diff --git a/.gitignore b/.gitignore
index 413c2da..0e32120 100644
--- a/.gitignore
+++ b/.gitignore
@@ -167,6 +167,8 @@ cython_debug/
 .ruff_cache
 .idea
 .openapi/
+openapi/openapi-dev.json
+.github/copilot-instructions.md
 # Makefile
 make/local.mk
 
diff --git a/mpt_api_client/models/model.py b/mpt_api_client/models/model.py
index d3736b5..0da3323 100644
--- a/mpt_api_client/models/model.py
+++ b/mpt_api_client/models/model.py
@@ -1,6 +1,7 @@
 import re
 from collections import UserList
 from collections.abc import Iterable
+from types import MappingProxyType
 from typing import Any, Self, get_args, get_origin, override
 
 from mpt_api_client.http.types import Response
@@ -12,9 +13,47 @@
 _SNAKE_CASE_BOUNDARY = re.compile(r"([a-z0-9])([A-Z])")
 _SNAKE_CASE_ACRONYM = re.compile(r"(?<=[A-Z])(?=[A-Z][a-z0-9])")
 
+# Explicit bidirectional mappings for API field names that contain two or more consecutive
+# uppercase letters (e.g. PPx1, unitLP). The generic regex cannot round-trip these correctly,
+# so we maintain an explicit lookup table that is checked before the regex is applied.
+_FIELD_NAME_MAPPINGS: MappingProxyType[str, str] = MappingProxyType({
+    # PP* price columns
+    "PPx1": "ppx1",
+    "PPxM": "ppxm",
+    "PPxY": "ppxy",
+    # SP* price columns
+    "SPx1": "spx1",
+    "SPxM": "spxm",
+    "SPxY": "spxy",
+    # LP* price columns
+    "LPx1": "lpx1",
+    "LPxM": "lpxm",
+    "LPxY": "lpxy",
+    # unit + 2-letter acronym suffix
+    "unitLP": "unit_lp",
+    "unitPP": "unit_pp",
+    "unitSP": "unit_sp",
+    # total + 2-letter acronym suffix
+    "totalGT": "total_gt",
+    "totalPP": "total_pp",
+    "totalSP": "total_sp",
+    "totalST": "total_st",
+})
+
+_FIELD_NAME_MAPPINGS_REVERSE: MappingProxyType[str, str] = MappingProxyType({
+    snake: camel for camel, snake in _FIELD_NAME_MAPPINGS.items()
+})
+
 
 def to_snake_case(key: str) -> str:
-    """Converts a camelCase string to snake_case."""
+    """Converts a camelCase string to snake_case.
+
+    Explicit mappings in ``_FIELD_NAME_MAPPINGS`` take priority over the generic
+    regex for fields that contain two or more consecutive uppercase letters.
+    """
+    mapped = _FIELD_NAME_MAPPINGS.get(key)
+    if mapped is not None:
+        return mapped
     if "_" in key and key.islower():
         return key
     # Common pattern for PascalCase/camelCase conversion
@@ -24,7 +63,14 @@ def to_snake_case(key: str) -> str:
 
 
 def to_camel_case(key: str) -> str:
-    """Converts a snake_case string to camelCase."""
+    """Converts a snake_case string to camelCase.
+
+    Explicit mappings in ``_FIELD_NAME_MAPPINGS_REVERSE`` take priority over the
+    generic logic for fields that contain two or more consecutive uppercase letters.
+    """
+    mapped = _FIELD_NAME_MAPPINGS_REVERSE.get(key)
+    if mapped is not None:
+        return mapped
     parts = key.split("_")
     return parts[0] + "".join(x.title() for x in parts[1:])  # noqa: WPS111 WPS221
 
diff --git a/mpt_api_client/resources/catalog/authorizations.py b/mpt_api_client/resources/catalog/authorizations.py
index e49513b..a9756bb 100644
--- a/mpt_api_client/resources/catalog/authorizations.py
+++ b/mpt_api_client/resources/catalog/authorizations.py
@@ -6,10 +6,37 @@
     ManagedResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 
 
 class Authorization(Model):
-    """Authorization resource."""
+    """Authorization resource.
+
+    Attributes:
+        name: Authorization name.
+        external_ids: External identifiers for the authorization.
+        currency: Currency code associated with the authorization.
+        notes: Additional notes.
+        product: Reference to the product.
+        vendor: Reference to the vendor.
+        owner: Reference to the owner account.
+        statistics: Authorization statistics.
+        journal: Journal reference.
+        eligibility: Eligibility information.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    external_ids: BaseModel | None
+    currency: str | None
+    notes: str | None
+    product: BaseModel | None
+    vendor: BaseModel | None
+    owner: BaseModel | None
+    statistics: BaseModel | None
+    journal: BaseModel | None
+    eligibility: BaseModel | None
+    audit: BaseModel | None
 
 
 class AuthorizationsServiceConfig:
diff --git a/mpt_api_client/resources/catalog/items.py b/mpt_api_client/resources/catalog/items.py
index 0fb88e4..c171a24 100644
--- a/mpt_api_client/resources/catalog/items.py
+++ b/mpt_api_client/resources/catalog/items.py
@@ -6,6 +6,7 @@
     ManagedResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.mixins import (
     AsyncPublishableMixin,
     PublishableMixin,
@@ -13,7 +14,33 @@
 
 
 class Item(Model):  # noqa: WPS110
-    """Item resource."""
+    """Item resource.
+
+    Attributes:
+        name: Item name.
+        description: Item description.
+        external_ids: External identifiers for the item.
+        group: Reference to the item group.
+        unit: Reference to the unit of measure.
+        terms: Reference to the terms and conditions.
+        quantity_not_applicable: Whether quantity is not applicable to this item.
+        status: Item status.
+        product: Reference to the product.
+        parameters: List of parameters associated with this item.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    description: str | None
+    external_ids: BaseModel | None
+    group: BaseModel | None
+    unit: BaseModel | None
+    terms: BaseModel | None
+    quantity_not_applicable: bool | None
+    status: str | None
+    product: BaseModel | None
+    parameters: list[BaseModel] | None
+    audit: BaseModel | None
 
 
 class ItemsServiceConfig:
diff --git a/mpt_api_client/resources/catalog/listings.py b/mpt_api_client/resources/catalog/listings.py
index 1780a47..ea87a2a 100644
--- a/mpt_api_client/resources/catalog/listings.py
+++ b/mpt_api_client/resources/catalog/listings.py
@@ -6,10 +6,35 @@
     ManagedResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 
 
