diff --git a/githubkit/versions/ghec_v2022_11_28/models/group_0631.py b/githubkit/versions/ghec_v2022_11_28/models/group_0631.py
index c75ddb9d6..8b919eb32 100644
--- a/githubkit/versions/ghec_v2022_11_28/models/group_0631.py
+++ b/githubkit/versions/ghec_v2022_11_28/models/group_0631.py
@@ -46,7 +46,7 @@ class WebhookCodeScanningAlertAppearedInBranchPropAlert(GitHubModel):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ] = Field(description="The reason for dismissing or closing the alert.")
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/ghec_v2022_11_28/models/group_0633.py b/githubkit/versions/ghec_v2022_11_28/models/group_0633.py
index 15f8e6194..c2fb9a0b2 100644
--- a/githubkit/versions/ghec_v2022_11_28/models/group_0633.py
+++ b/githubkit/versions/ghec_v2022_11_28/models/group_0633.py
@@ -46,7 +46,7 @@ class WebhookCodeScanningAlertClosedByUserPropAlert(GitHubModel):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ] = Field(description="The reason for dismissing or closing the alert.")
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/ghec_v2022_11_28/models/group_0639.py b/githubkit/versions/ghec_v2022_11_28/models/group_0639.py
index 575cb4a37..7c2b1d015 100644
--- a/githubkit/versions/ghec_v2022_11_28/models/group_0639.py
+++ b/githubkit/versions/ghec_v2022_11_28/models/group_0639.py
@@ -46,7 +46,7 @@ class WebhookCodeScanningAlertReopenedPropAlert(GitHubModel):
     dismissed_reason: Union[str, None] = Field(
         description="The reason for dismissing or closing the alert. Can be one of: `false positive`, `won't fix`, and `used in tests`."
     )
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/ghec_v2022_11_28/models/group_0641.py b/githubkit/versions/ghec_v2022_11_28/models/group_0641.py
index b110bda61..fa34b19cd 100644
--- a/githubkit/versions/ghec_v2022_11_28/models/group_0641.py
+++ b/githubkit/versions/ghec_v2022_11_28/models/group_0641.py
@@ -44,7 +44,7 @@ class WebhookCodeScanningAlertReopenedByUserPropAlert(GitHubModel):
     dismissed_reason: None = Field(
         description="The reason for dismissing or closing the alert. Can be one of: `false positive`, `won't fix`, and `used in tests`."
     )
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/ghec_v2022_11_28/models/group_0643.py b/githubkit/versions/ghec_v2022_11_28/models/group_0643.py
index 644f4ef8d..a03b9c606 100644
--- a/githubkit/versions/ghec_v2022_11_28/models/group_0643.py
+++ b/githubkit/versions/ghec_v2022_11_28/models/group_0643.py
@@ -46,7 +46,7 @@ class WebhookCodeScanningAlertUpdatedAssignmentPropAlert(GitHubModel):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ] = Field(description="The reason for dismissing or closing the alert.")
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/ghec_v2022_11_28/types/group_0631.py b/githubkit/versions/ghec_v2022_11_28/types/group_0631.py
index dc50f2cfa..d82927834 100644
--- a/githubkit/versions/ghec_v2022_11_28/types/group_0631.py
+++ b/githubkit/versions/ghec_v2022_11_28/types/group_0631.py
@@ -32,7 +32,7 @@ class WebhookCodeScanningAlertAppearedInBranchPropAlertType(TypedDict):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
@@ -64,7 +64,7 @@ class WebhookCodeScanningAlertAppearedInBranchPropAlertTypeForResponse(TypedDict
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
diff --git a/githubkit/versions/ghec_v2022_11_28/types/group_0633.py b/githubkit/versions/ghec_v2022_11_28/types/group_0633.py
index 9821e77a8..7318acbc2 100644
--- a/githubkit/versions/ghec_v2022_11_28/types/group_0633.py
+++ b/githubkit/versions/ghec_v2022_11_28/types/group_0633.py
@@ -32,7 +32,7 @@ class WebhookCodeScanningAlertClosedByUserPropAlertType(TypedDict):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
@@ -70,7 +70,7 @@ class WebhookCodeScanningAlertClosedByUserPropAlertTypeForResponse(TypedDict):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
