diff --git a/config/feature_flags/development/highlight_diffs_optimize_memory_usage.yml b/config/feature_flags/development/highlight_diffs_optimize_memory_usage.yml
deleted file mode 100644
index fb480d2fc9378aef577f99ce4320d5d807d8cb7e..0000000000000000000000000000000000000000
--- a/config/feature_flags/development/highlight_diffs_optimize_memory_usage.yml
+++ /dev/null
@@ -1,8 +0,0 @@
----
-name: highlight_diffs_optimize_memory_usage
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/92456
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/367890
-milestone: '15.3'
-type: development
-group: group::source code
-default_enabled: false
diff --git a/lib/gitlab/diff/highlight_cache.rb b/lib/gitlab/diff/highlight_cache.rb
index 88f396fa7b919bf3cdaac6e4f231b6dfc1018ba9..7cfe0086f57a70490a6df77216c7217e87c8eb6c 100644
--- a/lib/gitlab/diff/highlight_cache.rb
+++ b/lib/gitlab/diff/highlight_cache.rb
@@ -7,7 +7,6 @@ class HighlightCache
       include Gitlab::Utils::StrongMemoize
 
       EXPIRATION = 1.day
-      PREVIOUS_EXPIRATION_PERIOD = 7.days
       VERSION = 2
 
       delegate :diffable,     to: :@diff_collection
@@ -75,28 +74,14 @@ def key
             Feature.enabled?(:use_marker_ranges, diffable.project),
             Feature.enabled?(:diff_line_syntax_highlighting, diffable.project)
           ]
+          options_for_key = OpenSSL::Digest::SHA256.hexdigest(options.join)
 
-          options_for_key =
-            if Feature.enabled?(:highlight_diffs_optimize_memory_usage, diffable.project)
-              [OpenSSL::Digest::SHA256.hexdigest(options.join)]
-            else
-              options
-            end
-
-          ['highlighted-diff-files', diffable.cache_key, VERSION, *options_for_key].join(":")
+          ['highlighted-diff-files', diffable.cache_key, VERSION, options_for_key].join(":")
         end
       end
 
       private
 
-      def expiration_period
-        if Feature.enabled?(:highlight_diffs_optimize_memory_usage, diffable.project)
-          EXPIRATION
-        else
-          PREVIOUS_EXPIRATION_PERIOD
-        end
-      end
-
       def set_highlighted_diff_lines(diff_file, content)
         diff_file.highlighted_diff_lines = content.map do |line|
           Gitlab::Diff::Line.safe_init_from_hash(line)
@@ -153,7 +138,7 @@ def write_to_redis_hash(hash)
 
             # HSETs have to have their expiration date manually updated
             #
-            redis.expire(key, expiration_period)
+            redis.expire(key, EXPIRATION)
           end
 
           record_memory_usage(fetch_memory_usage(redis, key))
diff --git a/spec/lib/gitlab/diff/highlight_cache_spec.rb b/spec/lib/gitlab/diff/highlight_cache_spec.rb
index 4a8b338506dabe4dc80dcd81dcd7ab208faa198b..1d1ffc8c2758f48b7ac0b554921d3798f6d40f2a 100644
--- a/spec/lib/gitlab/diff/highlight_cache_spec.rb
+++ b/spec/lib/gitlab/diff/highlight_cache_spec.rb
@@ -127,20 +127,6 @@
 
       cache.write_if_empty
     end
-
-    context 'when highlight_diffs_optimize_memory_usage is disabled' do
-      before do
-        stub_feature_flags(highlight_diffs_optimize_memory_usage: false)
-      end
-
-      it 'sets the previous expiration period' do
-        Gitlab::Redis::Cache.with do |redis|
-          expect(redis).to receive(:expire).with(cache.key, described_class::PREVIOUS_EXPIRATION_PERIOD)
-        end
-
-        cache.write_if_empty
-      end
-    end
   end
 
   describe '#write_if_empty' do
@@ -304,15 +290,5 @@ def options_hash(options_array)
         is_expected.to eq("highlighted-diff-files:#{cache.diffable.cache_key}:2:#{options_hash([cache.diff_options, true, false])}")
       end
     end
-
-    context 'when highlight_diffs_optimize_memory_usage is disabled' do
-      before do
-        stub_feature_flags(highlight_diffs_optimize_memory_usage: false)
-      end
-
-      it 'uses the options hash as a part of the cache key' do
-        is_expected.to eq("highlighted-diff-files:#{cache.diffable.cache_key}:2:#{cache.diff_options}:true:true")
-      end
-    end
   end
 end