diff --git a/docling/datamodel/pipeline_options.py b/docling/datamodel/pipeline_options.py
index 348278a1..354b997d 100644
--- a/docling/datamodel/pipeline_options.py
+++ b/docling/datamodel/pipeline_options.py
@@ -39,18 +39,15 @@ class AcceleratorOptions(BaseSettings):
     )
 
     num_threads: int = 4
-    device: AcceleratorDevice = AcceleratorDevice.AUTO
+    device: str = "auto"
 
     @validator("device")
     def validate_device(cls, value):
-        # Allow both Enum and str inputs
-        if isinstance(value, AcceleratorDevice):
-            return value
-        # Validate as a string
+        # "auto", "cpu", "cuda", "mps", or "cuda:N"
         if value in {d.value for d in AcceleratorDevice} or re.match(
             r"^cuda(:\d+)?$", value
         ):
-            return AcceleratorDevice(value)
+            return value
         raise ValueError(
             "Invalid device option. Use 'auto', 'cpu', 'mps', 'cuda', or 'cuda:N'."
         )
@@ -58,19 +55,8 @@ class AcceleratorOptions(BaseSettings):
     @model_validator(mode="before")
     @classmethod
     def check_alternative_envvars(cls, data: Any) -> Any:
-        r"""
-        Set num_threads from the "alternative" envvar OMP_NUM_THREADS.
-        The alternative envvar is used only if it is valid and the regular envvar is not set.
-
-        Notice: The standard pydantic settings mechanism with parameter "aliases" does not provide
-        the same functionality. In case the alias envvar is set and the user tries to override the
-        parameter in settings initialization, Pydantic treats the parameter provided in __init__()
-        as an extra input instead of simply overwriting the evvar value for that parameter.
-        """
         if isinstance(data, dict):
             input_num_threads = data.get("num_threads")
-
-            # Check if to set the num_threads from the alternative envvar
             if input_num_threads is None:
                 docling_num_threads = os.getenv("DOCLING_NUM_THREADS")
                 omp_num_threads = os.getenv("OMP_NUM_THREADS")