diff --git a/open_instruct/dataset_transformation.py b/open_instruct/dataset_transformation.py
index 1cb21af1f1..643880a661 100644
--- a/open_instruct/dataset_transformation.py
+++ b/open_instruct/dataset_transformation.py
@@ -979,40 +979,6 @@ def preference_tulu_filter_v1(row: Dict[str, Any], tokenizer: PreTrainedTokenize
     return any(x != -100 for x in row[CHOSEN_LABELS_KEY]) and any(x != -100 for x in row[REJECTED_LABELS_KEY])
 
 
-def preference_span_search_mask_out(
-    row: Dict[str, Any],
-    tokenizer: PreTrainedTokenizer,
-    max_seq_length: int,
-    chosen_key: str = DEFAULT_CHOSEN_KEY,
-    rejected_key: str = DEFAULT_REJECTED_KEY,
-):
-    """
-    Here we assume each example has a rejected and chosen field, both of which are a list of messages.
-    Each message is a dict with 'role' and 'content' fields.
-    We assume only the last message is different, and the prompt is contained in the list of messages.
-    """
-    chosen_messages = row[chosen_key]
-    rejected_messages = row[rejected_key]
-    if len(chosen_messages) == 0:
-        raise ValueError("chosen messages field is empty.")
-    if len(rejected_messages) == 0:
-        raise ValueError("rejected messages field is empty.")
-
-    chosen_encoded = sft_span_seach_mask_out({DEFAULT_SFT_MESSAGES_KEY: chosen_messages}, tokenizer, max_seq_length)
-    rejected_encoded = sft_span_seach_mask_out(
-        {DEFAULT_SFT_MESSAGES_KEY: rejected_messages}, tokenizer, max_seq_length
-    )
-
-    return {
-        CHOSEN_INPUT_IDS_KEY: chosen_encoded["input_ids"],
-        CHOSEN_LABELS_KEY: chosen_encoded["labels"],
-        CHOSEN_ATTENTION_MASK_KEY: chosen_encoded["attention_mask"],
-        REJECTED_INPUT_IDS_KEY: rejected_encoded["input_ids"],
-        REJECTED_LABELS_KEY: rejected_encoded["labels"],
-        REJECTED_ATTENTION_MASK_KEY: rejected_encoded["attention_mask"],
-    }
-
-
 def rlvr_tokenize_v1(
     row: Dict[str, Any],
     tokenizer: PreTrainedTokenizer,
@@ -1098,7 +1064,6 @@ def rlvr_filter_v1(
     "preference_tokenize_v1": (preference_tokenize_v1, "map"),
     "preference_filter_v1": (preference_filter_v1, "filter"),
     "preference_tulu_tokenize_and_truncate_v1": (preference_tulu_tokenize_and_truncate_v1_2, "map"),
-    "preference_span_search_mask_out": (preference_span_search_mask_out, "map"),
     "preference_tulu_filter_v1": (preference_tulu_filter_v1, "filter"),
     "rlvr_tokenize_v1": (rlvr_tokenize_v2, "map"),
     "rlvr_filter_v1": (rlvr_filter_v1, "filter"),