feat(train): add list_hyperparameters() for pre-trainer HP discovery

Add a public utility function that returns available hyperparameters
for a model/technique/training_type combination without requiring a
fully constructed trainer object.

This enables tools and scripts to discover valid hyperparameter names,
defaults, and ranges before setting up training infrastructure (model
package groups, datasets, roles, etc.).

Motivation: COE 398545 identified that hardcoded HP names in downstream
consumers break when recipe templates rename parameters. Dynamic
discovery at code-generation time prevents this class of failure.

Usage:
    from sagemaker.train import list_hyperparameters
    hp = list_hyperparameters('model-name', 'SFT', 'LORA')
    hp.get_info()  # display all params
    hp.get_info('learning_rate')  # display one param

Author: Joshua Towner

sagemaker-train/src/sagemaker/train/__init__.py

@@ -119,4 +119,7 @@ def __getattr__(name):
     elif name == "HyperPodCompute":
         from sagemaker.core.training.configs import HyperPodCompute
         return HyperPodCompute
+    elif name == "list_hyperparameters":
+        from sagemaker.train.common_utils.finetune_utils import list_hyperparameters
+        return list_hyperparameters
     raise AttributeError(f"module '{__name__}' has no attribute '{name}'")

sagemaker-train/src/sagemaker/train/common_utils/finetune_utils.py

@@ -1880,3 +1880,57 @@ def extract_image_from_hyperpod_template(template_content: str) -> Optional[str]
         if image_match:
             return image_match.group(1).strip()
     return None
+
+
+def list_hyperparameters(
+    model: str,
+    technique: Union[str, CustomizationTechnique] = "SFT",
+    training_type: Union[str, TrainingType] = "LORA",
+    hub_name: Optional[str] = None,
+    sagemaker_session: Optional[Session] = None,
+) -> FineTuningOptions:
+    """List available hyperparameters for a model and fine-tuning technique.
+
+    Returns a FineTuningOptions object containing all tunable parameters with
+    their defaults, types, and valid ranges, without requiring a fully
+    constructed trainer.
+
+    Args:
+        model: SageMakerHub model name (e.g. "huggingface-llm-qwen2-5-7b-instruct").
+        technique: Customization technique. One of "SFT", "DPO", "RLVR",
+            "RLAIF", "CPT", or a CustomizationTechnique enum value.
+        training_type: Training type. One of "LORA", "FULL", or a
+            TrainingType enum value.
+        hub_name: Hub to query. Defaults to "SageMakerPublicHub".
+        sagemaker_session: Optional SageMaker session. If not provided,
+            a default session is created.
+
+    Returns:
+        FineTuningOptions: Object with .get_info() for display and attribute
+        access for programmatic use.
+
+    Example:
+        >>> from sagemaker.train import list_hyperparameters
+        >>> hp = list_hyperparameters("huggingface-llm-qwen2-5-7b-instruct", "SFT", "LORA")
+        >>> hp.get_info()  # Display all parameters with defaults and ranges
+        >>> hp.get_info("learning_rate")  # Display info for a single parameter
+    """
+    technique_val = (
+        technique.value if isinstance(technique, CustomizationTechnique) else technique
+    )
+    training_type_val = (
+        training_type if isinstance(training_type, str) else training_type.value
+    )
+
+    session = sagemaker_session or TrainDefaults.get_sagemaker_session(
+        sagemaker_session=None
+    )
+
+    options, _, _ = _get_fine_tuning_options_and_model_arn(
+        model_name=model,
+        customization_technique=technique_val,
+        training_type=TrainingType(training_type_val),
+        sagemaker_session=session,
+        hub_name=hub_name,
+    )
+    return options

sagemaker-train/tests/integ/train/test_list_hyperparameters_integration.py

@@ -0,0 +1,76 @@
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"). You
+# may not use this file except in compliance with the License. A copy of
+# the License is located at
+#
+#     http://aws.amazon.com/apache2.0/
+#
+# or in the "license" file accompanying this file. This file is
+# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
+# ANY KIND, either express or implied. See the License for the specific
+# language governing permissions and limitations under the License.
+"""Integration tests for list_hyperparameters utility."""
+from __future__ import absolute_import
+
+import pytest
+from sagemaker.train.common_utils.finetune_utils import list_hyperparameters
+from sagemaker.train.common import FineTuningOptions, TrainingType, CustomizationTechnique
+
+
+class TestListHyperparametersInteg:
+    """Integration tests for list_hyperparameters against live SageMakerPublicHub."""
+
+    def test_sft_lora_returns_expected_params(self):
+        """SFT LORA returns a FineTuningOptions with known hyperparameters."""
+        hp = list_hyperparameters("huggingface-llm-qwen2-5-7b-instruct", "SFT", "LORA")
+
+        assert isinstance(hp, FineTuningOptions)
+        assert "learning_rate" in hp._specs
+        assert "global_batch_size" in hp._specs
+        assert "lora_rank" in hp._specs
+        assert hp._specs["learning_rate"]["type"] == "float"
+
+    def test_dpo_lora_has_additional_params(self):
+        """DPO LORA returns params including adam_beta (not present in SFT)."""
+        hp = list_hyperparameters("huggingface-llm-qwen2-5-7b-instruct", "DPO", "LORA")
+
+        assert isinstance(hp, FineTuningOptions)
+        assert "adam_beta" in hp._specs
+        assert "learning_rate" in hp._specs
+
+    def test_rlvr_lora_returns_params(self):
+        """RLVR LORA returns FineTuningOptions with RL-specific params."""
+        hp = list_hyperparameters("meta-textgeneration-llama-3-1-8b-instruct", "RLVR", "LORA")
+
+        assert isinstance(hp, FineTuningOptions)
+        assert "learning_rate" in hp._specs
+        assert len(hp._specs) > 10
+
+    def test_accepts_enum_values(self):
+        """Accepts CustomizationTechnique and TrainingType enums."""
+        hp = list_hyperparameters(
+            "huggingface-llm-qwen2-5-7b-instruct",
+            CustomizationTechnique.SFT,
+            TrainingType.LORA,
+        )
+
+        assert isinstance(hp, FineTuningOptions)
+        assert "learning_rate" in hp._specs
+
+    def test_get_info_does_not_raise(self):
+        """get_info() runs without error on returned object."""
+        hp = list_hyperparameters("huggingface-llm-qwen2-5-7b-instruct", "SFT", "LORA")
+        # Should print without raising
+        hp.get_info("learning_rate")
+
+    def test_invalid_model_raises(self):
+        """Non-existent model raises an error."""
+        with pytest.raises(Exception):
+            list_hyperparameters("nonexistent-model-xyz-123", "SFT", "LORA")
+
+    def test_invalid_technique_raises(self):
+        """Technique not available for model raises an error."""
+        # PPO is not available on Qwen 2.5
+        with pytest.raises(Exception):
+            list_hyperparameters("huggingface-llm-qwen2-5-7b-instruct", "PPO", "LORA")

