diff --git a/tildes/requirements-dev.txt b/tildes/requirements-dev.txt
index 1634bef..5c94104 100644
--- a/tildes/requirements-dev.txt
+++ b/tildes/requirements-dev.txt
@@ -37,7 +37,7 @@ jinja2==3.1.6
 lupa==2.5
 mako==1.3.10
 markupsafe==3.0.2
-marshmallow==3.25.1
+marshmallow==4.0.1
 matplotlib-inline==0.1.7
 mccabe==0.7.0
 mypy==1.17.1
@@ -119,7 +119,7 @@ urllib3==2.5.0
 venusian==3.1.1
 waitress==3.0.2
 wcwidth==0.2.13
-webargs==8.0.0
+webargs==8.7.0
 webassets==2.0
 webencodings==0.5.1
 webob==1.8.9
diff --git a/tildes/requirements.in b/tildes/requirements.in
index a7ee0cf..3520044 100644
--- a/tildes/requirements.in
+++ b/tildes/requirements.in
@@ -10,7 +10,7 @@ html5lib
 invoke
 ipython
 lupa
-marshmallow==3.25.1 # TODO: Upgrade Marshmallow https://marshmallow.readthedocs.io/en/latest/upgrading.html
+marshmallow
 Pillow
 pip-tools
 prometheus-client
@@ -36,6 +36,6 @@ SQLAlchemy-Utils
 stripe==2.6.0 # TODO: Figure out if we can update this
 titlecase
 unicodedata2
-webargs==8.0.0 # TODO: Updating webargs causes an issue with parsing URLs, figure out if we can fix this
+webargs
 wrapt
 zope.sqlalchemy==1.5 # TODO: Figure out if we can update this
diff --git a/tildes/requirements.txt b/tildes/requirements.txt
index 477544c..11fb8c0 100644
--- a/tildes/requirements.txt
+++ b/tildes/requirements.txt
@@ -25,7 +25,7 @@ jinja2==3.1.6
 lupa==2.5
 mako==1.3.10
 markupsafe==3.0.2
-marshmallow==3.25.1
+marshmallow==4.0.1
 matplotlib-inline==0.1.7
 packaging==25.0
 parso==0.8.4
@@ -73,7 +73,7 @@ unicodedata2==16.0.0
 urllib3==2.5.0
 venusian==3.1.1
 wcwidth==0.2.13
-webargs==8.0.0
+webargs==8.7.0
 webassets==2.0
 webencodings==0.5.1
 webob==1.8.9
diff --git a/tildes/tests/test_markdown_field.py b/tildes/tests/test_markdown_field.py
index 753f84c..16b6c09 100644
--- a/tildes/tests/test_markdown_field.py
+++ b/tildes/tests/test_markdown_field.py
@@ -1,13 +1,14 @@
 # Copyright (c) 2018 Tildes contributors <code@tildes.net>
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-from marshmallow import Schema, ValidationError
+from marshmallow import ValidationError
 from pytest import raises
 
+from tildes.schemas.base import BaseTildesSchema
 from tildes.schemas.fields import Markdown
 
 
-class MarkdownFieldTestSchema(Schema):
+class MarkdownFieldTestSchema(BaseTildesSchema):
     """Simple schema class with a standard Markdown field."""
 
     markdown = Markdown()
diff --git a/tildes/tests/test_simplestring_field.py b/tildes/tests/test_simplestring_field.py
index 651392e..0a29fe6 100644
--- a/tildes/tests/test_simplestring_field.py
+++ b/tildes/tests/test_simplestring_field.py
@@ -1,13 +1,14 @@
 # Copyright (c) 2018 Tildes contributors <code@tildes.net>
 # SPDX-License-Identifier: AGPL-3.0-or-later
 
-from marshmallow import Schema, ValidationError
+from marshmallow import ValidationError
 from pytest import raises
 
+from tildes.schemas.base import BaseTildesSchema
 from tildes.schemas.fields import SimpleString
 
 
-class SimpleStringTestSchema(Schema):
+class SimpleStringTestSchema(BaseTildesSchema):
     """Simple schema class with a standard SimpleString field."""
 
     subject = SimpleString()
diff --git a/tildes/tildes/json.py b/tildes/tildes/json.py
index 57313f3..7e0101b 100644
--- a/tildes/tildes/json.py
+++ b/tildes/tildes/json.py
@@ -11,6 +11,7 @@ from tildes.models import DatabaseModel
 from tildes.models.group import Group
 from tildes.models.topic import Topic
 from tildes.models.user import User
+from tildes.schemas.context import TildesSchemaContext, TildesSchemaContextDict
 
 
 def serialize_model(model_item: DatabaseModel, request: Request) -> dict:
@@ -25,11 +26,12 @@ def serialize_model(model_item: DatabaseModel, request: Request) -> dict:
 
 def serialize_topic(topic: Topic, request: Request) -> dict:
     """Return serializable data for a Topic."""
-    context = {}
+    context: TildesSchemaContextDict = {}
     if not request.has_permission("view_author", topic):
         context["hide_username"] = True
 
