Twitter Inc is building a new feature that will allow users to post tweets as long as 10,000 characters, technology news website Re/code reported on Tuesday.Twitter, which currently has a 140-character limit, may launch the service toward the end of the first quarter but has not set an official date, Re/code reported, citing sources familiar with the plans.The sources said the character limit could change before the final version of the product is unveiled.The micro-blogging website, in an attempt to keep the current look for the Twitter timeline, is testing a version of the product which displays 140-character long tweets but expands to reveal more content when users click on the tweet, Re/code said.Twitter has been experimenting under Jack Dorsey - the company's co-founder who returned as chief executive in October - to make the service more engaging.In the few months under Dorsey, Twitter introduced the 'Momentstarget="_blank"'>