diff --git a/stix2/custom.py b/stix2/custom.py
index a00498b..802fd07 100644
--- a/stix2/custom.py
+++ b/stix2/custom.py
@@ -53,7 +53,10 @@ def _custom_marking_builder(cls, type, properties, version):
     return _CustomMarking
 
 
-def _custom_observable_builder(cls, type, properties, version):
+def _custom_observable_builder(cls, type, properties, version, id_contrib_props=None):
+    if id_contrib_props is None:
+        id_contrib_props = []
+
     class _CustomObservable(cls, _Observable):
 
         if not re.match(TYPE_REGEX, type):
@@ -98,6 +101,8 @@ def _custom_observable_builder(cls, type, properties, version):
 
         _type = type
         _properties = OrderedDict(properties)
+        if version != '2.0':
+            _id_contributing_properties = id_contrib_props
 
         def __init__(self, **kwargs):
             _Observable.__init__(self, **kwargs)
diff --git a/stix2/v21/observables.py b/stix2/v21/observables.py
index ed560a6..e8c1925 100644
--- a/stix2/v21/observables.py
+++ b/stix2/v21/observables.py
@@ -966,7 +966,7 @@ class X509Certificate(_Observable):
         self._check_at_least_one_property(att_list)
 
 
-def CustomObservable(type='x-custom-observable', properties=None):
+def CustomObservable(type='x-custom-observable', properties=None, id_contrib_props=None):
     """Custom STIX Cyber Observable Object type decorator.
 
     Example:
@@ -987,7 +987,7 @@ def CustomObservable(type='x-custom-observable', properties=None):
             properties,
             [('extensions', ExtensionsProperty(spec_version='2.1', enclosing_type=type))],
         ]))
-        return _custom_observable_builder(cls, type, _properties, '2.1')
+        return _custom_observable_builder(cls, type, _properties, '2.1', id_contrib_props)
     return wrapper
 
 

Custom SCOs don't support `_id_contributing_properties`
When creating custom SCOs, cannot specify the `_id_contributing_properties` property to define which properties should be used for the custom SCOs' deterministic IDs
diff --git a/stix2/test/v21/test_custom.py b/stix2/test/v21/test_custom.py
index 9c650eb..b46288d 100644
--- a/stix2/test/v21/test_custom.py
+++ b/stix2/test/v21/test_custom.py
@@ -1,3 +1,5 @@
+import uuid
+
 import pytest
 
 import stix2
@@ -665,6 +667,76 @@ def test_observed_data_with_custom_observable_object():
     assert ob_data.objects['0'].property1 == 'something'
 
 
+def test_custom_observable_object_det_id_1():
+    @stix2.v21.CustomObservable(
+        'x-det-id-observable-1', [
+            ('property1', stix2.properties.StringProperty(required=True)),
+            ('property2', stix2.properties.IntegerProperty()),
+        ], [
+            'property1',
+        ],
+    )
+    class DetIdObs1():
+        pass
+
+    dio_1 = DetIdObs1(property1='I am property1!', property2=42)
+    dio_2 = DetIdObs1(property1='I am property1!', property2=24)
+    assert dio_1.property1 == dio_2.property1 == 'I am property1!'
+    assert dio_1.id == dio_2.id
+
+    uuid_obj = uuid.UUID(dio_1.id[-36:])
+    assert uuid_obj.variant == uuid.RFC_4122
+    assert uuid_obj.version == 5
+
+    dio_3 = DetIdObs1(property1='I am property1!', property2=42)
+    dio_4 = DetIdObs1(property1='I am also property1!', property2=24)
+    assert dio_3.property1 == 'I am property1!'
+    assert dio_4.property1 == 'I am also property1!'
+    assert dio_3.id != dio_4.id
+
+
+def test_custom_observable_object_det_id_2():
+    @stix2.v21.CustomObservable(
+        'x-det-id-observable-2', [
+            ('property1', stix2.properties.StringProperty(required=True)),
+            ('property2', stix2.properties.IntegerProperty()),
+        ], [
+            'property1', 'property2',
+        ],
+    )
+    class DetIdObs2():
+        pass
+
+    dio_1 = DetIdObs2(property1='I am property1!', property2=42)
+    dio_2 = DetIdObs2(property1='I am property1!', property2=42)
+    assert dio_1.property1 == dio_2.property1 == 'I am property1!'
+    assert dio_1.property2 == dio_2.property2 == 42
+    assert dio_1.id == dio_2.id
+
+    dio_3 = DetIdObs2(property1='I am property1!', property2=42)
+    dio_4 = DetIdObs2(property1='I am also property1!', property2=42)
+    assert dio_3.property1 == 'I am property1!'
+    assert dio_4.property1 == 'I am also property1!'
+    assert dio_3.property2 == dio_4.property2 == 42
+    assert dio_3.id != dio_4.id
+
+
+def test_custom_observable_object_no_id_contrib_props():
+    @stix2.v21.CustomObservable(
+        'x-det-id-observable-3', [
+            ('property1', stix2.properties.StringProperty(required=True)),
+        ],
+    )
+    class DetIdObs3():
+        pass
+
+    dio = DetIdObs3(property1="I am property1!")
+
+    uuid_obj = uuid.UUID(dio.id[-36:])
+    assert uuid_obj.variant == uuid.RFC_4122
+    assert uuid_obj.version == 4
+
+
 @stix2.v21.CustomExtension(
     stix2.v21.DomainName, 'x-new-ext', [
         ('property1', stix2.properties.StringProperty(required=True)),