-    return topic.schema_class(context=context).dump(topic)
+    with TildesSchemaContext(context):
+        return topic.schema_class().dump(topic)
 
 
 def includeme(config: Configurator) -> None:
diff --git a/tildes/tildes/schemas/base.py b/tildes/tildes/schemas/base.py
new file mode 100644
index 0000000..1ab6b3c
--- /dev/null
+++ b/tildes/tildes/schemas/base.py
@@ -0,0 +1,37 @@
+# Copyright (c) 2018 Tildes contributors <code@tildes.net>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+"""Base Marshmallow schema."""
+
+
+from typing import Any, Optional
+from marshmallow import Schema
+from tildes.schemas.context import TildesSchemaContext, TildesSchemaContextDict
+
+
+class BaseTildesSchema(Schema):
+    """Base Marshmallow schema for Tildes schemas.
+
+    Adds common code like the context dict.
+    """
+
+    context: TildesSchemaContextDict
+
+    def __init__(
+        self, context: Optional[TildesSchemaContextDict] = None, **kwargs: Any
+    ):
+        """Pass an optional context, and forward Schema arguments to superclass."""
+        super().__init__(**kwargs)
+        self.context = context if context else {}
+
+    def get_context_value(self, key: str) -> Any:
+        """Get a value from the context dict.
+
+        Any active TildesSchemaContext, e.g. set using a "with" statement,
+        takes precedence. If there is no active TildesSchemaContext, then
+        it takes the value from the dict passed in __init__ instead.
+        """
+        result = TildesSchemaContext.get(default=self.context).get(key)
+        if result:
+            return result
+        return self.context.get(key)
diff --git a/tildes/tildes/schemas/comment.py b/tildes/tildes/schemas/comment.py
index 01cfdd0..550b506 100644
--- a/tildes/tildes/schemas/comment.py
+++ b/tildes/tildes/schemas/comment.py
@@ -3,13 +3,12 @@
 
 """Validation/dumping schema for comments."""
 
-from marshmallow import Schema
-
 from tildes.enums import CommentLabelOption
+from tildes.schemas.base import BaseTildesSchema
 from tildes.schemas.fields import Enum, ID36, Markdown, SimpleString
 
 
-class CommentSchema(Schema):
+class CommentSchema(BaseTildesSchema):
     """Marshmallow schema for comments."""
 
     comment_id36 = ID36()
@@ -17,8 +16,8 @@ class CommentSchema(Schema):
     parent_comment_id36 = ID36()
 
 
-class CommentLabelSchema(Schema):
+class CommentLabelSchema(BaseTildesSchema):
     """Marshmallow schema for comment labels."""
 
     name = Enum(CommentLabelOption)
-    reason = SimpleString(max_length=1000, missing=None)
+    reason = SimpleString(max_length=1000, load_default=None)
diff --git a/tildes/tildes/schemas/context.py b/tildes/tildes/schemas/context.py
new file mode 100644
index 0000000..1064486
--- /dev/null
+++ b/tildes/tildes/schemas/context.py
@@ -0,0 +1,30 @@
+# Copyright (c) 2018 Tildes contributors <code@tildes.net>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+"""Context variables that can be used with Marshmallow schemas."""
+import typing
+
+from marshmallow.experimental.context import Context
+
+
+class TildesSchemaContextDict(typing.TypedDict, total=False):
+    """Context for Tildes Marshmallow schemas.
+
+    For convenience, we use one unified class instead of one per schema,
+    so it can be passed down through different schemas in a subgraph.
+    For example, if a Topic contains a reference to a User,
+    one instance of TildesContext can configure both the Topic and User.
+    """
+
+    # Applies to UserSchema
+    hide_username: bool
+    # Applies to UserSchema
+    check_breached_passwords: bool
+    # Applies to UserSchema
+    username_trim_whitespace: bool
+
+    # Applies to GroupSchema
+    fix_path_capitalization: bool
+
+
+TildesSchemaContext = Context[TildesSchemaContextDict]
diff --git a/tildes/tildes/schemas/fields.py b/tildes/tildes/schemas/fields.py
index 48ff185..6510106 100644
--- a/tildes/tildes/schemas/fields.py
+++ b/tildes/tildes/schemas/fields.py
@@ -22,7 +22,7 @@ from tildes.lib.string import simplify_string
 DataType = Optional[Mapping[str, Any]]
 
 
-class Enum(Field):
+class Enum(Field[enum.Enum]):
     """Field for a native Python Enum (or subclasses)."""
 
     def __init__(
@@ -34,9 +34,12 @@ class Enum(Field):
         self._enum_class = enum_class
 
     def _serialize(
-        self, value: enum.Enum, attr: str | None, obj: object, **kwargs: Any
-    ) -> str:
+        self, value: enum.Enum | None, attr: str | None, obj: object, **kwargs: Any
+    ) -> str | None:
         """Serialize the enum value - lowercase version of its name."""
+        if value is None:
+            return None
+
         return value.name.lower()
 
     def _deserialize(
@@ -64,7 +67,7 @@ class ID36(String):
         super().__init__(validate=Regexp(ID36_REGEX), **kwargs)
 
 
-class ShortTimePeriod(Field):
+class ShortTimePeriod(Field[Optional[SimpleHoursPeriod]]):
     """Field for short time period strings like "4h" and "2d".
 
