Index change event
S&P 500, MidCap 400 & SmallCap 600 Additions & Index Changes: CIEN, ARWR, ADT & OSW – 4th February 2026
On 4 February 2026, S&P Dow Jones Indices announced 8 index changes affecting 6 companies in the S&P 500, S&P MidCap 400 and S&P SmallCap 600. The most notable move was Ciena joining the S&P 500 from the S&P MidCap 400.
Announced
2026-02-04
Effective
February 8, 2026 at 4:00:00 PM
Indexes Affected
S&P 500, S&P MidCap 400, S&P SmallCap 600
8
Index Changes in Total
4
Additions
4
Deletions
2
Companies that changed index
What happened to the prices
By the next day's close, the 4 additions with price data had peaked at an average of +5.45%, against +0.03% for Dynavax Technologies, the only deletion with price data. The largest mover was OneSpaWorld Holdings, with a peak of +9.71%. The moves are measured from the first extended-hours price after the 17:15 ET announcement.
OneSpaWorld Holdings went against the other additions: its next-day open was +4.73% from the first price after the announcement, while the 4 additions averaged -1.16%.
In Short
8 index changes: 4 additions and 4 deletions.
2 companies moved from one S&P index to another, out of 6 in total.
Largest peak move: OneSpaWorld Holdings, +9.71% 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.
S&P 500 Additions: Ciena (CIEN)
1 company joined the S&P 500 and 1 left, effective 9 February 2026. Ciena moved up from the S&P MidCap 400 and Dayforce left the S&P family. Ciena peaked at +7.31% by the next day's close.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Ciena | CIEN | S&P MidCap 400 | S&P 500 | 02/09/2026 |
S&P MidCap 400 Additions: Arrowhead Pharmaceuticals (ARWR)
1 company joined the S&P MidCap 400 and 1 left, effective 9 February 2026. Arrowhead Pharmaceuticals moved up from the S&P SmallCap 600 and Ciena moved up to the S&P 500. Arrowhead Pharmaceuticals peaked at +2.23% by the next day's close.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Arrowhead Pharmaceuticals | ARWR | S&P SmallCap 600 | S&P MidCap 400 | 02/09/2026 |
S&P SmallCap 600 Additions: ADT (ADT) and OneSpaWorld Holdings (OSW)
2 companies joined the S&P SmallCap 600 and 2 left, effective 9 and 10 February 2026. ADT and OneSpaWorld Holdings are new to the S&P family; Arrowhead Pharmaceuticals moved up to the S&P MidCap 400; Dynavax Technologies left the S&P family. The 2 additions with price data peaked at an average of +6.12% by the next day's close, led by OneSpaWorld Holdings at +9.71%.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
ADT | ADT | S&P SmallCap 600 | 02/09/2026 | |
OneSpaWorld Holdings | OSW | S&P SmallCap 600 | 02/10/2026 |
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 |
|---|---|---|---|---|---|---|---|---|---|---|
Ciena | CIEN | S&P MidCap 400 | S&P 500 | 253.50 | 264.20 | +2.62% | +0.23% | -0.70% | -8.16% | +7.31% |
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 |
|---|---|---|---|---|---|---|---|---|---|---|
Arrowhead Pharmaceuticals | ARWR | S&P SmallCap 600 | S&P MidCap 400 | 68.06 | 68.00 | -0.96% | +0.09% | +1.03% | -1.47% | +2.23% |
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 |
|---|---|---|---|---|---|---|---|---|---|---|
ADT | ADT | S&P SmallCap 600 | 7.75 | 7.92 | +1.64% | +2.40% | +2.03% | +0.25% | +2.53% | |
OneSpaWorld Holdings | OSW | S&P SmallCap 600 | 20.07 | 20.40 | +3.38% | +3.73% | +6.62% | +4.73% | +9.71% |
Not a Investment Advice
This page is research about past price behaviour. It is not a recommendation to buy or sell.