Unless you prefer to individually manage Akismet accounts in your Multisite blog farm, you’re better-off modifying your wp-config.php and adding the lines below to use a single Network key:
/** Define WordPress.com API Key */
define(‘WPCOM_API_KEY’,'your_api_key’);
Whether you Network Activate prior or after is up to you but its of course always best to do it after prepping everything.
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