     Also supports the string "all" which will be converted to None.
@@ -100,7 +103,7 @@ class ShortTimePeriod(Field):
         return value.as_short_form()
 
 
-class Markdown(Field):
+class Markdown(Field[str]):
     """Field for markdown strings (comments, text topic, messages, etc.)."""
 
     DEFAULT_MAX_LENGTH = 50000
@@ -132,13 +135,13 @@ class Markdown(Field):
         return value
 
     def _serialize(
-        self, value: str, attr: str | None, obj: object, **kwargs: Any
-    ) -> str:
+        self, value: str | None, attr: str | None, obj: object, **kwargs: Any
+    ) -> str | None:
         """Serialize the value (no-op in this case)."""
         return value
 
 
-class SimpleString(Field):
+class SimpleString(Field[str]):
     """Field for "simple" strings, suitable for uses like subject, title, etc.
 
     These strings should generally not contain any special formatting (such as
@@ -169,13 +172,13 @@ class SimpleString(Field):
         return simplify_string(value)
 
     def _serialize(
-        self, value: str, attr: str | None, obj: object, **kwargs: Any
-    ) -> str:
+        self, value: str | None, attr: str | None, obj: object, **kwargs: Any
+    ) -> str | None:
         """Serialize the value (no-op in this case)."""
         return value
 
 
-class Ltree(Field):
+class Ltree(Field[sqlalchemy_utils.Ltree]):
     """Field for postgresql ltree type."""
 
     # note that this regex only checks whether all of the chars are individually valid,
diff --git a/tildes/tildes/schemas/group.py b/tildes/tildes/schemas/group.py
index 1659cb8..53575b8 100644
--- a/tildes/tildes/schemas/group.py
+++ b/tildes/tildes/schemas/group.py
@@ -7,10 +7,12 @@ import re
 from typing import Any
 
 import sqlalchemy_utils
-from marshmallow import pre_load, Schema, validates
+from marshmallow import pre_load, validates
 from marshmallow.exceptions import ValidationError
 from marshmallow.fields import DateTime
+from marshmallow.types import UnknownOption
 
+from tildes.schemas.base import BaseTildesSchema
 from tildes.schemas.fields import Ltree, Markdown, SimpleString
 
 
@@ -30,7 +32,7 @@ GROUP_PATH_ELEMENT_VALID_REGEX = re.compile(
 SHORT_DESCRIPTION_MAX_LENGTH = 200
 
 
-class GroupSchema(Schema):
+class GroupSchema(BaseTildesSchema):
     """Marshmallow schema for groups."""
 
     path = Ltree(required=True)
@@ -41,10 +43,12 @@ class GroupSchema(Schema):
     sidebar_markdown = Markdown(allow_none=True)
 
     @pre_load
-    def prepare_path(self, data: dict, many: bool, partial: Any) -> dict:
+    def prepare_path(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> dict:
         """Prepare the path value before it's validated."""
         # pylint: disable=unused-argument
-        if not self.context.get("fix_path_capitalization"):
+        if not self.get_context_value("fix_path_capitalization"):
             return data
 
         if "path" not in data or not isinstance(data["path"], str):
@@ -57,8 +61,9 @@ class GroupSchema(Schema):
         return new_data
 
     @validates("path")
-    def validate_path(self, value: sqlalchemy_utils.Ltree) -> None:
+    def validate_path(self, value: sqlalchemy_utils.Ltree, data_key: str) -> None:
         """Validate the path field, raising an error if an issue exists."""
+        # pylint: disable=unused-argument
         # check each element for length and against validity regex
         path_elements = value.path.split(".")
         for element in path_elements:
@@ -69,7 +74,9 @@ class GroupSchema(Schema):
                 raise ValidationError("Path element %s is invalid" % element)
 
     @pre_load
-    def prepare_sidebar_markdown(self, data: dict, many: bool, partial: Any) -> dict:
+    def prepare_sidebar_markdown(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> dict:
         """Prepare the sidebar_markdown value before it's validated."""
         # pylint: disable=unused-argument
         if "sidebar_markdown" not in data:
diff --git a/tildes/tildes/schemas/group_wiki_page.py b/tildes/tildes/schemas/group_wiki_page.py
index ea4229f..31a849d 100644
--- a/tildes/tildes/schemas/group_wiki_page.py
+++ b/tildes/tildes/schemas/group_wiki_page.py
@@ -3,15 +3,14 @@
 
 """Validation/dumping schema for group wiki pages."""
 