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest pytest-cov coverage
3.7
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.13
antlr4-python3-runtime==4.9.3
attrs==24.2.0
Babel==2.14.0
backcall==0.2.0
beautifulsoup4==4.13.3
bleach==6.0.0
bump2version==1.0.1
bumpversion==0.6.0
cachetools==5.5.2
certifi @ file:///croot/certifi_1671487769961/work/certifi
cfgv==3.3.1
chardet==5.2.0
charset-normalizer==3.4.1
colorama==0.4.6
coverage==7.2.7
decorator==5.1.1
defusedxml==0.7.1
distlib==0.3.9
docutils==0.17.1
entrypoints==0.4
exceptiongroup==1.2.2
fastjsonschema==2.21.1
filelock==3.12.2
identify==2.5.24
idna==3.10
imagesize==1.4.1
importlib-metadata==6.7.0
importlib-resources==5.12.0
iniconfig==2.0.0
ipython==7.34.0
jedi==0.19.2
Jinja2==3.1.6
jsonschema==4.17.3
jupyter_client==7.4.9
jupyter_core==4.12.0
jupyterlab-pygments==0.2.2
MarkupSafe==2.1.5
matplotlib-inline==0.1.6
mistune==3.0.2
nbclient==0.7.4
nbconvert==7.6.0
nbformat==5.8.0
nbsphinx==0.4.3
nest-asyncio==1.6.0
nodeenv==1.9.1
packaging==24.0
pandocfilters==1.5.1
parso==0.8.4
pexpect==4.9.0
pickleshare==0.7.5
pkgutil_resolve_name==1.3.10
platformdirs==4.0.0
pluggy==1.2.0
pre-commit==2.21.0
prompt_toolkit==3.0.48
ptyprocess==0.7.0
Pygments==2.17.2
pyproject-api==1.5.3
pyrsistent==0.19.3
pytest==7.4.4
pytest-cov==4.1.0
python-dateutil==2.9.0.post0
pytz==2025.2
PyYAML==6.0.1
pyzmq==26.2.1
requests==2.31.0
simplejson==3.20.1
six==1.17.0
snowballstemmer==2.2.0
soupsieve==2.4.1
Sphinx==1.8.6
sphinx-prompt==1.5.0
sphinxcontrib-serializinghtml==1.1.5
sphinxcontrib-websupport==1.2.4
-e git+https://github.com/oasis-open/cti-python-stix2.git@30a59ad77669cda8260640f99d6d8ff3a7574640#egg=stix2
stix2-patterns==2.0.0
tinycss2==1.2.1
tomli==2.0.1
tornado==6.2
tox==4.8.0
traitlets==5.9.0
typing_extensions==4.7.1
urllib3==2.0.7
virtualenv==20.26.6
wcwidth==0.2.13
webencodings==0.5.1
zipp==3.15.0

