diff --git a/example_data/config.yaml b/example_data/config.yaml
index 99d0a10..9a95182 100644
--- a/example_data/config.yaml
+++ b/example_data/config.yaml
@@ -32,7 +32,6 @@ model:
   name: UNetBackbone
   input_height: 128
   in_channels: 1
-  out_channels: 32
   encoder:
     layers:
       - name: FreqCoordConvDown
diff --git a/src/batdetect2/config.py b/src/batdetect2/config.py
index f0274af..9b51dfa 100644
--- a/src/batdetect2/config.py
+++ b/src/batdetect2/config.py
@@ -12,7 +12,7 @@ from batdetect2.evaluate.config import (
     get_default_eval_config,
 )
 from batdetect2.inference.config import InferenceConfig
-from batdetect2.models.backbones import BackboneConfig
+from batdetect2.models.backbones import BackboneConfig, UNetBackboneConfig
 from batdetect2.postprocess.config import PostprocessConfig
 from batdetect2.preprocess.config import PreprocessingConfig
 from batdetect2.targets.config import TargetConfig
@@ -32,7 +32,7 @@ class BatDetect2Config(BaseConfig):
     evaluation: EvaluationConfig = Field(
         default_factory=get_default_eval_config
     )
-    model: BackboneConfig = Field(default_factory=BackboneConfig)
+    model: BackboneConfig = Field(default_factory=UNetBackboneConfig)
     preprocess: PreprocessingConfig = Field(
         default_factory=PreprocessingConfig
     )
diff --git a/src/batdetect2/core/configs.py b/src/batdetect2/core/configs.py
index c39533c..60d4266 100644
--- a/src/batdetect2/core/configs.py
+++ b/src/batdetect2/core/configs.py
@@ -8,11 +8,11 @@ configuration data from files, with optional support for accessing nested
 configuration sections.
 """
 
-from typing import Any, Type, TypeVar
+from typing import Any, Type, TypeVar, Union, overload
 
 import yaml
 from deepmerge.merger import Merger
-from pydantic import BaseModel, ConfigDict
+from pydantic import BaseModel, ConfigDict, TypeAdapter
 from soundevent.data import PathLike
 
 __all__ = [
@@ -67,7 +67,10 @@ class BaseConfig(BaseModel):
         return cls.model_validate(yaml.safe_load(yaml_str))
 
 
-T = TypeVar("T", bound=BaseModel)
+T = TypeVar("T")
+T_Model = TypeVar("T_Model", bound=BaseModel)
+
+Schema = Union[Type[T_Model], TypeAdapter[T]]
 
 
 def get_object_field(obj: dict, current_key: str) -> Any:
@@ -129,24 +132,41 @@ def get_object_field(obj: dict, current_key: str) -> Any:
     return get_object_field(subobj, rest)
 
 
+@overload
 def load_config(
     path: PathLike,
-    schema: Type[T],
+    schema: Type[T_Model],
     field: str | None = None,
-) -> T:
+) -> T_Model: ...
+
+
+@overload
+def load_config(
+    path: PathLike,
+    schema: TypeAdapter[T],
+    field: str | None = None,
+) -> T: ...
+
+
+def load_config(
+    path: PathLike,
+    schema: Type[T_Model] | TypeAdapter[T],
+    field: str | None = None,
+) -> T_Model | T:
     """Load and validate configuration data from a file against a schema.
 
     Reads a YAML file, optionally extracts a specific section using dot
     notation, and then validates the resulting data against the provided
-    Pydantic `schema`.
+    Pydantic schema.
 
     Parameters
     ----------
     path : PathLike
         The path to the configuration file (typically `.yaml`).
-    schema : Type[T]
-        The Pydantic `BaseModel` subclass that defines the expected structure
-        and types for the configuration data.
+    schema : Type[T_Model] | TypeAdapter[T]
+        Either a Pydantic `BaseModel` subclass or a `TypeAdapter` instance
+        that defines the expected structure and types for the configuration
+        data.
     field : str, optional
         A dot-separated string indicating a nested section within the YAML
         file to extract before validation. If None (default), the entire
@@ -156,8 +176,8 @@ def load_config(
 
     Returns
     -------
-    T
-        An instance of the provided `schema`, populated and validated with
+    T_Model | T
+        An instance of the schema type, populated and validated with
         data from the configuration file.
 
