diff --git a/python/sglang/srt/hardware_backend/npu/allocator_npu.py b/python/sglang/srt/hardware_backend/npu/allocator_npu.py
index e59dbf6a0..bbc3e9dec 100644
--- a/python/sglang/srt/hardware_backend/npu/allocator_npu.py
+++ b/python/sglang/srt/hardware_backend/npu/allocator_npu.py
@@ -141,7 +141,7 @@ class NPUPagedTokenToKVPoolAllocator(PagedTokenToKVPoolAllocator):
         if free_index.numel() == 0:
             return
 
-        if self.is_not_in_free_group:
+        if self.free_group is None:
             device = free_index.device
             free_page_indices = torch.unique(free_index.cpu() // self.page_size)
             free_page_indices = free_page_indices.to(device)
diff --git a/python/sglang/srt/mem_cache/allocator/base.py b/python/sglang/srt/mem_cache/allocator/base.py
index 103324dcd..ef1de7121 100644
--- a/python/sglang/srt/mem_cache/allocator/base.py
+++ b/python/sglang/srt/mem_cache/allocator/base.py
@@ -44,8 +44,8 @@ class BaseTokenToKVPoolAllocator(abc.ABC):
 
         self.free_pages = None
         self.release_pages = None
-        self.is_not_in_free_group = True
-        self.free_group = []
+        # None: free right away. A list: hold frees until free_group_end().
+        self.free_group: list[torch.Tensor] | None = None
 
     @property
     def size_full(self):
@@ -61,13 +61,12 @@ class BaseTokenToKVPoolAllocator(abc.ABC):
         return self._kvcache
 
     def free_group_begin(self):
-        self.is_not_in_free_group = False
         self.free_group = []
 
     def free_group_end(self):
-        self.is_not_in_free_group = True
-        if self.free_group:
-            self.free(torch.cat(self.free_group))
+        pending, self.free_group = self.free_group, None
+        if pending:
+            self.free(torch.cat(pending))
 
     @staticmethod
     def _copy_for_free_group(free_index: torch.Tensor) -> torch.Tensor:
diff --git a/python/sglang/srt/mem_cache/allocator/hisparse.py b/python/sglang/srt/mem_cache/allocator/hisparse.py
index 8ebfee249..dc283b617 100644
--- a/python/sglang/srt/mem_cache/allocator/hisparse.py
+++ b/python/sglang/srt/mem_cache/allocator/hisparse.py
@@ -61,8 +61,7 @@ class HiSparseTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
 
         self.free_pages = None
         self.release_pages = None
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
         self.clear()
         self._kvcache.register_mapping(
             weakref.proxy(self.full_to_hisparse_device_index_mapping)
@@ -166,8 +165,6 @@ class HiSparseTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         return buffer_indices
 
     def free_hisparse_indices(self, buffer_indices: torch.Tensor):
-        # disable free group mechanism for device buffer free
-        self.hisparse_attn_allocator.is_not_in_free_group = True
         self.hisparse_attn_allocator.free(buffer_indices[buffer_indices > 0])
 
     def get_last_loc_compressed(self, last_locs: torch.Tensor):
@@ -246,9 +243,9 @@ class HiSparseTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         self.hisparse_attn_allocator.clear()
         # Note: the last item is -1, we don't clear it, see the comment in __init__
         self.full_to_hisparse_device_index_mapping[:-1].fill_(0)
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
 
+    # No deferred frees: free() must clear the full-to-hisparse mapping at once.
     def free_group_begin(self):
         return
 
@@ -258,11 +255,8 @@ class HiSparseTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
     def free(self, free_index: torch.Tensor):
         if free_index.numel() == 0:
             return
-        if self.is_not_in_free_group:
-            self.logical_attn_allocator.free(free_index)
-            self.free_hisparse(free_index)
-        else:
-            self.free_group.append(self._copy_for_free_group(free_index))
+        self.logical_attn_allocator.free(free_index)
+        self.free_hisparse(free_index)
         assert (
             self.logical_attn_allocator.available_size()
             <= self.logical_attn_allocator.size
@@ -321,8 +315,7 @@ class DeepSeekV4HiSparseTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         self.need_sort = logical_attn_allocator.need_sort
         self.free_pages = None
         self.release_pages = None
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
         self.clear()
 
