diff --git a/api/origin_trials_api.py b/api/origin_trials_api.py
index 4e087bb34629..0b49b564bd92 100644
--- a/api/origin_trials_api.py
+++ b/api/origin_trials_api.py
@@ -71,21 +71,19 @@ def find_use_counter_value(
   if (not settings.PROD and body['ot_creation__bypass_file_checks'] and
       body['ot_creation__bypass_file_checks']['value']):
     return 0
-  use_counter_name = body.get(
-      'ot_webfeature_use_counter', {}).get('value')
-  webfeature_use_counter = body.get(
-      'ot_webfeature_use_counter', {}).get('value')
+  use_counter_name = (body['ot_webfeature_use_counter']['value']
+                      if body['ot_webfeature_use_counter'] else None)
   is_webdx_use_counter = (
-      webfeature_use_counter and
-      webfeature_use_counter.startswith('WebDXFeature::'))
+      use_counter_name and
+      use_counter_name.startswith('WebDXFeature::'))
 
   match: re.Match | None = None
-  if webfeature_use_counter and is_webdx_use_counter:
+  if use_counter_name and is_webdx_use_counter:
     # Remove "WebDXFeature::" prefix.
     expression = f'(?<={use_counter_name[14:]} = )[0-9]+'
     match = re.search(expression,
                       chromium_files_dict['webdxfeature_file'])
-  elif webfeature_use_counter:
+  elif use_counter_name:
     expression = f'(?<={use_counter_name} = )[0-9]+'
     match = re.search(expression,
                       chromium_files_dict['webfeature_file'])
@@ -119,8 +117,8 @@ def _validate_creation_args(
     """Check that all provided OT creation arguments are valid."""
 
     validation_errors: dict[str, str] = {}
-    chromium_trial_name = body.get(
-        'ot_chromium_trial_name', {}).get('value')
+    chromium_trial_name = (body['ot_chromium_trial_name']['value']
+                           if body['ot_chromium_trial_name'] else None)
     if chromium_trial_name is None:
       self.abort(400, 'Chromium trial name not specified.')
 
@@ -141,9 +139,11 @@ def _validate_creation_args(
       validation_errors['ot_chromium_trial_name'] = (
           'Origin trial feature name not found in file')
 
-    if not body.get('ot_is_deprecation_trial', {}).get('value', False):
-      webfeature_use_counter = body.get(
-          'ot_webfeature_use_counter', {}).get('value')
+    is_dep_trial = (body['ot_is_deprecation_trial']
+                    and body['ot_is_deprecation_trial']['value'])
+    if not is_dep_trial:
+      webfeature_use_counter = (body['ot_webfeature_use_counter']['value']
+                                if body['ot_webfeature_use_counter'] else None)
       # Client will add a prefix to a WebDXFeature use counter.
       is_webdx_use_counter = (
           webfeature_use_counter and
@@ -168,7 +168,9 @@ def _validate_creation_args(
           validation_errors['ot_webfeature_use_counter'] = (
               'UseCounter not landed in webdx_feature.mojom')
 
-    if body.get('ot_has_third_party_support', {}).get('value', False):
+    has_third_party_support = (body['ot_has_third_party_support']['value']
+                               if body['ot_has_third_party_support'] else None)
+    if has_third_party_support:
       for feature in enabled_features_json['data']:
         if (feature.get('origin_trial_feature_name') == chromium_trial_name and
             not feature.get('origin_trial_allows_third_party', False)):
@@ -177,7 +179,9 @@ def _validate_creation_args(
               'set in runtime_enabled_features.json5. Feature name: '
               f'{feature["name"]}')
 
-    if body.get('ot_is_critical_trial', {}).get('value', False):
+    is_critical_trial = (body['ot_is_critical_trial']['value']
+                         if body['ot_is_critical_trial'] else None)
+    if is_critical_trial:
       if (f'blink::mojom::OriginTrialFeature::k{chromium_trial_name}'
           not in chromium_files['grace_period_file']):
         validation_errors['ot_is_critical_trial'] = (
diff --git a/api/origin_trials_api_test.py b/api/origin_trials_api_test.py
index 7a03b7b20e61..91e1b371284a 100644
--- a/api/origin_trials_api_test.py
+++ b/api/origin_trials_api_test.py
@@ -296,6 +296,38 @@ def test_validate_creation_args__valid_webfeature(
     expected = {}
     self.assertEqual(expected, result)
 
+  @mock.patch('framework.origin_trials_client.get_trials_list')
+  def test_validate_creation_args__valid_deprecation_trial(
+      self, mock_get_trials_list):
+    """No error messages should be returned if all args are valid for a
+    deprecation trial."""
+    mock_get_trials_list.return_value = self.mock_trials_list
+    body = {
+      'ot_chromium_trial_name': {
+        'form_field_name': 'ot_chromium_trial_name',
+        'value': 'ValidFeature',
+      },
+      'ot_webfeature_use_counter': None,
+      'ot_is_critical_trial': {
+        'form_field_name': 'ot_is_critical_trial',
+        'value': True,
+      },
+      'ot_is_deprecation_trial': {
+        'form_field_name': 'ot_is_deprecation_trial',
+        'value': True,
+      },
+      'ot_has_third_party_support': {
+        'form_field_name': 'ot_has_third_party_support',
+        'value': True,
+      },
+    }
+    # No exception should be raised.
+    with test_app.test_request_context(self.request_path):
+      result = self.handler._validate_creation_args(
+          body, self.mock_chromium_files_dict)
+    expected = {}
+    self.assertEqual(expected, result)
+
   @mock.patch('framework.origin_trials_client.get_trials_list')
   def test_validate_creation_args__valid_webdxfeature(
       self, mock_get_trials_list):
@@ -445,6 +477,7 @@ def test_validate_creation_args__missing_webfeature_use_counter(
         'form_field_name': 'ot_chromium_trial_name',
         'value': 'ValidFeature',
       },
+      'ot_webfeature_use_counter': None,
       'ot_is_critical_trial': {
         'form_field_name': 'ot_is_critical_trial',
         'value': False,
@@ -482,6 +515,7 @@ def test_validate_creation_args__missing_webfeature_use_counter_deprecation(
         'form_field_name': 'ot_is_critical_trial',
         'value': False,
       },
+      'ot_webfeature_use_counter': None,
       'ot_is_deprecation_trial': {
         'form_field_name': 'ot_is_deprecation_trial',
         'value': True,
@@ -540,6 +574,7 @@ def test_validate_creation_args__missing_chromium_trial_name(
         'form_field_name': 'ot_webfeature_use_counter',
         'value': 'kValidFeature',
       },
+      'ot_chromium_trial_name': None,
       'ot_is_critical_trial': {
         'form_field_name': 'ot_is_critical_trial',
         'value': False,