diff --git a/atroposlib/api/utils.py b/atroposlib/api/utils.py
index c2fef67c..5f95feb1 100644
--- a/atroposlib/api/utils.py
+++ b/atroposlib/api/utils.py
@@ -22,40 +22,63 @@ def grab_exact_from_heterogeneous_queue(
     :param batch_size:
     :return: batch, new_queue
     """
-    # check if we can even potentially grab a batch
-    if sum(len(item["tokens"]) for item in queue) < batch_size:
+
+    # Pass 1: precompute group sizes, total tokens and early exit if not enough tokens.
+    total_groups = len(queue)
+    if total_groups == 0:
         return None, queue
-    # Get max batch size
-    max_group_size = max(len(group["tokens"]) for group in queue)
-    group_sizes = set(len(group["tokens"]) for group in queue)
-    group_batching_storage = {i: [] for i in group_sizes}
-    # pack the groups into [max_group_size // group_size] packs
-    potential_batch = []
-    for i, item in enumerate(queue):
-        key = len(item["tokens"])
-        group_batching_storage[key].append({"group": item, "indx": i})
-        if len(group_batching_storage[key]) * key == max_group_size:
-            potential_batch.extend(group_batching_storage[key])
-            group_batching_storage[key] = []
-    if (
-        sum(len(grouped_items["group"]["tokens"]) for grouped_items in potential_batch)
-        < batch_size
-    ):
+
+    group_sizes = []
+    lengths = []
+    total_tokens = 0
+    max_group_size = 0
+
+    for item in queue:
+        l = len(item["tokens"])
+        lengths.append(l)
+        group_sizes.append(l)
+        total_tokens += l
+        if l > max_group_size:
+            max_group_size = l
+
+    if total_tokens < batch_size:
         return None, queue
-    # we have a batch
+
+    group_sizes_set = set(group_sizes)
+    group_batching_storage = {size: [] for size in group_sizes_set}
+
+    # Index into the queue and batch related indices into "packs"
+    potential_batch_indices = []
+    for i, group_size in enumerate(group_sizes):
+        group_batching_storage[group_size].append(i)
+        if len(group_batching_storage[group_size]) * group_size == max_group_size:
+            potential_batch_indices.extend(group_batching_storage[group_size])
+            group_batching_storage[group_size].clear()  # much faster than = []
+
+    # Calculate total batch tokens only once (avoid repeated sums)
+    potential_batch_token_total = sum(lengths[i] for i in potential_batch_indices)
+    if potential_batch_token_total < batch_size:
+        return None, queue
+
+    # Batch selection
     batch = []
-    indxes_to_remove_from_queue = []
-    for item in potential_batch:
-        group = item["group"]
-        indx = item["indx"]
+    batch_indices = []
+    running_tokens = 0
+    for idx in potential_batch_indices:
+        group = queue[idx]
         batch.append(group)
-        indxes_to_remove_from_queue.append(indx)
-        if sum(len(item["tokens"]) for item in batch) == batch_size:
+        batch_indices.append(idx)
+        running_tokens += lengths[idx]
+        if running_tokens == batch_size:
             break
-    if sum(len(item["tokens"]) for item in batch) != batch_size:
+        elif running_tokens > batch_size:
+            # Should never happen due to problem constraints, but sanity check
+            return None, queue
+
+    if running_tokens != batch_size:
         return None, queue
-    # remove the items from the queue
-    new_queue = [
-        item for i, item in enumerate(queue) if i not in indxes_to_remove_from_queue
-    ]
+
+    # Construct new_queue with a single pass, using a set for O(1) lookup
+    batch_indices_set = set(batch_indices)
+    new_queue = [item for i, item in enumerate(queue) if i not in batch_indices_set]
     return batch, new_queue