diff --git a/pyproject.toml b/pyproject.toml
index 2ed3a8632..9c473d7ea 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -25,6 +25,7 @@ dependencies = [
   "cookiecutter~=2.1",
   "json-e>=2.7",
   "mozilla-repo-urls",
+  "msgspec>=0.20.0",
   "PyYAML>=5.3.1",
   "redo>=2.0",
   "requests>=2.25",
diff --git a/src/taskgraph/config.py b/src/taskgraph/config.py
index d0b0f7ce6..b9a2b57d2 100644
--- a/src/taskgraph/config.py
+++ b/src/taskgraph/config.py
@@ -13,7 +13,7 @@
 
 from .util.caches import CACHES
 from .util.python_path import find_object
-from .util.schema import Schema, optionally_keyed_by, validate_schema
+from .util.schema import LegacySchema, optionally_keyed_by, validate_schema
 from .util.vcs import get_repository
 from .util.yaml import load_yaml
 
@@ -21,7 +21,7 @@
 
 
 #: Schema for the graph config
-graph_config_schema = Schema(
+graph_config_schema = LegacySchema(
     {
         # The trust-domain for this graph.
         # (See https://firefox-source-docs.mozilla.org/taskcluster/taskcluster/taskgraph.html#taskgraph-trust-domain)  # noqa
diff --git a/src/taskgraph/decision.py b/src/taskgraph/decision.py
index a0c5381a8..888ad12fe 100644
--- a/src/taskgraph/decision.py
+++ b/src/taskgraph/decision.py
@@ -20,7 +20,7 @@
 from taskgraph.taskgraph import TaskGraph
 from taskgraph.util import json
 from taskgraph.util.python_path import find_object
-from taskgraph.util.schema import Schema, validate_schema
+from taskgraph.util.schema import LegacySchema, validate_schema
 from taskgraph.util.vcs import get_repository
 from taskgraph.util.yaml import load_yaml
 
@@ -40,7 +40,7 @@
 
 
 #: Schema for try_task_config.json version 2
-try_task_config_schema_v2 = Schema(
+try_task_config_schema_v2 = LegacySchema(
     {
         Optional("parameters"): {str: object},
     }
diff --git a/src/taskgraph/transforms/base.py b/src/taskgraph/transforms/base.py
index 42705c3c5..a1d50ea4f 100644
--- a/src/taskgraph/transforms/base.py
+++ b/src/taskgraph/transforms/base.py
@@ -12,7 +12,7 @@
 
 from ..config import GraphConfig
 from ..parameters import Parameters
-from ..util.schema import Schema, validate_schema
+from ..util.schema import LegacySchema, validate_schema
 
 
 @dataclass(frozen=True)
@@ -138,7 +138,7 @@ def add_validate(self, schema):
 
 @dataclass
 class ValidateSchema:
-    schema: Schema
+    schema: LegacySchema
 
     def __call__(self, config, tasks):
         for task in tasks:
diff --git a/src/taskgraph/transforms/chunking.py b/src/taskgraph/transforms/chunking.py
index d8ad89dd2..59818337b 100644
--- a/src/taskgraph/transforms/chunking.py
+++ b/src/taskgraph/transforms/chunking.py
@@ -7,11 +7,11 @@
 from voluptuous import ALLOW_EXTRA, Optional, Required
 
 from taskgraph.transforms.base import TransformSequence
-from taskgraph.util.schema import Schema
+from taskgraph.util.schema import LegacySchema
 from taskgraph.util.templates import substitute
 
 #: Schema for chunking transforms
-CHUNK_SCHEMA = Schema(
+CHUNK_SCHEMA = LegacySchema(
     {
         # Optional, so it can be used for a subset of tasks in a kind
         Optional(
diff --git a/src/taskgraph/transforms/docker_image.py b/src/taskgraph/transforms/docker_image.py
index 8ded711ac..0898cc79d 100644
--- a/src/taskgraph/transforms/docker_image.py
+++ b/src/taskgraph/transforms/docker_image.py
@@ -13,7 +13,7 @@
 from taskgraph.transforms.base import TransformSequence
 from taskgraph.util import json
 from taskgraph.util.docker import create_context_tar, generate_context_hash
-from taskgraph.util.schema import Schema
+from taskgraph.util.schema import LegacySchema
 
 from .task import task_description_schema
 
@@ -32,7 +32,7 @@
 transforms = TransformSequence()
 
