diff --git a/tools/spectral/ipa/__tests__/IPA121DateTimeFieldsMentionISO8601.test.js b/tools/spectral/ipa/__tests__/IPA121DateTimeFieldsMentionISO8601.test.js
new file mode 100644
index 0000000000..ebe3f89e0b
--- /dev/null
+++ b/tools/spectral/ipa/__tests__/IPA121DateTimeFieldsMentionISO8601.test.js
@@ -0,0 +1,261 @@
+import testRule from './__helpers__/testRule.js';
+import { DiagnosticSeverity } from '@stoplight/types';
+
+testRule('xgen-IPA-121-date-time-fields-mention-iso-8601', [
+  {
+    name: 'valid when date-time format mentions ISO 8601 in description',
+    document: {
+      components: {
+        schemas: {
+          TestSchema: {
+            properties: {
+              createdAt: {
+                type: 'string',
+                format: 'date-time',
+                description: 'The creation timestamp in ISO 8601 format in UTC.',
+              },
+              updatedOn: {
+                type: 'string',
+                format: 'date-time',
+                description: 'When the resource was last updated. Uses ISO 8601 datetime format in UTC.',
+              },
+            },
+          },
+        },
+        parameters: {
+          TestParameter: {
+            name: 'createdAt',
+            in: 'query',
+            description: 'The creation timestamp in ISO 8601 format in UTC.',
+            schema: {
+              type: 'string',
+              format: 'date-time',
+            },
+          },
+        },
+      },
+    },
+    errors: [],
+  },
+  {
+    name: 'valid with non-date-time format',
+    document: {
+      components: {
+        schemas: {
+          TestSchema: {
+            properties: {
+              username: {
+                type: 'string',
+                description: 'The username for login.',
+              },
+              age: {
+                type: 'integer',
+                description: 'Age in years.',
+              },
+            },
+          },
+        },
+      },
+    },
+    errors: [],
+  },
+  {
+    name: 'invalid when date-time format has no description',
+    document: {
+      components: {
+        schemas: {
+          TestSchema: {
+            properties: {
+              createdAt: {
+                type: 'string',
+                format: 'date-time',
+              },
+              modifiedAt: {
+                type: 'string',
+                format: 'date-time',
+                description: 'The modification timestamp.',
+              },
+            },
+          },
+        },
+        parameters: {
+          TestParameter: {
+            name: 'createdAt',
+            in: 'query',
+            description: 'The creation timestamp',
+            schema: {
+              type: 'string',
+              format: 'date-time',
+            },
+          },
+        },
+      },
+      paths: {
+        '/resources': {
+          post: {
+            requestBody: {
+              content: {
+                'application/json': {
+                  schema: {
+                    properties: {
+                      $ref: '#/components/schemas/TestSchema',
+                    },
+                  },
+                },
+              },
+            },
+          },
+        },
+      },
+    },
+    errors: [
+      {
+        code: 'xgen-IPA-121-date-time-fields-mention-iso-8601',
+        message:
+          'API producers must use ISO 8601 date-time format in UTC for all timestamps. Fields must note ISO 8601 and UTC in their description.',
+        path: ['components', 'schemas', 'TestSchema', 'properties', 'createdAt'],
+        severity: DiagnosticSeverity.Warning,
+      },
+      {
+        code: 'xgen-IPA-121-date-time-fields-mention-iso-8601',
+        message:
+          'API producers must use ISO 8601 date-time format in UTC for all timestamps. Fields must note ISO 8601 and UTC in their description.',
+        path: ['components', 'schemas', 'TestSchema', 'properties', 'modifiedAt'],
+        severity: DiagnosticSeverity.Warning,
+      },
+      {
+        code: 'xgen-IPA-121-date-time-fields-mention-iso-8601',
+        message:
+          'API producers must use ISO 8601 date-time format in UTC for all timestamps. Fields must note ISO 8601 and UTC in their description.',
+        path: ['components', 'parameters', 'TestParameter'],
+        severity: DiagnosticSeverity.Warning,
+      },
+    ],
+  },
+  {
+    name: 'exception',
+    document: {
+      components: {
+        schemas: {
+          TestSchema: {
