Twitter has freed up more of the 140 characters by removing @usernames from the reply post count.
In simple terms, you're getting the full 140 characters.

Who you are replying to will appear above the Tweet text rather than within the Tweet text itself, so you have more characters to have conversations.

You can tap on “Replying to…” to easily see and control who’s part of your conversation.

When reading a conversation, you’ll actually see what people are saying, rather than seeing lots of @usernames at the start of a Tweet.

[blog.twitter.com...]