-from marshmallow import Schema
-
+from tildes.schemas.base import BaseTildesSchema
 from tildes.schemas.fields import Markdown, SimpleString
 
 
 PAGE_NAME_MAX_LENGTH = 40
 
 
-class GroupWikiPageSchema(Schema):
+class GroupWikiPageSchema(BaseTildesSchema):
     """Marshmallow schema for group wiki pages."""
 
     page_name = SimpleString(max_length=PAGE_NAME_MAX_LENGTH)
diff --git a/tildes/tildes/schemas/listing.py b/tildes/tildes/schemas/listing.py
index 4cdc783..aeb1305 100644
--- a/tildes/tildes/schemas/listing.py
+++ b/tildes/tildes/schemas/listing.py
@@ -5,23 +5,27 @@
 
 from typing import Any
 
-from marshmallow import pre_load, Schema, validates_schema, ValidationError
+from marshmallow import pre_load, validates_schema, ValidationError
 from marshmallow.fields import Boolean, Integer
+from marshmallow.types import UnknownOption
 from marshmallow.validate import Range
 
 from tildes.enums import TopicSortOption
+from tildes.schemas.base import BaseTildesSchema
 from tildes.schemas.fields import Enum, ID36, Ltree, PostType, ShortTimePeriod
 
 
-class PaginatedListingSchema(Schema):
+class PaginatedListingSchema(BaseTildesSchema):
     """Marshmallow schema to validate arguments for a paginated listing page."""
 
-    after = ID36(missing=None)
-    before = ID36(missing=None)
-    per_page = Integer(validate=Range(min=1, max=100), missing=50)
+    after = ID36(load_default=None)
+    before = ID36(load_default=None)
+    per_page = Integer(validate=Range(min=1, max=100), load_default=50)
 
     @validates_schema
-    def either_after_or_before(self, data: dict, many: bool, partial: Any) -> None:
+    def either_after_or_before(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> None:
         """Fail validation if both after and before were specified."""
         # pylint: disable=unused-argument
         if data.get("after") and data.get("before"):
@@ -32,15 +36,15 @@ class TopicListingSchema(PaginatedListingSchema):
     """Marshmallow schema to validate arguments for a topic listing page."""
 
     period = ShortTimePeriod(allow_none=True)
-    order = Enum(TopicSortOption, missing=None)
-    tag = Ltree(missing=None)
-    unfiltered = Boolean(missing=False)
-    all_subgroups = Boolean(missing=False)
-    rank_start = Integer(data_key="n", validate=Range(min=1), missing=None)
+    order = Enum(TopicSortOption, load_default=None)
+    tag = Ltree(load_default=None)
+    unfiltered = Boolean(load_default=False)
+    all_subgroups = Boolean(load_default=False)
+    rank_start = Integer(data_key="n", validate=Range(min=1), load_default=None)
 
     @pre_load
     def reset_rank_start_on_first_page(
-        self, data: dict, many: bool, partial: Any
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
     ) -> dict:
         """Reset rank_start to 1 if this is a first page (no before/after)."""
         # pylint: disable=unused-argument
@@ -62,11 +66,11 @@ class MixedListingSchema(PaginatedListingSchema):
     of just one or the other.
     """
 
-    anchor_type = PostType(missing=None)
+    anchor_type = PostType(load_default=None)
 
     @pre_load
     def set_anchor_type_from_before_or_after(
-        self, data: dict, many: bool, partial: Any
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
     ) -> dict:
         """Set the anchor_type if before or after has a special value indicating type.
 
diff --git a/tildes/tildes/schemas/message.py b/tildes/tildes/schemas/message.py
index 2f16075..c82ccaa 100644
--- a/tildes/tildes/schemas/message.py
+++ b/tildes/tildes/schemas/message.py
@@ -3,16 +3,16 @@
 
 """Validation/dumping schemas for messages."""
 
-from marshmallow import Schema
 from marshmallow.fields import DateTime, String
 
+from tildes.schemas.base import BaseTildesSchema
 from tildes.schemas.fields import ID36, Markdown, SimpleString
 
 
 SUBJECT_MAX_LENGTH = 200
 
 
-class MessageConversationSchema(Schema):
+class MessageConversationSchema(BaseTildesSchema):
     """Marshmallow schema for message conversations."""
 
     conversation_id36 = ID36()
@@ -22,7 +22,7 @@ class MessageConversationSchema(Schema):
     created_time = DateTime(dump_only=True)
 
 
-class MessageReplySchema(Schema):
+class MessageReplySchema(BaseTildesSchema):
     """Marshmallow schema for message replies."""
 
     reply_id36 = ID36()
diff --git a/tildes/tildes/schemas/topic.py b/tildes/tildes/schemas/topic.py
index 41e2aae..1cd52ab 100644
--- a/tildes/tildes/schemas/topic.py
+++ b/tildes/tildes/schemas/topic.py
@@ -7,10 +7,12 @@ import re
 from typing import Any
 from urllib.parse import urlparse
 
-from marshmallow import pre_load, Schema, validates, validates_schema, ValidationError
+from marshmallow import pre_load, validates, validates_schema, ValidationError
 from marshmallow.fields import DateTime, List, Nested, String, URL
+from marshmallow.types import UnknownOption
 
 from tildes.lib.url_transform import apply_url_transformations
+from tildes.schemas.base import BaseTildesSchema
 from tildes.schemas.fields import Enum, ID36, Markdown, SimpleString
 from tildes.schemas.group import GroupSchema
 from tildes.schemas.user import UserSchema
@@ -20,7 +22,7 @@ TITLE_MAX_LENGTH = 200
 TAG_SYNONYMS = {"spoiler": ["spoilers"]}
 