 class Listing(Model):
-    """Listing resource."""
+    """Listing resource.
+
+    Attributes:
+        authorization: Reference to the authorization.
+        product: Reference to the product.
+        vendor: Reference to the vendor.
+        seller: Reference to the seller.
+        price_list: Reference to the associated price list.
+        primary: Whether this is the primary listing.
+        notes: Additional notes.
+        statistics: Listing statistics.
+        eligibility: Eligibility information.
+        audit: Audit information (created, updated events).
+    """
+
+    authorization: BaseModel | None
+    product: BaseModel | None
+    vendor: BaseModel | None
+    seller: BaseModel | None
+    price_list: BaseModel | None
+    primary: bool | None
+    notes: str | None
+    statistics: BaseModel | None
+    eligibility: BaseModel | None
+    audit: BaseModel | None
 
 
 class ListingsServiceConfig:
diff --git a/mpt_api_client/resources/catalog/price_list_items.py b/mpt_api_client/resources/catalog/price_list_items.py
index ece1656..11779ce 100644
--- a/mpt_api_client/resources/catalog/price_list_items.py
+++ b/mpt_api_client/resources/catalog/price_list_items.py
@@ -8,10 +8,55 @@
     UpdateMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 
 
 class PriceListItem(Model):
-    """Price List Item resource."""
+    """Price List Item resource.
+
+    Attributes:
+        status: Price list item status.
+        description: Price list item description.
+        reason_for_change: Reason for the price change.
+        unit_lp: Unit list price.
+        unit_pp: Unit purchase price.
+        markup: Markup percentage.
+        margin: Margin percentage.
+        unit_sp: Unit sell price.
+        ppx1: Purchase price for 1-year term.
+        ppxm: Purchase price for monthly term.
+        ppxy: Purchase price for yearly term.
+        spx1: Sell price for 1-year term.
+        spxm: Sell price for monthly term.
+        spxy: Sell price for yearly term.
+        lpx1: List price for 1-year term.
+        lpxm: List price for monthly term.
+        lpxy: List price for yearly term.
+        price_list: Reference to the parent price list.
+        item: Reference to the associated item.
+        audit: Audit information (created, updated events).
+    """
+
+    status: str | None
+    description: str | None
+    reason_for_change: str | None
+    unit_lp: float | None
+    unit_pp: float | None
+    markup: float | None
+    margin: float | None
+    unit_sp: float | None
+    ppx1: float | None
+    ppxm: float | None
+    ppxy: float | None
+    spx1: float | None
+    spxm: float | None
+    spxy: float | None
+    lpx1: float | None
+    lpxm: float | None
+    lpxy: float | None
+    price_list: BaseModel | None
+    item: BaseModel | None
+    audit: BaseModel | None
 
 
 class PriceListItemsServiceConfig:
diff --git a/mpt_api_client/resources/catalog/price_lists.py b/mpt_api_client/resources/catalog/price_lists.py
index 9c5eaad..6a216cd 100644
--- a/mpt_api_client/resources/catalog/price_lists.py
+++ b/mpt_api_client/resources/catalog/price_lists.py
@@ -6,6 +6,7 @@
     ManagedResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.price_list_items import (
     AsyncPriceListItemsService,
     PriceListItemsService,
@@ -13,7 +14,31 @@
 
 
 class PriceList(Model):
-    """Price List resource."""
+    """Price List resource.
+
+    Attributes:
+        currency: Currency code for this price list.
+        precision: Decimal precision for prices.
+        default_markup: Default markup percentage.
+        default_margin: Default margin percentage.
+        notes: Additional notes.
+        external_ids: External identifiers for the price list.
+        statistics: Price list statistics.
+        product: Reference to the associated product.
+        vendor: Reference to the vendor.
+        audit: Audit information (created, updated events).
+    """
+
+    currency: str | None
+    precision: int | None
+    default_markup: float | None
+    default_margin: float | None
+    notes: str | None
+    external_ids: BaseModel | None
+    statistics: BaseModel | None
+    product: BaseModel | None
+    vendor: BaseModel | None
+    audit: BaseModel | None
 
 
 class PriceListsServiceConfig:
diff --git a/mpt_api_client/resources/catalog/pricing_policies.py b/mpt_api_client/resources/catalog/pricing_policies.py
index 23b6667..80c16bf 100644
--- a/mpt_api_client/resources/catalog/pricing_policies.py
+++ b/mpt_api_client/resources/catalog/pricing_policies.py
@@ -9,6 +9,7 @@
     ManagedResourceMixin,
 )
 from mpt_api_client.models import Model, ResourceData
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.pricing_policy_attachments import (
     AsyncPricingPolicyAttachmentsService,
     PricingPolicyAttachmentsService,
@@ -16,7 +17,33 @@
 
 
 class PricingPolicy(Model):
-    """Pricing policy resource."""
+    """Pricing policy resource.
+
+    Attributes:
+        name: Pricing policy name.
+        external_ids: External identifiers for the pricing policy.
+        client: Reference to the client account.
+        eligibility: Eligibility information.
+        markup: Markup percentage.
+        margin: Margin percentage.
+        notes: Additional notes.
+        products: List of associated products.
+        status: Pricing policy status.
+        statistics: Pricing policy statistics.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    external_ids: BaseModel | None
+    client: BaseModel | None
+    eligibility: BaseModel | None
+    markup: float | None
+    margin: float | None
+    notes: str | None
+    products: list[BaseModel] | None
+    status: str | None
+    statistics: BaseModel | None
+    audit: BaseModel | None
 
 
 class PricingPoliciesServiceConfig:
diff --git a/mpt_api_client/resources/catalog/pricing_policy_attachments.py b/mpt_api_client/resources/catalog/pricing_policy_attachments.py
index 6362ee1..c414b3c 100644
--- a/mpt_api_client/resources/catalog/pricing_policy_attachments.py
+++ b/mpt_api_client/resources/catalog/pricing_policy_attachments.py
@@ -10,10 +10,31 @@
     ModifiableResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 
 
 class PricingPolicyAttachment(Model):
-    """Pricing Policy Attachment resource."""
+    """Pricing Policy Attachment resource.
+
+    Attributes:
+        name: Attachment name.
+        type: Attachment type.
+        size: File size in bytes.
+        description: Attachment description.
+        file_name: Original file name.
+        content_type: MIME content type of the attachment.
+        status: Attachment status.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    type: str | None
+    size: int | None
+    description: str | None
+    file_name: str | None
+    content_type: str | None
+    status: str | None
+    audit: BaseModel | None
 
 
 class PricingPolicyAttachmentsServiceConfig:
diff --git a/mpt_api_client/resources/catalog/product_term_variants.py b/mpt_api_client/resources/catalog/product_term_variants.py
index bee9c30..5c5328c 100644
--- a/mpt_api_client/resources/catalog/product_term_variants.py
+++ b/mpt_api_client/resources/catalog/product_term_variants.py
@@ -10,6 +10,7 @@
     ModifiableResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.mixins import (
     AsyncPublishableMixin,
     PublishableMixin,
@@ -17,7 +18,35 @@
 
