How to license 2021 using Language Cloud Trados Live subscription. 
Activating Trados Studio with a cloud subscription
Subscription licensing
Starting with SDL Trados Studio 2021, you can also activate Trados Studio Freelance and Professional with a subscription available for any of the SDL cloud offerings: SDL Trados Live Essential, SDL Trados Live Team or SDL Language Cloud Translation Management .
Subscriptions benefits
- access to cloud projects
 - access to the Online Editor to translate and review cloud project files from a browser
 - access to Trados Live mobile app to work on cloud projects from your tablet or smartphone
 - lower entry price and the ability to pay-as-you-go
 - receive first all the latest features, fixes and security updates
 
Activating Trados Studio with a cloud subscription
If you are member of a cloud account that includes a Trados Studio license, you can activate the latest version of Trados Studio when connecting to a cloud account from Trados Studio.
- Open Trados Studio:
- If you are using a Trial or an unlicensed version, Trados Studio displays the Product Activation window.
 - If you have a perpetual license and you want to switch to a subscription, open the Help tab > Product activation. Deactivate your current license and select the Language Cloud Subscription tab.
 
 - Click the Language Cloud Subscription tab in the SDL Trados Studio 2021 Product Activation window.
 - Enter the email address and password associated with your cloud account and click Log In. Trados Studio shows all the cloud accounts that you are a member of.
 - Select the account corresponding to the cloud project on which you want to work and which includes a Trados Studio license. To review the resources available for the selected account, click on the name of the Language Cloud package.
 - If the selected account includes a Trados Studio license and you are currently using an unlicensed version, an Activate button is displayed. Click this to license Trados Studio and show your cloud subscription type.
 - Click OK to close the window and restart Trados Studio with the new subscription license.
 
See this article with screenshots:
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