 
-class TopicSchema(Schema):
+class TopicSchema(BaseTildesSchema):
     """Marshmallow schema for topics."""
 
     topic_id36 = ID36()
@@ -36,7 +38,9 @@ class TopicSchema(Schema):
     group = Nested(GroupSchema, dump_only=True)
 
     @pre_load
-    def prepare_title(self, data: dict, many: bool, partial: Any) -> dict:
+    def prepare_title(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> dict:
         """Prepare the title before it's validated."""
         # pylint: disable=unused-argument
         if "title" not in data:
@@ -56,7 +60,9 @@ class TopicSchema(Schema):
         return new_data
 
     @pre_load
-    def prepare_tags(self, data: dict, many: bool, partial: Any) -> dict:
+    def prepare_tags(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> dict:
         """Prepare the tags before they're validated."""
         # pylint: disable=unused-argument
         if "tags" not in data:
@@ -98,7 +104,7 @@ class TopicSchema(Schema):
         return new_data
 
     @validates("tags")
-    def validate_tags(self, value: list[str]) -> None:
+    def validate_tags(self, value: list[str], data_key: str) -> None:
         """Validate the tags field, raising an error if an issue exists.
 
         Note that tags are validated by ensuring that each tag would be a valid group
@@ -107,6 +113,7 @@ class TopicSchema(Schema):
         between groups and tags. For example, a popular tag in a group could be
         converted into a sub-group easily.
         """
+        # pylint: disable=unused-argument
         group_schema = GroupSchema(partial=True)
         for tag in value:
             try:
@@ -115,7 +122,9 @@ class TopicSchema(Schema):
                 raise ValidationError("Tag %s is invalid" % tag) from exc
 
     @pre_load
-    def prepare_markdown(self, data: dict, many: bool, partial: Any) -> dict:
+    def prepare_markdown(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> dict:
         """Prepare the markdown value before it's validated."""
         # pylint: disable=unused-argument
         if "markdown" not in data:
@@ -130,7 +139,9 @@ class TopicSchema(Schema):
         return new_data
 
     @pre_load
-    def prepare_link(self, data: dict, many: bool, partial: Any) -> dict:
+    def prepare_link(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> dict:
         """Prepare the link value before it's validated."""
         # pylint: disable=unused-argument
         if "link" not in data:
@@ -157,7 +168,9 @@ class TopicSchema(Schema):
         return new_data
 
     @validates_schema
-    def link_or_markdown(self, data: dict, many: bool, partial: Any) -> None:
+    def link_or_markdown(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> None:
         """Fail validation unless at least one of link or markdown were set."""
         # pylint: disable=unused-argument
         if "link" not in data and "markdown" not in data:
diff --git a/tildes/tildes/schemas/user.py b/tildes/tildes/schemas/user.py
index 44bf55f..f73b7a8 100644
--- a/tildes/tildes/schemas/user.py
+++ b/tildes/tildes/schemas/user.py
@@ -6,12 +6,14 @@
 import re
 from typing import Any
 
-from marshmallow import post_dump, pre_load, Schema, validates, validates_schema
+from marshmallow import post_dump, pre_load, validates, validates_schema
 from marshmallow.exceptions import ValidationError
 from marshmallow.fields import DateTime, Email, String
+from marshmallow.types import UnknownOption
 from marshmallow.validate import Length, Regexp
 
 from tildes.lib.password import is_breached_password
+from tildes.schemas.base import BaseTildesSchema
 from tildes.schemas.fields import Markdown
 
 
@@ -41,7 +43,7 @@ EMAIL_ADDRESS_NOTE_MAX_LENGTH = 100
 BIO_MAX_LENGTH = 2000
 
 
-class UserSchema(Schema):
+class UserSchema(BaseTildesSchema):
     """Marshmallow schema for users."""
 
     username = String(
@@ -63,7 +65,7 @@ class UserSchema(Schema):
     def anonymize_username(self, data: dict, many: bool) -> dict:
         """Hide the username if the dumping context specifies to do so."""
         # pylint: disable=unused-argument
-        if not self.context.get("hide_username"):
+        if not self.get_context_value("hide_username"):
             return data
 
         if "username" not in data:
@@ -77,7 +79,7 @@ class UserSchema(Schema):
 
     @validates_schema
     def username_pass_not_substrings(
-        self, data: dict, many: bool, partial: Any
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
     ) -> None:
         """Ensure the username isn't in the password and vice versa."""
         # pylint: disable=unused-argument
@@ -96,12 +98,13 @@ class UserSchema(Schema):
             raise ValidationError("Username cannot contain password")
 
     @validates("password")
-    def password_not_breached(self, value: str) -> None:
+    def password_not_breached(self, value: str, data_key: str) -> None:
         """Validate that the password is not in the breached-passwords list.
 
