diff --git a/src/anemoi/utils/builder.py b/src/anemoi/utils/builder.py
new file mode 100644
index 0000000..39076dc
--- /dev/null
+++ b/src/anemoi/utils/builder.py
@@ -0,0 +1,306 @@
+# (C) Copyright 2024-2026 Anemoi contributors.
+#
+# This software is licensed under the terms of the Apache Licence Version 2.0
+# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# In applying this licence, ECMWF does not waive the privileges and immunities
+# granted to it by virtue of its status as an intergovernmental organisation
+# nor does it submit to any jurisdiction.
+
+"""Hydra-free object construction from configuration dictionaries.
+
+This module provides :class:`Builder`, a small dependency-injection engine that
+turns a configuration mapping (the same ``{"_target_": ..., ...}`` shape that
+Hydra understands) into live Python objects, *without* depending on Hydra.
+
+The intent is that classes stop calling ``hydra.utils.instantiate`` inside their
+own constructors. Instead a :class:`Builder` is injected and used to construct
+polymorphic sub-objects, which are then passed to constructors as ordinary
+parameters (object injection). Classes that only ever receive fully-built
+sub-objects need no knowledge of configuration or of this module at all.
+
+Supported keys in a spec mapping mirror the subset of Hydra features used across
+the Anemoi packages:
+
+``_target_``
+    Dotted import path of the callable (class or function) to invoke.
+``_partial_``
+    If truthy, return :func:`functools.partial` bound with the resolved
+    arguments instead of calling the target.
+``_recursive_``
+    If ``False``, nested specs are passed through unchanged rather than being
+    built. Defaults to ``True``.
+``_convert_``
+    Accepted for Hydra compatibility. ``"none"`` (the default) leaves mapping
+    and sequence values untouched; ``"all"``/``"partial"`` convert OmegaConf
+    containers to plain Python ``dict``/``list``.
+"""
+
+from __future__ import annotations
+
+import functools
+import importlib
+from collections.abc import Mapping
+from collections.abc import Sequence
+from typing import Any
+
+__all__ = ["Builder", "BuilderError", "as_dict", "build", "build_all", "locate"]
+
+
+class BuilderError(Exception):
+    """Raised when a configuration spec cannot be built into an object."""
+
+
+def locate(path: str) -> Any:
+    """Resolve a dotted import ``path`` to the object it names.
+
+    Supports both module attributes (``package.module.name``) and nested
+    attribute access (``package.module.Class.member``).
+    """
+    if not path:
+        raise BuilderError("Empty target path")
+
+    parts = path.split(".")
+    # Import the longest importable module prefix, then walk attributes.
+    module = None
+    index = len(parts)
+    while index > 0:
+        try:
+            module = importlib.import_module(".".join(parts[:index]))
+            break
+        except ModuleNotFoundError:
+            index -= 1
+    if module is None:
+        # Try importing the first component to surface the real ImportError.
+        try:
+            importlib.import_module(parts[0])
+        except ImportError as exc:  # pragma: no cover - re-raised with context
+            raise BuilderError(f"Could not import target {path!r}: {exc}") from exc
+        raise BuilderError(f"Could not import target {path!r}")
+
+    obj = module
+    for attr in parts[index:]:
+        try:
+            obj = getattr(obj, attr)
+        except AttributeError as exc:
+            raise BuilderError(f"Could not resolve attribute {attr!r} of target {path!r}") from exc
+    return obj
+
+
+def _is_mapping(value: Any) -> bool:
+    return isinstance(value, Mapping)
+
+
+def _is_sequence(value: Any) -> bool:
+    return isinstance(value, Sequence) and not isinstance(value, (str, bytes))
+
+
+def _to_container(value: Any) -> Any:
+    """Best-effort conversion of OmegaConf containers to plain Python types."""
+    try:
+        from omegaconf import OmegaConf
+
+        if OmegaConf.is_config(value):
+            return OmegaConf.to_container(value, resolve=True)
+    except ImportError:
+        pass
+    return value
+
+
+def _has_nested_target(value: Any) -> bool:
+    """Return True if ``value`` contains a ``_target_`` spec at any depth."""