name: cti-python-stix2
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2022.12.7=py37h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.4.4=h6a678d5_1
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=22.3.1=py37h06a4308_0
  - python=3.7.16=h7a1cb2a_0
  - readline=8.2=h5eee18b_0
  - setuptools=65.6.3=py37h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.38.4=py37h06a4308_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.13
      - antlr4-python3-runtime==4.9.3
      - attrs==24.2.0
      - babel==2.14.0
      - backcall==0.2.0
      - beautifulsoup4==4.13.3
      - bleach==6.0.0
      - bump2version==1.0.1
      - bumpversion==0.6.0
      - cachetools==5.5.2
      - cfgv==3.3.1
      - chardet==5.2.0
      - charset-normalizer==3.4.1
      - colorama==0.4.6
      - coverage==7.2.7
      - decorator==5.1.1
      - defusedxml==0.7.1
      - distlib==0.3.9
      - docutils==0.17.1
      - entrypoints==0.4
      - exceptiongroup==1.2.2
      - fastjsonschema==2.21.1
      - filelock==3.12.2
      - identify==2.5.24
      - idna==3.10
      - imagesize==1.4.1
      - importlib-metadata==6.7.0
      - importlib-resources==5.12.0
      - iniconfig==2.0.0
      - ipython==7.34.0
      - jedi==0.19.2
      - jinja2==3.1.6
      - jsonschema==4.17.3
      - jupyter-client==7.4.9
      - jupyter-core==4.12.0
      - jupyterlab-pygments==0.2.2
      - markupsafe==2.1.5
      - matplotlib-inline==0.1.6
      - mistune==3.0.2
      - nbclient==0.7.4
      - nbconvert==7.6.0
      - nbformat==5.8.0
      - nbsphinx==0.4.3
      - nest-asyncio==1.6.0
      - nodeenv==1.9.1
      - packaging==24.0
      - pandocfilters==1.5.1
      - parso==0.8.4
      - pexpect==4.9.0
      - pickleshare==0.7.5
      - pkgutil-resolve-name==1.3.10
      - platformdirs==4.0.0
      - pluggy==1.2.0
      - pre-commit==2.21.0
      - prompt-toolkit==3.0.48
      - ptyprocess==0.7.0
      - pygments==2.17.2
      - pyproject-api==1.5.3
      - pyrsistent==0.19.3
      - pytest==7.4.4
      - pytest-cov==4.1.0
      - python-dateutil==2.9.0.post0
      - pytz==2025.2
      - pyyaml==6.0.1
      - pyzmq==26.2.1
      - requests==2.31.0
      - simplejson==3.20.1
      - six==1.17.0
      - snowballstemmer==2.2.0
      - soupsieve==2.4.1
      - sphinx==1.8.6
      - sphinx-prompt==1.5.0
      - sphinxcontrib-serializinghtml==1.1.5
      - sphinxcontrib-websupport==1.2.4
      - stix2-patterns==2.0.0
      - tinycss2==1.2.1
      - tomli==2.0.1
      - tornado==6.2
      - tox==4.8.0
      - traitlets==5.9.0
      - typing-extensions==4.7.1
      - urllib3==2.0.7
      - virtualenv==20.26.6
      - wcwidth==0.2.13
      - webencodings==0.5.1
      - zipp==3.15.0
prefix: /opt/conda/envs/cti-python-stix2