 #: Schema for docker_image transforms
-docker_image_schema = Schema(
+docker_image_schema = LegacySchema(
     {
         Required(
             "name",
diff --git a/src/taskgraph/transforms/fetch.py b/src/taskgraph/transforms/fetch.py
index 797ab71e2..e165eec31 100644
--- a/src/taskgraph/transforms/fetch.py
+++ b/src/taskgraph/transforms/fetch.py
@@ -18,14 +18,14 @@
 
 from ..util import path
 from ..util.cached_tasks import add_optimization
-from ..util.schema import Schema, validate_schema
+from ..util.schema import LegacySchema, validate_schema
 from ..util.treeherder import join_symbol
 from .base import TransformSequence
 
 CACHE_TYPE = "content.v1"
 
 #: Schema for fetch transforms
-FETCH_SCHEMA = Schema(
+FETCH_SCHEMA = LegacySchema(
     {
         Required(
             "name",
@@ -87,12 +87,12 @@
 
 @dataclass(frozen=True)
 class FetchBuilder:
-    schema: Schema
+    schema: LegacySchema
     builder: Callable
 
 
 def fetch_builder(name, schema):
-    schema = Schema({Required("type"): name}).extend(schema)
+    schema = LegacySchema({Required("type"): name}).extend(schema)
 
     def wrap(func):
         fetch_builders[name] = FetchBuilder(schema, func)  # type: ignore
diff --git a/src/taskgraph/transforms/from_deps.py b/src/taskgraph/transforms/from_deps.py
index 6bf5c6ec9..c03148c99 100644
--- a/src/taskgraph/transforms/from_deps.py
+++ b/src/taskgraph/transforms/from_deps.py
@@ -20,11 +20,11 @@
 from taskgraph.transforms.run import fetches_schema
 from taskgraph.util.attributes import attrmatch
 from taskgraph.util.dependencies import GROUP_BY_MAP, get_dependencies
-from taskgraph.util.schema import Schema, validate_schema
+from taskgraph.util.schema import LegacySchema, validate_schema
 from taskgraph.util.set_name import SET_NAME_MAP
 
 #: Schema for from_deps transforms
-FROM_DEPS_SCHEMA = Schema(
+FROM_DEPS_SCHEMA = LegacySchema(
     {
         Required("from-deps"): {
             Optional(
diff --git a/src/taskgraph/transforms/matrix.py b/src/taskgraph/transforms/matrix.py
index 476507284..855bffa41 100644
--- a/src/taskgraph/transforms/matrix.py
+++ b/src/taskgraph/transforms/matrix.py
@@ -13,11 +13,11 @@
 from voluptuous import ALLOW_EXTRA, Extra, Optional, Required
 
 from taskgraph.transforms.base import TransformSequence
-from taskgraph.util.schema import Schema
+from taskgraph.util.schema import LegacySchema
 from taskgraph.util.templates import substitute_task_fields
 
 #: Schema for matrix transforms
-MATRIX_SCHEMA = Schema(
+MATRIX_SCHEMA = LegacySchema(
     {
         Required("name"): str,
         Optional("matrix"): {
diff --git a/src/taskgraph/transforms/notify.py b/src/taskgraph/transforms/notify.py
index 9c0152dad..a7d118f10 100644
--- a/src/taskgraph/transforms/notify.py
+++ b/src/taskgraph/transforms/notify.py
@@ -11,7 +11,7 @@
 from voluptuous import ALLOW_EXTRA, Any, Exclusive, Optional, Required
 
 from taskgraph.transforms.base import TransformSequence
-from taskgraph.util.schema import Schema, optionally_keyed_by, resolve_keyed_by
+from taskgraph.util.schema import LegacySchema, optionally_keyed_by, resolve_keyed_by
 
 _status_type = Any(
     "on-completed",
@@ -55,7 +55,7 @@
 """Map each type to its primary key that will be used in the route."""
 