 
 class TermVariant(Model):
-    """Term variant resource."""
+    """Term variant resource.
+
+    Attributes:
+        type: Variant type.
+        asset_url: URL to the term variant asset.
+        language_code: Language code for this variant.
+        name: Variant name.
+        description: Variant description.
+        status: Variant status.
+        filename: Original file name.
+        size: File size in bytes.
+        content_type: MIME content type of the file.
+        terms_and_conditions: Reference to the parent terms and conditions.
+        file_id: Identifier of the uploaded file.
+        audit: Audit information (created, updated events).
+    """
+
+    type: str | None
+    asset_url: str | None
+    language_code: str | None
+    name: str | None
+    description: str | None
+    status: str | None
+    filename: str | None
+    size: int | None
+    content_type: str | None
+    terms_and_conditions: BaseModel | None
+    file_id: str | None
+    audit: BaseModel | None
 
 
 class TermVariantServiceConfig:
diff --git a/mpt_api_client/resources/catalog/product_terms.py b/mpt_api_client/resources/catalog/product_terms.py
index 9afd7b5..611cd5a 100644
--- a/mpt_api_client/resources/catalog/product_terms.py
+++ b/mpt_api_client/resources/catalog/product_terms.py
@@ -6,6 +6,7 @@
     ManagedResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.mixins import AsyncPublishableMixin, PublishableMixin
 from mpt_api_client.resources.catalog.product_term_variants import (
     AsyncTermVariantService,
@@ -14,7 +15,23 @@
 
 
 class Term(Model):
-    """Term resource."""
+    """Term resource.
+
+    Attributes:
+        name: Term name.
+        description: Term description.
+        display_order: Display order of the term.
+        status: Term status.
+        product: Reference to the product.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    description: str | None
+    display_order: int | None
+    status: str | None
+    product: BaseModel | None
+    audit: BaseModel | None
 
 
 class TermServiceConfig:
diff --git a/mpt_api_client/resources/catalog/products.py b/mpt_api_client/resources/catalog/products.py
index cfe04dd..b6c6f57 100644
--- a/mpt_api_client/resources/catalog/products.py
+++ b/mpt_api_client/resources/catalog/products.py
@@ -12,6 +12,7 @@
     UpdateFileMixin,
 )
 from mpt_api_client.models import Model, ResourceData
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.mixins import (
     AsyncPublishableMixin,
     PublishableMixin,
@@ -51,7 +52,33 @@
 
 
 class Product(Model):
-    """Product resource."""
+    """Product resource.
+
+    Attributes:
+        name: Product name.
+        short_description: Short description of the product.
+        long_description: Long description of the product.
+        external_ids: External identifiers for the product.
+        website: Product website URL.
+        icon: URL or identifier for the product icon.
+        status: Product status.
+        vendor: Reference to the vendor account.
+        settings: Product settings.
+        statistics: Product statistics.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    short_description: str | None
+    long_description: str | None
+    external_ids: BaseModel | None
+    website: str | None
+    icon: str | None
+    status: str | None
+    vendor: BaseModel | None
+    settings: BaseModel | None
+    statistics: BaseModel | None
+    audit: BaseModel | None
 
 
 class ProductsServiceConfig:
diff --git a/mpt_api_client/resources/catalog/products_documents.py b/mpt_api_client/resources/catalog/products_documents.py
index c0f59ba..b3ad483 100644
--- a/mpt_api_client/resources/catalog/products_documents.py
+++ b/mpt_api_client/resources/catalog/products_documents.py
@@ -6,6 +6,7 @@
     ModifiableResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.mixins import (
     AsyncDocumentMixin,
     DocumentMixin,
@@ -13,7 +14,33 @@
 
 
 class Document(Model):
-    """Document resource."""
+    """Document resource.
+
+    Attributes:
+        name: Document name.
+        type: Document type.
+        description: Document description.
+        status: Document status.
+        filename: Original file name.
+        size: File size in bytes.
+        content_type: MIME content type of the document.
+        url: URL to access the document.
+        language: Language code of the document.
+        product: Reference to the product.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    type: str | None
+    description: str | None
+    status: str | None
+    filename: str | None
+    size: int | None
+    content_type: str | None
+    url: str | None
+    language: str | None
+    product: BaseModel | None
+    audit: BaseModel | None
 
 
 class DocumentServiceConfig:
diff --git a/mpt_api_client/resources/catalog/products_item_groups.py b/mpt_api_client/resources/catalog/products_item_groups.py
index 29cfdaa..b4f76ad 100644
--- a/mpt_api_client/resources/catalog/products_item_groups.py
+++ b/mpt_api_client/resources/catalog/products_item_groups.py
@@ -6,10 +6,35 @@
     ManagedResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 
 
 class ItemGroup(Model):
-    """Item Group resource."""
+    """Item Group resource.
+
+    Attributes:
+        name: Item group name.
+        label: Display label for the item group.
+        description: Item group description.
+        display_order: Display order of the group.
+        default: Whether this is the default item group.
+        multiple: Whether multiple items can be selected from this group.
+        required: Whether a selection from this group is required.
+        item_count: Number of items in this group.
+        product: Reference to the product.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    label: str | None
+    description: str | None
+    display_order: int | None
+    default: bool | None
+    multiple: bool | None
+    required: bool | None
+    item_count: int | None
+    product: BaseModel | None
+    audit: BaseModel | None
 
 
 class ItemGroupsServiceConfig:
diff --git a/mpt_api_client/resources/catalog/products_media.py b/mpt_api_client/resources/catalog/products_media.py
index 767add5..c4d5018 100644
--- a/mpt_api_client/resources/catalog/products_media.py
+++ b/mpt_api_client/resources/catalog/products_media.py
@@ -6,6 +6,7 @@
     ModifiableResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.mixins import (
     AsyncMediaMixin,
     MediaMixin,
@@ -13,7 +14,33 @@
 
 
 class Media(Model):
-    """Media resource."""
+    """Media resource.
+
+    Attributes:
+        name: Media name.
+        type: Media type.
+        description: Media description.
+        status: Media status.
+        filename: Original file name.
+        size: File size in bytes.
+        content_type: MIME content type of the media file.
+        display_order: Display order of the media item.
+        url: URL to access the media file.
+        product: Reference to the product.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    type: str | None
+    description: str | None
+    status: str | None
+    filename: str | None
+    size: int | None
+    content_type: str | None
+    display_order: int | None
+    url: str | None
+    product: BaseModel | None
+    audit: BaseModel | None
 
