Primary Offering Prospectus - Form 424B2

Contingent Income Auto-Callable Securities Due November , 2027

Based on the Performance of the Common Stock of QUALCOMM Incorporated

Principal at Risk Securities

Overview

(Key Terms continued on next page)

(1) Citigroup Global Markets Holdings Inc. currently expects that the estimated value of the securities on the pricing date will be at least $918.50 per security, which will be less than the issue price. The estimated value of the securities is based on CGMI's proprietary pricing models and our internal funding rate. It is not an indication of actual profit to CGMI or other of our affiliates, nor is it an indication of the price, if any, at which CGMI or any other person may be willing to buy the securities from you at any time after issuance. See "Valuation of the Securities" in this pricing supplement.

(2) CGMI, an affiliate of Citigroup Global Markets Holdings Inc. and the underwriter of the sale of the securities, is acting as principal and will receive an underwriting fee of $22.50 for each $1,000.00 security sold in this offering. Certain selected dealers, including Morgan Stanley Wealth Management, and their financial advisors will collectively receive from CGMI a fixed selling concession of $17.50 for each $1,000.00 security they sell. Additionally, it is possible that CGMI and its affiliates may profit from expected hedging activity related to this offering, even if the value of the securities declines. See "Use of Proceeds and Hedging" in the accompanying prospectus.

(3) Reflects a structuring fee payable to Morgan Stanley Wealth Management by CGMI of $5.00 for each security.

Investing in the securities involves risks not associated with an investment in conventional debt securities. See "Summary Risk Factors" beginning on page PS-9.

Neither the Securities and Exchange Commission (the "SEC") nor any state securities commission has approved or disapproved of the securities or determined that this pricing supplement and the accompanying product supplement, prospectus supplement and prospectus are truthful or complete. Any representation to the contrary is a criminal offense.

You should read this pricing supplement together with the accompanying product supplement, prospectus supplement and prospectus, each of which can be accessed via the hyperlinks below:

Product Supplement No. EA-04-10 dated March 7, 2023 Prospectus Supplement and Prospectus each dated March 7, 2023

The securities are not bank deposits and are not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency, nor are they obligations of, or guaranteed by, a bank.

Additional Information

General. The terms of the securities are set forth in the accompanying product supplement, prospectus supplement and prospectus, as supplemented by this pricing supplement. The accompanying product supplement, prospectus supplement and prospectus contain important disclosures that are not repeated in this pricing supplement. For example, certain events may occur that could affect whether you receive a contingent coupon payment on a contingent coupon payment date as well as your payment at maturity or, in the case of a delisting of the underlying shares, could give us the right to call the securities prior to maturity for an amount that may be less than the stated principal amount. These events, including market disruption events and other events affecting the underlying shares, and their consequences are described in the accompanying product supplement in the sections "Description of the Securities-Consequences of a Market Disruption Event; Postponement of a Valuation Date," "Description of the Securities-Certain Additional Terms for Securities Linked to an Underlying Company or an Underlying ETF-Dilution and Reorganization Adjustments" and "-Delisting of an Underlying Company" and not in this pricing supplement. It is important that you read the accompanying product supplement, prospectus supplement and prospectus together with this pricing supplement before deciding whether to invest in the securities. Certain terms used but not defined in this pricing supplement are defined in the accompanying product supplement.

Dilution and Reorganization Adjustments. The initial share price and the downside threshold price are each a "Relevant Price" for purposes of the section "Description of the Securities- Certain Additional Terms for Securities Linked to an Underlying Company or an Underlying ETF-Dilution and Reorganization Adjustments" in the accompanying product supplement. Accordingly, the initial share price and the downside threshold price are each subject to adjustment upon the occurrence of any of the events described in that section.

Investment Summary

The securities provide an opportunity for investors to earn a quarterly contingent coupon payment, which is an amount equal to $31.75 (3.175% of the stated principal amount) per security, with respect to each quarterly valuation date on which the closing price of the underlying shares is greater than or equal to 70.00% of the initial share price, which we refer to as the downside threshold price. The quarterly contingent coupon payment, if any, will be payable quarterly on the relevant contingent coupon payment date, which is the third business day after the related valuation date or, in the case of the quarterly contingent coupon payment, if any, with respect to the final valuation date, the maturity date. If the closing price of the underlying shares is less than the downside threshold price on any valuation date, investors will receive no quarterly contingent coupon payment for the related quarterly period. If the closing price of the underlying shares is less than the downside threshold price on one or more valuation dates and, on a subsequent valuation date, the closing price of the underlying shares is greater than or equal to the downside threshold price, your quarterly contingent coupon payment for that subsequent valuation date will include all previously unpaid quarterly contingent coupon payments (without interest on amounts previously unpaid). However, if the closing price of the underlying shares is less than the downside threshold price on any valuation date and on each subsequent valuation date thereafter, you will not receive the unpaid quarterly contingent coupon payments in respect of those valuation dates. It is possible that the closing price of the underlying shares could be below the downside threshold price on all of the valuation dates so that you will receive no quarterly contingent coupon payments. We refer to these payments as contingent because there is no guarantee that you will receive a payment on any contingent coupon payment date.