 #: Schema for notify transforms
-NOTIFY_SCHEMA = Schema(
+NOTIFY_SCHEMA = LegacySchema(
     {
         Exclusive("notify", "config"): {
             Required("recipients"): [Any(*_recipients)],
diff --git a/src/taskgraph/transforms/run/__init__.py b/src/taskgraph/transforms/run/__init__.py
index 29406e7cd..ed3d7bf02 100644
--- a/src/taskgraph/transforms/run/__init__.py
+++ b/src/taskgraph/transforms/run/__init__.py
@@ -21,7 +21,7 @@
 from taskgraph.util import json
 from taskgraph.util import path as mozpath
 from taskgraph.util.python_path import import_sibling_modules
-from taskgraph.util.schema import Schema, validate_schema
+from taskgraph.util.schema import LegacySchema, validate_schema
 from taskgraph.util.taskcluster import get_artifact_prefix
 from taskgraph.util.workertypes import worker_type_implementation
 
@@ -38,7 +38,7 @@
 }
 
 #: Schema for a run transforms
-run_description_schema = Schema(
+run_description_schema = LegacySchema(
     {
         Optional(
             "name",
@@ -457,7 +457,7 @@ def wrap(func):
 
 
 @run_task_using(
-    "always-optimized", "always-optimized", Schema({"using": "always-optimized"})
+    "always-optimized", "always-optimized", LegacySchema({"using": "always-optimized"})
 )
 def always_optimized(config, task, taskdesc):
     pass
diff --git a/src/taskgraph/transforms/run/index_search.py b/src/taskgraph/transforms/run/index_search.py
index 7436f010f..d5c0c6109 100644
--- a/src/taskgraph/transforms/run/index_search.py
+++ b/src/taskgraph/transforms/run/index_search.py
@@ -12,13 +12,13 @@
 
 from taskgraph.transforms.base import TransformSequence
 from taskgraph.transforms.run import run_task_using
-from taskgraph.util.schema import Schema
+from taskgraph.util.schema import LegacySchema
 
 transforms = TransformSequence()
 
 
 #: Schema for run.using index-search
-run_task_schema = Schema(
+run_task_schema = LegacySchema(
     {
         Required("using"): "index-search",
         Required(
diff --git a/src/taskgraph/transforms/run/run_task.py b/src/taskgraph/transforms/run/run_task.py
index 9d76380d8..ce81d7d23 100644
--- a/src/taskgraph/transforms/run/run_task.py
+++ b/src/taskgraph/transforms/run/run_task.py
@@ -19,7 +19,7 @@
 from taskgraph.transforms.task import taskref_or_string
 from taskgraph.util import path, taskcluster
 from taskgraph.util.caches import CACHES
-from taskgraph.util.schema import Schema
+from taskgraph.util.schema import LegacySchema
 
 EXEC_COMMANDS = {
     "bash": ["bash", "-cx"],
@@ -28,7 +28,7 @@
 
 
 #: Schema for run.using run_task
-run_task_schema = Schema(
+run_task_schema = LegacySchema(
     {
         Required(
             "using",
diff --git a/src/taskgraph/transforms/run/toolchain.py b/src/taskgraph/transforms/run/toolchain.py
index 58d318043..77406ad61 100644
--- a/src/taskgraph/transforms/run/toolchain.py
+++ b/src/taskgraph/transforms/run/toolchain.py
@@ -18,13 +18,13 @@
 )
 from taskgraph.util import path as mozpath
 from taskgraph.util.hash import hash_paths
-from taskgraph.util.schema import Schema
+from taskgraph.util.schema import LegacySchema
 from taskgraph.util.shell import quote as shell_quote
 
 CACHE_TYPE = "toolchains.v3"
 
 #: Schema for run.using toolchain
-toolchain_run_schema = Schema(
+toolchain_run_schema = LegacySchema(
     {
         Required(
             "using",
diff --git a/src/taskgraph/transforms/task.py b/src/taskgraph/transforms/task.py
index 7c834dcc7..59efbd8f3 100644
--- a/src/taskgraph/transforms/task.py
+++ b/src/taskgraph/transforms/task.py
@@ -23,8 +23,8 @@
 from taskgraph.util.hash import hash_path
 from taskgraph.util.keyed_by import evaluate_keyed_by
 from taskgraph.util.schema import (
+    LegacySchema,
     OptimizationSchema,
-    Schema,
     optionally_keyed_by,
     resolve_keyed_by,
     taskref_or_string,
@@ -48,7 +48,7 @@ def run_task_suffix():
 