         Requires check_breached_passwords be True in the schema's context.
         """
-        if not self.context.get("check_breached_passwords"):
+        # pylint: disable=unused-argument
+        if not self.get_context_value("check_breached_passwords"):
             return
 
         if is_breached_password(value):
@@ -111,13 +114,15 @@ class UserSchema(Schema):
             )
 
     @pre_load
-    def username_trim_whitespace(self, data: dict, many: bool, partial: Any) -> dict:
+    def username_trim_whitespace(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> dict:
         """Trim leading/trailing whitespace around the username.
 
         Requires username_trim_whitespace be True in the schema's context.
         """
         # pylint: disable=unused-argument
-        if not self.context.get("username_trim_whitespace"):
+        if not self.get_context_value("username_trim_whitespace"):
             return data
 
         if "username" not in data:
@@ -130,7 +135,9 @@ class UserSchema(Schema):
         return new_data
 
     @pre_load
-    def prepare_email_address(self, data: dict, many: bool, partial: Any) -> dict:
+    def prepare_email_address(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> dict:
         """Prepare the email address value before it's validated."""
         # pylint: disable=unused-argument
         if "email_address" not in data:
@@ -148,7 +155,9 @@ class UserSchema(Schema):
         return new_data
 
     @pre_load
-    def prepare_bio_markdown(self, data: dict, many: bool, partial: Any) -> dict:
+    def prepare_bio_markdown(
+        self, data: dict, many: bool, partial: Any, unknown: UnknownOption
+    ) -> dict:
         """Prepare the bio_markdown value before it's validated."""
         # pylint: disable=unused-argument
         if "bio_markdown" not in data:
diff --git a/tildes/tildes/views/api/web/comment.py b/tildes/tildes/views/api/web/comment.py
index f5b1e74..63e2f17 100644
--- a/tildes/tildes/views/api/web/comment.py
+++ b/tildes/tildes/views/api/web/comment.py
@@ -335,7 +335,7 @@ def delete_label_comment(request: Request, name: CommentLabelOption) -> Response
 @ic_view_config(
     route_name="comment_mark_read", request_method="PUT", permission="mark_read"
 )
-@use_kwargs({"mark_all_previous": Boolean(missing=False)}, location="query")
+@use_kwargs({"mark_all_previous": Boolean(load_default=False)}, location="query")
 def put_mark_comments_read(request: Request, mark_all_previous: bool) -> Response:
     """Mark comment(s) read, clearing notifications.
 
diff --git a/tildes/tildes/views/api/web/group.py b/tildes/tildes/views/api/web/group.py
index ccb90ab..b717f5d 100644
--- a/tildes/tildes/views/api/web/group.py
+++ b/tildes/tildes/views/api/web/group.py
@@ -86,7 +86,7 @@ def delete_subscribe_group(request: Request) -> dict:
 @use_kwargs(
     {
         "order": Enum(TopicSortOption),
-        "period": ShortTimePeriod(allow_none=True, missing=None),
+        "period": ShortTimePeriod(allow_none=True, load_default=None),
     },
     location="form",
 )
diff --git a/tildes/tildes/views/api/web/topic.py b/tildes/tildes/views/api/web/topic.py
index 2d28557..40cb98f 100644
--- a/tildes/tildes/views/api/web/topic.py
+++ b/tildes/tildes/views/api/web/topic.py
@@ -158,7 +158,8 @@ def get_topic_tags(request: Request) -> dict:
     permission="tag",
 )
 @use_kwargs(
-    {"tags": String(missing=""), "conflict_check": String(missing="")}, location="form"
+    {"tags": String(load_default=""), "conflict_check": String(load_default="")},
+    location="form",
 )
 def put_tag_topic(request: Request, tags: str, conflict_check: str) -> dict:
     """Apply tags to a topic with Intercooler."""
diff --git a/tildes/tildes/views/api/web/user.py b/tildes/tildes/views/api/web/user.py
index a9b70f3..c5aa2ee 100644
--- a/tildes/tildes/views/api/web/user.py
+++ b/tildes/tildes/views/api/web/user.py
@@ -23,6 +23,7 @@ from tildes.lib.datetime import SimpleHoursPeriod
 from tildes.lib.string import separate_string
 from tildes.models.log import Log
 from tildes.models.user import User, UserInviteCode
+from tildes.schemas.context import TildesSchemaContext, TildesSchemaContextDict
 from tildes.schemas.fields import Enum, ShortTimePeriod
 from tildes.schemas.topic import TopicSchema
 from tildes.schemas.user import UserSchema
@@ -54,12 +55,13 @@ def patch_change_password(
     user = request.context
 
     # enable checking the new password against the breached-passwords list
-    user.schema.context["check_breached_passwords"] = True
+    context: TildesSchemaContextDict = {"check_breached_passwords": True}
 
     if new_password != new_password_confirm:
         raise HTTPUnprocessableEntity("New password and confirmation do not match.")
 
