AcmeDemoBundle.php

<?php
namespace Acme\DemoBundle;
use Symfony\Component\HttpKernel\Bundle\Bundle;

class AcmeDemoBundle extends Bundle
{
}

config.yml

jms_serializer:
    metadata:
        auto_detection: true
        cache: array
        debug: "%kernel.debug%"
        file_cache:
            dir: "%kernel.cache_dir%/serializer"
        directories:
            AcmeDemoBundle:
                namespace_prefix: Acme\\DemoBundle
                path: "@AcmeDemoBundle/Resources/config/serializer"

Model.Something.yml

# Acme/DemoBundle/Resources/config/serializer/Model.Something.yml

Acme\DemoBundle\Model\Something:
    exclusion_policy: ALL