S&P 500, MidCap 400 & SmallCap 600 Additions & Index Changes: TWLO, WK, FORM, CTVA, OLN & VYLR – 1st October 2026
S&P Index Changes Announced October 1, 2026
S&P Dow Jones Indices announced several S&P index changes on October 1, 2026, including new additions to the S&P 500, S&P MidCap 400 and S&P SmallCap 600. The latest S&P additions include Twilio (TWLO) and Vylor (VYLR) in the S&P 500, FormFactor (FORM) and Corteva (CTVA) in the S&P MidCap 400, and Workiva (WK) and Olin (OLN) in the S&P SmallCap 600. Most of the changes become effective before the market opens on October 6, 2026.
S&P 500 Additions: Twilio (TWLO) and Vylor (VYLR)
S&P Dow Jones Indices announced new S&P 500 additions on October 1, 2026. Twilio (NYSE: TWLO) will be added to the S&P 500, replacing Warner Bros. Discovery (WBD), effective before the market opens on October 6, 2026. Twilio is currently an S&P MidCap 400 constituent and is classified in the Information Technology sector. Vylor (NYSE: VYLR) was also added to the S&P 500 on October 1 following its spin-off from Corteva (CTVA), replacing Corteva in the index.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Vylor | VYLR | S&P 500 | 01/10/2026 | |
Twilio | TWLO | S&P MidCap 400 | S&P 500 | 06/10/2026 |
S&P MidCap 400 Additions: FormFactor (FORM) and Corteva (CTVA)
The latest S&P index changes also include two additions to the S&P MidCap 400. FormFactor (NASDAQ: FORM) will move from the S&P SmallCap 600 to the S&P MidCap 400, replacing Twilio (TWLO). Corteva (NYSE: CTVA) will move from the S&P 500 to the S&P MidCap 400, replacing Olin (OLN). Both changes become effective before trading opens on October 6, 2026.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Corteva | CTVA | S&P 500 | S&P MidCap 400 | 06/10/2026 |
FormFactor | FORM | S&P SmallCap 600 | S&P MidCap 400 | 06/10/2026 |
S&P SmallCap 600 Additions: Workiva (WK) and Olin (OLN)
The latest S&P SmallCap 600 additions are Workiva (NYSE: WK) and Olin (NYSE: OLN). Workiva will be newly added to the S&P SmallCap 600, replacing FormFactor (FORM), while Olin will move from the S&P MidCap 400 to the S&P SmallCap 600, replacing Qorvo (QRVO). Both S&P SmallCap 600 index changes take effect before the market opens on October 6, 2026. Workiva is classified in Information Technology, while Olin is classified in Materials.
Company | Ticker | Source Index | Final Index | Effective Date |
|---|---|---|---|---|
Olin | OLN | S&P MidCap 400 | S&P SmallCap 600 | 06/10/2026 |
Workiva | WK | S&P SmallCap 600 | 06/10/2026 |
How Did the S&P 500 Additions React 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 |
|---|---|---|---|---|---|---|---|---|---|---|
Vylor | VYLR | None | S&P 500 | 67.85 | 69.7 | 0.43% | -1.00% | -1.42% | 2.38% | |
Twilio | TWLO | S&P MidCap 400 | S&P 500 | 299.9104 | 304.94 | 0.02% | 0.35% | -0.01% | -1.14% | 0.24% |
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 | 12.5 | 12.48 | -0.08% | -0.32% | 2.64% | -0.76% | 4.48% |
Formfactor | FORM | S&P SmallCap 600 | S&P MidCap 400 | 148.44 | 147.7 | -0.18% | 0.00% | 1.93% | 2.36% |
S&P SmallCap 600 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 |
|---|---|---|---|---|---|---|---|---|---|---|
Olin | OLN | S&P MidCap 400 | S&P SmallCap 600 | 15.96 | 16.1992 | -0.45% | -1.97% | -0.09% | ||
Workiva | WK | None | S&P SmallCap 600 | 69.63 | 70.64 | 1.93% | 3.50% | 3.99% |