 
 #: Schema for the task transforms
-task_description_schema = Schema(
+task_description_schema = LegacySchema(
     {
         Required(
             "label",
@@ -430,14 +430,14 @@ def get_default_deadline(graph_config, project):
 
 @dataclass(frozen=True)
 class PayloadBuilder:
-    schema: Schema
+    schema: LegacySchema
     builder: Callable
 
 
 def payload_builder(name, schema):
-    schema = Schema({Required("implementation"): name, Optional("os"): str}).extend(
-        schema
-    )
+    schema = LegacySchema(
+        {Required("implementation"): name, Optional("os"): str}
+    ).extend(schema)
 
     def wrap(func):
         assert name not in payload_builders, f"duplicate payload builder name {name}"
diff --git a/src/taskgraph/transforms/task_context.py b/src/taskgraph/transforms/task_context.py
index 815c582de..e38648cd3 100644
--- a/src/taskgraph/transforms/task_context.py
+++ b/src/taskgraph/transforms/task_context.py
@@ -3,12 +3,12 @@
 from voluptuous import ALLOW_EXTRA, Any, Optional, Required
 
 from taskgraph.transforms.base import TransformSequence
-from taskgraph.util.schema import Schema
+from taskgraph.util.schema import LegacySchema
 from taskgraph.util.templates import deep_get, substitute_task_fields
 from taskgraph.util.yaml import load_yaml
 
 #: Schema for the task_context transforms
-SCHEMA = Schema(
+SCHEMA = LegacySchema(
     {
         Optional("name"): str,
         Optional(
diff --git a/src/taskgraph/util/dependencies.py b/src/taskgraph/util/dependencies.py
index 94d47b8d5..17c41d732 100644
--- a/src/taskgraph/util/dependencies.py
+++ b/src/taskgraph/util/dependencies.py
@@ -7,7 +7,7 @@
 
 from taskgraph.task import Task
 from taskgraph.transforms.base import TransformConfig
-from taskgraph.util.schema import Schema
+from taskgraph.util.schema import LegacySchema
 
 # Define a collection of group_by functions
 GROUP_BY_MAP = {}
@@ -36,7 +36,7 @@ def group_by_all(config, tasks):
     return [[task for task in tasks]]
 
 
-@group_by("attribute", schema=Schema(str))
+@group_by("attribute", schema=LegacySchema(str))
 def group_by_attribute(config, tasks, attr):
     groups = {}
     for task in tasks:
diff --git a/src/taskgraph/util/schema.py b/src/taskgraph/util/schema.py
index 3c5f4c955..9f256f69d 100644
--- a/src/taskgraph/util/schema.py
+++ b/src/taskgraph/util/schema.py
@@ -2,67 +2,109 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-
 import pprint
 import re
 from collections.abc import Mapping
+from functools import reduce
+from typing import Literal, Optional, Union
 
+import msgspec
 import voluptuous
 
 import taskgraph
 from taskgraph.util.keyed_by import evaluate_keyed_by, iter_dot_path
 
+# Common type definitions that are used across multiple schemas
+TaskPriority = Literal[
+    "highest", "very-high", "high", "medium", "low", "very-low", "lowest"
+]
+
 