sagemaker-train/tests/unit/train/common_utils/test_finetune_utils.py

@@ -1604,3 +1604,95 @@ def test_returns_none_when_enum_empty_list(self, mock_spec):
     def test_returns_none_on_exception(self, mock_spec):
         mock_spec.side_effect = RuntimeError("hub content unavailable")
         assert self._call() is None
+
+
+class TestListHyperparameters:
+    """Tests for the list_hyperparameters public API."""
+
+    @patch('sagemaker.train.common_utils.finetune_utils._get_hub_content_metadata')
+    @patch('boto3.client')
+    def test_list_hyperparameters_returns_finetuning_options(self, mock_boto_client, mock_get_hub_content):
+        """list_hyperparameters returns a FineTuningOptions object with correct params."""
+        from sagemaker.train.common_utils.finetune_utils import list_hyperparameters
+        from sagemaker.train.common import FineTuningOptions
+
+        mock_get_hub_content.return_value = {
+            'hub_content_arn': "arn:aws:sagemaker:us-west-2:123456789012:model/test-model",
+            'hub_content_document': {
+                "GatedBucket": False,
+                "RecipeCollection": [
+                    {
+                        "CustomizationTechnique": "SFT",
+                        "SmtjRecipeTemplateS3Uri": "s3://bucket/template.json",
+                        "SmtjOverrideParamsS3Uri": "s3://bucket/params.json",
+                        "Peft": "LORA"
+                    }
+                ]
+            }
+        }
+
+        mock_s3_client = Mock()
+        mock_boto_client.return_value = mock_s3_client
+        mock_s3_client.get_object.return_value = {
+            "Body": Mock(read=Mock(return_value=json.dumps({
+                "learning_rate": {"type": "float", "default": 0.0001, "min": 5e-7, "max": 0.001, "required": True},
+                "global_batch_size": {"type": "integer", "default": 8, "required": True},
+                "max_epochs": {"type": "integer", "default": 5, "min": 1, "max": 100, "required": True},
+            }).encode()))
+        }
+
+        mock_session = Mock()
+        mock_session.boto_session.region_name = "us-west-2"
+        mock_session.boto_session.client.return_value = mock_s3_client
+
+        with patch('sagemaker.train.common_utils.finetune_utils.TrainDefaults.get_sagemaker_session', return_value=mock_session):
+            result = list_hyperparameters("test-model", "SFT", "LORA", sagemaker_session=mock_session)
+
+        assert isinstance(result, FineTuningOptions)
+        assert result.learning_rate == 0.0001
+        assert result.global_batch_size == 8
+        assert result.max_epochs == 5
+
+    @patch('sagemaker.train.common_utils.finetune_utils._get_hub_content_metadata')
+    @patch('boto3.client')
+    def test_list_hyperparameters_accepts_enum_values(self, mock_boto_client, mock_get_hub_content):
+        """list_hyperparameters accepts both string and enum values for technique/training_type."""
+        from sagemaker.train.common_utils.finetune_utils import list_hyperparameters
+        from sagemaker.train.common import CustomizationTechnique, TrainingType
+
+        mock_get_hub_content.return_value = {
+            'hub_content_arn': "arn:aws:sagemaker:us-west-2:123456789012:model/test-model",
+            'hub_content_document': {
+                "GatedBucket": False,
+                "RecipeCollection": [
+                    {
+                        "CustomizationTechnique": "DPO",
+                        "SmtjRecipeTemplateS3Uri": "s3://bucket/template.json",
+                        "SmtjOverrideParamsS3Uri": "s3://bucket/params.json",
+                        "Peft": "LORA"
+                    }
+                ]
+            }
+        }
+
+        mock_s3_client = Mock()
+        mock_boto_client.return_value = mock_s3_client
+        mock_s3_client.get_object.return_value = {
+            "Body": Mock(read=Mock(return_value=json.dumps({
+                "learning_rate": {"type": "float", "default": 0.0001, "required": True},
+            }).encode()))
+        }
+
+        mock_session = Mock()
+        mock_session.boto_session.region_name = "us-west-2"
+        mock_session.boto_session.client.return_value = mock_s3_client
+
+        with patch('sagemaker.train.common_utils.finetune_utils.TrainDefaults.get_sagemaker_session', return_value=mock_session):
+            result = list_hyperparameters(
+                "test-model",
+                CustomizationTechnique.DPO,
+                TrainingType.LORA,
+                sagemaker_session=mock_session,
+            )
+
+        assert result.learning_rate == 0.0001