-    user.change_password(old_password, new_password)
+    with TildesSchemaContext(context):
+        user.change_password(old_password, new_password)
 
     return Response("Your password has been updated")
 
@@ -357,7 +359,7 @@ def get_invite_code(request: Request) -> dict:
 @use_kwargs(
     {
         "order": Enum(TopicSortOption),
-        "period": ShortTimePeriod(allow_none=True, missing=None),
+        "period": ShortTimePeriod(allow_none=True, load_default=None),
     },
     location="form",
 )
diff --git a/tildes/tildes/views/bookmarks.py b/tildes/tildes/views/bookmarks.py
index 4c68b01..3b046d6 100644
--- a/tildes/tildes/views/bookmarks.py
+++ b/tildes/tildes/views/bookmarks.py
@@ -15,7 +15,7 @@ from tildes.views.decorators import use_kwargs
 
 @view_config(route_name="bookmarks", renderer="bookmarks.jinja2")
 @use_kwargs(PaginatedListingSchema())
-@use_kwargs({"post_type": PostType(data_key="type", missing="topic")})
+@use_kwargs({"post_type": PostType(data_key="type", load_default="topic")})
 def get_bookmarks(
     request: Request,
     after: Optional[str],
diff --git a/tildes/tildes/views/decorators.py b/tildes/tildes/views/decorators.py
index 677d3b8..b3637fa 100644
--- a/tildes/tildes/views/decorators.py
+++ b/tildes/tildes/views/decorators.py
@@ -4,7 +4,7 @@
 """Contains decorators for view functions."""
 
 from collections.abc import Callable
-from typing import Any, Union
+from typing import Any
 
 from marshmallow import EXCLUDE
 from marshmallow.fields import Field
@@ -16,7 +16,7 @@ from webargs import pyramidparser
 
 
 def use_kwargs(
-    argmap: Union[Schema, dict[str, Field]], location: str = "query", **kwargs: Any
+    argmap: Schema | dict[str, Field], location: str = "query", **kwargs: Any
 ) -> Callable:
     """Wrap the webargs @use_kwargs decorator with preferred default modifications.
 
@@ -36,7 +36,7 @@ def use_kwargs(
 
     argmap.unknown = EXCLUDE
 
-    return pyramidparser.use_kwargs(argmap, location=location, **kwargs)
+    return pyramidparser.use_kwargs(argmap, location=location, unknown=None, **kwargs)
 
 
 def ic_view_config(**kwargs: Any) -> Callable:
diff --git a/tildes/tildes/views/login.py b/tildes/tildes/views/login.py
index b6f519d..ef68091 100644
--- a/tildes/tildes/views/login.py
+++ b/tildes/tildes/views/login.py
@@ -26,7 +26,7 @@ from tildes.views.decorators import not_logged_in, rate_limit_view, use_kwargs
 @view_config(
     route_name="login", renderer="login.jinja2", permission=NO_PERMISSION_REQUIRED
 )
-@use_kwargs({"from_url": String(missing="")})
+@use_kwargs({"from_url": String(load_default="")})
 @not_logged_in
 def get_login(request: Request, from_url: str) -> dict:
     """Display the login form."""
@@ -65,7 +65,7 @@ def finish_login(request: Request, user: User, redirect_url: str) -> HTTPFound:
     ),
     location="form",
 )
-@use_kwargs({"from_url": String(missing="")}, location="form")
+@use_kwargs({"from_url": String(load_default="")}, location="form")
 @not_logged_in
 @rate_limit_view("login")
 def post_login(
@@ -148,7 +148,8 @@ def post_login(
 @not_logged_in
 @rate_limit_view("login_two_factor")
 @use_kwargs(
-    {"code": String(missing=""), "from_url": String(missing="")}, location="form"
+    {"code": String(load_default=""), "from_url": String(load_default="")},
+    location="form",
 )
 def post_login_two_factor(request: Request, code: str, from_url: str) -> NoReturn:
     """Process a log in request with 2FA."""
diff --git a/tildes/tildes/views/message.py b/tildes/tildes/views/message.py
index 05f1452..95ecafe 100644
--- a/tildes/tildes/views/message.py
+++ b/tildes/tildes/views/message.py
@@ -18,7 +18,7 @@ from tildes.views.decorators import use_kwargs
 @view_config(
     route_name="new_message", renderer="new_message.jinja2", permission="message"
 )
-@use_kwargs({"subject": String(missing=""), "message": String(missing="")})
+@use_kwargs({"subject": String(load_default=""), "message": String(load_default="")})
 def get_new_message_form(request: Request, subject: str, message: str) -> dict:
     """Form for entering a new private message to send."""
     return {
diff --git a/tildes/tildes/views/register.py b/tildes/tildes/views/register.py
index bab4a45..4a44d88 100644
--- a/tildes/tildes/views/register.py
+++ b/tildes/tildes/views/register.py
@@ -22,7 +22,7 @@ from tildes.views.decorators import not_logged_in, rate_limit_view, use_kwargs
 @view_config(
     route_name="register", renderer="register.jinja2", permission=NO_PERMISSION_REQUIRED
 )
-@use_kwargs({"code": String(missing="")})
+@use_kwargs({"code": String(load_default="")})
 @not_logged_in
 def get_register(request: Request, code: str) -> dict:
     """Display the registration form."""
diff --git a/tildes/tildes/views/settings.py b/tildes/tildes/views/settings.py
index 0af7577..280e446 100644
--- a/tildes/tildes/views/settings.py
+++ b/tildes/tildes/views/settings.py
@@ -22,6 +22,7 @@ from tildes.models.comment import Comment, CommentLabel, CommentTree
 from tildes.models.group import Group
 from tildes.models.topic import Topic
 from tildes.models.user import User
+from tildes.schemas.context import TildesSchemaContextDict, TildesSchemaContext
 from tildes.schemas.user import (
     BIO_MAX_LENGTH,
     EMAIL_ADDRESS_NOTE_MAX_LENGTH,
@@ -151,12 +152,13 @@ def post_settings_password_change(
 ) -> Response:
     """Change the logged-in user's password."""
     # enable checking the new password against the breached-passwords list
-    request.user.schema.context["check_breached_passwords"] = True
+    context: TildesSchemaContextDict = {"check_breached_passwords": True}
 
