GTM4WP For Developers
If you are a theme author or other 3rd party plugin author, here are some articles about how you can extend GTM4WP and what you need to do in order to keep your theme compatible with GTM4WP.
Google Tag Manager Environments
Setup GTM environments to separate your production environment from your developer and sandbox sites.
Hard code GTM parameters
Set your Google Tag Manager container and environment parameters in wp-config.php