 
 class MediaServiceConfig:
diff --git a/mpt_api_client/resources/catalog/products_templates.py b/mpt_api_client/resources/catalog/products_templates.py
index 963bc1b..a052f6b 100644
--- a/mpt_api_client/resources/catalog/products_templates.py
+++ b/mpt_api_client/resources/catalog/products_templates.py
@@ -6,10 +6,27 @@
     ManagedResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 
 
 class Template(Model):
-    """Template resource."""
+    """Template resource.
+
+    Attributes:
+        name: Template name.
+        content: Template content.
+        type: Template type.
+        default: Whether this is the default template.
+        product: Reference to the product.
+        audit: Audit information (created, updated events).
+    """
+
+    name: str | None
+    content: str | None
+    type: str | None
+    default: bool | None
+    product: BaseModel | None
+    audit: BaseModel | None
 
 
 class TemplatesServiceConfig:
diff --git a/mpt_api_client/resources/catalog/units_of_measure.py b/mpt_api_client/resources/catalog/units_of_measure.py
index 151e5de..9e4066d 100644
--- a/mpt_api_client/resources/catalog/units_of_measure.py
+++ b/mpt_api_client/resources/catalog/units_of_measure.py
@@ -6,10 +6,23 @@
     ManagedResourceMixin,
 )
 from mpt_api_client.models import Model
+from mpt_api_client.models.model import BaseModel
 
 
 class UnitOfMeasure(Model):
-    """Unit of Measure resource."""
+    """Unit of Measure resource.
+
+    Attributes:
+        description: Unit of measure description.
+        name: Unit of measure name.
+        statistics: Unit of measure statistics.
+        audit: Audit information (created, updated events).
+    """
+
+    description: str | None
+    name: str | None
+    statistics: BaseModel | None
+    audit: BaseModel | None
 
 
 class UnitsOfMeasureServiceConfig:
diff --git a/tests/unit/models/test_model.py b/tests/unit/models/test_model.py
index 9082303..8285efb 100644
--- a/tests/unit/models/test_model.py
+++ b/tests/unit/models/test_model.py
@@ -2,7 +2,12 @@
 from httpx import Response
 
 from mpt_api_client.models import Meta, Model
-from mpt_api_client.models.model import BaseModel, ModelList, to_snake_case  # noqa: WPS347
+from mpt_api_client.models.model import (  # noqa: WPS347
+    BaseModel,
+    ModelList,
+    to_camel_case,
+    to_snake_case,
+)
 
 
 class AgreementDummy(Model):  # noqa: WPS431
@@ -326,3 +331,33 @@ def test_process_value_scalar_list_elements():
 
     assert isinstance(container.tags, ModelList)
     assert list(container.tags) == ["a", "b", "c"]
+
+
+@pytest.mark.parametrize(
+    ("camel", "snake"),
+    [
+        ("PPx1", "ppx1"),
+        ("SPxM", "spxm"),
+        ("unitLP", "unit_lp"),
+        ("totalGT", "total_gt"),
+    ],
+)
+def test_to_snake_case_consecutive_uppercase(camel, snake):
+    result = to_snake_case(camel)  # act
+
+    assert result == snake
+
+
+@pytest.mark.parametrize(
+    ("snake", "camel"),
+    [
+        ("ppx1", "PPx1"),
+        ("spxm", "SPxM"),
+        ("unit_lp", "unitLP"),
+        ("total_gt", "totalGT"),
+    ],
+)
+def test_to_camel_case_consecutive_uppercase(snake, camel):
+    result = to_camel_case(snake)  # act
+
+    assert result == camel
diff --git a/tests/unit/resources/catalog/test_authorizations.py b/tests/unit/resources/catalog/test_authorizations.py
index a7ab0e2..351ef90 100644
--- a/tests/unit/resources/catalog/test_authorizations.py
+++ b/tests/unit/resources/catalog/test_authorizations.py
@@ -1,7 +1,9 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.authorizations import (
     AsyncAuthorizationsService,
+    Authorization,
     AuthorizationsService,
 )
 
@@ -16,6 +18,24 @@ def async_authorizations_service(async_http_client):
     return AsyncAuthorizationsService(http_client=async_http_client)
 
 
+@pytest.fixture
+def authorization_data():
+    return {
+        "id": "AUT-001",
+        "name": "My Authorization",
+        "currency": "USD",
+        "notes": "Some notes",
+        "externalIds": {"vendor": "ext-001"},
+        "product": {"id": "PRD-001", "name": "My Product"},
+        "vendor": {"id": "ACC-001", "name": "Vendor"},
+        "owner": {"id": "ACC-002", "name": "Owner"},
+        "statistics": {"items": 5},
+        "journal": {"id": "JRN-001"},
+        "eligibility": {"status": "Eligible"},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 @pytest.mark.parametrize("method", ["get", "create", "update", "delete", "iterate"])
 def test_mixins_present(authorizations_service, method):
     result = hasattr(authorizations_service, method)
@@ -28,3 +48,28 @@ def test_async_mixins_present(async_authorizations_service, method):
     result = hasattr(async_authorizations_service, method)
 
     assert result is True
+
+
+def test_authorization_primitive_fields(authorization_data):
+    result = Authorization(authorization_data)
+
+    assert result.to_dict() == authorization_data
+
+
+def test_authorization_nested_base_models(authorization_data):
+    result = Authorization(authorization_data)
+
+    assert isinstance(result.external_ids, BaseModel)
+    assert isinstance(result.product, BaseModel)
+    assert isinstance(result.vendor, BaseModel)
+    assert isinstance(result.statistics, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_authorization_optional_fields_absent():
+    result = Authorization({"id": "AUT-001"})
+
+    assert result.id == "AUT-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "currency")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_items.py b/tests/unit/resources/catalog/test_items.py
index 52451c7..bf52688 100644
--- a/tests/unit/resources/catalog/test_items.py
+++ b/tests/unit/resources/catalog/test_items.py
@@ -1,6 +1,7 @@
 import pytest
 
-from mpt_api_client.resources.catalog.items import AsyncItemsService, ItemsService
+from mpt_api_client.models.model import BaseModel
+from mpt_api_client.resources.catalog.items import AsyncItemsService, Item, ItemsService
 
 
 @pytest.fixture
@@ -13,6 +14,24 @@ def async_items_service(async_http_client):
     return AsyncItemsService(http_client=async_http_client)
 