diff --git a/githubkit/versions/ghec_v2022_11_28/types/group_0639.py b/githubkit/versions/ghec_v2022_11_28/types/group_0639.py
index ae3b8f28c..53ad19146 100644
--- a/githubkit/versions/ghec_v2022_11_28/types/group_0639.py
+++ b/githubkit/versions/ghec_v2022_11_28/types/group_0639.py
@@ -30,7 +30,7 @@ class WebhookCodeScanningAlertReopenedPropAlertType(TypedDict):
     ]
     dismissed_comment: NotRequired[Union[str, None]]
     dismissed_reason: Union[str, None]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     instances_url: NotRequired[str]
     most_recent_instance: NotRequired[
@@ -59,7 +59,7 @@ class WebhookCodeScanningAlertReopenedPropAlertTypeForResponse(TypedDict):
     ]
     dismissed_comment: NotRequired[Union[str, None]]
     dismissed_reason: Union[str, None]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     instances_url: NotRequired[str]
     most_recent_instance: NotRequired[
diff --git a/githubkit/versions/ghec_v2022_11_28/types/group_0641.py b/githubkit/versions/ghec_v2022_11_28/types/group_0641.py
index eaff0c9fe..b90622307 100644
--- a/githubkit/versions/ghec_v2022_11_28/types/group_0641.py
+++ b/githubkit/versions/ghec_v2022_11_28/types/group_0641.py
@@ -28,7 +28,7 @@ class WebhookCodeScanningAlertReopenedByUserPropAlertType(TypedDict):
     dismissed_by: None
     dismissed_comment: NotRequired[Union[str, None]]
     dismissed_reason: None
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
@@ -55,7 +55,7 @@ class WebhookCodeScanningAlertReopenedByUserPropAlertTypeForResponse(TypedDict):
     dismissed_by: None
     dismissed_comment: NotRequired[Union[str, None]]
     dismissed_reason: None
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
diff --git a/githubkit/versions/ghec_v2022_11_28/types/group_0643.py b/githubkit/versions/ghec_v2022_11_28/types/group_0643.py
index 17d694b79..85e04c1bb 100644
--- a/githubkit/versions/ghec_v2022_11_28/types/group_0643.py
+++ b/githubkit/versions/ghec_v2022_11_28/types/group_0643.py
@@ -32,7 +32,7 @@ class WebhookCodeScanningAlertUpdatedAssignmentPropAlertType(TypedDict):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
@@ -64,7 +64,7 @@ class WebhookCodeScanningAlertUpdatedAssignmentPropAlertTypeForResponse(TypedDic
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
diff --git a/githubkit/versions/v2022_11_28/models/group_0540.py b/githubkit/versions/v2022_11_28/models/group_0540.py
index c75ddb9d6..8b919eb32 100644
--- a/githubkit/versions/v2022_11_28/models/group_0540.py
+++ b/githubkit/versions/v2022_11_28/models/group_0540.py
@@ -46,7 +46,7 @@ class WebhookCodeScanningAlertAppearedInBranchPropAlert(GitHubModel):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ] = Field(description="The reason for dismissing or closing the alert.")
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/v2022_11_28/models/group_0542.py b/githubkit/versions/v2022_11_28/models/group_0542.py
index 15f8e6194..c2fb9a0b2 100644
--- a/githubkit/versions/v2022_11_28/models/group_0542.py
+++ b/githubkit/versions/v2022_11_28/models/group_0542.py
@@ -46,7 +46,7 @@ class WebhookCodeScanningAlertClosedByUserPropAlert(GitHubModel):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ] = Field(description="The reason for dismissing or closing the alert.")
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/v2022_11_28/models/group_0548.py b/githubkit/versions/v2022_11_28/models/group_0548.py
index 575cb4a37..7c2b1d015 100644
--- a/githubkit/versions/v2022_11_28/models/group_0548.py
+++ b/githubkit/versions/v2022_11_28/models/group_0548.py
@@ -46,7 +46,7 @@ class WebhookCodeScanningAlertReopenedPropAlert(GitHubModel):
     dismissed_reason: Union[str, None] = Field(
         description="The reason for dismissing or closing the alert. Can be one of: `false positive`, `won't fix`, and `used in tests`."