+            properties: {
+              createdAt: {
+                type: 'string',
+                format: 'date-time',
+                description: 'The creation timestamp.',
+                'x-xgen-IPA-exception': {
+                  'xgen-IPA-121-date-time-fields-mention-iso-8601': 'Legacy field format',
+                },
+              },
+            },
+          },
+        },
+        parameters: {
+          TestParameter: {
+            name: 'createdAt',
+            in: 'query',
+            description: 'The creation timestamp',
+            schema: {
+              type: 'string',
+              format: 'date-time',
+            },
+            'x-xgen-IPA-exception': {
+              'xgen-IPA-121-date-time-fields-mention-iso-8601': 'Legacy field format',
+            },
+          },
+        },
+      },
+    },
+    errors: [],
+  },
+  {
+    name: 'test with parameters in path operation',
+    document: {
+      paths: {
+        '/resources': {
+          get: {
+            parameters: [
+              {
+                name: 'since',
+                in: 'query',
+                description: 'Filter resources created since this ISO 8601 timestamp in UTC',
+                schema: {
+                  type: 'string',
+                  format: 'date-time',
+                },
+              },
+              {
+                name: 'until',
+                in: 'query',
+                description: 'Filter resources created until this timestamp', // Missing ISO 8601 and UTC
+                schema: {
+                  type: 'string',
+                  format: 'date-time',
+                },
+              },
+            ],
+          },
+        },
+      },
+    },
+    errors: [
+      {
+        code: 'xgen-IPA-121-date-time-fields-mention-iso-8601',
+        message:
+          'API producers must use ISO 8601 date-time format in UTC for all timestamps. Fields must note ISO 8601 and UTC in their description.',
+        path: ['paths', '/resources', 'get', 'parameters', '1'],
+        severity: DiagnosticSeverity.Warning,
+      },
+    ],
+  },
+  {
+    name: 'test with requestBody properties',
+    document: {
+      paths: {
+        '/resources': {
+          post: {
+            requestBody: {
+              content: {
+                'application/json': {
+                  schema: {
+                    properties: {
+                      scheduledFor: {
+                        type: 'string',
+                        format: 'date-time',
+                        description: 'When to schedule the job using ISO 8601 format in UTC.',
+                      },
+                      expiresAt: {
+                        type: 'string',
+                        format: 'date-time',
+                        description: 'When this resource expires.', // Missing ISO 8601 and UTC
+                      },
+                    },
+                  },
+                },
+              },
+            },
+          },
+        },
+      },
+    },
+    errors: [
+      {
+        code: 'xgen-IPA-121-date-time-fields-mention-iso-8601',
+        message:
+          'API producers must use ISO 8601 date-time format in UTC for all timestamps. Fields must note ISO 8601 and UTC in their description.',
+        path: [
+          'paths',
+          '/resources',
+          'post',
+          'requestBody',
+          'content',
+          'application/json',
+          'schema',
+          'properties',
+          'expiresAt',
+        ],
+        severity: DiagnosticSeverity.Warning,
+      },
+    ],
+  },
+]);
diff --git a/tools/spectral/ipa/ipa-spectral.yaml b/tools/spectral/ipa/ipa-spectral.yaml
index 10d0ce7384..50fa4ea782 100644
--- a/tools/spectral/ipa/ipa-spectral.yaml
+++ b/tools/spectral/ipa/ipa-spectral.yaml
@@ -14,6 +14,7 @@ extends:
   - ./rulesets/IPA-117.yaml
   - ./rulesets/IPA-118.yaml
   - ./rulesets/IPA-119.yaml
+  - ./rulesets/IPA-121.yaml
   - ./rulesets/IPA-123.yaml
   - ./rulesets/IPA-125.yaml
 
diff --git a/tools/spectral/ipa/rulesets/IPA-121.yaml b/tools/spectral/ipa/rulesets/IPA-121.yaml
new file mode 100644
index 0000000000..60d95f94fd
--- /dev/null
+++ b/tools/spectral/ipa/rulesets/IPA-121.yaml
@@ -0,0 +1,22 @@
+# IPA-121: Datetime
+# http://go/ipa/121
+
+functions:
+  - IPA121DateTimeFieldsMentionISO8601
+
+rules:
+  xgen-IPA-121-date-time-fields-mention-iso-8601:
+    description: |
+      Fields with format="date-time" should mention ISO 8601 and UTC in their description.