     Raises
@@ -183,6 +203,9 @@ def load_config(
     if field:
         config = get_object_field(config, field)
 
+    if isinstance(schema, TypeAdapter):
+        return schema.validate_python(config or {})
+
     return schema.model_validate(config or {})
 
 
@@ -193,7 +216,7 @@ default_merger = Merger(
 )
 
 
-def merge_configs(config1: T, config2: T) -> T:
+def merge_configs(config1: T_Model, config2: T_Model) -> T_Model:
     """Merge two configuration objects."""
     model = type(config1)
     dict1 = config1.model_dump()
diff --git a/src/batdetect2/models/__init__.py b/src/batdetect2/models/__init__.py
index 80e00ba..195e4a2 100644
--- a/src/batdetect2/models/__init__.py
+++ b/src/batdetect2/models/__init__.py
@@ -31,9 +31,9 @@ from typing import List
 import torch
 
 from batdetect2.models.backbones import (
+    BackboneConfig,
     UNetBackbone,
     UNetBackboneConfig,
-    BackboneConfig,
     build_backbone,
     load_backbone_config,
 )
diff --git a/src/batdetect2/models/backbones.py b/src/batdetect2/models/backbones.py
index 07bc4b8..a83555a 100644
--- a/src/batdetect2/models/backbones.py
+++ b/src/batdetect2/models/backbones.py
@@ -22,7 +22,7 @@ from typing import Annotated, Literal, Tuple, Union
 
 import torch
 import torch.nn.functional as F
-from pydantic import Field
+from pydantic import Field, TypeAdapter
 from soundevent import data
 
 from batdetect2.core.configs import BaseConfig, load_config
@@ -57,7 +57,6 @@ class UNetBackboneConfig(BaseConfig):
     encoder: EncoderConfig = DEFAULT_ENCODER_CONFIG
     bottleneck: BottleneckConfig = DEFAULT_BOTTLENECK_CONFIG
     decoder: DecoderConfig = DEFAULT_DECODER_CONFIG
-    out_channels: int = 32
 
 
 backbone_registry: Registry[BackboneModel, []] = Registry("backbone")
@@ -293,4 +292,8 @@ def load_backbone_config(
     path: data.PathLike,
     field: str | None = None,
 ) -> BackboneConfig:
-    return load_config(path, schema=BackboneConfig, field=field)
+    return load_config(
+        path,
+        schema=TypeAdapter(BackboneConfig),
+        field=field,
+    )
diff --git a/src/batdetect2/models/blocks.py b/src/batdetect2/models/blocks.py
index fa42bdf..e21ce2f 100644
--- a/src/batdetect2/models/blocks.py
+++ b/src/batdetect2/models/blocks.py
@@ -27,7 +27,7 @@ A unified factory function `build_layer` allows creating instances
 of these blocks based on configuration objects.
 """
 
-from typing import Annotated, List, Literal, Protocol, Tuple, Union
+from typing import Annotated, List, Literal, Tuple, Union
 
 import torch
 import torch.nn.functional as F
diff --git a/src/batdetect2/models/bottleneck.py b/src/batdetect2/models/bottleneck.py
index 290fb64..420ec2c 100644
--- a/src/batdetect2/models/bottleneck.py
+++ b/src/batdetect2/models/bottleneck.py
@@ -27,7 +27,6 @@ from batdetect2.models.blocks import (
     VerticalConv,
     build_layer,
 )
-
 from batdetect2.typing.models import BottleneckProtocol
 
 __all__ = [
@@ -159,9 +158,7 @@ class BottleneckConfig(BaseConfig):
     """
 
     channels: int
-    layers: List[BottleneckLayerConfig] = Field(
-        default_factory=list,
-    )
+    layers: List[BottleneckLayerConfig] = Field(default_factory=list)
 
