automatically split out reasoning trace from dataset (#2579)

* automatically split out reasoning trace from dataset

* chore: lint

* fix import

src/axolotl/prompt_strategies/chat_template.py

@@ -228,6 +228,7 @@ class ChatTemplateStrategy(PromptTokenizingStrategy):
         train_on_eos: Optional[str] = None,
         train_on_eot: Optional[str] = None,
         eot_tokens: Optional[List[str]] = None,
+        split_thinking: Optional[bool] = False,
     ):
         super().__init__(prompter, tokenizer, train_on_inputs, sequence_len)
         self.prompter: ChatTemplatePrompter = prompter
@@ -247,6 +248,7 @@ class ChatTemplateStrategy(PromptTokenizingStrategy):
         self.eot_tokens = (
             eot_tokens if eot_tokens is not None else [self.tokenizer.eos_token]
         )
+        self.split_thinking = split_thinking
 
         self.images = "images"
 
@@ -655,6 +657,22 @@ class ChatTemplateStrategy(PromptTokenizingStrategy):
                 transformed_message["role"], transformed_message["role"]
             )
 
+        # TODO handle reasoning_content with split_thinking
+        # if the role is assistant that we want to use reasoning_content
+        if self.split_thinking and transformed_message["role"] == "assistant":
+            content = transformed_message["content"]
+            pairs = [("<think>", "</think>"), ("<reasoning>", "</reasoning>")]
+            for pair in pairs:
+                if pair[0] in content and pair[1] in content:
+                    start_idx = content.find(pair[0])
+                    end_idx = content.find(pair[1])
+                    thinking_content = content[start_idx + len(pair[0]) : end_idx]
+                    transformed_message["reasoning_content"] = thinking_content.strip()
+                    transformed_message["content"] = content[
+                        end_idx + len(pair[1]) :
+                    ].lstrip()
+                    break
+
         # Determine which keys in the original message were not mapped
         mapped_values = set(self.prompter.message_property_mappings.values())
         remaining_keys = set(message) - mapped_values
@@ -689,6 +707,7 @@ class StrategyLoader:
             "train_on_eos": ds_cfg.get("train_on_eos", "turn"),
             "train_on_eot": ds_cfg.get("train_on_eot", None),
             "eot_tokens": cfg.get("eot_tokens", None),  # loads from cfg, not ds_cfg
+            "split_thinking": ds_cfg.get("split_thinking", False),
         }
 
     def __call__(

src/axolotl/utils/schemas/datasets.py

@@ -50,6 +50,7 @@ class SFTDataset(BaseModel):
     message_property_mappings: dict[str, str] | None = None
     message_field_training: str | None = None
     message_field_training_detail: str | None = None
+    split_thinking: bool | None = None
     logprobs_field: str | None = None
     temperature: float | None = None
     roles_to_train: list[str] | None = None

tests/conftest.py

@@ -90,6 +90,12 @@ def download_qwen_2_5_half_billion_model():
     snapshot_download_w_retry("Qwen/Qwen2.5-0.5B", repo_type="model")
 
 
+@pytest.fixture(scope="session", autouse=True)
+def download_qwen3_half_billion_model():
+    # download the model
+    snapshot_download_w_retry("Qwen/Qwen3-0.6B", repo_type="model")
+
+
 @pytest.fixture(scope="session", autouse=True)
 def download_tatsu_lab_alpaca_dataset():
     # download the dataset

tests/prompt_strategies/test_chat_templates_thinking.py

@@ -0,0 +1,118 @@
+"""
+Tests for splitting reasoning/thinking from content into separate field
+"""
+
+import logging
+
+import pytest
+from datasets import Dataset
+from transformers import AutoTokenizer
+
+from axolotl.prompt_strategies.chat_template import (
+    load,
+)
+from axolotl.utils.dict import DictDefault
+
+from tests.hf_offline_utils import enable_hf_offline
+
+logging.basicConfig(level=logging.DEBUG)
+LOG = logging.getLogger("axolotl")
+
+
+@pytest.fixture(name="messages_w_reasoning")
+def messages_w_reasoning_fixture():
+    return Dataset.from_list(
+        [
+            {
+                "messages": [
+                    {
+                        "role": "user",
+                        "content": "hello",
+                    },
+                    {
+                        "role": "assistant",
+                        "content": "<think>lorem</think>\nwelcome",
+                    },
+                ]
+            }
+        ]
+    )
+
+
+@pytest.fixture(name="qwen3_tokenizer")
+@enable_hf_offline
+def qwen3_tokenizer_fixture(
+    download_qwen3_half_billion_model,
+):  # pylint: disable=unused-argument
+    tokenizer = AutoTokenizer.from_pretrained("Qwen/Qwen3-0.6B")
+
+    return tokenizer
+
+
+class TestSplitThinking:
+    """
+    test class to make sure datasets with reasoning content conforms to the chat_template strategy
+    """
+
+    def test_splits_think(self, messages_w_reasoning, qwen3_tokenizer):
+        # pylint: disable=duplicate-code
+        strategy = load(
+            qwen3_tokenizer,
+            DictDefault(
+                {
+                    "train_on_inputs": False,
+                    "sequence_len": 512,
+                }
+            ),
+            DictDefault(
+                {
+                    "chat_template": "qwen3",
+                    "message_field_role": "role",
+                    "message_field_content": "content",
+                    "message_property_mappings": {
+                        "role": "role",
+                        "content": "content",
+                    },
+                    "roles": {
+                        "user": ["user"],
+                        "assistant": ["assistant"],
+                        "system": ["system"],
+                    },
+                    "field_messages": "messages",
+                    "split_thinking": True,
+                }
+            ),
+        )
+        transformed_prompt = strategy.get_conversation_thread(messages_w_reasoning[0])
+        assert transformed_prompt[0]["role"] == "user"
+        assert transformed_prompt[1]["role"] == "assistant"
+        assert transformed_prompt[1]["reasoning_content"] == "lorem"
+        assert transformed_prompt[1]["content"] == "welcome"
+
+        res = strategy.tokenize_prompt(messages_w_reasoning[0])
+        input_ids = res["input_ids"]
+        # fmt: off
+        expected_input_ids = [
+            151644,  # im_start
+            872,  # user
+            198,  # \n
+            14990,  # hello
+            151645,  # im_end
+            198,  # \n
+            151644,  # im_start
+            77091,  # assistant
+            198,  # \n
+            151667,  # think
+            198,  # \n
+            385, 1826,  # lorem
+            198,  # \n
+            151668,  # /think
+            271,  # \n
+            34084,  # welcome
+            151645,  # im_end
+            198,  # \n
+        ]
+        # fmt: on
+        assert (
+            input_ids == expected_input_ids
+        ), f"Input IDs mismatch: {input_ids} != {expected_input_ids}"