SEI Stock Jumps 5% After-Hours As S&P 600 Inclusion Sparks Buying

SEI will replace Catalyst Pharmaceuticals in the index, effective prior to the open of trading on Wednesday, July 15.

• The change follows Angelini Pharma S.p.A.’s pending acquisition of Catalyst. 
• SEI has already seen strong momentum this year, driven by its growing Power Solutions business.
• Solaris is scheduled to report second-quarter 2026 results later this month.

Shares of Solaris Energy Infrastructure, Inc. (SEI) rose 5% in after-hours trading on Thursday after S&P Dow Jones Indices announced that the company will join the S&P SmallCap 600 Index.

SEI will replace Catalyst Pharmaceuticals (CPRX) in the index, effective prior to the open of trading on Wednesday, July 15. The change follows Angelini Pharma S.p.A.’s pending acquisition of Catalyst, a deal expected to close soon, subject to final conditions.

Impact On SEI Stock

When a company is acquired and expected to be taken private or delisted, S&P removes it from the benchmark and adds a replacement that meets the index’s size, liquidity, and profitability criteria. Index inclusions often trigger short-term buying from passive funds and ETFs that track the S&P SmallCap 600.

SEI has already seen strong momentum this year, driven by its growing Power Solutions business, which supplies modular power generation equipment for data centers and other high-demand applications. The company has secured multiple long-term contracts with major technology customers, totaling more than 2 GW of capacity.

In early July, Solaris acquired Global Energy Services Alliance (GESA), a specialized power generation services company, for roughly $55 million in cash plus stock, adding operations, maintenance, and technical service expertise. Earlier in May, it raised approximately $2 billion through a senior notes offering.

In the first quarter of 2026, Solaris reported revenue of $196 million and adjusted core profit of approximately $84 million, representing year-over-year growth of 79%. For the full year 2025, revenue nearly doubled while adjusted core profit jumped 137% to $244 million, reflecting strong execution on new power contracts. Solaris is scheduled to report second-quarter 2026 results later this month.

How Did SEI Retail Traders React?

On Stocktwits, retail sentiment around SEI stock stayed within the bearish territory over the past 24 hours, while message volume stayed at normal levels.

According to data from Koyfin, 13 of the 14 analysts covering SEI stock rate it ‘Buy’ or higher, while one rates it ‘Hold.’ The stock has a 12-month average price target of $94.34, representing a potential upside of 38% from its Thursday’s closing price.

SEI stock has gained about 48% year-to-date. 

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