Index change event
S&P SmallCap 600 Additions & Index Changes: MIR – 4th September 2025
On 4 September 2025, S&P Dow Jones Indices announced 2 index changes affecting 2 companies in the S&P SmallCap 600. Mirion Technologies replaced GMS in the S&P SmallCap 600.
Announced
2025-09-04
Effective
September 8, 2025 at 5:00:00 PM
Indexes Affected
S&P SmallCap 600
2
Index Changes in Total
1
Additions
1
Deletions
0
Companies that changed index
What happened to the prices
By the next day's close, Mirion Technologies, the only addition with price data, had peaked at +8.55%; the deletion, GMS, has no usable price data for this date. The moves are measured from the first extended-hours price after the 17:15 ET announcement.
Only Mirion Technologies has next-day prices, so there is no group to compare it with: it opened the next day at +3.05% from the first price after the announcement.
In Short
2 index changes: 1 addition and 1 deletion.
No company moved from one S&P index to another in this announcement.
Largest peak move: Mirion Technologies, +8.55% by the next day's close.
The changes, index by index
An empty cell means the company was not in the S&P family before, or left it.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
S&P SmallCap 600 Additions: Mirion Technologies (MIR)
1 company joined the S&P SmallCap 600 and 1 left, effective 9 September 2025. Mirion Technologies is new to the S&P family and GMS left the S&P family. Mirion Technologies peaked at +8.55% by the next day's close.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Mirion Technologies | MIR | S&P SmallCap 600 | 09/09/2025 |
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Price reaction
The close price is the last price before the announcement. All percentages are measured from the open price after the announcement.
S&P 500 Additions Changes
Company | Ticker | Source Index | Final Index | Close Price | Open Price at Announcement | % Change +5 min | % Change +30 min | % Change at 20:00 Hrs | % Change by Next Day Open | % Highest Change by Next Day Close |
|---|---|---|---|---|---|---|---|---|---|---|
S&P MidCap 400 Additions Changes
Company | Ticker | Source Index | Final Index | Close Price | Open Price at Announcement | % Change +5 min | % Change +30 min | % Change at 20:00 Hrs | % Change by Next Day Open | % Highest Change by Next Day Close |
|---|---|---|---|---|---|---|---|---|---|---|
S&P SmallCap 600 Additions Changes
Not a Investment Advice
Company | Ticker | Source Index | Final Index | Close Price | Open Price at Announcement | % Change +5 min | % Change +30 min | % Change at 20:00 Hrs | % Change by Next Day Open | % Highest Change by Next Day Close |
|---|---|---|---|---|---|---|---|---|---|---|
Mirion Technologies | MIR | S&P SmallCap 600 | 20.99 | 21.28 | +5.64% | +5.69% | +4.56% | +3.05% | +8.55% |
Not a Investment Advice
This page is research about past price behaviour. It is not a recommendation to buy or sell.