+    if _is_mapping(value):
+        if "_target_" in value:
+            return True
+        return any(_has_nested_target(v) for v in value.values())
+    if _is_sequence(value):
+        return any(_has_nested_target(v) for v in value)
+    return False
+
+
+class Builder:
+    """Construct objects from configuration specs via object injection.
+
+    A ``Builder`` can optionally carry a root configuration mapping so that
+    sub-configurations can be looked up by dotted key with :meth:`get`. Its
+    central method, :meth:`build`, turns a single spec into a live object while
+    merging in runtime-computed keyword arguments.
+
+    Parameters
+    ----------
+    config : Mapping, optional
+        Root configuration this builder carries, enabling :meth:`get`.
+    """
+
+    def __init__(self, config: Mapping | None = None) -> None:
+        self.config = config
+
+    # -- configuration access -------------------------------------------------
+    def get(self, key: str, default: Any = None) -> Any:
+        """Return ``config[key]`` following dotted ``key`` notation."""
+        node: Any = self.config
+        if node is None:
+            return default
+        for part in key.split("."):
+            if _is_mapping(node) and part in node:
+                node = node[part]
+            else:
+                try:
+                    node = getattr(node, part)
+                except AttributeError:
+                    return default
+        return node
+
+    # -- construction ---------------------------------------------------------
+    def build(self, spec: Any, *args: Any, **runtime_kwargs: Any) -> Any:
+        """Build an object from ``spec``.
+
+        Parameters
+        ----------
+        spec : Mapping or Sequence or Any
+            A ``{"_target_": ...}`` mapping is instantiated. A sequence is built
+            element-wise. Any other value is returned unchanged.
+        *args
+            Positional arguments forwarded to the target callable.
+        **runtime_kwargs
+            Keyword arguments forwarded to the target callable. They override
+            values of the same name coming from the spec. Reserved control keys
+            (``_partial_``, ``_recursive_``, ``_convert_``) may also be passed to
+            override the spec.
+
+        Returns
+        -------
+        Any
+            The constructed object (or a :func:`functools.partial` when partial).
+        """
+        return self._construct(spec, args, runtime_kwargs, recursive=True)
+
+    __call__ = build
+
+    def _construct(
+        self,
+        spec: Any,
+        args: tuple,
+        runtime_kwargs: dict,
+        *,
+        recursive: bool,
+    ) -> Any:
+        if _is_mapping(spec) and "_target_" in spec:
+            return self._construct_target(spec, args, runtime_kwargs, recursive=recursive)
+
+        # Non-target values ignore positional/keyword runtime overrides. Pure-data
+        # structures (no nested target) are returned unchanged to preserve their
+        # container type (e.g. OmegaConf DictConfig), mirroring ``_convert_=none``.
+        if _is_mapping(spec):
+            if not recursive or not _has_nested_target(spec):
+                return spec
+            return {key: self._construct(value, (), {}, recursive=recursive) for key, value in spec.items()}
+
+        if _is_sequence(spec):
+            if not recursive or not _has_nested_target(spec):
+                return spec
+            return [self._construct(value, (), {}, recursive=recursive) for value in spec]
+
+        return spec
+
+    def _construct_target(
+        self,
+        spec: Mapping,
+        args: tuple,
+        runtime_kwargs: dict,
+        *,
+        recursive: bool,
+    ) -> Any:
+        control = {"_target_", "_partial_", "_recursive_", "_convert_", "_args_"}
+
+        target_path = spec["_target_"]
+        partial = runtime_kwargs.pop("_partial_", spec.get("_partial_", False))
+        recursive = runtime_kwargs.pop("_recursive_", spec.get("_recursive_", recursive))
+        convert = runtime_kwargs.pop("_convert_", spec.get("_convert_", "none"))
+        recursive = bool(recursive)
+
+        target = target_path if callable(target_path) else locate(str(target_path))
+
+        positional = list(spec.get("_args_", ()))
+        positional = [self._maybe_build(v, recursive, convert) for v in positional]
+        positional.extend(args)
+
+        kwargs: dict[str, Any] = {}
+        for key, value in spec.items():
+            if key in control:
+                continue
+            kwargs[key] = self._maybe_build(value, recursive, convert)
+
+        # Runtime kwargs override spec-derived ones.