         self.hisparse_kvcache.register_mapping(
@@ -444,7 +437,6 @@ class DeepSeekV4HiSparseTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
                 surplus_pages = torch.unique(surplus // self.hisparse_page_size)
                 pure_surplus = surplus_pages[~torch.isin(surplus_pages, buffer_pages)]
                 if pure_surplus.numel() > 0:
-                    self.hisparse_attn_allocator.is_not_in_free_group = True
                     self.hisparse_attn_allocator.free(
                         pure_surplus * self.hisparse_page_size
                     )
@@ -474,7 +466,6 @@ class DeepSeekV4HiSparseTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         return buffer_indices
 
     def free_hisparse_indices(self, buffer_indices: torch.Tensor):
-        self.hisparse_attn_allocator.is_not_in_free_group = True
         self.hisparse_attn_allocator.free(buffer_indices[buffer_indices > 0])
 
     def get_last_loc_compressed(self, last_locs: torch.Tensor):
@@ -575,14 +566,13 @@ class DeepSeekV4HiSparseTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         self.hisparse_attn_allocator.clear()
 
         self.full_to_hisparse_device_index_mapping[:-1].fill_(0)
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
 
     def free(self, free_index: torch.Tensor):
         if free_index.numel() == 0:
             return
 
-        if self.is_not_in_free_group:
+        if self.free_group is None:
             self.logical_attn_allocator.free(free_index)
         else:
             self.free_group.append(self._copy_for_free_group(free_index))
diff --git a/python/sglang/srt/mem_cache/allocator/paged.py b/python/sglang/srt/mem_cache/allocator/paged.py
index b092911f2..f21c077f6 100755
--- a/python/sglang/srt/mem_cache/allocator/paged.py
+++ b/python/sglang/srt/mem_cache/allocator/paged.py
@@ -262,7 +262,7 @@ class PagedTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         if free_index.numel() == 0:
             return
 
-        if self.is_not_in_free_group:
+        if self.free_group is None:
             self._release_page_ids(torch.unique(free_index // self.page_size))
         else:
             self.free_group.append(self._copy_for_free_group(free_index))
@@ -293,7 +293,7 @@ class PagedTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
                 torch.unique(free_index.cpu() // ps),
             )
 
-        if self.is_not_in_free_group:
+        if self.free_group is None:
             self._release_page_ids(*(p // ps for p in pieces))
             if self.debug_mode:
                 self._debug_check_no_duplicate_pages()
@@ -333,8 +333,7 @@ class PagedTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         self.free_pages = torch.arange(
             1, self.num_pages + 1, dtype=torch.int64, device=self.device
         )
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
         self.free_page_reps_group = []
         self.release_pages = torch.empty((0,), dtype=torch.int64, device=self.device)
 
diff --git a/python/sglang/srt/mem_cache/allocator/swa.py b/python/sglang/srt/mem_cache/allocator/swa.py
index f3540340f..2deffeeb1 100644
--- a/python/sglang/srt/mem_cache/allocator/swa.py
+++ b/python/sglang/srt/mem_cache/allocator/swa.py
@@ -93,8 +93,7 @@ class SWATokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         self.need_sort = need_sort
         self.free_pages = None
         self.release_pages = None
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
         self.swa_free_group = []
 
         self._kvcache = kvcache
@@ -319,7 +318,7 @@ class SWATokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
             return
 
         # NOTE: the API is not idempotent.
-        if self.is_not_in_free_group:
+        if self.free_group is None:
             self.full_attn_allocator.free(free_index)
             self.free_swa(free_index)
         else:
@@ -363,7 +362,7 @@ class SWATokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         swa_indices = swa_indices[swa_indices > 0]
         self.clear_full_to_swa_mapping(mapping_indices)
 