     )
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/v2022_11_28/models/group_0550.py b/githubkit/versions/v2022_11_28/models/group_0550.py
index b110bda61..fa34b19cd 100644
--- a/githubkit/versions/v2022_11_28/models/group_0550.py
+++ b/githubkit/versions/v2022_11_28/models/group_0550.py
@@ -44,7 +44,7 @@ class WebhookCodeScanningAlertReopenedByUserPropAlert(GitHubModel):
     dismissed_reason: None = Field(
         description="The reason for dismissing or closing the alert. Can be one of: `false positive`, `won't fix`, and `used in tests`."
     )
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/v2022_11_28/models/group_0552.py b/githubkit/versions/v2022_11_28/models/group_0552.py
index 644f4ef8d..a03b9c606 100644
--- a/githubkit/versions/v2022_11_28/models/group_0552.py
+++ b/githubkit/versions/v2022_11_28/models/group_0552.py
@@ -46,7 +46,7 @@ class WebhookCodeScanningAlertUpdatedAssignmentPropAlert(GitHubModel):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ] = Field(description="The reason for dismissing or closing the alert.")
-    fixed_at: Missing[None] = Field(
+    fixed_at: Missing[Union[_dt.datetime, None]] = Field(
         default=UNSET,
         description="The time that the alert was fixed in ISO 8601 format: `YYYY-MM-DDTHH:MM:SSZ`.",
     )
diff --git a/githubkit/versions/v2022_11_28/types/group_0540.py b/githubkit/versions/v2022_11_28/types/group_0540.py
index dc50f2cfa..d82927834 100644
--- a/githubkit/versions/v2022_11_28/types/group_0540.py
+++ b/githubkit/versions/v2022_11_28/types/group_0540.py
@@ -32,7 +32,7 @@ class WebhookCodeScanningAlertAppearedInBranchPropAlertType(TypedDict):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
@@ -64,7 +64,7 @@ class WebhookCodeScanningAlertAppearedInBranchPropAlertTypeForResponse(TypedDict
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
diff --git a/githubkit/versions/v2022_11_28/types/group_0542.py b/githubkit/versions/v2022_11_28/types/group_0542.py
index 9821e77a8..7318acbc2 100644
--- a/githubkit/versions/v2022_11_28/types/group_0542.py
+++ b/githubkit/versions/v2022_11_28/types/group_0542.py
@@ -32,7 +32,7 @@ class WebhookCodeScanningAlertClosedByUserPropAlertType(TypedDict):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
@@ -70,7 +70,7 @@ class WebhookCodeScanningAlertClosedByUserPropAlertTypeForResponse(TypedDict):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
diff --git a/githubkit/versions/v2022_11_28/types/group_0548.py b/githubkit/versions/v2022_11_28/types/group_0548.py
index ae3b8f28c..53ad19146 100644
--- a/githubkit/versions/v2022_11_28/types/group_0548.py
+++ b/githubkit/versions/v2022_11_28/types/group_0548.py
@@ -30,7 +30,7 @@ class WebhookCodeScanningAlertReopenedPropAlertType(TypedDict):
     ]
     dismissed_comment: NotRequired[Union[str, None]]
     dismissed_reason: Union[str, None]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     instances_url: NotRequired[str]
     most_recent_instance: NotRequired[
@@ -59,7 +59,7 @@ class WebhookCodeScanningAlertReopenedPropAlertTypeForResponse(TypedDict):
     ]
     dismissed_comment: NotRequired[Union[str, None]]
     dismissed_reason: Union[str, None]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     instances_url: NotRequired[str]
     most_recent_instance: NotRequired[
diff --git a/githubkit/versions/v2022_11_28/types/group_0550.py b/githubkit/versions/v2022_11_28/types/group_0550.py
index eaff0c9fe..b90622307 100644
--- a/githubkit/versions/v2022_11_28/types/group_0550.py
+++ b/githubkit/versions/v2022_11_28/types/group_0550.py
@@ -28,7 +28,7 @@ class WebhookCodeScanningAlertReopenedByUserPropAlertType(TypedDict):
     dismissed_by: None
     dismissed_comment: NotRequired[Union[str, None]]
     dismissed_reason: None
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
@@ -55,7 +55,7 @@ class WebhookCodeScanningAlertReopenedByUserPropAlertTypeForResponse(TypedDict):
     dismissed_by: None
     dismissed_comment: NotRequired[Union[str, None]]
     dismissed_reason: None
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