 def validate_schema(schema, obj, msg_prefix):
     """
     Validate that object satisfies schema.  If not, generate a useful exception
     beginning with msg_prefix.
+
+    Args:
+        schema: A voluptuous.Schema or msgspec-based StructSchema type
+        obj: Object to validate
+        msg_prefix: Prefix for error messages
     """
     if taskgraph.fast:
         return
+
     try:
-        schema(obj)
-    except voluptuous.MultipleInvalid as exc:
-        msg = [msg_prefix]
-        for error in exc.errors:
-            msg.append(str(error))
-        raise Exception("\n".join(msg) + "\n" + pprint.pformat(obj))
+        # Handle voluptuous Schema
+        if isinstance(schema, voluptuous.Schema):
+            schema(obj)
+        # Handle msgspec-based schemas (StructSchema and its subclasses)
+        elif isinstance(schema, type) and issubclass(schema, msgspec.Struct):
+            # Check if it's our Struct subclass with validate method
+            if issubclass(schema, Schema):
+                schema.validate(obj)
+            else:
+                # Fall back to msgspec.convert for validation
+                msgspec.convert(obj, schema)
+        else:
+            raise TypeError(f"Unsupported schema type: {type(schema)}")
+    except (
+        voluptuous.MultipleInvalid,
+        msgspec.ValidationError,
+        msgspec.DecodeError,
+    ) as exc:
+        if isinstance(exc, voluptuous.MultipleInvalid):
+            msg = [msg_prefix]
+            for error in exc.errors:
+                msg.append(str(error))
+            raise Exception("\n".join(msg) + "\n" + pprint.pformat(obj))
+        else:
+            raise Exception(f"{msg_prefix}\n{str(exc)}\n{pprint.pformat(obj)}")
+
+
+def UnionTypes(*types):
+    """Use `functools.reduce` to simulate `Union[*allowed_types]` on older
+    Python versions.
+    """
+    return reduce(lambda a, b: Union[a, b], types)
 
 
-def optionally_keyed_by(*arguments):
+def optionally_keyed_by(*arguments, use_msgspec=False):
     """
-    Mark a schema value as optionally keyed by any of a number of fields.  The
-    schema is the last argument, and the remaining fields are taken to be the
-    field names.  For example:
-
-        'some-value': optionally_keyed_by(
-            'test-platform', 'build-platform',
-            Any('a', 'b', 'c'))
+    Mark a schema value as optionally keyed by any of a number of fields.
 
-    The resulting schema will allow nesting of `by-test-platform` and
-    `by-build-platform` in either order.
+    Args:
+        *arguments: Field names followed by the schema
+        use_msgspec: If True, return msgspec type hints; if False, return voluptuous validator
     """
-    schema = arguments[-1]
-    fields = arguments[:-1]
-
-    def validator(obj):
-        if isinstance(obj, dict) and len(obj) == 1:
-            k, v = list(obj.items())[0]
-            if k.startswith("by-") and k[len("by-") :] in fields:
-                res = {}
-                for kk, vv in v.items():
-                    try:
-                        res[kk] = validator(vv)
-                    except voluptuous.Invalid as e:
-                        e.prepend([k, kk])
-                        raise
-                return res
-        return Schema(schema)(obj)
-
-    # set to assist autodoc
-    setattr(validator, "schema", schema)
-    setattr(validator, "fields", fields)
-    return validator
+    if use_msgspec:
+        # msgspec implementation - return type hints
+        _type = arguments[-1]
+        fields = arguments[:-1]
+        bykeys = [Literal[f"by-{field}"] for field in fields]
+        return Union[_type, dict[UnionTypes(*bykeys), dict[str, _type]]]
+    else:
+        # voluptuous implementation - return validator function
+        schema = arguments[-1]
+        fields = arguments[:-1]
+
+        def validator(obj):
+            if isinstance(obj, dict) and len(obj) == 1:
+                k, v = list(obj.items())[0]
+                if k.startswith("by-") and k[len("by-") :] in fields:
+                    res = {}
+                    for kk, vv in v.items():
+                        try:
+                            res[kk] = validator(vv)
+                        except voluptuous.Invalid as e:
+                            e.prepend([k, kk])
+                            raise
+                    return res
+            return LegacySchema(schema)(obj)
+
+        # set to assist autodoc
+        setattr(validator, "schema", schema)
+        setattr(validator, "fields", fields)
+        return validator
 
 
 def resolve_keyed_by(
@@ -199,7 +241,7 @@ def check_identifier(path, k):
     iter("schema", schema.schema)
 
 
-class Schema(voluptuous.Schema):
+class LegacySchema(voluptuous.Schema):
     """
     Operates identically to voluptuous.Schema, but applying some taskgraph-specific checks
     in the process.
@@ -218,7 +260,7 @@ def extend(self, *args, **kwargs):
         if self.check:
             check_schema(schema)
         # We want twice extend schema to be checked too.
-        schema.__class__ = Schema
+        schema.__class__ = LegacySchema
         return schema
 
     def _compile(self, schema):
@@ -230,6 +272,103 @@ def __getitem__(self, item):
         return self.schema[item]  # type: ignore
 
