New Delhi, Aug. 14 -- Shares of social networking platform Reddit gained 15% at the Wall Street opening bell, surging to around $181.70 apiece, after the company is set to join the S&P 500 next week upon meeting the benchmark's eligibility requirements.

The inclusion is part of an off-cycle change that will see Reddit replace AvalonBay Communities (AVB), which is being acquired by existing index member Equity Residential.

Since the development does not reflect any change in the company's fundamentals, stocks often gain following index inclusion, as fund managers tracking the benchmark are required to buy shares to align their portfolios with the index changes.

Reddit will be added to the benchmark index before the start of trading on 1...