Before the market opened on December 11, Ares Management — a private-credit powerhouse with nearly $600 billion under management — slid into the S&P 500, replacing Kellanov. Kellanov completed its $35.9 billion sale to Mars that day.
In the SmallCap 600, Vital Farms replaced Heidrick & Struggles after the executive-search firm closed its $1.3 billion take-private one day earlier. In two years, Blackstone, KKR, Apollo and now Ares have turned alternative asset managers into core S&P 500 holdings, while classic consumer and professional-services names are taken private. Trillions in index-tracking money now flows more directly into private-credit risk — just as regulators launch the first major stress test of the sector.
The Bank of England's December 2025 exercise, involving all four S&P-listed alternative giants, signals that the U.S. stock market has quietly tilted toward Wall Street's dealmakers as their business model faces unprecedented scrutiny.
11 events
Latest: December 11th, 2025 · 5 months ago
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December 2025
Ares enters S&P 500; Kellanova and Heidrick exit key indexes
LatestMarket Event
Before the U.S. market opens, Ares Management officially joins the S&P 500, displacing Kellanova as Mars prepares to close its acquisition. In parallel, Vital Farms joins the S&P SmallCap 600 in place of Heidrick & Struggles. Index‑tracking and benchmark‑aware investors rebalance, sending fresh flows into Ares and Vital Farms and out of the departing names.
Mars formally closes $35.9 billion Kellanova acquisition
M&A
Mars completes its purchase of Kellanova the same day the snack company exits the S&P 500, creating a combined snacking business with $36 billion in annual revenues, 9 billion-dollar brands, and operations in more than 145 markets with 50,000 employees. Mars Snacking will be headquartered in Chicago.
Heidrick & Struggles closes its all‑cash sale to Advent International and Corvex Private Equity one day ahead of its removal from the S&P SmallCap 600, earlier than the initially expected Q1 2026 timeline. The 70‑year‑old executive search firm's common stock ceases trading on Nasdaq. Former EY Global Chair Carmine Di Sibio joins as Chairman of the Board of Managers.
EU signs off on Mars–Kellanova deal; S&P announces Ares index switch
Regulatory / Index Change
The European Commission clears Mars’s $36 billion Kellanova takeover, removing the last major antitrust obstacle and allowing closing on December 11. That same day, S&P Dow Jones Indices announces that Ares will replace Kellanova in the S&P 500, while Vital Farms will replace Heidrick & Struggles in the S&P SmallCap 600.
Bank of England launches major private credit stress test
Regulatory
The Bank of England begins its second system‑wide exploratory scenario exercise, focused on how private markets operate under stress and their implications for UK financial stability. Participants include all four S&P 500‑listed alternative managers — Ares, Blackstone, KKR and Apollo — plus Goldman Sachs, Carlyle, CVC, Bain Capital, ICG and Permira. The exercise will run through 2026 with a final report in early 2027, marking the first comprehensive regulatory stress test of the $16 trillion global private markets sector.
October 2025
Advent and Corvex strike $1.3 billion deal to take Heidrick private
M&A
Heidrick & Struggles agrees to an all‑cash take‑private led by Advent International and Corvex Private Equity at $59 per share. The deal continues a resurgence in private-equity buyouts and sets up Heidrick’s removal from the S&P SmallCap 600 once the transaction closes.
January 2025
S&P raises size thresholds for index additions
Rules
S&P Dow Jones Indices hikes the required unadjusted market cap for new S&P 500 additions to $20.5 billion, with higher bands for the MidCap 400 and SmallCap 600. The change makes it harder for smaller companies to graduate into the benchmarks and entrenches today’s large‑cap leaders.
December 2024
Apollo Global Management added to S&P 500
Index Change
S&P Dow Jones Indices slots Apollo and Workday into the S&P 500, removing Qorvo and Amentum. With Apollo joining Blackstone and KKR, alternative asset managers become a visible cluster within the index’s financials sector.
August 2024
Mars agrees to buy Kellanova in $35.9 billion snacks megadeal
M&A
Mars announces a cash deal to acquire Kellanova, the Kellogg spinoff behind Pringles and Cheez‑It, for $83.50 a share. The transaction, among the snack sector’s largest, sets up Kellanova’s eventual removal from major indexes once regulatory approvals arrive.
June 2024
KKR joins S&P 500 at June 2024 rebalance
Index Change
At its June rebalance, S&P adds KKR, CrowdStrike and GoDaddy to the S&P 500 and removes Robert Half, Comerica and Illumina. The move deepens the index’s exposure to private equity and private credit via KKR’s diversified platform.
September 2023
Blackstone becomes first mega private-equity firm in S&P 500
Index Change
S&P Dow Jones Indices adds Blackstone and Airbnb to the S&P 500 at the quarterly rebalance, booting Lincoln National and Newell Brands. It’s the first time a giant listed private‑equity group joins the benchmark, signaling that alternative managers have grown too big to ignore.
Historical Context
3 moments from history that rhyme with this story — and how they unfolded.
1 of 3
2007
Blackstone’s 2007 IPO: Private Equity Steps Onto Public Markets
Blackstone went public in June 2007, near the peak of the pre‑crisis buyout boom. The offering crystalized huge founder wealth and gave public investors direct exposure to private equity’s fee streams and carry, even as critics warned about cyclicality and opacity.
Then
The stock initially struggled through the financial crisis as deal activity and valuations collapsed, reinforcing fears about cyclicality.
Now
Blackstone rebounded, crossed $1 trillion in AUM, and eventually earned S&P 500 membership in 2023, legitimizing private equity as a core public‑market sector.
Why this matters now
Ares’s S&P 500 entry is the logical next step in a journey that began when firms like Blackstone first invited public shareholders into the private‑markets business model.
2 of 3
2020
Tesla Joins the S&P 500, Supercharging Passive Flows Into a Single Stock
After years of debate, S&P Dow Jones Indices added Tesla to the S&P 500 in December 2020, forcing index funds and closet trackers to buy tens of billions of dollars’ worth of stock. The move intensified scrutiny of how index decisions anoint winners and shape flows.
Then
Tesla’s inclusion triggered significant rebalancing volume and highlighted how concentrated bets can become when a popular stock enters a major index.
Now
The episode cemented public awareness that index construction is an active choice with market consequences, not a neutral mirror of the economy.
Why this matters now
Ares’s inclusion similarly channels passive flows into a specialized, controversial business model — private credit — underscoring how index committees now shape exposure to entire financial structures.
3 of 3
1999–2000
Dot‑Com Darlings Flood the S&P 500 Before the 2000 Crash
During the late 1990s tech boom, S&P and other indices added a wave of high‑flying internet and telecom stocks. Many soon collapsed when the bubble burst, leaving passive investors overexposed to a frothy sector at the worst possible time.
Then
Index investors suffered steep losses as speculative names imploded, prompting questions about whether inclusions had come too late in the cycle.
Now
Index providers refined profitability and liquidity screens, but the episode left a lasting lesson: sector waves can distort benchmarks just as they peak.
Why this matters now
Today’s rise of alternative asset managers and private credit in the S&P 500 raises a similar question: are benchmarks baking in a boom sector just as its risks become systemic?
