At a glance
CPST charges 0.69% a year, below the 0.86% average of the 7 funds most like it (the cheapest of 8). It has $32.2M in assets, the 8th largest of that group. Over the past year it returned +4.9% with distributions reinvested (S&P 500: +11.5%), the weakest of those 8 funds.
The short version
Calamos S&P 500 Structured Alt Protection ETF – September (CPST) holds FLEX options on the SPDR S&P 500 ETF Trust (SPY) rather than stocks. Over each September-to-August outcome period, it seeks to absorb 100% of SPY's price losses before fees while capping gains (6.59% before fees for the period ending August 31, 2026). Its 0.69% expense ratio is the lowest in its peer group, but it has paid no distributions and forgoes SPY's dividends.
Price history
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CPST +4.9% over the year to Oct 27, 2026, total return with distributions reinvested.
How it has behaved
| YTD | 1 yr | 3 yr | 5 yr | 10 yr | Since start | |
|---|---|---|---|---|---|---|
| CPST price data to Oct 27, 2026 | +4.5% | +4.9% | — | — | — | +6.3% |
- Over the year to Oct 27, 2026, CPST returned +4.9%, 8th of 8 among similar funds.
- Its worst full calendar year was 2025 (+6.7%); its best was 2025 (+6.7%).
- The deepest fall in its price history was 3.8% (Feb 19, 2025 to Apr 8, 2025), recovered by May 15, 2025.
Show as a table
| Year | Price data |
|---|---|
| 2026 (to date) | +4.5% |
| 2025 | +6.7% |
| 2008 financial crisis stocks fell Oct 9, 2007 – Mar 9, 2009 | Before this security existed |
|---|---|
| 2020 COVID crash stocks fell Feb 19, 2020 – Mar 23, 2020 | Before this security existed |
| 2022 bear market stocks fell Jan 3, 2022 – Oct 12, 2022 | Before this security existed |
What's inside
As of Jul 31, 2026, the fund held 0 securities; the ten largest made up 0% of assets.
| Holding | Weight |
|---|
By country
By asset type
What changed recently
- Over the three months to Jul 31, 2026, investors withdrew a net $693K (creations minus redemptions, per the N-PORT report).
- Monthly total returns reported for that quarter: +0.76%, +0.36%, +0.47%.
How it works
CPST is an actively managed Calamos ETF that holds FLEX options instead of stocks. FLEX options are exchange-traded contracts with customized strike prices (the level where an option starts paying off) and expiration dates, guaranteed for settlement by the Options Clearing Corporation. They reference the SPDR S&P 500 ETF Trust (SPY), a unit investment trust tracking the S&P 500 Index. CPST's results reflect SPY's price only, not its dividends.
Each outcome period runs from September 1 to August 31. As of July 31, 2026, the fund held three SPY FLEX options expiring August 31, 2026: a call with a very low $4.45 strike that moves almost in step with SPY; a $645.05 put, which gains as SPY falls; and a sold call at $687.56 that caps gains. For that period, the cap was 6.59% and protection 100% before fees, or 5.90% and 99.31% after fees.
Those targets apply only to shares held for the entire period, measured from the first day's share value. Shares purchased later or sold early can end up far from them, since protection applies only at the period's end. Each September the fund rolls into new options: protection stays at 100%, but the cap resets with market conditions. The fund's website previews each new cap range about a week ahead.
What it really costs
- CPST charges 0.69% a year, versus an average of 0.86% for the similar funds below (1st of 8, cheapest first).
- Using the prospectus's standard example, $10,000 invested would cost about $70 in the first year and $859 over 10 years (assuming a 5% annual return).
| Cost of $10,000 (SEC example) | 1 yr | 3 yrs | 5 yrs | 10 yrs |
|---|---|---|---|---|
| CPST | $70 | $221 | $384 | $859 |
Structure and tax notes
- Organized as a unit investment trust: it cannot lend out its securities or reinvest dividends between payouts, which can create a small drag versus similar open-end ETFs.
- Uses options to limit losses within a range (the buffer) in exchange for a cap on gains over each outcome period; results depend on when you buy relative to the period start.
In a retirement portfolio
It aims to absorb 100% of SPY's price losses before fees over each full September-to-August period, trading away gains above a preset cap.
CPST launched in September 2024, so it has no record in the 2008, 2020 or 2022 downturns. Its only full calendar year, 2025, brought a 6.7% gain. Protection counts only at each period's end, and the value can dip before then: its deepest drop, 3.8% from February 19 to April 8, 2025, took about 1.2 months to recover. Shares cashed out mid-period in a slump could lose money. The fund has made no distributions, so raising cash means parting with shares. The cap also holds back gains; it returned 4.9% over the year to October 27, 2026.