+        kwargs.update(runtime_kwargs)
+
+        try:
+            if partial:
+                return functools.partial(target, *positional, **kwargs)
+            return target(*positional, **kwargs)
+        except BuilderError:
+            raise
+        except Exception as exc:  # noqa: BLE001 - re-raise with context
+            raise BuilderError(f"Error building {target_path!r}: {exc}") from exc
+
+    def _maybe_build(self, value: Any, recursive: bool, convert: str) -> Any:
+        """Build nested targets when recursing, otherwise return value as-is."""
+        if _is_mapping(value) and "_target_" in value:
+            if recursive:
+                return self._construct(value, (), {}, recursive=recursive)
+            return _to_container(value) if convert in ("all", "partial") else value
+
+        if recursive and (_is_mapping(value) or _is_sequence(value)):
+            return self._construct(value, (), {}, recursive=recursive)
+
+        if convert in ("all", "partial"):
+            return _to_container(value)
+        return value
+
+
+def build(spec: Any, *args: Any, **runtime_kwargs: Any) -> Any:
+    """Build a single ``spec`` using a throw-away :class:`Builder`.
+
+    Convenience for call sites that do not need a configuration-carrying builder.
+    """
+    return Builder().build(spec, *args, **runtime_kwargs)
+
+
+def build_all(specs: Mapping | Sequence, **runtime_kwargs: Any) -> Any:
+    """Build a homogeneous collection of specs, injecting the same kwargs into each.
+
+    Unlike recursive :func:`build`, this forwards ``runtime_kwargs`` to *every*
+    element, which is what the many "list/dict of ``_target_`` configs" call sites
+    need (node/edge attributes, boundings, scalers, callbacks, pipeline stages).
+
+    Parameters
+    ----------
+    specs : Mapping or Sequence
+        A mapping ``{name: spec}`` or a sequence ``[spec, ...]``. Strings/bytes are
+        rejected (they are not collections of specs).
+    **runtime_kwargs
+        Keyword arguments forwarded to the target of each element.
+
+    Returns
+    -------
+    dict or list
+        Built objects, preserving the input container kind (``dict`` for a mapping,
+        ``list`` for a sequence).
+    """
+    if _is_mapping(specs):
+        return {name: build(spec, **runtime_kwargs) for name, spec in specs.items()}
+    if _is_sequence(specs):
+        return [build(spec, **runtime_kwargs) for spec in specs]
+    raise BuilderError(f"build_all expects a mapping or sequence, got {type(specs).__name__}")
+
+
+def as_dict(config: Any) -> Any:
+    """Convert a configuration object to plain Python containers.
+
+    Backward-compatibility shim for the Hydra boundary: an OmegaConf
+    ``DictConfig``/``ListConfig`` is materialised (with interpolations resolved)
+    into ``dict``/``list``; any other value (including ``DotDict`` and plain
+    ``dict``) is returned unchanged. Downstream code then operates purely on plain
+    dicts and built objects, free of Hydra/OmegaConf.
+    """
+    return _to_container(config)
diff --git a/tests/test_builder.py b/tests/test_builder.py
new file mode 100644
index 0000000..14b50fb
--- /dev/null
+++ b/tests/test_builder.py
@@ -0,0 +1,155 @@
+# (C) Copyright 2024-2026 Anemoi contributors.
+#
+# This software is licensed under the terms of the Apache Licence Version 2.0
+# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# In applying this licence, ECMWF does not waive the privileges and immunities
+# granted to it by virtue of its status as an intergovernmental organisation
+# nor does it submit to any jurisdiction.
