Duolingo had a user base of around 3 million. By July 2013, the service had grown to 5 million users and was rated the #1 free education app in the Google Play store. In February 2014, Duolingo announced that it had raised $20 million from a Series C funding round led by Kleiner Caufield & Byers, with prior investors also participating. At this time, Duolingo had 34 employees and reported having about 25 million registered users and 12.5 million active users, though it later reported a figure closer to 60 million users. In June 2015, Duolingo announced that it had raised $45 million from a Series D funding round led by Google Capital, bringing its total funding to $83.3 million. The round valued the company at around $470 million, with 100 million registered users globally. In April 2016, it was reported that Duolingo had more than 18 million monthly users. In July 2017, Duolingo announced that it had raised $25 million in a Series E funding round led by Drive Capital, bringing its total funding to $108.3 million. The round valued Duolingo at $700 million, and the company reported passing 200 million registered users, with 25 million active users. It was reported that Duolingo had 95 employees. Funds from the Series E round would be directed toward creating initiatives such as a related educational flashcard app, TinyCards, and testbeds for initiatives related to reading and listening comprehension. On 1 August 2018, Duolingo surpassed 300 million registered users. In December 2019, it was announced that Duolingo raised $30 million in a Series F funding round from Alphabet's investment company CapitalG. The round valued Duolingo at $1.5 billion. Duolingo reported 30 million active users at this time. Headcount at the company had increased to 200, and new offices had been opened in Seattle, New York and Beijing. Duolingo planned to use the funds to develop new products and further expand its team in sectors like engineering, business development, design, curriculum and content creators, community outreach, and marketing. In October 2013, Duolingo launched a crowdsourced language incubator. In March 2021, Duolingo announced that it will be ending its volunteer contributor program and donating money to its volunteer contributors who helped to make Duolingo. The company said that from now on, language courses will be maintained and developed by professional linguists aligning with CEFR standards. On 28 June 2021, Duolingo filed for an initial