 
+@pytest.fixture
+def item_data():
+    return {
+        "id": "ITM-001",
+        "name": "My Item",
+        "description": "Item description",
+        "externalIds": {"vendor": "ext-001"},
+        "group": {"id": "GRP-001", "name": "Group"},
+        "unit": {"id": "UOM-001", "name": "Each"},
+        "terms": {"id": "TRM-001", "name": "Terms"},
+        "quantityNotApplicable": False,
+        "status": "Active",
+        "product": {"id": "PRD-001", "name": "My Product"},
+        "parameters": [{"id": "PRM-001", "name": "Param"}],
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 @pytest.mark.parametrize(
     "method",
     [
@@ -49,3 +68,28 @@ def test_async_mixins_present(async_items_service, method):
     result = hasattr(async_items_service, method)
 
     assert result is True
+
+
+def test_item_primitive_fields(item_data):
+    result = Item(item_data)
+
+    assert result.to_dict() == item_data
+
+
+def test_item_nested_base_models(item_data):
+    result = Item(item_data)
+
+    assert isinstance(result.external_ids, BaseModel)
+    assert isinstance(result.group, BaseModel)
+    assert isinstance(result.unit, BaseModel)
+    assert isinstance(result.product, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_item_optional_fields_absent():
+    result = Item({"id": "ITM-001"})
+
+    assert result.id == "ITM-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "status")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_listings.py b/tests/unit/resources/catalog/test_listings.py
index b048dd9..7d7e04a 100644
--- a/tests/unit/resources/catalog/test_listings.py
+++ b/tests/unit/resources/catalog/test_listings.py
@@ -1,7 +1,9 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.listings import (
     AsyncListingsService,
+    Listing,
     ListingsService,
 )
 
@@ -16,6 +18,23 @@ def async_listings_service(async_http_client):
     return AsyncListingsService(http_client=async_http_client)
 
 
+@pytest.fixture
+def listing_data():
+    return {
+        "id": "LST-001",
+        "authorization": {"id": "AUT-001", "name": "My Auth"},
+        "product": {"id": "PRD-001", "name": "My Product"},
+        "vendor": {"id": "ACC-001", "name": "Vendor"},
+        "seller": {"id": "ACC-002", "name": "Seller"},
+        "priceList": {"id": "PRC-001", "currency": "USD"},
+        "primary": True,
+        "notes": "Some notes",
+        "statistics": {"items": 3},
+        "eligibility": {"status": "Eligible"},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 @pytest.mark.parametrize("method", ["get", "create", "update", "delete", "iterate"])
 def test_mixins_present(listings_service, method):
     result = hasattr(listings_service, method)
@@ -28,3 +47,28 @@ def test_async_mixins_present(async_listings_service, method):
     result = hasattr(async_listings_service, method)
 
     assert result is True
+
+
+def test_listing_primitive_fields(listing_data):
+    result = Listing(listing_data)
+
+    assert result.to_dict() == listing_data
+
+
+def test_listing_nested_base_models(listing_data):
+    result = Listing(listing_data)
+
+    assert isinstance(result.authorization, BaseModel)
+    assert isinstance(result.product, BaseModel)
+    assert isinstance(result.price_list, BaseModel)
+    assert isinstance(result.statistics, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_listing_optional_fields_absent():
+    result = Listing({"id": "LST-001"})
+
+    assert result.id == "LST-001"
+    assert not hasattr(result, "notes")
+    assert not hasattr(result, "primary")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_price_list_items.py b/tests/unit/resources/catalog/test_price_list_items.py
index 4002a94..80032ac 100644
--- a/tests/unit/resources/catalog/test_price_list_items.py
+++ b/tests/unit/resources/catalog/test_price_list_items.py
@@ -1,7 +1,9 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.price_list_items import (
     AsyncPriceListItemsService,
+    PriceListItem,
     PriceListItemsService,
 )
 
@@ -20,6 +22,33 @@ def async_price_list_items_service(async_http_client):
     )
 
 
+@pytest.fixture
+def price_list_item_data():
+    return {
+        "id": "PLI-001",
+        "status": "Active",
+        "description": "Item description",
+        "reasonForChange": "Price update",
+        "unitLP": 100.0,
+        "unitPP": 80.0,
+        "markup": 25.0,
+        "margin": 20.0,
+        "unitSP": 90.0,
+        "PPx1": 80.0,
+        "PPxM": 7.0,
+        "PPxY": 84.0,
+        "SPx1": 90.0,
+        "SPxM": 8.0,
+        "SPxY": 96.0,
+        "LPx1": 100.0,
+        "LPxM": 9.0,
+        "LPxY": 108.0,
+        "priceList": {"id": "PRC-001", "currency": "USD"},
+        "item": {"id": "ITM-001", "name": "My Item"},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 @pytest.fixture
 def test_endpoint(price_list_items_service):
     result = price_list_items_service.path == "/public/v1/catalog/price-lists/ITM-0000-0001/items"
@@ -48,3 +77,36 @@ def test_async_methods_present(async_price_list_items_service, method):
     result = hasattr(async_price_list_items_service, method)
 
     assert result is True
+
+
+def test_price_list_item_primitive_fields(price_list_item_data):
+    result = PriceListItem(price_list_item_data)
+
+    assert result.to_dict() == price_list_item_data
+
+
+def test_price_list_item_price_fields(price_list_item_data):
+    result = PriceListItem(price_list_item_data)
+
+    assert result.unit_lp == pytest.approx(100.0)
+    assert result.unit_pp == pytest.approx(80.0)
+    assert result.unit_sp == pytest.approx(90.0)
+    assert result.spxm == pytest.approx(8.0)
+    assert result.lpx1 == pytest.approx(100.0)
+
+
+def test_price_list_item_nested_models(price_list_item_data):
+    result = PriceListItem(price_list_item_data)
+
+    assert isinstance(result.price_list, BaseModel)
+    assert isinstance(result.item, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_price_list_item_optional_fields_absent():
+    result = PriceListItem({"id": "PLI-001"})
+
+    assert result.id == "PLI-001"
+    assert not hasattr(result, "status")
+    assert not hasattr(result, "unit_lp")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_price_lists.py b/tests/unit/resources/catalog/test_price_lists.py
index ab37716..ad3e943 100644
--- a/tests/unit/resources/catalog/test_price_lists.py
+++ b/tests/unit/resources/catalog/test_price_lists.py
@@ -1,11 +1,13 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.price_list_items import (
     AsyncPriceListItemsService,
     PriceListItemsService,
 )
 from mpt_api_client.resources.catalog.price_lists import (
     AsyncPriceListsService,
+    PriceList,
     PriceListsService,
 )
 
@@ -20,6 +22,23 @@ def async_price_lists_service(http_client):
     return AsyncPriceListsService(http_client=http_client)
 