-        if not self.is_not_in_free_group:
+        if self.free_group is not None:
             # Resolve ownership now. A cache action later in this group may
             # install a new mapping for the same full index.
             self.swa_free_group.append(swa_indices)
@@ -408,8 +407,7 @@ class SWATokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         self.full_attn_allocator.clear()
         # Note: the last item is -1, we don't clear it, see the comment in __init__
         self.full_to_swa_index_mapping[:-1].fill_(0)
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
         self.swa_free_group = []
 
     def get_cpu_copy(self, indices, mamba_indices=None):
@@ -460,8 +458,7 @@ class PureSWATokenToKVPoolAllocator(SWATokenToKVPoolAllocator):
 
         self.free_pages = None
         self.release_pages = None
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
 
         self._kvcache = kvcache
         self.swa_attn_allocator.clear()
@@ -505,7 +502,7 @@ class PureSWATokenToKVPoolAllocator(SWATokenToKVPoolAllocator):
     def free(self, free_index: torch.Tensor):
         if free_index.numel() == 0:
             return
-        if self.is_not_in_free_group:
+        if self.free_group is None:
             self.swa_attn_allocator.free(free_index[free_index > 0])
         else:
             self.free_group.append(self._copy_for_free_group(free_index))
@@ -514,22 +511,21 @@ class PureSWATokenToKVPoolAllocator(SWATokenToKVPoolAllocator):
     def free_swa(self, free_index: torch.Tensor):
         if free_index.numel() == 0:
             return
-        if self.is_not_in_free_group:
+        if self.free_group is None:
             self.swa_attn_allocator.free(free_index[free_index > 0])
         else:
             self.free_group.append(self._copy_for_free_group(free_index))
 
+    # Not inherited: the SWA parent's hooks drive swa_free_group,
+    # which this pure-SWA variant does not have.
     def free_group_begin(self):
-        self.is_not_in_free_group = False
         self.free_group = []
 
     def free_group_end(self):
-        self.is_not_in_free_group = True
-        if self.free_group:
-            self.free(torch.cat(self.free_group))
-        self.free_group = []
+        pending, self.free_group = self.free_group, None
+        if pending:
+            self.free(torch.cat(pending))
 
     def clear(self):
         self.swa_attn_allocator.clear()
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
diff --git a/python/sglang/srt/mem_cache/allocator/token.py b/python/sglang/srt/mem_cache/allocator/token.py
index 06aceef12..fd0f32682 100644
--- a/python/sglang/srt/mem_cache/allocator/token.py
+++ b/python/sglang/srt/mem_cache/allocator/token.py
@@ -44,8 +44,7 @@ class TokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         self.free_pages = torch.arange(
             1, self.size + 1, dtype=torch.int64, device=self.device
         )
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
         self.release_pages = torch.empty((0,), dtype=torch.int64, device=self.device)
 
     def available_size(self):
@@ -67,7 +66,7 @@ class TokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         if free_index.numel() == 0:
             return
 
-        if self.is_not_in_free_group:
+        if self.free_group is None:
             if self.need_sort:
                 self.release_pages = torch.cat((self.release_pages, free_index))
             else:
diff --git a/python/sglang/srt/mem_cache/multi_ended_allocator.py b/python/sglang/srt/mem_cache/multi_ended_allocator.py
index 46eef0302..4e8680a8e 100644
--- a/python/sglang/srt/mem_cache/multi_ended_allocator.py
+++ b/python/sglang/srt/mem_cache/multi_ended_allocator.py
@@ -288,8 +288,7 @@ class MultiEndedAllocator(BaseTokenToKVPoolAllocator):
             )
         else:
             self.free_virtual_ids = None
-        self.is_not_in_free_group = True
-        self.free_group: List[torch.Tensor] = []
+        self.free_group = None
         self._inverse_history.clear()
         self._free_phys_pages = torch.empty(0, dtype=torch.int64, device=self.device)
         self._pending_reuse.clear()
@@ -980,7 +979,7 @@ class MultiEndedAllocator(BaseTokenToKVPoolAllocator):
         with record_function("MultiEndedAlloc.free"):
             if free_index is None or free_index.numel() == 0:
                 return
-            if not self.is_not_in_free_group:
+            if self.free_group is not None:
                 self.free_group.append(self._copy_for_free_group(free_index))
                 return
             if self.lazy_compaction:
@@ -1703,19 +1702,6 @@ class MultiEndedAllocator(BaseTokenToKVPoolAllocator):
             f"Caller: {callers}."
         )
 