 
 DEFAULT_BOTTLENECK_CONFIG: BottleneckConfig = BottleneckConfig(
diff --git a/tests/test_models/test_backbones.py b/tests/test_models/test_backbones.py
new file mode 100644
index 0000000..f04fcfa
--- /dev/null
+++ b/tests/test_models/test_backbones.py
@@ -0,0 +1,252 @@
+"""Tests for backbone configuration loading and the backbone registry.
+
+Covers:
+- UNetBackboneConfig default construction and field values.
+- build_backbone with default and explicit configs.
+- load_backbone_config loading from a YAML file.
+- load_backbone_config with a nested field path.
+- load_backbone_config round-trip: YAML → config → build_backbone.
+- Registry registration and dispatch for UNetBackbone.
+- BackboneConfig discriminated union validation.
+"""
+
+from pathlib import Path
+from typing import Callable
+
+import pytest
+
+from batdetect2.models.backbones import (
+    BackboneConfig,
+    UNetBackbone,
+    UNetBackboneConfig,
+    backbone_registry,
+    build_backbone,
+    load_backbone_config,
+)
+from batdetect2.typing.models import BackboneModel
+
+# ---------------------------------------------------------------------------
+# UNetBackboneConfig
+# ---------------------------------------------------------------------------
+
+
+def test_unet_backbone_config_defaults():
+    """Default config has expected field values."""
+    config = UNetBackboneConfig()
+
+    assert config.name == "UNetBackbone"
+    assert config.input_height == 128
+    assert config.in_channels == 1
+
+
+def test_unet_backbone_config_custom_fields():
+    """Custom field values are stored correctly."""
+    config = UNetBackboneConfig(in_channels=2, input_height=64)
+
+    assert config.in_channels == 2
+    assert config.input_height == 64
+
+
+def test_unet_backbone_config_extra_fields_ignored():
+    """Extra/unknown fields are silently ignored (BaseConfig behaviour)."""
+    config = UNetBackboneConfig.model_validate(
+        {"name": "UNetBackbone", "unknown_field": 99}
+    )
+
+    assert config.name == "UNetBackbone"
+    assert not hasattr(config, "unknown_field")
+
+
+# ---------------------------------------------------------------------------
+# build_backbone
+# ---------------------------------------------------------------------------
+
+
+def test_build_backbone_default():
+    """Building with no config uses UNetBackbone defaults."""
+    backbone = build_backbone()
+
+    assert isinstance(backbone, UNetBackbone)
+    assert backbone.input_height == 128
+
+
+def test_build_backbone_custom_config():
+    """Building with a custom config propagates input_height and in_channels."""
+    config = UNetBackboneConfig(in_channels=2, input_height=64)
+    backbone = build_backbone(config)
+
+    assert isinstance(backbone, UNetBackbone)
+    assert backbone.input_height == 64
+    assert backbone.encoder.in_channels == 2
+
+
+def test_build_backbone_returns_backbone_model():
+    """build_backbone always returns a BackboneModel instance."""
+    backbone = build_backbone()
+
+    assert isinstance(backbone, BackboneModel)
+
+
+# ---------------------------------------------------------------------------
+# Registry
+# ---------------------------------------------------------------------------
+
+
+def test_registry_has_unet_backbone():
+    """The backbone registry has UNetBackbone registered."""
+    config_types = backbone_registry.get_config_types()
+
+    assert UNetBackboneConfig in config_types
+
+
+def test_registry_config_type_is_unet_backbone_config():
+    """The config type stored for UNetBackbone is UNetBackboneConfig."""
+    config_type = backbone_registry.get_config_type("UNetBackbone")
+
+    assert config_type is UNetBackboneConfig
+
+
+def test_registry_build_dispatches_correctly():
+    """Registry.build dispatches to UNetBackbone.from_config."""
+    config = UNetBackboneConfig(input_height=128)
+    backbone = backbone_registry.build(config)
+
+    assert isinstance(backbone, UNetBackbone)
+
+
+def test_registry_build_unknown_name_raises():
+    """Registry.build raises NotImplementedError for an unknown config name."""
+
+    class FakeConfig:
+        name = "NonExistentBackbone"
+
+    with pytest.raises(NotImplementedError):
+        backbone_registry.build(FakeConfig())  # type: ignore[arg-type]
+
+
+# ---------------------------------------------------------------------------
+# BackboneConfig discriminated union
+# ---------------------------------------------------------------------------
+
+
+def test_backbone_config_validates_unet_from_dict():
+    """BackboneConfig TypeAdapter resolves to UNetBackboneConfig via name."""
+    from pydantic import TypeAdapter
+
+    adapter = TypeAdapter(BackboneConfig)
+    config = adapter.validate_python(
+        {"name": "UNetBackbone", "input_height": 64}
+    )
+
+    assert isinstance(config, UNetBackboneConfig)
+    assert config.input_height == 64
+
+
+def test_backbone_config_invalid_name_raises():
+    """BackboneConfig validation raises for an unknown name discriminator."""
+    from pydantic import TypeAdapter, ValidationError
+
+    adapter = TypeAdapter(BackboneConfig)
+    with pytest.raises(ValidationError):
+        adapter.validate_python({"name": "NonExistentBackbone"})
+
+
+# ---------------------------------------------------------------------------
+# load_backbone_config
+# ---------------------------------------------------------------------------
+
+
+def test_load_backbone_config_from_yaml(
+    create_temp_yaml: Callable[[str], Path],
+):
+    """load_backbone_config loads a UNetBackboneConfig from a YAML file."""
+    yaml_content = """\
+name: UNetBackbone
+input_height: 64
+in_channels: 2
+"""
+    path = create_temp_yaml(yaml_content)
+    config = load_backbone_config(path)
+
+    assert isinstance(config, UNetBackboneConfig)
+    assert config.input_height == 64
+    assert config.in_channels == 2
+
+
+def test_load_backbone_config_with_field(
+    create_temp_yaml: Callable[[str], Path],
+):
+    """load_backbone_config extracts a nested field before validation."""
+    yaml_content = """\
+model:
+  name: UNetBackbone
+  input_height: 32
+"""
+    path = create_temp_yaml(yaml_content)
+    config = load_backbone_config(path, field="model")
+
+    assert isinstance(config, UNetBackboneConfig)
+    assert config.input_height == 32
+
+
+def test_load_backbone_config_defaults_on_minimal_yaml(
+    create_temp_yaml: Callable[[str], Path],
+):
+    """Minimal YAML with only name fills remaining fields with defaults."""
+    yaml_content = "name: UNetBackbone\n"
+    path = create_temp_yaml(yaml_content)
+    config = load_backbone_config(path)
+
+    assert isinstance(config, UNetBackboneConfig)
+    assert config.input_height == UNetBackboneConfig().input_height
+    assert config.in_channels == UNetBackboneConfig().in_channels
+
+
+def test_load_backbone_config_extra_fields_ignored(
+    create_temp_yaml: Callable[[str], Path],
+):
+    """Extra YAML fields are silently ignored when loading backbone config."""
+    yaml_content = """\
+name: UNetBackbone
+input_height: 128
+deprecated_field: 99
+"""
+    path = create_temp_yaml(yaml_content)
+    config = load_backbone_config(path)
+
+    assert isinstance(config, UNetBackboneConfig)
+    assert config.input_height == 128
+
+
+# ---------------------------------------------------------------------------
+# Round-trip: YAML → config → build_backbone
+# ---------------------------------------------------------------------------
+
+
+def test_round_trip_yaml_to_build_backbone(
+    create_temp_yaml: Callable[[str], Path],
+):
+    """A backbone config loaded from YAML can be used directly with build_backbone."""
+    yaml_content = """\
+name: UNetBackbone
+input_height: 128
+in_channels: 1
+"""
+    path = create_temp_yaml(yaml_content)
+    config = load_backbone_config(path)
+    backbone = build_backbone(config)
+
+    assert isinstance(backbone, UNetBackbone)
+    assert backbone.input_height == 128
+
+
+def test_load_backbone_config_from_example_data(example_data_dir: Path):
+    """load_backbone_config loads the real example config correctly."""
+    config = load_backbone_config(
+        example_data_dir / "config.yaml",
+        field="model",
+    )
+
+    assert isinstance(config, UNetBackboneConfig)
+    assert config.input_height == 128
+    assert config.in_channels == 1
diff --git a/tests/test_models/test_detectors.py b/tests/test_models/test_detectors.py
index a2b4b69..0edb694 100644
--- a/tests/test_models/test_detectors.py
+++ b/tests/test_models/test_detectors.py
@@ -2,7 +2,7 @@ import numpy as np
 import pytest
 import torch
 
