Ciena Set to Join S&P 500; Arrowhead Pharmaceuticals to Join S&P MidCap 400; ADT and OneSpaWorld Holdings to Join S&P SmallCap 600

Rhea-AI Summary

ADT (NYSE: ADT) will join the S&P SmallCap 600 effective prior to the opening of trading on Feb 9, 2026, as part of index changes by S&P Dow Jones Indices. The rebalancing also adds Ciena (CIEN) to the S&P 500 and moves Arrowhead Pharmaceuticals (ARWR) into the S&P MidCap 400 on Feb 9; OneSpaWorld (OSW) joins the SmallCap 600 on Feb 10.

Dayforce was removed following an acquisition by Thoma Bravo, and Dynavax was deleted ahead of its pending acquisition by Sanofi.

Positive

• Ciena added to S&P 500 on Feb 9, 2026
• ADT added to S&P SmallCap 600 on Feb 9, 2026
• OneSpaWorld added to S&P SmallCap 600 on Feb 10, 2026
• Arrowhead moved into S&P MidCap 400 on Feb 9, 2026

Negative

• Dayforce removed from S&P 500 after Thoma Bravo acquisition
• Arrowhead removed from S&P SmallCap 600 on Feb 9, 2026
• Dynavax removed from S&P SmallCap 600 ahead of pending Sanofi deal

News Market Reaction – SPGI

-2.96%

-2.96% Session close to close

In the Feb 5 session, SPGI declined 2.96%, reflecting a moderate negative market reaction.

Data tracked by StockTitan Argus on the day of publication.

Market Context

This announcement details upcoming S&P DJI index changes, including Ciena joining the S&P 500 and sh...

Analysis

This announcement details upcoming S&P DJI index changes, including Ciena joining the S&P 500 and shifts within the S&P MidCap 400 and S&P SmallCap 600. For SPGI, such updates underscore the centrality of its index franchise and the regular cadence of rebalancing tied to corporate actions. Investors may track how frequently these changes occur, their visibility across markets, and how index activity fits alongside SPGI’s broader product, governance, and capital-allocation disclosures.

Key Figures

Effective date (first changes): Feb 9, 2026 Effective date (second changes): Feb 10, 2026 First index invention year: 1884

3 metrics

Effective date (first changes) Feb 9, 2026 Index additions/deletions for CIEN, DAY, ARWR, ADT

Effective date (second changes) Feb 10, 2026 Index changes for OSW and DVAX

First index invention year 1884 Year Charles Dow created the first index

Historical Context

5 past events · Latest: Apr 07 (Positive)

Pattern 5 events

Date	Event	Sentiment	24h Move	Catalyst
Apr 07	Employee benefits program	Positive	+1.6%	SPGI matching U.S. child savings contributions for eligible employees’ families.
Apr 07	Index reconstitution	Neutral	+1.6%	Diebold Nixdorf added to S&P SmallCap 600, replacing Sealed Air after acquisition.
Apr 07	Product launch	Positive	-0.9%	CARFAX introduced VIN-specific Future Reliability metric using extensive data sources.
Apr 06	Management change	Positive	+0.7%	Appointment of Renato Negro as Chief Accounting Officer for Mobility spin-off.
Apr 02	Index reconstitution	Neutral	+0.7%	Atmus Filtration Technologies added to S&P SmallCap 600, replacing Air Lease.

24h Move is the share-price change in the day after each event; other market factors may also have contributed.

Pattern Detected

Recent SPGI and S&P DJI news, including index changes and product launches, has generally seen modestly positive price reactions, with occasional small divergences.

Recent Company History

Over the last few months, SPGI-related news has centered on index changes, product innovation and corporate structuring. Index-addition announcements for other companies and SmallCap 600 changes on April 2–10, 2026 saw SPGI move around +0.68%. A CARFAX feature launch on April 7, 2026 coincided with a -0.93% reaction, while employee and management updates produced gains near +0.68–1.6%. Today’s index-composition announcement for CIEN, ARWR, ADT and OSW fits this ongoing cadence of S&P DJI index updates within SPGI’s broader franchise.

Key Terms

s&p 500, s&p midcap 400, s&p smallcap 600, gics sector

4 terms

s&p 500 financial

"Ciena Corp. (NYSE: CIEN) will replace Dayforce Inc. (NYSE: DAY) in the S&P 500,"

The S&P 500 is a broad stock market index that tracks the performance of 500 large U.S. companies, weighted so bigger firms have a larger impact. Investors use it like a thermometer or benchmark to judge how the overall U.S. stock market or a portfolio is doing; movements in the index influence investor sentiment, fund performance, and many passive investment products that aim to match its returns.

View in glossary

s&p midcap 400 financial

"S&P SmallCap 600 constituent Arrowhead Pharmaceuticals Inc. (NASD: ARWR) will replace Ciena in the S&P MidCap 400,"

The S&P MidCap 400 is a group of 400 companies that are smaller than the big, well-known corporations but larger than tiny startups. It helps investors see how medium-sized companies are performing in the stock market, acting like a barometer for this middle-sized group of businesses.

s&p smallcap 600 financial

"ADT Inc. (NYSE: ADT) will replace Arrowhead Pharmaceuticals in the S&P SmallCap 600 effective prior to the opening"

A stock market index made up of 600 small-cap U.S. companies chosen to represent the performance of smaller publicly traded firms. It matters to investors because it acts like a temperature gauge for the small-company segment of the market, serving as a benchmark for fund managers, a basis for index funds and ETFs, and a way to compare returns and risk when building a diversified portfolio.

