Index change event
S&P 500, MidCap 400 & SmallCap 600 Additions & Index Changes: TWLO, VYLR, CTVA, FORM, OLN & WK – 1st October 2026
On 1 October 2026, S&P Dow Jones Indices announced 12 index changes affecting 8 companies in the S&P 500, S&P MidCap 400 and S&P SmallCap 600. The most notable move was Vylor joining the S&P 500.
Announced
2026-10-01
Effective
September 30, 2026 at 5:00:00 PM
Indexes Affected
S&P 500, S&P MidCap 400, S&P SmallCap 600
12
Index Changes in Total
6
Additions
6
Deletions
4
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 +3.81%, against +2.01% for the 4 deletions. The largest mover was Corteva, with a peak of +4.48%. The moves are measured from the first extended-hours price after the announcement, except for 1 name with no recorded trade after 17:15 ET, measured from the 16:00 ET close.
Vylor went against the other additions: its next-day open was -1.42% from the post-announcement price, while the 4 additions averaged +0.68%.
In Short
12 index changes: 6 additions and 6 deletions.
4 companies moved from one S&P index to another, out of 8 in total.
Largest peak move: Corteva, +4.48% 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: Twilio (TWLO) and Vylor (VYLR)
2 companies joined the S&P 500 and 2 left, effective 1 and 6 October 2026. Twilio moved up from the S&P MidCap 400; Vylor is new to the S&P family; Corteva moved down to the S&P MidCap 400; Warner Bros. Discovery left the S&P family. The 2 additions with price data peaked at an average of +3.82% by the next day's close, led by Vylor at +4.02%.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Twilio | TWLO | S&P MidCap 400 | S&P 500 | 10/06/2026 |
Vylor | VYLR | S&P 500 | 10/01/2026 |
S&P MidCap 400 Additions: Corteva (CTVA) and Formfactor (FORM)
2 companies joined the S&P MidCap 400 and 2 left, effective 6 October 2026. Corteva moved down from the S&P 500; Formfactor moved up from the S&P SmallCap 600; Twilio moved up to the S&P 500; Olin moved down to the S&P SmallCap 600. The 2 additions with price data peaked at an average of +4.04% by the next day's close, led by Corteva at +4.48%.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Corteva | CTVA | S&P 500 | S&P MidCap 400 | 10/06/2026 |
Formfactor | FORM | S&P SmallCap 600 | S&P MidCap 400 | 10/06/2026 |
S&P SmallCap 600 Additions: Olin (OLN) and Workiva (WK)
2 companies joined the S&P SmallCap 600 and 2 left, effective 6 October 2026. Olin moved down from the S&P MidCap 400; Workiva is new to the S&P family; Formfactor moved up to the S&P MidCap 400; Qorvo left the S&P family. The 2 additions with price data peaked at an average of +2.15% by the next day's close, led by Workiva at +3.99%.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Olin | OLN | S&P MidCap 400 | S&P SmallCap 600 | 10/06/2026 |
Workiva | WK | S&P SmallCap 600 | 10/06/2026 |
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Price reaction
The close price is the last price before the announcement. Percentages are measured from the open price after the announcement, or from the close for a company with no price after it.
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 |
|---|---|---|---|---|---|---|---|---|---|---|
Twilio | TWLO | S&P MidCap 400 | S&P 500 | 301.27 | 304.94 | +0.34% | +0.08% | -0.01% | -1.14% | +3.63% |
Vylor | VYLR | S&P 500 | 68.26 | 69.70 | +0.19% | +1.58% | -1.00% | -1.42% | +4.02% |
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 |
|---|---|---|---|---|---|---|---|---|---|---|
Corteva | CTVA | S&P 500 | S&P MidCap 400 | 12.57 | 12.48 | +0.10% | -0.48% | +2.64% | -0.76% | +4.48% |
Formfactor | FORM | S&P SmallCap 600 | S&P MidCap 400 | 148.44 | 147.70 | 0.00% | -0.18% | 0.00% | +1.77% | +3.59% |
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 |
|---|---|---|---|---|---|---|---|---|---|---|
Olin | OLN | S&P MidCap 400 | S&P SmallCap 600 | 15.96 | 16.20 | 0.00% | +0.31% | -0.45% | -1.97% | +0.31% |
Workiva | WK | S&P SmallCap 600 | 69.63 | 70.64 | +1.03% | +1.03% | +1.93% | +3.50% | +3.99% |
Not a Investment Advice
This page is research about past price behaviour. It is not a recommendation to buy or sell.