     if new_password != new_password_confirm:
         raise HTTPUnprocessableEntity("New password and confirmation do not match.")
 
-    request.user.change_password(old_password, new_password)
+    with TildesSchemaContext(context):
+        request.user.change_password(old_password, new_password)
 
     return Response("Your password has been updated")
 
diff --git a/tildes/tildes/views/topic.py b/tildes/tildes/views/topic.py
index 376cd8e..336a15d 100644
--- a/tildes/tildes/views/topic.py
+++ b/tildes/tildes/views/topic.py
@@ -48,7 +48,7 @@ DefaultSettings = namedtuple("DefaultSettings", ["order", "period"])
 @view_config(route_name="group_topics", request_method="POST", permission="topic.post")
 @use_kwargs(TopicSchema(only=("title", "markdown", "link")), location="form")
 @use_kwargs(
-    {"tags": String(missing=""), "confirm_repost": Boolean(missing=False)},
+    {"tags": String(load_default=""), "confirm_repost": Boolean(load_default=False)},
     location="form",
 )
 def post_group_topics(
@@ -345,7 +345,7 @@ def get_group_topics(  # noqa
 @view_config(route_name="search", renderer="search.jinja2")
 @view_config(route_name="group_search", renderer="search.jinja2")
 @use_kwargs(TopicListingSchema(only=("after", "before", "order", "per_page", "period")))
-@use_kwargs({"search": String(data_key="q", missing="")})
+@use_kwargs({"search": String(data_key="q", load_default="")})
 def get_search(
     request: Request,
     order: Optional[TopicSortOption],
@@ -414,7 +414,7 @@ def get_search(
 @view_config(
     route_name="new_topic", renderer="new_topic.jinja2", permission="topic.post"
 )
-@use_kwargs({"title": String(missing=""), "link": String(missing="")})
+@use_kwargs({"title": String(load_default=""), "link": String(load_default="")})
 def get_new_topic_form(request: Request, title: str, link: str) -> dict:
     """Form for entering a new topic to post."""
     group = request.context
@@ -424,7 +424,7 @@ def get_new_topic_form(request: Request, title: str, link: str) -> dict:
 
 @view_config(route_name="topic", renderer="topic.jinja2")
 @view_config(route_name="topic_no_title", renderer="topic.jinja2")
-@use_kwargs({"comment_order": Enum(CommentTreeSortOption, missing=None)})
+@use_kwargs({"comment_order": Enum(CommentTreeSortOption, load_default=None)})
 def get_topic(request: Request, comment_order: CommentTreeSortOption) -> dict:
     """View a single topic."""
     topic = request.context
diff --git a/tildes/tildes/views/user.py b/tildes/tildes/views/user.py
index 71d4695..d9b38e7 100644
--- a/tildes/tildes/views/user.py
+++ b/tildes/tildes/views/user.py
@@ -25,8 +25,8 @@ from tildes.views.decorators import use_kwargs
 @use_kwargs(MixedListingSchema())
 @use_kwargs(
     {
-        "post_type": PostType(data_key="type", missing=None),
-        "order_name": String(data_key="order", missing="new"),
+        "post_type": PostType(data_key="type", load_default=None),
+        "order_name": String(data_key="order", load_default="new"),
     }
 )
 def get_user(
@@ -94,8 +94,8 @@ def get_user(
 @use_kwargs(
     {
         "post_type": PostType(data_key="type", required=True),
-        "order_name": String(data_key="order", missing="new"),
-        "search": String(data_key="q", missing=""),
+        "order_name": String(data_key="order", load_default="new"),
+        "search": String(data_key="q", load_default=""),
     }
 )
 def get_user_search(
diff --git a/tildes/tildes/views/votes.py b/tildes/tildes/views/votes.py
index ba5f798..ffdb619 100644
--- a/tildes/tildes/views/votes.py
+++ b/tildes/tildes/views/votes.py
@@ -15,7 +15,7 @@ from tildes.views.decorators import use_kwargs
 
 @view_config(route_name="votes", renderer="votes.jinja2")
 @use_kwargs(PaginatedListingSchema())
-@use_kwargs({"post_type": PostType(data_key="type", missing="topic")})
+@use_kwargs({"post_type": PostType(data_key="type", load_default="topic")})
 def get_voted_posts(
     request: Request,
     after: Optional[str],