From https://once.com/writebook

config/initializers/enable_yjit.rb

@@ -0,0 +1,11 @@
+# Automatically enable YJIT as of Ruby 3.3, as it brings very
+# sizeable performance improvements.
+
+# If you are deploying to a memory constrained environment
+# you may want to delete this file, but otherwise it's free
+# performance.
+if defined? RubyVM::YJIT.enable
+  Rails.application.config.after_initialize do
+    RubyVM::YJIT.enable
+  end
+end