+      It collects adoption metrics at schema property level and parameter level
+    message: '{{error}} https://mdb.link/mongodb-atlas-openapi-validation#xgen-IPA-121-date-time-fields-mention-iso-8601'
+    given:
+      - $.paths..parameters[*]
+      - $.components.parameters[*]
+      - $.components.schemas..properties[*]
+      - $.paths..requestBody..schema..properties[*]
+      - $.paths..responses..schema..properties[*]
+    resolved: false
+    severity: warn
+    then:
+      function: IPA121DateTimeFieldsMentionISO8601
diff --git a/tools/spectral/ipa/rulesets/README.md b/tools/spectral/ipa/rulesets/README.md
index d1754972d2..ff9890bda9 100644
--- a/tools/spectral/ipa/rulesets/README.md
+++ b/tools/spectral/ipa/rulesets/README.md
@@ -802,6 +802,18 @@ All cloudProviderEnumValues should be listed in the enum array.
 
 
 
+### IPA-121
+
+Rules are based on [http://go/ipa/IPA-121](http://go/ipa/IPA-121).
+
+#### xgen-IPA-121-date-time-fields-mention-iso-8601
+
+ ![warn](https://img.shields.io/badge/warning-yellow) 
+Fields with format="date-time" should mention ISO 8601 and UTC in their description.
+It collects adoption metrics at schema property level and parameter level
+
+
+
 ### IPA-123
 
 Rules are based on [http://go/ipa/IPA-123](http://go/ipa/IPA-123).
diff --git a/tools/spectral/ipa/rulesets/functions/IPA121DateTimeFieldsMentionISO8601.js b/tools/spectral/ipa/rulesets/functions/IPA121DateTimeFieldsMentionISO8601.js
new file mode 100644
index 0000000000..2dac2f5355
--- /dev/null
+++ b/tools/spectral/ipa/rulesets/functions/IPA121DateTimeFieldsMentionISO8601.js
@@ -0,0 +1,36 @@
+import { hasException } from './utils/exceptions.js';
+import { collectAdoption, collectAndReturnViolation, collectException } from './utils/collectionUtils.js';
+
+const RULE_NAME = 'xgen-IPA-121-date-time-fields-mention-iso-8601';
+const ERROR_MESSAGE =
+  'API producers must use ISO 8601 date-time format in UTC for all timestamps. Fields must note ISO 8601 and UTC in their description.';
+
+export default (input, options, { path }) => {
+  const fieldType = path[path.length - 2];
+
+  if (hasException(input, RULE_NAME)) {
+    collectException(input, RULE_NAME, path);
+    return;
+  }
+
+  let format;
+  let description = input.description;
+  if (fieldType === 'parameters') {
+    format = input.schema?.format;
+  } else if (fieldType === 'properties') {
+    format = input.format;
+  }
+
+  if (format === 'date-time') {
+    if (!description?.includes('ISO 8601') && !description?.includes('UTC')) {
+      return collectAndReturnViolation(path, RULE_NAME, [
+        {
+          path,
+          message: ERROR_MESSAGE,
+        },
+      ]);
+    }
+
+    collectAdoption(path, RULE_NAME);
+  }
+};