| Q | A | ---------------- | ----- | Bug report? | yes | Feature request? | no | BC Break report? | no | RFC? | no | Symfony version | 3.4.0-BETA4 Looks like using a custom container class was broken between 3.4-BETA3 and 3.4-BETA4. I think https://github.com/symfony/symfony/pull/24922 is the culprit. Because there is now a namespace in the generated container file, the custom container class can't be found.