diff --git a/src/aignostics/platform/_sdk_metadata.py b/src/aignostics/platform/_sdk_metadata.py
index f980bc4fd..e5b296712 100644
--- a/src/aignostics/platform/_sdk_metadata.py
+++ b/src/aignostics/platform/_sdk_metadata.py
@@ -86,6 +86,7 @@ class GPUConfig(BaseModel):
         le=60 * 60,
         description="Maximum run duration in minutes when using FLEX_START provisioning mode (1-3600). "
         "Required when provisioning_mode is FLEX_START, must be None otherwise.",
+        exclude_if=lambda v: v is None,  # Exclude from serialization if None
     )
 
     @model_validator(mode="after")
diff --git a/tests/aignostics/platform/sdk_metadata_test.py b/tests/aignostics/platform/sdk_metadata_test.py
index 54b514135..a9637ba19 100644
--- a/tests/aignostics/platform/sdk_metadata_test.py
+++ b/tests/aignostics/platform/sdk_metadata_test.py
@@ -7,10 +7,14 @@
 import pytest
 from pydantic import ValidationError
 
+from aignostics.platform import DEFAULT_GPU_PROVISIONING_MODE, DEFAULT_GPU_TYPE, DEFAULT_MAX_GPUS_PER_SLIDE
 from aignostics.platform._sdk_metadata import (
     ITEM_SDK_METADATA_SCHEMA_VERSION,
     SDK_METADATA_SCHEMA_VERSION,
     VALIDATION_CASE_TAG_PREFIX,
+    GPUConfig,
+    GPUType,
+    ProvisioningMode,
     ValidationCase,
     build_item_sdk_metadata,
     build_run_sdk_metadata,
@@ -996,8 +1000,6 @@ def test_pipeline_config_defaults() -> None:
         """Test that pipeline configuration uses correct defaults."""
         from aignostics.platform import (
             DEFAULT_CPU_PROVISIONING_MODE,
-            DEFAULT_GPU_PROVISIONING_MODE,
-            DEFAULT_GPU_TYPE,
             DEFAULT_MAX_GPUS_PER_SLIDE,
             PipelineConfig,
         )
@@ -1255,3 +1257,30 @@ def test_metadata_with_invalid_validation_case_tag() -> None:
         with pytest.raises(ValidationError) as exc:
             validate_run_sdk_metadata(metadata)
         assert "validation_case" in str(exc.value)
+
+
+class TestGPUConfig:
+    """Test cases for GPUConfig model."""
+
+    @pytest.mark.unit
+    @staticmethod
+    def test_model_dump_should_include_flex_start_max_duration_if_provided() -> None:
+        """Test that flex_start_max_run_duration_minutes is included in model dump if provided."""
+        config = GPUConfig(
+            gpu_type=GPUType.L4,
+            provisioning_mode=ProvisioningMode.FLEX_START,
+            max_gpus_per_slide=DEFAULT_MAX_GPUS_PER_SLIDE,
+            flex_start_max_run_duration_minutes=1,
+        )
+        assert "flex_start_max_run_duration_minutes" in config.model_dump()
+
+    @pytest.mark.unit
+    @staticmethod
+    def test_model_dump_should_exclude_flex_start_max_duration_if_not_provided() -> None:
+        """Test that flex_start_max_run_duration_minutes is excluded in model dump if not provided."""
+        config = GPUConfig(
+            gpu_type=GPUType.L4,
+            provisioning_mode=ProvisioningMode.SPOT,
+            max_gpus_per_slide=DEFAULT_MAX_GPUS_PER_SLIDE,
+        )
+        assert "flex_start_max_run_duration_minutes" not in config.model_dump()