 
+@pytest.fixture
+def price_list_data():
+    return {
+        "id": "PRC-001",
+        "currency": "USD",
+        "precision": 2,
+        "defaultMarkup": 25.0,
+        "defaultMargin": 20.0,
+        "notes": "Some notes",
+        "externalIds": {"vendor": "ext-001"},
+        "statistics": {"items": 10},
+        "product": {"id": "PRD-001", "name": "My Product"},
+        "vendor": {"id": "ACC-001", "name": "Vendor"},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 @pytest.mark.parametrize("method", ["get", "create", "update", "delete", "iterate"])
 def test_mixins_present(price_lists_service, method):
     result = hasattr(price_lists_service, method)
@@ -58,3 +77,28 @@ def test_async_property_services(async_price_lists_service, service_method, expe
 
     assert isinstance(result, expected_model_class)
     assert result.endpoint_params == {"price_list_id": "ITM-0000-0001"}
+
+
+def test_price_list_primitive_fields(price_list_data):
+    result = PriceList(price_list_data)
+
+    assert result.to_dict() == price_list_data
+
+
+def test_price_list_nested_fields_are_base_models(price_list_data):
+    result = PriceList(price_list_data)
+
+    assert isinstance(result.external_ids, BaseModel)
+    assert isinstance(result.statistics, BaseModel)
+    assert isinstance(result.product, BaseModel)
+    assert isinstance(result.vendor, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_price_list_optional_fields_absent():
+    result = PriceList({"id": "PRC-001"})
+
+    assert result.id == "PRC-001"
+    assert not hasattr(result, "currency")
+    assert not hasattr(result, "precision")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_pricing_policies.py b/tests/unit/resources/catalog/test_pricing_policies.py
index 628391f..9aabafb 100644
--- a/tests/unit/resources/catalog/test_pricing_policies.py
+++ b/tests/unit/resources/catalog/test_pricing_policies.py
@@ -2,9 +2,11 @@
 import pytest
 import respx
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.pricing_policies import (
     AsyncPricingPoliciesService,
     PricingPoliciesService,
+    PricingPolicy,
 )
 from mpt_api_client.resources.catalog.pricing_policy_attachments import (
     AsyncPricingPolicyAttachmentsService,
@@ -22,6 +24,24 @@ def async_pricing_policies_service(async_http_client):
     return AsyncPricingPoliciesService(http_client=async_http_client)
 
 
+@pytest.fixture
+def pricing_policy_data():
+    return {
+        "id": "PRP-001",
+        "name": "My Policy",
+        "notes": "Some notes",
+        "status": "Active",
+        "markup": 25.0,
+        "margin": 20.0,
+        "externalIds": {"vendor": "ext-001"},
+        "client": {"id": "ACC-001", "name": "Client"},
+        "eligibility": {"status": "Eligible"},
+        "products": [{"id": "PRD-001", "name": "My Product"}],
+        "statistics": {"items": 5},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 def test_activate(pricing_policies_service):
     pricing_policy_expected = {
         "id": "PRP-0000-0001",
@@ -160,3 +180,28 @@ def test_async_mixins_present(async_pricing_policies_service, method):
     result = hasattr(async_pricing_policies_service, method)
 
     assert result is True
+
+
+def test_pricing_policy_primitive_fields(pricing_policy_data):
+    result = PricingPolicy(pricing_policy_data)
+
+    assert result.to_dict() == pricing_policy_data
+
+
+def test_pricing_policy_nested_models(pricing_policy_data):
+    result = PricingPolicy(pricing_policy_data)
+
+    assert isinstance(result.external_ids, BaseModel)
+    assert isinstance(result.client, BaseModel)
+    assert isinstance(result.eligibility, BaseModel)
+    assert isinstance(result.statistics, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_pricing_policy_optional_fields_absent():
+    result = PricingPolicy({"id": "PRP-001"})
+
+    assert result.id == "PRP-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "status")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_pricing_policy_attachments.py b/tests/unit/resources/catalog/test_pricing_policy_attachments.py
index 061918a..ec92397 100644
--- a/tests/unit/resources/catalog/test_pricing_policy_attachments.py
+++ b/tests/unit/resources/catalog/test_pricing_policy_attachments.py
@@ -1,7 +1,9 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.pricing_policy_attachments import (
     AsyncPricingPolicyAttachmentsService,
+    PricingPolicyAttachment,
     PricingPolicyAttachmentsService,
 )
 
@@ -22,6 +24,21 @@ def async_pricing_policy_attachments_service(
     )
 
 
+@pytest.fixture
+def pricing_policy_attachment_data():
+    return {
+        "id": "ATT-001",
+        "name": "Terms of Service",
+        "type": "Document",
+        "size": 1024,
+        "description": "Attachment description",
+        "fileName": "terms.pdf",
+        "contentType": "application/pdf",
+        "status": "Active",
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 def test_endpoint(pricing_policy_attachments_service) -> None:
     result = (
         pricing_policy_attachments_service.path
@@ -52,3 +69,24 @@ def test_async_methods_present(async_pricing_policy_attachments_service, method:
     result = hasattr(async_pricing_policy_attachments_service, method)
 
     assert result is True
+
+
+def test_pricing_policy_attach_primitives(pricing_policy_attachment_data):
+    result = PricingPolicyAttachment(pricing_policy_attachment_data)
+
+    assert result.to_dict() == pricing_policy_attachment_data
+
+
+def test_pricing_policy_attachment_nested_models(pricing_policy_attachment_data):
+    result = PricingPolicyAttachment(pricing_policy_attachment_data)
+
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_pricing_policy_attachment_absent():
+    result = PricingPolicyAttachment({"id": "ATT-001"})
+
+    assert result.id == "ATT-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "status")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_product_term_variants.py b/tests/unit/resources/catalog/test_product_term_variants.py
index a028c89..940ff4f 100644
--- a/tests/unit/resources/catalog/test_product_term_variants.py
+++ b/tests/unit/resources/catalog/test_product_term_variants.py
@@ -2,8 +2,10 @@
 
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.product_term_variants import (
     AsyncTermVariantService,
+    TermVariant,
     TermVariantService,
 )
 
@@ -23,6 +25,25 @@ def async_term_variant_service(async_http_client: Any) -> AsyncTermVariantServic
     )
 