-    # -- free-group --
-
-    def free_group_begin(self) -> None:
-        self.is_not_in_free_group = False
-        self.free_group = []
-
-    def free_group_end(self) -> None:
-        self.is_not_in_free_group = True
-        if self.free_group:
-            merged = torch.cat(self.free_group)
-            self.free_group = []
-            self.free(merged)
-
 
 class UnifiedMambaTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
     """Composite allocator for the MHA (full-attn) + Mamba hybrid pair.
@@ -1786,8 +1772,7 @@ class UnifiedMambaTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         # pure PHYSICAL store. The full-attn KV pool needs no allocator either —
         # write locations are resolved in the attention metadata.
 
-        self.is_not_in_free_group = True
-        self.free_group: List[torch.Tensor] = []
+        self.free_group = None
         # Base init left these None; we use watermark math, not free-lists.
         self.free_pages = torch.empty(0, dtype=torch.int64, device=device)
         self.release_pages = torch.empty(0, dtype=torch.int64, device=device)
@@ -1970,31 +1955,17 @@ class UnifiedMambaTokenToKVPoolAllocator(BaseTokenToKVPoolAllocator):
         with record_function("UnifiedMambaAlloc.free"):
             if free_index is None or free_index.numel() == 0:
                 return
-            if not self.is_not_in_free_group:
+            if self.free_group is not None:
                 self.free_group.append(self._copy_for_free_group(free_index))
                 return
             self.full_attn_allocator.free(free_index)
             self.full_attn_allocator.clear_inverse_history()
             self.mamba_allocator.clear_inverse_history()
 
-    def free_group_begin(self) -> None:
-        self.is_not_in_free_group = False
-        self.free_group = []
-
-    def free_group_end(self) -> None:
-        self.is_not_in_free_group = True
-        if self.free_group:
-            merged = torch.cat(self.free_group)
-            self.free_group = []
-            self.full_attn_allocator.free(merged)
-            self.full_attn_allocator.clear_inverse_history()
-            self.mamba_allocator.clear_inverse_history()
-
     def clear(self) -> None:
         self.full_attn_allocator.clear()
         self.mamba_allocator.clear()
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
 
     # -- Lazy compaction hooks --
 
@@ -2131,8 +2102,7 @@ class UnifiedSWATokenToKVPoolAllocator(SWATokenToKVPoolAllocator):
             swa_allocator=self.swa_attn_allocator,
         )
 
-        self.is_not_in_free_group = True
-        self.free_group: List[torch.Tensor] = []
+        self.free_group = None
         # Empty (not None) for the leak checker.
         self.free_pages = torch.empty(0, dtype=torch.int64, device=device)
         self.release_pages = torch.empty(0, dtype=torch.int64, device=device)
@@ -2439,7 +2409,7 @@ class UnifiedSWATokenToKVPoolAllocator(SWATokenToKVPoolAllocator):
         with record_function("UnifiedSWAAlloc.free"):
             if free_index is None or free_index.numel() == 0:
                 return
-            if not self.is_not_in_free_group:
+            if self.free_group is not None:
                 self.free_group.append(self._copy_for_free_group(free_index))
                 return
             # Free both peers; the per-sub-pool v2p IS the mapping, so order isn't
@@ -2491,24 +2461,10 @@ class UnifiedSWATokenToKVPoolAllocator(SWATokenToKVPoolAllocator):
         # Paired with set_full_to_swa_mapping: shared mode has no mapping tensor.
         return
 
-    # -- free-group --
-
-    def free_group_begin(self) -> None:
-        self.is_not_in_free_group = False
-        self.free_group = []
-
-    def free_group_end(self) -> None:
-        self.is_not_in_free_group = True
-        if self.free_group:
-            merged = torch.cat(self.free_group)
-            self.free_group = []
-            self.free(merged)
-
     def clear(self) -> None:
         self.full_attn_allocator.clear()
         self.swa_attn_allocator.clear()
-        self.is_not_in_free_group = True
-        self.free_group = []
+        self.free_group = None
 
     # -- Lazy compaction hooks --