Reddit Inc. will be added to the S&P 500 next week as part of an off-cycle change, S&P Dow Jones Indices said Thursday. The announcement sent the social networking platform's shares surging more than 10% in after-hours trading. The inclusion reflects Reddit's growing market value and marks a milestone for the company, which went public last year. The stock jump came after the close of regular trading, following the index provider's announcement. Reddit will officially become a component of the S&P 500 on the scheduled date next week, as determined by the index committee. The move is expected to increase demand for Reddit's shares, as index funds tracking the S&P 500 will need to buy the stock to match the index composition.