+
+import functools
+
+import pytest
+
+from anemoi.utils.builder import Builder
+from anemoi.utils.builder import BuilderError
+from anemoi.utils.builder import as_dict
+from anemoi.utils.builder import build
+from anemoi.utils.builder import build_all
+from anemoi.utils.builder import locate
+
+
+class Widget:
+    def __init__(self, a, b=2, child=None):
+        self.a = a
+        self.b = b
+        self.child = child
+
+
+class Child:
+    def __init__(self, name="x"):
+        self.name = name
+
+
+def test_locate_module_attribute():
+    assert locate("math.sqrt")(4) == 2.0
+
+
+def test_locate_nested_attribute():
+    assert locate("tests.test_builder.Widget") is Widget
+
+
+def test_locate_bad_path_raises():
+    with pytest.raises(BuilderError):
+        locate("nonexistent.module.thing")
+
+
+def test_build_simple_target():
+    obj = build({"_target_": "tests.test_builder.Widget", "a": 1})
+    assert isinstance(obj, Widget)
+    assert obj.a == 1 and obj.b == 2
+
+
+def test_runtime_kwargs_override_spec():
+    obj = build({"_target_": "tests.test_builder.Widget", "a": 1, "b": 3}, b=9)
+    assert obj.b == 9
+
+
+def test_positional_runtime_args():
+    obj = build({"_target_": "tests.test_builder.Widget"}, 7)
+    assert obj.a == 7
+
+
+def test_partial_returns_callable():
+    factory = build({"_target_": "tests.test_builder.Widget", "_partial_": True, "b": 5})
+    assert isinstance(factory, functools.partial)
+    obj = factory(a=1)
+    assert obj.a == 1 and obj.b == 5
+
+
+def test_recursive_builds_nested_target():
+    obj = build(
+        {
+            "_target_": "tests.test_builder.Widget",
+            "a": 1,
+            "child": {"_target_": "tests.test_builder.Child", "name": "deep"},
+        }
+    )
+    assert isinstance(obj.child, Child)
+    assert obj.child.name == "deep"
+
+
+def test_non_recursive_passes_nested_spec_through():
+    child_spec = {"_target_": "tests.test_builder.Child", "name": "deep"}
+    obj = build(
+        {
+            "_target_": "tests.test_builder.Widget",
+            "a": 1,
+            "child": child_spec,
+            "_recursive_": False,
+        }
+    )
+    assert obj.child == child_spec
+
+
+def test_non_target_mapping_returned_as_is():
+    spec = {"a": 1, "b": 2}
+    assert build(spec) == spec
+
+
+def test_recursive_preserves_pure_data_container_identity():
+    # A pure-data nested mapping (no _target_) is passed through unchanged.
+    data = {"x": 1, "y": [1, 2, 3]}
+    obj = build({"_target_": "tests.test_builder.Widget", "a": 1, "child": data})
+    assert obj.child is data
+
+
+def test_builder_get_dotted():
+    b = Builder({"model": {"num_channels": 512}})
+    assert b.get("model.num_channels") == 512
+    assert b.get("model.missing", "d") == "d"
+
+
+def test_build_error_wraps_target_failure():
+    with pytest.raises(BuilderError):
+        build({"_target_": "tests.test_builder.Widget"})  # missing required 'a'
+
+
+def test_build_all_mapping_injects_kwargs():
+    objs = build_all(
+        {
+            "one": {"_target_": "tests.test_builder.Widget", "a": 1},
+            "two": {"_target_": "tests.test_builder.Widget", "a": 2},
+        },
+        b=7,
+    )
+    assert set(objs) == {"one", "two"}
+    assert objs["one"].a == 1 and objs["one"].b == 7
+    assert objs["two"].a == 2 and objs["two"].b == 7
+
+
+def test_build_all_sequence_preserves_order():
+    objs = build_all(
+        [
+            {"_target_": "tests.test_builder.Widget", "a": 1},
+            {"_target_": "tests.test_builder.Widget", "a": 2},
+        ]
+    )
+    assert [o.a for o in objs] == [1, 2]
+
+
+def test_build_all_rejects_scalar():
+    with pytest.raises(BuilderError):
+        build_all("not-a-collection")
+
+
+def test_as_dict_passes_plain_dict_through():
+    d = {"a": 1, "b": {"c": 2}}
+    assert as_dict(d) is d
+
+
+def test_as_dict_materialises_omegaconf():
+    OmegaConf = pytest.importorskip("omegaconf").OmegaConf
+    cfg = OmegaConf.create({"a": 1, "b": "${a}"})
+    out = as_dict(cfg)
+    assert isinstance(out, dict) and out == {"a": 1, "b": 1}