diff --git a/githubkit/versions/v2022_11_28/types/group_0552.py b/githubkit/versions/v2022_11_28/types/group_0552.py
index 17d694b79..85e04c1bb 100644
--- a/githubkit/versions/v2022_11_28/types/group_0552.py
+++ b/githubkit/versions/v2022_11_28/types/group_0552.py
@@ -32,7 +32,7 @@ class WebhookCodeScanningAlertUpdatedAssignmentPropAlertType(TypedDict):
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[_dt.datetime, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
@@ -64,7 +64,7 @@ class WebhookCodeScanningAlertUpdatedAssignmentPropAlertTypeForResponse(TypedDic
     dismissed_reason: Union[
         None, Literal["false positive", "won't fix", "used in tests"]
     ]
-    fixed_at: NotRequired[None]
+    fixed_at: NotRequired[Union[str, None]]
     html_url: str
     most_recent_instance: NotRequired[
         Union[
diff --git a/githubkit/versions/versions.lock b/githubkit/versions/versions.lock
index 3a9f0c7d8..b29cb2282 100644
--- a/githubkit/versions/versions.lock
+++ b/githubkit/versions/versions.lock
@@ -143,6 +143,11 @@ source = "https://raw.githubusercontent.com/github/rest-api-description/ee16ba11
 "/components/schemas/webhook-workflow-run-requested/properties/workflow_run/properties/pull_requests/items/properties/number" = {type = "integer"}
 "/components/schemas/webhook-code-scanning-alert-fixed/properties/alert/properties/fixed_at" = {type = ["string", "null"], format = "date-time"}
 "/components/schemas/webhook-code-scanning-alert-fixed/properties/alert/properties/state/enum" = {"<add>" = ["dismissed"]}
+"/components/schemas/webhook-code-scanning-alert-closed-by-user/properties/alert/properties/fixed_at" = {type = ["string", "null"], format = "date-time"}
+"/components/schemas/webhook-code-scanning-alert-appeared-in-branch/properties/alert/properties/fixed_at" = {type = ["string", "null"], format = "date-time"}
+"/components/schemas/webhook-code-scanning-alert-reopened/properties/alert/properties/fixed_at" = {type = ["string", "null"], format = "date-time"}
+"/components/schemas/webhook-code-scanning-alert-reopened-by-user/properties/alert/properties/fixed_at" = {type = ["string", "null"], format = "date-time"}
+"/components/schemas/webhook-code-scanning-alert-updated-assignment/properties/alert/properties/fixed_at" = {type = ["string", "null"], format = "date-time"}
 "/webhooks/repository-dispatch-sample.collected/post" = {operationId = "repository-dispatch"}
 "/components/schemas/webhooks_answer/properties/parent_id" = {type = ["integer", "null"]}
 "/components/schemas/dependabot-alert-with-repository/properties/dependency/properties/relationship/enum" = {"<add>" = ["inconclusive"]}
diff --git a/pyproject.toml b/pyproject.toml
index 91cae4a62..840937772 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -561,6 +561,29 @@ source = "descriptions-next/ghec/ghec.2022-11-28.json"
 "/components/schemas/webhook-code-scanning-alert-fixed/properties/alert/properties/state/enum" = { "<add>" = [
   "dismissed",
 ] }
+# https://github.com/yanyongyu/githubkit/issues/279
+# https://github.com/github/rest-api-description/issues/6081
+"/components/schemas/webhook-code-scanning-alert-closed-by-user/properties/alert/properties/fixed_at" = { type = [
+  "string",
+  "null",
+], format = "date-time" }
+# other same issues
+"/components/schemas/webhook-code-scanning-alert-appeared-in-branch/properties/alert/properties/fixed_at" = { type = [
+  "string",
+  "null",
+], format = "date-time" }
+"/components/schemas/webhook-code-scanning-alert-reopened/properties/alert/properties/fixed_at" = { type = [
+  "string",
+  "null",
+], format = "date-time" }
+"/components/schemas/webhook-code-scanning-alert-reopened-by-user/properties/alert/properties/fixed_at" = { type = [
+  "string",
+  "null",
+], format = "date-time" }
+"/components/schemas/webhook-code-scanning-alert-updated-assignment/properties/alert/properties/fixed_at" = { type = [
+  "string",
+  "null",
+], format = "date-time" }
 
 # webhook repository dispatch action can be any string
 "/webhooks/repository-dispatch-sample.collected/post" = { operationId = "repository-dispatch" }