gics sector financial

"Ticker | GICS Sector"

GICS sector is one of the major industry groupings from the Global Industry Classification Standard, a system that sorts companies into consistent categories (like Technology or Health Care) based on the primary business they do. Investors use these sectors like folders in a filing cabinet to compare companies, build diversified portfolios, and track how whole parts of the market are performing rather than focusing on single stocks.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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NEW YORK, Feb. 4, 2026 /PRNewswire/ -- S&P Dow Jones Indices will make the following changes to the S&P 500, S&P MidCap 400, S&P SmallCap 600: 

• S&P MidCap 400 constituent Ciena Corp. (NYSE: CIEN) will replace Dayforce Inc. (NYSE: DAY) in the S&P 500, S&P SmallCap 600 constituent Arrowhead Pharmaceuticals Inc. (NASD: ARWR) will replace Ciena in the S&P MidCap 400, and ADT Inc. (NYSE: ADT) will replace Arrowhead Pharmaceuticals in the S&P SmallCap 600 effective prior to the opening of trading on Monday, February 9. Thoma Bravo L.P. acquired Dayforce in a deal that closed today.
• OneSpaWorld Holdings Ltd. (NASD: OSW) will replace Dynavax Technologies Corp. (NASD: DVAX) in the S&P SmallCap 600 effective prior to the opening of trading on Tuesday, February 10. Sanofi is acquiring Dynavax Technologies in a deal expected to be completed soon pending final closing conditions.

Following is a summary of the changes that will take place prior to the open of trading on the effective date:

Effective Date	Index Name	Action	Company Name	Ticker	GICS Sector
Feb 9, 2026	S&P 500	Addition	Ciena	CIEN	Information Technology
Feb 9, 2026	S&P 500	Deletion	Dayforce	DAY	Industrials
Feb 9, 2026	S&P MidCap 400	Addition	Arrowhead Pharmaceuticals	ARWR	Health Care
Feb 9, 2026	S&P MidCap 400	Deletion	Ciena	CIEN	Information Technology
Feb 9, 2026	S&P SmallCap 600	Addition	ADT	ADT	Consumer Discretionary
Feb 9, 2026	S&P SmallCap 600	Deletion	Arrowhead Pharmaceuticals	ARWR	Health Care
Feb 10, 2026	S&P SmallCap 600	Addition	OneSpaWorld Holdings	OSW	Consumer Discretionary
Feb 10, 2026	S&P SmallCap 600	Deletion	Dynavax Technologies	DVAX	Health Care

ABOUT S&P DOW JONES INDICES

S&P Dow Jones Indices is the largest global resource for essential index-based concepts, data and research, and home to iconic financial market indicators, such as the S&P 500® and the Dow Jones Industrial Average®. More assets are invested in products based on our indices than products based on indices from any other provider in the world. Since Charles Dow invented the first index in 1884, S&P DJI has been innovating and developing indices across the spectrum of asset classes helping to define the way investors measure and trade the markets.

S&P Dow Jones Indices is a division of S&P Global (NYSE: SPGI), which provides essential intelligence for individuals, companies, and governments to make decisions with confidence. For more information, visit www.spglobal.com/spdji/en/. 

FOR MORE INFORMATION:

S&P Dow Jones Indices
index_services@spglobal.com

Media Inquiries
spdji.comms@spglobal.com

View original content:https://www.prnewswire.com/news-releases/ciena-set-to-join-sp-500-arrowhead-pharmaceuticals-to-join-sp-midcap-400-adt-and-onespaworld-holdings-to-join-sp-smallcap-600-302679569.html

SOURCE S&P Dow Jones Indices

FAQ

When will ADT (ADT) join the S&P SmallCap 600?

ADT will join the S&P SmallCap 600 prior to the opening of trading on Feb 9, 2026. According to S&P Dow Jones Indices, this is part of a scheduled rebalancing affecting multiple indexes and takes effect at the market open on that date.

Why was Dayforce (DAY) removed from the S&P 500 on Feb 9, 2026?

Dayforce was removed from the S&P 500 because Thoma Bravo completed an acquisition of Dayforce. According to S&P Dow Jones Indices, the deal closed and the company no longer met index inclusion criteria, prompting the deletion effective Feb 9, 2026.

What does Ciena's (CIEN) addition to the S&P 500 mean for investors?

Ciena's addition places CIEN in the S&P 500 effective Feb 9, 2026, which may increase passive fund demand. According to S&P Dow Jones Indices, index inclusion typically prompts reweighting by index-tracking funds at the open on the effective date.

How does Arrowhead Pharmaceuticals (ARWR) moving to the S&P MidCap 400 affect its index status?

Arrowhead will be added to the S&P MidCap 400 and removed from the S&P SmallCap 600 prior to trading on Feb 9, 2026. According to S&P Dow Jones Indices, the change reflects index reconstitution and will alter which funds track ARWR.

When does OneSpaWorld (OSW) join the S&P SmallCap 600 and what is the effective date?

OneSpaWorld will join the S&P SmallCap 600 effective prior to the opening of trading on Feb 10, 2026. According to S&P Dow Jones Indices, OSW replaces Dynavax in the SmallCap 600 on that effective date.

Was the Dynavax (DVAX) removal tied to a transaction, and what is the timing?

Dynavax was deleted from the S&P SmallCap 600 effective Feb 10, 2026 ahead of a pending acquisition by Sanofi. According to S&P Dow Jones Indices, the removal aligns with the announced transaction awaiting final closing conditions.