Two months ago, Twitter’s most dedicated fans threw a fit when news of a potentially major change in the service came to light: the 140-character limit, long one of Twitter’s defining characteristics, might be going away.

Keep calm and tweet on, Twitter loyalists. The limit is here to stay.

Jack Dorsey, co-founder and chief executive of Twitter, assuaged people’s concerns in an interview with the “Today” show on Friday, confirming that the company will keep tweets at 140 characters.

“It’s staying. It’s a good constraint for us,” Mr. Dorsey said in the interview, which took place on the 10th birthday of Twitter. “It allows for of-the-moment brevity.”

Mr. Dorsey’s response — at an economical length of 81 characters — is likely to calm the hard-core base of Twitter supporters who have been vocally resistant to any major changes to the network, home to more than 320 million regular users. For years, those in Twitter’s top ranks have been hesitant to make drastic changes to the service for fear of losing some of those most active users.