 
+@pytest.fixture
+def term_variant_data():
+    return {
+        "id": "TRV-001",
+        "type": "PDF",
+        "assetUrl": "https://example.com/file.pdf",
+        "languageCode": "en-US",
+        "name": "English Terms",
+        "description": "English language terms",
+        "status": "Active",
+        "filename": "terms.pdf",
+        "size": 2048,
+        "contentType": "application/pdf",
+        "termsAndConditions": {"id": "TRM-001", "name": "Terms of Service"},
+        "fileId": "FILE-001",
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 def test_endpoint(term_variant_service: TermVariantService) -> None:
     result = (
         term_variant_service.path == "/public/v1/catalog/products/PRD-001/terms/TRM-001/variants"
@@ -60,3 +81,25 @@ def test_async_methods_present(
     result = hasattr(async_term_variant_service, method)
 
     assert result is True
+
+
+def test_term_variant_primitive_fields(term_variant_data: dict) -> None:
+    result = TermVariant(term_variant_data)
+
+    assert result.to_dict() == term_variant_data
+
+
+def test_term_variant_nested_base_models(term_variant_data: dict) -> None:
+    result = TermVariant(term_variant_data)
+
+    assert isinstance(result.terms_and_conditions, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_term_variant_optional_fields_absent() -> None:
+    result = TermVariant({"id": "TRV-001"})
+
+    assert result.id == "TRV-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "status")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_product_terms.py b/tests/unit/resources/catalog/test_product_terms.py
index f638410..941d817 100644
--- a/tests/unit/resources/catalog/test_product_terms.py
+++ b/tests/unit/resources/catalog/test_product_terms.py
@@ -2,12 +2,14 @@
 
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.product_term_variants import (
     AsyncTermVariantService,
     TermVariantService,
 )
 from mpt_api_client.resources.catalog.product_terms import (
     AsyncTermService,
+    Term,
     TermService,
 )
 
@@ -24,6 +26,19 @@ def async_term_service(async_http_client: Any) -> AsyncTermService:
     )
 
 
+@pytest.fixture
+def term_data():
+    return {
+        "id": "TRM-001",
+        "name": "Terms of Service",
+        "description": "Standard terms",
+        "displayOrder": 1,
+        "status": "Active",
+        "product": {"id": "PRD-001", "name": "My Product"},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 def test_endpoint(term_service: TermService) -> None:
     result = term_service.path == "/public/v1/catalog/products/PRD-001/terms"
 
@@ -68,3 +83,25 @@ def test_async_variants_property(async_term_service: AsyncTermService) -> None:
     assert isinstance(result, AsyncTermVariantService)
     assert result.http_client == async_term_service.http_client
     assert result.endpoint_params == {"product_id": "PRD-001", "term_id": "TCS-001"}
+
+
+def test_term_primitive_fields(term_data: dict) -> None:
+    result = Term(term_data)
+
+    assert result.to_dict() == term_data
+
+
+def test_term_nested_fields_are_base_models(term_data: dict) -> None:
+    result = Term(term_data)
+
+    assert isinstance(result.product, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_term_optional_fields_absent() -> None:
+    result = Term({"id": "TRM-001"})
+
+    assert result.id == "TRM-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "status")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_products.py b/tests/unit/resources/catalog/test_products.py
index 6ba3e93..4f5c802 100644
--- a/tests/unit/resources/catalog/test_products.py
+++ b/tests/unit/resources/catalog/test_products.py
@@ -2,11 +2,12 @@
 import pytest
 import respx
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.product_terms import (
     AsyncTermService,
     TermService,
 )
-from mpt_api_client.resources.catalog.products import AsyncProductsService, ProductsService
+from mpt_api_client.resources.catalog.products import AsyncProductsService, Product, ProductsService
 from mpt_api_client.resources.catalog.products_documents import (
     AsyncDocumentService,
     DocumentService,
@@ -227,6 +228,49 @@ def test_sync_product_update(products_service, tmp_path):
     assert result.to_dict() == expected_response
 
 
+@pytest.fixture
+def product_data():
+    return {
+        "id": "PRD-001",
+        "name": "My Product",
+        "shortDescription": "Short desc",
+        "longDescription": "Long description of the product",
+        "externalIds": {"vendor": "ext-001"},
+        "website": "https://example.com",
+        "icon": "https://example.com/icon.png",
+        "status": "Active",
+        "vendor": {"id": "ACC-001", "name": "Vendor"},
+        "settings": {"allowCustomization": True},
+        "statistics": {"listings": 3},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
+def test_product_primitive_fields(product_data):
+    result = Product(product_data)
+
+    assert result.to_dict() == product_data
+
+
+def test_product_nested_fields_are_base_models(product_data):
+    result = Product(product_data)
+
+    assert isinstance(result.external_ids, BaseModel)
+    assert isinstance(result.vendor, BaseModel)
+    assert isinstance(result.settings, BaseModel)
+    assert isinstance(result.statistics, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_product_optional_fields_absent():
+    result = Product({"id": "PRD-001"})
+
+    assert result.id == "PRD-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "status")
+    assert not hasattr(result, "audit")
+
+
 async def test_async_product_update(async_products_service, tmp_path):
     product_id = "PRD-456"
     update_data = {"name": "Async Updated Product", "category": "Gadgets"}
diff --git a/tests/unit/resources/catalog/test_products_documents.py b/tests/unit/resources/catalog/test_products_documents.py
index 8d65275..af22ccf 100644
--- a/tests/unit/resources/catalog/test_products_documents.py
+++ b/tests/unit/resources/catalog/test_products_documents.py
@@ -1,7 +1,9 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.products_documents import (
     AsyncDocumentService,
+    Document,
     DocumentService,
 )
 
@@ -18,6 +20,24 @@ def async_document_service(async_http_client) -> AsyncDocumentService:
     )
 
 
+@pytest.fixture
+def document_data():
+    return {
+        "id": "DOC-001",
+        "name": "User Guide",
+        "type": "UserGuide",
+        "description": "Product user guide",
+        "status": "Active",
+        "filename": "guide.pdf",
+        "size": 4096,
+        "contentType": "application/pdf",
+        "url": "https://example.com/guide.pdf",
+        "language": "en",
+        "product": {"id": "PRD-001", "name": "My Product"},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 def test_endpoint(document_service) -> None:
     result = document_service.path == "/public/v1/catalog/products/PRD-001/documents"
 
@@ -48,3 +68,25 @@ def test_async_methods_present(async_document_service, method: str) -> None:
     result = hasattr(async_document_service, method)
 
     assert result is True
+
+
+def test_document_primitive_fields(document_data):
+    result = Document(document_data)
+
+    assert result.to_dict() == document_data
+
+
+def test_document_nested_fields_are_base_models(document_data):
+    result = Document(document_data)
+
+    assert isinstance(result.product, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_document_optional_fields_absent():
+    result = Document({"id": "DOC-001"})
+
+    assert result.id == "DOC-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "status")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_products_item_groups.py b/tests/unit/resources/catalog/test_products_item_groups.py
index 23fe588..a0eb6f8 100644
--- a/tests/unit/resources/catalog/test_products_item_groups.py
+++ b/tests/unit/resources/catalog/test_products_item_groups.py
@@ -1,7 +1,9 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.products_item_groups import (
     AsyncItemGroupsService,
+    ItemGroup,
     ItemGroupsService,
 )
 
