An out-of-cycle rebalance in the Nasdaq 100 is adding another layer of wrinkles to stock trading with a flood of options expiring Friday.

The special index rebalance, intended to reduce the dominance of technology megacaps, may see passive investors use the last window to bring their portfolios in line with the benchmark before the changes take effect Monday. The revamp is set to boost the presence of smaller members, with two-way transactions likely reaching $60 billion, according to an estimate by Min Moon, a strategist at JPMorgan Chase & Co.

The Nasdaq 100 fell 2.5% at 3:29 p.m. Thursday — set for the biggest drop since December, while a version stripping out the market cap bias was down half of that size.

The tech-heavy index’s rejig coincides with a monthly options event at a time when traders are anxiously waiting for corporate earnings and next week’s Federal Reserve policy meeting for clues on the market’s outlook. Stocks have defied all gloom warnings this year, charging into a bull run and forcing traders to flock to bullish options to play catch-up.

About $2.4 trillion of options contracts tied to stocks and indexes are scheduled to mature, according to an estimate by Rocky Fishman, founder of derivatives analytical firm Asym 500. The event known as OpEx generally sees Wall Street managers either roll over existing positions or start new ones.

With equities mired in a summer lull — July is on course to be the second-slowest month of trading in two years, Friday’s duo events are expected to spur trading volume and violent price swings. That’d also provide an opportunity of liquidity for money managers needing to adjust big holdings.

“I would look into the illiquid stocks that are getting money added to them as opposed to the very liquid stocks that are probably going to be sold for,” said Dennis Davitt, a fund manager at Millbank Dartmoor Portsmouth. “There may be fireworks.”

Stocks slipped Thursday for the first time this week as fresh signs of labor-market resiliency bolstered the case for at least another interest-rate hike this year. Disappointing earnings from Netflix Inc. and Tesla Inc. also weighed on the market.

Read more: Meta Faces Nasdaq Cut Even Though It Missed Rebalance Level (1)

--With assistance from Sam Potter.