 
+class Schema(
+    msgspec.Struct,
+    kw_only=True,
+    omit_defaults=True,
+    rename="kebab",
+    forbid_unknown_fields=True,
+):
+    """
+    Base schema class that extends msgspec.Struct.
+
+    This allows schemas to be defined directly as:
+
+        class MySchema(Schema):
+            foo: str
+            bar: int = 10
+
+    Instead of wrapping msgspec.Struct types.
+    Most schemas use kebab-case renaming by default.
+
+    By default, forbid_unknown_fields is True, meaning extra fields
+    will cause validation errors. Child classes can override this by
+    setting forbid_unknown_fields=False in their class definition:
+
+        class MySchema(Schema, forbid_unknown_fields=False):
+            foo: str
+    """
+
+    @classmethod
+    def validate(cls, data):
+        """Validate data against this schema."""
+        if taskgraph.fast:
+            return data
+
+        try:
+            return msgspec.convert(data, cls)
+        except (msgspec.ValidationError, msgspec.DecodeError) as e:
+            raise msgspec.ValidationError(str(e))
+
+
+class IndexSearchOptimizationSchema(Schema):
+    """Search the index for the given index namespaces."""
+
+    index_search: list[str]
+
+
+class SkipUnlessChangedOptimizationSchema(Schema):
+    """Skip this task if none of the given file patterns match."""
+
+    skip_unless_changed: list[str]
+
+
+# Create a class for optimization types to avoid dict union issues
+class OptimizationTypeSchema(Schema, forbid_unknown_fields=False):
+    """Schema that accepts various optimization configurations."""
+
+    index_search: Optional[list[str]] = None
+    skip_unless_changed: Optional[list[str]] = None
+
+    def __post_init__(self):
+        """Ensure at least one optimization type is provided."""
+        if not self.index_search and not self.skip_unless_changed:
+            # Allow empty schema for other dict-based optimizations
+            pass
+
+
+OptimizationType = Union[None, OptimizationTypeSchema]
+
+
+# Task reference types using msgspec
+class TaskReferenceSchema(Schema):
+    """Reference to another task (msgspec version)."""
+
+    task_reference: str
+
+
+class ArtifactReferenceSchema(Schema):
+    """Reference to a task artifact (msgspec version)."""
+
+    artifact_reference: str
+
+
+class TaskRefTypeSchema(Schema, forbid_unknown_fields=False):
+    """Schema that accepts either task-reference or artifact-reference (msgspec version)."""
+
+    task_reference: Optional[str] = None
+    artifact_reference: Optional[str] = None
+
+    def __post_init__(self):
+        """Ensure exactly one reference type is provided."""
+        if self.task_reference and self.artifact_reference:
+            raise ValueError("Cannot have both task-reference and artifact-reference")
+        if not self.task_reference and not self.artifact_reference:
+            raise ValueError("Must have either task-reference or artifact-reference")
+
+
+taskref_or_string_msgspec = Union[str, TaskRefTypeSchema]
+
 OptimizationSchema = voluptuous.Any(
     # always run this task (default)
     None,
diff --git a/template/{{cookiecutter.project_name}}/taskcluster/{{cookiecutter.project_slug}}_taskgraph/transforms/hello.py b/template/{{cookiecutter.project_name}}/taskcluster/{{cookiecutter.project_slug}}_taskgraph/transforms/hello.py
index 6729f2f57..f63b5feab 100644
--- a/template/{{cookiecutter.project_name}}/taskcluster/{{cookiecutter.project_slug}}_taskgraph/transforms/hello.py
+++ b/template/{{cookiecutter.project_name}}/taskcluster/{{cookiecutter.project_slug}}_taskgraph/transforms/hello.py
@@ -1,9 +1,9 @@
 from voluptuous import ALLOW_EXTRA, Required
 
 from taskgraph.transforms.base import TransformSequence
-from taskgraph.util.schema import Schema
+from taskgraph.util.schema import LegacySchema
 