-from batdetect2.models.backbones import BackboneConfig
+from batdetect2.models.backbones import UNetBackboneConfig
 from batdetect2.models.detectors import Detector, build_detector
 from batdetect2.models.heads import BBoxHead, ClassifierHead
 from batdetect2.typing.models import ModelOutput
@@ -28,7 +28,7 @@ def test_build_detector_default():
 def test_build_detector_custom_config():
     """Test building a detector with a custom BackboneConfig."""
     num_classes = 3
-    config = BackboneConfig(in_channels=2, input_height=128)
+    config = UNetBackboneConfig(in_channels=2, input_height=128)
 
     model = build_detector(num_classes=num_classes, config=config)
 
@@ -41,7 +41,7 @@ def test_detector_forward_pass_shapes(dummy_spectrogram):
     """Test that the forward pass produces correctly shaped outputs."""
     num_classes = 4
     # Build model matching the dummy input shape
-    config = BackboneConfig(in_channels=1, input_height=256)
+    config = UNetBackboneConfig(in_channels=1, input_height=256)
     model = build_detector(num_classes=num_classes, config=config)
 
     # Process the spectrogram through the model
@@ -108,7 +108,7 @@ def test_detector_forward_pass_with_preprocessor(sample_preprocessor):
 
     # Build model matching the preprocessor's output shape
     # The preprocessor output is (B, C, H, W) -> spec.shape[1] is C, spec.shape[2] is H
-    config = BackboneConfig(
+    config = UNetBackboneConfig(
         in_channels=spec.shape[1], input_height=spec.shape[2]
     )
     model = build_detector(num_classes=3, config=config)