If the closing price of the underlying shares is greater than or equal to the initial share price on any potential redemption date (beginning approximately three months after the issue date), the securities will be automatically redeemed for an early redemption payment equal to the stated principal amount plus the quarterly contingent coupon payment with respect to the related potential redemption date (including any previously unpaid quarterly contingent coupon payments). If the securities have not previously been automatically redeemed and the final share price is greater than or equal to the downside threshold price, the payment at maturity will also be the sum of the stated principal amount and the quarterly contingent coupon payment due at maturity (including any previously unpaid quarterly contingent coupon payments). However, if the securities have not previously been automatically redeemed and the final share price is less than the downside threshold price, investors will be exposed to the decline in the closing price of the underlying shares, as compared to the initial share price, on a 1-to-1 basis (and, in addition, will not receive any quarterly contingent coupon payment at maturity, including any previously unpaid quarterly contingent coupon payments). Under these circumstances, the payment at maturity will be (i) the stated principal amount plus (ii) (a) the stated principal amount times (b) the share return, which means that the payment at maturity will be less than 70.00% of the stated principal amount of the securities and could be zero. Investors in the securities must be willing to accept the risk of losing their entire principal and also the risk of receiving few or no quarterly contingent coupon payments over the term of the securities. In addition, investors will not participate in any appreciation of the underlying shares.

Key Investment Rationale

The securities offer investors an opportunity to earn a quarterly contingent coupon payment equal to 3.175% of the stated principal amount with respect to each valuation date on which the closing price of the underlying shares is greater than or equal to 70.00% of the initial share price, which we refer to as the downside threshold price. The securities may be automatically redeemed prior to maturity for the stated principal amount per security plus the applicable quarterly contingent coupon payment (including any previously unpaid quarterly contingent coupon payments), and the payment at maturity will vary depending on the final share price, as follows:

How the Securities Work

The following diagrams illustrate potential payments on the securities. The first diagram illustrates how to determine whether a contingent coupon payment will be paid with respect to a quarterly valuation date. The second diagram illustrates how to determine whether the securities will be automatically redeemed following a potential redemption date. The third diagram illustrates how to determine the payment at maturity if the securities are not automatically redeemed prior to maturity.

Diagram #1: Quarterly Contingent Coupon Payments

Diagram #2: Automatic Early Redemption

Diagram #3: Payment at Maturity if No Automatic Early Redemption Occurs

For more information about contingent coupon payments and the payment upon an early automatic redemption or at maturity in different hypothetical scenarios, see "Hypothetical Examples" starting on page PS-7.

Hypothetical Examples

The below examples are based on the following terms:

In Examples 1 and 2, the closing price of the underlying shares fluctuates over the term of the securities and the closing price of the underlying shares is greater than or equal to the initial share price on one of the potential redemption dates, which begin approximately three months after the issue date. Because the closing price of the underlying shares is greater than or equal to the initial share price on one of the potential redemption dates, the securities are automatically redeemed following the relevant potential redemption date. In Examples 3 and 4, the closing price of the underlying shares on each potential redemption date is less than the initial share price, and, consequently, the securities are not automatically redeemed prior to, and remain outstanding until, maturity.

* The early redemption payment includes the unpaid quarterly contingent coupon payment with respect to the potential redemption date on which the closing price of the underlying shares is greater than or equal to the initial share price (together with any previously unpaid quarterly contingent coupon payments) and the securities are automatically redeemed as a result.

In Example 1, the securities are automatically redeemed following the first valuation date (which is the first potential redemption date) as the closing price of the underlying shares on that potential redemption date is greater than the initial share price. You receive the early redemption payment, calculated as follows:

stated principal amount + quarterly contingent coupon payment = $1,000 + $31.75 = $1,031.75

In this example, the automatic early redemption feature limits the term of your investment to approximately three months and you may not be able to reinvest at comparable terms or returns. If the securities are redeemed early, you will stop receiving quarterly contingent coupons.