stix2/test/v21/test_custom.py::test_custom_observable_object_det_id_1 stix2/test/v21/test_custom.py::test_custom_observable_object_det_id_2
stix2/test/v21/test_custom.py::test_identity_custom_property stix2/test/v21/test_custom.py::test_identity_custom_property_invalid stix2/test/v21/test_custom.py::test_identity_custom_property_allowed stix2/test/v21/test_custom.py::test_parse_identity_custom_property[{\n stix2/test/v21/test_custom.py::test_custom_property_object_in_bundled_object stix2/test/v21/test_custom.py::test_custom_properties_object_in_bundled_object stix2/test/v21/test_custom.py::test_custom_property_dict_in_bundled_object stix2/test/v21/test_custom.py::test_custom_properties_dict_in_bundled_object stix2/test/v21/test_custom.py::test_custom_property_in_observed_data stix2/test/v21/test_custom.py::test_custom_property_object_in_observable_extension stix2/test/v21/test_custom.py::test_custom_property_dict_in_observable_extension stix2/test/v21/test_custom.py::test_identity_custom_property_revoke stix2/test/v21/test_custom.py::test_identity_custom_property_edit_markings stix2/test/v21/test_custom.py::test_custom_marking_no_init_1 stix2/test/v21/test_custom.py::test_custom_marking_no_init_2 stix2/test/v21/test_custom.py::test_custom_object_raises_exception stix2/test/v21/test_custom.py::test_custom_object_type stix2/test/v21/test_custom.py::test_custom_object_no_init_1 stix2/test/v21/test_custom.py::test_custom_object_no_init_2 stix2/test/v21/test_custom.py::test_custom_object_invalid_type_name stix2/test/v21/test_custom.py::test_parse_custom_object_type stix2/test/v21/test_custom.py::test_parse_unregistered_custom_object_type stix2/test/v21/test_custom.py::test_parse_unregistered_custom_object_type_w_allow_custom stix2/test/v21/test_custom.py::test_custom_observable_object_1 stix2/test/v21/test_custom.py::test_custom_observable_object_2 stix2/test/v21/test_custom.py::test_custom_observable_object_3 stix2/test/v21/test_custom.py::test_custom_observable_raises_exception stix2/test/v21/test_custom.py::test_custom_observable_object_no_init_1 stix2/test/v21/test_custom.py::test_custom_observable_object_no_init_2 stix2/test/v21/test_custom.py::test_custom_observable_object_invalid_type_name stix2/test/v21/test_custom.py::test_custom_observable_object_invalid_ref_property stix2/test/v21/test_custom.py::test_custom_observable_object_invalid_refs_property stix2/test/v21/test_custom.py::test_custom_observable_object_invalid_refs_list_property stix2/test/v21/test_custom.py::test_custom_no_properties_raises_exception stix2/test/v21/test_custom.py::test_custom_wrong_properties_arg_raises_exception stix2/test/v21/test_custom.py::test_parse_custom_observable_object stix2/test/v21/test_custom.py::test_parse_unregistered_custom_observable_object stix2/test/v21/test_custom.py::test_parse_unregistered_custom_observable_object_with_no_type stix2/test/v21/test_custom.py::test_parse_observed_data_with_custom_observable stix2/test/v21/test_custom.py::test_parse_invalid_custom_observable_object stix2/test/v21/test_custom.py::test_observable_custom_property stix2/test/v21/test_custom.py::test_observable_custom_property_invalid stix2/test/v21/test_custom.py::test_observable_custom_property_allowed stix2/test/v21/test_custom.py::test_observed_data_with_custom_observable_object stix2/test/v21/test_custom.py::test_custom_observable_object_no_id_contrib_props stix2/test/v21/test_custom.py::test_custom_extension_raises_exception stix2/test/v21/test_custom.py::test_custom_extension stix2/test/v21/test_custom.py::test_custom_extension_wrong_observable_type stix2/test/v21/test_custom.py::test_custom_extension_with_list_and_dict_properties_observable_type[{\n stix2/test/v21/test_custom.py::test_custom_extension_invalid_observable stix2/test/v21/test_custom.py::test_custom_extension_invalid_type_name stix2/test/v21/test_custom.py::test_custom_extension_no_properties stix2/test/v21/test_custom.py::test_custom_extension_empty_properties stix2/test/v21/test_custom.py::test_custom_extension_dict_properties stix2/test/v21/test_custom.py::test_custom_extension_no_init_1 stix2/test/v21/test_custom.py::test_custom_extension_no_init_2 stix2/test/v21/test_custom.py::test_parse_observable_with_custom_extension stix2/test/v21/test_custom.py::test_custom_and_spec_extension_mix stix2/test/v21/test_custom.py::test_parse_observable_with_unregistered_custom_extension[{\n stix2/test/v21/test_custom.py::test_register_custom_object stix2/test/v21/test_custom.py::test_extension_property_location stix2/test/v21/test_custom.py::test_custom_object_nested_dictionary[{\n
stix2/v21/observables.py stix2/custom.py
stix2/v21/observables.py stix2/custom.py