diff --git a/readthedocs/projects/tasks/search.py b/readthedocs/projects/tasks/search.py
index 4168fb61c8d..5e783115e84 100644
--- a/readthedocs/projects/tasks/search.py
+++ b/readthedocs/projects/tasks/search.py
@@ -203,7 +203,9 @@ def _create_imported_files_and_search_index(
 
             # Create the imported file only if it's a top-level 404 file,
             # or if it's an index file. We don't need to keep track of all files.
-            if relpath == "404.html" or filename in ["index.html", "README.html"]:
+            # TODO: delete README.html from this list after deprecation.
+            tryfiles = ["index.html", "README.html"]
+            if relpath == "404.html" or filename in tryfiles:
                 html_files_to_save.append(html_file)
 
     # We first index the files in ES, and then save the objects in the DB.
diff --git a/readthedocs/proxito/views/serve.py b/readthedocs/proxito/views/serve.py
index 4f44d51fa07..fe7cdeff889 100644
--- a/readthedocs/proxito/views/serve.py
+++ b/readthedocs/proxito/views/serve.py
@@ -41,6 +41,7 @@
     ServeRedirectMixin,
     StorageFileNotFound,
 )
+from readthedocs.proxito.views.utils import allow_readme_html_as_index
 from readthedocs.redirects.exceptions import InfiniteRedirectException
 from readthedocs.storage import build_media_storage
 
@@ -641,12 +642,16 @@ def _get_index_file_redirect(self, request, project, version, filename, full_pat
         - /en/latest/foo -> /en/latest/foo/README.html
         - /en/latest/foo/ -> /en/latest/foo/README.html
         """
-        tryfiles = ["index.html", "README.html"]
-        # If the path ends with `/`, we already tried to serve
-        # the `/index.html` file, so we only need to test for
-        # the `/README.html` file.
-        if full_path.endswith("/"):
-            tryfiles = ["README.html"]
+
+        if allow_readme_html_as_index():
+            tryfiles = ["index.html", "README.html"]
+            # If the path ends with `/`, we already tried to serve
+            # the `/index.html` file, so we only need to test for
+            # the `/README.html` file.
+            if full_path.endswith("/"):
+                tryfiles = ["README.html"]
+        else:
+            tryfiles = ["index.html"]
 
         tryfiles = [
             (filename.rstrip("/") + f"/{tryfile}").lstrip("/") for tryfile in tryfiles
@@ -664,7 +669,7 @@ def _get_index_file_redirect(self, request, project, version, filename, full_pat
             log.info("Redirecting to index file.", tryfile=tryfile)
             # Use urlparse so that we maintain GET args in our redirect
             parts = urlparse(full_path)
-            if tryfile.endswith("README.html"):
+            if allow_readme_html_as_index() and tryfile.endswith("README.html"):
                 new_path = parts.path.rstrip("/") + "/README.html"
             else:
                 new_path = parts.path.rstrip("/") + "/"
diff --git a/readthedocs/proxito/views/utils.py b/readthedocs/proxito/views/utils.py
index c33a76a3833..98612b0a4c3 100644
--- a/readthedocs/proxito/views/utils.py
+++ b/readthedocs/proxito/views/utils.py
@@ -1,4 +1,8 @@
+import datetime
+
+import pytz
 import structlog
+from django.conf import settings
 from django.http import HttpResponse
 from django.shortcuts import render
 
@@ -56,3 +60,25 @@ def proxito_404_page_handler(
     )
     r.status_code = http_status
     return r
+
+
+def allow_readme_html_as_index():
+    if not settings.RTD_ENFORCE_BROWNOUTS_FOR_DEPRECATIONS:
+        return True
+
+    tzinfo = pytz.timezone("America/Los_Angeles")
+    now = datetime.datetime.now(tz=tzinfo)
+
+    # Brownout dates as published in https://about.readthedocs.com/blog/2024/05/readme-html-deprecated/
+    # fmt: off
+    return not any([
+        # 12 hours browndate
+        datetime.datetime(2024, 6, 10, 0, 0, 0, tzinfo=tzinfo) < now < datetime.datetime(2024, 6, 10, 12, 0, 0, tzinfo=tzinfo),
+        # 24 hours browndate
+        datetime.datetime(2024, 6, 17, 0, 0, 0, tzinfo=tzinfo) < now < datetime.datetime(2024, 6, 18, 0, 0, 0, tzinfo=tzinfo),
+        # 48 hours browndate
+        datetime.datetime(2024, 6, 24, 0, 0, 0, tzinfo=tzinfo) < now < datetime.datetime(2024, 6, 26, 0, 0, 0, tzinfo=tzinfo),
+        # Deprecated after July 1st
+        datetime.datetime(2024, 7, 1, 0, 0, 0, tzinfo=tzinfo) < now,
+    ])
+    # fmt: on