New users in New Zealand and the Philippines will have to cough up $1 (£0.82) a year to access key features including the ability to tweet, retweet, like posts and reply to posts as part of a new trial.
Those who opt out of the subscription fee will only be able to read posts, watch videos and follow accounts.
The social media platform said that the aim is to "reduce spam, manipulation of our platform and bot activity".
New accounts will also be required to verify their phone number, though Musk has said that it will still be free to create "read only" accounts, which do not have key features.
Meanwhile, last month he suggested that all X users may have to pay for access so it is all getting potentially expensive.