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The Nintendo UK Twitter account has announced the launch date for Nintendo Switch Online. In a now deleted tweet, the social media account said it will begin on September 19, 2018, which would be September 18, 2018 in North America. It also says September 2018 Nintendo Direct will offer more information. The North American official website has also been updated with a September 18, 2018 launch date. (Thanks, Resetera!) Update: Nintendo followed up with an official announcement shortly after the deleted tweet:
#NintendoSwitchOnline memberships will start on 9/18. You can sign-up for a 7-day free trial from Nintendo #eShop at launch! We will introduce more information during the Nintendo Direct on 9/13.https://t.co/74Hzxk9spt pic.twitter.com/EJVFJH6F4I
— Nintendo of America (@NintendoAmerica) September 12, 2018
Here is a screenshot of the original tweet in question. 
Nintendo UK’s tweet also mentioned that there will be a seven-day free trial to begin with. As a reminder, the Nintendo Switch Online official website notes it will be $3.99 for one month, $7.99 for three months, $19.99 for twelve months, and $34.99 for a twelve-month family membership. The Nintendo Direct will be held at 3pm PT/5pm CT/6pm ET on September 13, 2018.
