Yes. If you're developing or making use of a project that uses our v3 API, you're still able to obtain a legacy v3 key to access TheTVDB's metadata via a subscription to the site. 

To obtain a legacy key, head to the subscribe page and follow the steps to create a subscription. Along with a legacy v3 key, your subscription will also provide you with a user PIN that you can use in conjunction with any user-supported v4 API key.