You gotta optimize your autoloader, yo.

package_manager/src/StageBase.php

@@ -445,18 +445,18 @@ abstract class StageBase implements LoggerAwareInterface {
     // the installed packages yet.
     if ($runtime) {
       self::validateRequirements($runtime);
-      $command = array_merge(['require', '--no-update'], $runtime);
+      $command = array_merge(['require', '--no-update', '--optimize-autoloader'], $runtime);
       $do_stage($command);
     }
     if ($dev) {
       self::validateRequirements($dev);
-      $command = array_merge(['require', '--dev', '--no-update'], $dev);
+      $command = array_merge(['require', '--dev', '--no-update', '--optimize-autoloader'], $dev);
       $do_stage($command);
     }
 
     // If constraints were changed, update those packages.
     if ($runtime || $dev) {
-      $command = array_merge(['update', '--with-all-dependencies'], $runtime, $dev);
+      $command = array_merge(['update', '--with-all-dependencies', '--optimize-autoloader'], $runtime, $dev);
       $do_stage($command);
     }
     $this->dispatch(new PostRequireEvent($this, $runtime, $dev));