_SENT_BLOCKS=1.
+            if sent_block_ids and __import__("os").environ.get("VLLM_EVICT_SENT_BLOCKS") == "1":
                 self.kv_cache_manager.evict_blocks(sent_block_ids)
 
     def _update_requests_with_invalid_blocks(