-HELLO_SCHEMA = Schema(
+HELLO_SCHEMA = LegacySchema(
     {
         Required("noun"): str,
     },
diff --git a/test/test_transforms_run_run_task.py b/test/test_transforms_run_run_task.py
index dec10dc0a..2ef25b9f2 100644
--- a/test/test_transforms_run_run_task.py
+++ b/test/test_transforms_run_run_task.py
@@ -10,7 +10,7 @@
 from taskgraph.transforms.run import make_task_description
 from taskgraph.transforms.task import payload_builders, set_defaults
 from taskgraph.util.caches import CACHES
-from taskgraph.util.schema import Schema, validate_schema
+from taskgraph.util.schema import LegacySchema, validate_schema
 from taskgraph.util.taskcluster import get_root_url
 from taskgraph.util.templates import merge
 
@@ -258,7 +258,7 @@ def inner(task, **kwargs):
         pprint(caches, indent=2)
 
         # Create a new schema object with just the part relevant to caches.
-        partial_schema = Schema(payload_builders[impl].schema.schema[key])
+        partial_schema = LegacySchema(payload_builders[impl].schema.schema[key])
         validate_schema(partial_schema, caches, "validation error")
 
         return caches
diff --git a/test/test_util_schema.py b/test/test_util_schema.py
index 59c354e6a..3364b2813 100644
--- a/test/test_util_schema.py
+++ b/test/test_util_schema.py
@@ -9,13 +9,13 @@
 
 import taskgraph
 from taskgraph.util.schema import (
-    Schema,
+    LegacySchema,
     optionally_keyed_by,
     resolve_keyed_by,
     validate_schema,
 )
 
-schema = Schema(
+schema = LegacySchema(
     {
         "x": int,
         "y": str,
@@ -39,26 +39,26 @@ class TestCheckSchema(unittest.TestCase):
     def test_schema(self):
         "Creating a schema applies taskgraph checks."
         with self.assertRaises(Exception):
-            Schema({"camelCase": int})
+            LegacySchema({"camelCase": int})
 
     def test_extend_schema(self):
         "Extending a schema applies taskgraph checks."
         with self.assertRaises(Exception):
-            Schema({"kebab-case": int}).extend({"camelCase": int})
+            LegacySchema({"kebab-case": int}).extend({"camelCase": int})
 
     def test_extend_schema_twice(self):
         "Extending a schema twice applies taskgraph checks."
         with self.assertRaises(Exception):
-            Schema({"kebab-case": int}).extend({"more-kebab": int}).extend(
+            LegacySchema({"kebab-case": int}).extend({"more-kebab": int}).extend(
                 {"camelCase": int}
             )
 
 
 def test_check_skipped(monkeypatch):
     """Schema not validated if 'check=False' or taskgraph.fast is unset."""
-    Schema({"camelCase": int}, check=False)  # assert no exception
+    LegacySchema({"camelCase": int}, check=False)  # assert no exception
     monkeypatch.setattr(taskgraph, "fast", True)
-    Schema({"camelCase": int})  # assert no exception
+    LegacySchema({"camelCase": int})  # assert no exception
 
 
 class TestResolveKeyedBy(unittest.TestCase):
diff --git a/uv.lock b/uv.lock
index c0efc03ba..54a5b5495 100644
--- a/uv.lock
+++ b/uv.lock
@@ -1,5 +1,5 @@
 version = 1
-revision = 3
+revision = 2
 requires-python = ">=3.9"
 resolution-markers = [
     "python_full_version >= '3.11'",
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 ]
 
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 [[package]]
 name = "multidict"
 version = "6.7.0"
@@ -2028,6 +2092,7 @@ dependencies = [
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     { name = "mozilla-repo-urls", version = "0.1.1", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.11'" },
     { name = "mozilla-repo-urls", version = "0.2.2", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.11'" },
+    { name = "msgspec" },
     { name = "pyyaml" },
     { name = "redo" },
     { name = "requests" },
@@ -2074,6 +2139,7 @@ requires-dist = [
     { name = "cookiecutter", specifier = "~=2.1" },
     { name = "json-e", specifier = ">=2.7" },
     { name = "mozilla-repo-urls" },
+    { name = "msgspec", specifier = ">=0.20.0" },
     { name = "orjson", marker = "extra == 'orjson'" },
     { name = "pyyaml", specifier = ">=5.3.1" },
     { name = "redo", specifier = ">=2.0" },