diff --git a/readthedocs/doc_builder/director.py b/readthedocs/doc_builder/director.py
index 11de6c27b4f..ad842e4bdc7 100644
--- a/readthedocs/doc_builder/director.py
+++ b/readthedocs/doc_builder/director.py
@@ -8,6 +8,7 @@
 * fetching instructions etc.
 """
 
+import datetime
 import os
 import tarfile
 
@@ -216,12 +217,20 @@ def checkout(self):
                 self.data.api_client.project(self.data.project.pk).patch(
                     {"has_ssh_key_with_write_access": has_ssh_key_with_write_access}
                 )
+
+            now = datetime.datetime.now(tz=datetime.timezone.utc)
+            hard_failure = now >= datetime.datetime(
+                2025, 12, 1, 0, 0, 0, tzinfo=datetime.timezone.utc
+            )
             if has_ssh_key_with_write_access:
-                self.attach_notification(
-                    attached_to=f"project/{self.data.project.pk}",
-                    message_id=MESSAGE_PROJECT_SSH_KEY_WITH_WRITE_ACCESS,
-                    dismissable=True,
-                )
+                if hard_failure and settings.RTD_ENFORCE_BROWNOUTS_FOR_DEPRECATIONS:
+                    raise BuildUserError(BuildUserError.SSH_KEY_WITH_WRITE_ACCESS)
+                else:
+                    self.attach_notification(
+                        attached_to=f"project/{self.data.project.pk}",
+                        message_id=MESSAGE_PROJECT_SSH_KEY_WITH_WRITE_ACCESS,
+                        dismissable=True,
+                    )
 
         identifier = self.data.build_commit or self.data.version.identifier
         log.info("Checking out.", identifier=identifier)
diff --git a/readthedocs/notifications/messages.py b/readthedocs/notifications/messages.py
index a2018b91983..d93cfdf1d04 100644
--- a/readthedocs/notifications/messages.py
+++ b/readthedocs/notifications/messages.py
@@ -226,7 +226,7 @@ def get_rendered_body(self):
                 """
                 This build has failed because the current deploy key on the repository was created with write permission.
                 For protection against abuse we've restricted use of these deploy keys.
-                A read-only deploy key will need to be set up <b>before July 31, 2025</b> to continue building this project.
+                A read-only deploy key will need to be set up <b>before December 1st, 2025</b> to continue building this project.
                 Read more about this in our <a href="https://about.readthedocs.com/blog/2025/07/ssh-keys-with-write-access/">blog post</a>.
                 """
             ).strip(),
diff --git a/readthedocs/projects/notifications.py b/readthedocs/projects/notifications.py
index 9b9e5d43e7a..a6bd1085308 100644
--- a/readthedocs/projects/notifications.py
+++ b/readthedocs/projects/notifications.py
@@ -186,7 +186,7 @@
                 """
                 This project has a deploy key with write access to the repository.
                 For protection against abuse we've restricted use of these deploy keys.
-                A read-only deploy key will need to be set up <b>before July 31, 2025</b> to continue building this project.
+                A read-only deploy key will need to be set up <b>before December 1st, 2025</b> to continue building this project.
                 Read more about this in our <a href="https://about.readthedocs.com/blog/2025/07/ssh-keys-with-write-access/">blog post</a>.
                 """
             ).strip(),