You must to go in the Setup Tabs and in the left menu Extension. Here, you must to re-generate the autoload arrays for active extensions. There is a new button for that.
You could expect that a fresh installation would have the autoloads pregenerated, but the fact is that you should consider autoload regeneration a basic step of every system PHP modification, upgrade or extension. It would be wise to check it on installation as well.
I have the same problem on ez 4.1.3 upgrade from 4.0.3. I have downloaded the version with ezc bundle. I have run the command: php bin/php/ezpgenerateautoloads.php -e
the output is:
Scanning for PHP-files.
Scan complete. Found 117 PHP files.
Searching for classes (tokenizing).
Found 40 classes, added 40 of them to the autoload array.
But the online editor dosn't works. I think I have a ezc installation problem.