Its 0.69% expense ratio is below the 0.86% peer average; in the SEC's standard example, $10,000 would cost about $70 in the first year and $859 over 10 years. Past results don't predict future ones, and a retirement plan needs to weigh the whole portfolio, not one fund.
Who it may suit — and who should look elsewhere
May suit
- Investors able to hold from September 1 to August 31 who want 100% protection against SPY price losses (before fees) and accept capped gains.
- Those who value a smooth ride: price swings were small, with 2.1% one-year volatility and a 3.8% deepest drop since launch (to October 27, 2026).
- Cost-conscious investors comparing defined-outcome funds: its 0.69% expense ratio is the lowest of eight compared, versus a 0.86% average.
Look elsewhere if
- Income seekers: CPST has made no distributions, and its returns exclude the dividends SPY pays.
- Investors seeking more upside: CPST's 4.9% one-year return to October 27, 2026, ranked last of eight similar funds; peers returned 9.5% to 12.9%.
- Anyone who may need the money before a period ends on August 31: shares sold mid-period may not get the full protection.
Close alternatives
Matched by other buffer (defined-outcome) funds, largest first.
| Fund | Cost | Net assets | 1 yr | 3 yr |
|---|---|---|---|---|
| CPST this fund | 0.69% | $32.2M | +4.9% | — |
| BUFR FT Vest Laddered Buffer ETF | 0.95% | $10.49B | +11.6% | +16.8% |
| BUFD FT Vest Laddered Deep Buffer ETF | 0.95% | $2.04B | +9.5% | +13.9% |
| PJAN Innovator U.S. Equity Power Buffer ETF - Ja… | 0.79% | $1.44B | +10.5% | +14.8% |
| PDEC Innovator U.S. Equity Power Buffer ETF - De… | 0.79% | $984.1M | +11.6% | +14.9% |
| FDEC FT Vest US Equity Buffer ETF - December | 0.85% | $1.31B | +12.9% | +18.5% |
| FJAN FT Vest US Equity Buffer ETF - January | 0.85% | $1.47B | +12.3% | +17.4% |
| FFEB FT Vest U.S. Equity Buffer Fund - February | 0.85% | $1.42B | +12.9% | +18.6% |
Questions investors ask
Can you lose money in CPST?
Yes, though for shares held through a full outcome period, the fund aims to limit losses to about its fees. CPST seeks to absorb 100% of SPY's price losses over each September-to-August period, but only before fees; after its 0.69% fee, protection for the period ending August 31, 2026, was 99.31%. Shares purchased after a period starts or sold before it ends can lose more. The prospectus says the protection isn't guaranteed, and the fund isn't FDIC-insured. Brokerage commissions and taxes reduce results further.
Does CPST pay dividends?
No. CPST has made no distributions, and income isn't part of its objective. It holds FLEX options on the SPDR S&P 500 ETF Trust (SPY) rather than the stocks themselves, and its returns reflect only SPY's price change, not the dividends SPY pays. Holders give up that dividend income in exchange for downside protection. Raising cash means cashing out shares, and doing so before a period ends can mean less than the stated protection.
What is the cap on CPST's returns?
It was 6.59% before fees, or 5.90% after fees, for the outcome period from September 1, 2025, through August 31, 2026. That is the most a shareholder holding for the full period could gain. The cap resets each September based on market conditions, so it usually changes from one period to the next, while the 100% protection level stays the same. The prospectus filed November 21, 2025, doesn't state later caps; the fund's website posts the expected range about a week before each period ends.
What's the difference between CPST and SPY?
SPY holds the stocks in the S&P 500 and passes along their full gains, losses and dividends. CPST holds FLEX options on SPY that aim to match SPY's price gains only up to a cap (6.59% before fees for the period ending August 31, 2026), while absorbing 100% of its price losses before fees over each full outcome period. CPST doesn't capture SPY's dividends and charges 0.69% a year. When SPY rises past the cap, CPST trails it.
What's the difference between CPST and BUFR?
CPST is cheaper and far smaller, and it targets 100% downside protection (before fees) over one September-to-August period. BUFR, the FT Vest Laddered Buffer ETF, is the largest fund in CPST's comparison group, at $10.5 billion as of August 31, 2026, versus CPST's $32.2 million as of July 31, 2026. As its name says, BUFR uses a laddered buffer approach, which generally means staggered outcome periods. CPST charges 0.69% versus BUFR's 0.95%, but returned 4.9% over the year to October 27, 2026, against BUFR's 11.6%.