@@ -18,6 +20,23 @@ def async_item_groups_service(async_http_client):
     )
 
 
+@pytest.fixture
+def item_group_data():
+    return {
+        "id": "GRP-001",
+        "name": "Standard Options",
+        "label": "Standard",
+        "description": "Standard option group",
+        "displayOrder": 1,
+        "default": True,
+        "multiple": False,
+        "required": True,
+        "itemCount": 5,
+        "product": {"id": "PRD-001", "name": "My Product"},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 def test_endpoint(item_groups_service):
     result = item_groups_service.path == "/public/v1/catalog/products/PRD-001/item-groups"
 
@@ -42,3 +61,25 @@ def test_async_methods_present(async_item_groups_service, method):
     result = hasattr(async_item_groups_service, method)
 
     assert result is True
+
+
+def test_item_group_primitive_fields(item_group_data):
+    result = ItemGroup(item_group_data)
+
+    assert result.to_dict() == item_group_data
+
+
+def test_item_group_nested_fields_are_base_models(item_group_data):
+    result = ItemGroup(item_group_data)
+
+    assert isinstance(result.product, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_item_group_optional_fields_absent():
+    result = ItemGroup({"id": "GRP-001"})
+
+    assert result.id == "GRP-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "default")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_products_media.py b/tests/unit/resources/catalog/test_products_media.py
index f4b023c..bd789af 100644
--- a/tests/unit/resources/catalog/test_products_media.py
+++ b/tests/unit/resources/catalog/test_products_media.py
@@ -1,7 +1,9 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.products_media import (
     AsyncMediaService,
+    Media,
     MediaService,
 )
 
@@ -18,6 +20,24 @@ def async_media_service(async_http_client) -> AsyncMediaService:
     )
 
 
+@pytest.fixture
+def media_data():
+    return {
+        "id": "MED-001",
+        "name": "Product Screenshot",
+        "type": "Image",
+        "description": "Main product screenshot",
+        "status": "Active",
+        "filename": "screenshot.png",
+        "size": 512000,
+        "contentType": "image/png",
+        "displayOrder": 1,
+        "url": "https://example.com/screenshot.png",
+        "product": {"id": "PRD-001", "name": "My Product"},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 def test_endpoint(media_service) -> None:
     result = media_service.path == "/public/v1/catalog/products/PRD-001/media"
 
@@ -48,3 +68,25 @@ def test_async_methods_present(async_media_service, method: str) -> None:
     result = hasattr(async_media_service, method)
 
     assert result is True
+
+
+def test_media_primitive_fields(media_data):
+    result = Media(media_data)
+
+    assert result.to_dict() == media_data
+
+
+def test_media_nested_fields_are_base_models(media_data):
+    result = Media(media_data)
+
+    assert isinstance(result.product, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_media_optional_fields_absent():
+    result = Media({"id": "MED-001"})
+
+    assert result.id == "MED-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "status")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_products_templates.py b/tests/unit/resources/catalog/test_products_templates.py
index 9c2443f..7a643a1 100644
--- a/tests/unit/resources/catalog/test_products_templates.py
+++ b/tests/unit/resources/catalog/test_products_templates.py
@@ -1,7 +1,9 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.products_templates import (
     AsyncTemplatesService,
+    Template,
     TemplatesService,
 )
 
@@ -18,6 +20,19 @@ def async_templates_service(async_http_client):
     )
 
 
+@pytest.fixture
+def template_data():
+    return {
+        "id": "TPL-001",
+        "name": "Order Confirmation",
+        "content": "<p>Your order has been confirmed.</p>",
+        "type": "Email",
+        "default": True,
+        "product": {"id": "PRD-001", "name": "My Product"},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 def test_endpoint(templates_service):
     result = templates_service.path == "/public/v1/catalog/products/PRD-001/templates"
 
@@ -42,3 +57,25 @@ def test_async_methods_present(async_templates_service, method):
     result = hasattr(async_templates_service, method)
 
     assert result is True
+
+
+def test_template_primitive_fields(template_data):
+    result = Template(template_data)
+
+    assert result.to_dict() == template_data
+
+
+def test_template_nested_fields_are_base_models(template_data):
+    result = Template(template_data)
+
+    assert isinstance(result.product, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_template_optional_fields_absent():
+    result = Template({"id": "TPL-001"})
+
+    assert result.id == "TPL-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "default")
+    assert not hasattr(result, "audit")
diff --git a/tests/unit/resources/catalog/test_units_of_measure.py b/tests/unit/resources/catalog/test_units_of_measure.py
index d471455..d85502a 100644
--- a/tests/unit/resources/catalog/test_units_of_measure.py
+++ b/tests/unit/resources/catalog/test_units_of_measure.py
@@ -1,7 +1,9 @@
 import pytest
 
+from mpt_api_client.models.model import BaseModel
 from mpt_api_client.resources.catalog.units_of_measure import (
     AsyncUnitsOfMeasureService,
+    UnitOfMeasure,
     UnitsOfMeasureService,
 )
 
@@ -16,6 +18,17 @@ def async_units_of_measure_service(async_http_client):
     return AsyncUnitsOfMeasureService(http_client=async_http_client)
 
 
+@pytest.fixture
+def unit_of_measure_data():
+    return {
+        "id": "UOM-001",
+        "description": "A single unit",
+        "name": "Each",
+        "statistics": {"items": 100},
+        "audit": {"created": {"at": "2024-01-01T00:00:00Z"}},
+    }
+
+
 @pytest.mark.parametrize("method", ["get", "create", "update", "delete", "iterate"])
 def test_mixins_present(units_of_measure_service, method):
     result = hasattr(units_of_measure_service, method)
@@ -28,3 +41,25 @@ def test_async_mixins_present(async_units_of_measure_service, method):
     result = hasattr(async_units_of_measure_service, method)
 
     assert result is True
+
+
+def test_unit_of_measure_primitive_fields(unit_of_measure_data):
+    result = UnitOfMeasure(unit_of_measure_data)
+
+    assert result.to_dict() == unit_of_measure_data
+
+
+def test_unit_of_measure_nested_models(unit_of_measure_data):
+    result = UnitOfMeasure(unit_of_measure_data)
+
+    assert isinstance(result.statistics, BaseModel)
+    assert isinstance(result.audit, BaseModel)
+
+
+def test_unit_of_measure_optional_fields_absent():
+    result = UnitOfMeasure({"id": "UOM-001"})
+
+    assert result.id == "UOM-001"
+    assert not hasattr(result, "name")
+    assert not hasattr(result, "description")
+    assert not hasattr(result, "audit")