In Example 2, as the closing price of the underlying shares on the first three valuation dates is greater than the downside threshold price, you receive the quarterly contingent coupon payment of $31.75 with respect to each of the first three valuation dates. As the closing price of the underlying shares on the fourth through sixth valuation dates is less than the downside threshold price, you would not receive a quarterly contingent coupon payment with respect to those valuation dates. However, as the closing price of the underlying shares on the seventh valuation date is greater than the downside threshold price, you would receive the quarterly contingent coupon payment with respect to the seventh valuation date plus the previously unpaid quarterly contingent coupon payment with respect to each of the fourth through sixth valuation dates. The closing price of the underlying shares is greater than the downside threshold price on each of the eighth through tenth valuation dates, and so you would receive a quarterly contingent coupon payment with respect to each of those valuation dates, and then following the eleventh valuation date (the last potential redemption date), the closing price of the underlying shares is greater than the initial

share price, so that the securities would be automatically redeemed and you would receive an automatic early redemption payment of $1,031.75, which includes the quarterly contingent coupon payment with respect to the eleventh valuation date.

In this example, the automatic early redemption feature limits the term of your investment to approximately two years and nine months and you may not be able to reinvest at comparable terms or returns. If the securities are redeemed early, you will stop receiving contingent coupon payments. Further, although the underlying shares have appreciated by 25% from the initial share price on the eleventh valuation date, you only receive $1,031.75 per security upon redemption and do not benefit from this appreciation.

* The final quarterly contingent coupon payment, if any, will be paid at maturity.

Examples 3 and 4 illustrate the payment at maturity per security based on the final share price.

In Example 3, the closing price of the underlying shares remains below the downside threshold price on each valuation date throughout the term of the securities. As a result, you do not receive any quarterly contingent coupon payment during the term of the securities and, at maturity, you are fully exposed to the decline in the closing price of the underlying shares. As the final share price is less than the downside threshold price, you would receive a cash payment at maturity calculated as follows:

stated principal amount + (stated principal amount × share return) = $1,000 + ($1,000 × -100%) = $0.00

In this example, because the underlying shares have lost all of their value by the final valuation date, the payment you receive at maturity would be equal to zero, and you would lose your entire investment. You may lose up to all of your investment in the securities.

In Example 4, the closing price of the underlying shares is less than the downside threshold price on each of the first eleven valuation dates but is greater than the downside threshold price on the final valuation date. As a result, at maturity you would be repaid the stated principal amount of the securities plus the contingent coupon payment due at maturity, which includes all previously unpaid quarterly contingent coupon payments.

The hypothetical returns and hypothetical payments on the securities shown above apply only if you hold the securities for their entire term or until automatic early redemption. These hypothetical examples do not reflect fees or expenses that would be associated with any sale in the secondary market. If these fees and expenses were included, the hypothetical returns and hypothetical payments shown above would likely be lower.

Summary Risk Factors

An investment in the securities is significantly riskier than an investment in conventional debt securities. The securities are subject to all of the risks associated with an investment in our conventional debt securities that are guaranteed by Citigroup Inc., including the risk that we and Citigroup Inc. may default on our obligations under the securities, and are also subject to risks associated with the underlying shares. Accordingly, the securities are appropriate only for investors who are capable of understanding the complexities and risks of the securities. You should consult your own financial, tax and legal advisors as to the risks of an investment in the securities and the appropriateness of the securities in light of your particular circumstances.

The following is a summary of certain key risk factors for investors in the securities. You should read this summary together with the more detailed description of risks relating to an investment in the securities contained in the section "Risk Factors Relating to the Securities" beginning on page EA-7 in the accompanying product supplement. You should also carefully read the risk factors included in the accompanying prospectus supplement and in the documents incorporated by reference in the accompanying prospectus, including Citigroup Inc.'s most recent Annual Report on Form 10-K and any subsequent Quarterly Reports on Form 10-Q, which describe risks relating to the business of Citigroup Inc. more generally.

Because there is not an active market for traded instruments referencing our outstanding debt obligations, CGMI determines our secondary market rate based on the market price of traded instruments referencing the debt obligations of Citigroup Inc., our parent company and the guarantor of all payments due on the securities, but subject to adjustments that CGMI makes in its sole discretion. As a result, our secondary market rate is not a market-determined measure of our creditworthiness, but rather reflects the market's perception of our parent company's creditworthiness as adjusted for discretionary factors such as CGMI's preferences with respect to purchasing the securities prior to maturity.

Non-U.S. investors should note that persons having withholding responsibility in respect of the securities may withhold on any coupon payment paid to a non-U.S. investor, generally at a rate of 30%. To the extent that we have withholding responsibility in respect of the securities, we intend to so withhold.

You should read carefully the discussion under "United States Federal Tax Considerations" and "Risk Factors Relating to the Securities" in the accompanying product supplement and "United States Federal Tax Considerations" in this pricing supplement. You should also consult your tax adviser regarding the U.S. federal tax consequences of an investment in the securities, as well as tax consequences arising under the laws of any state, local or non-U.S. taxing jurisdiction.

Information About QUALCOMM Incorporated

QUALCOMM Incorporated operates as a multinational semiconductor and telecommunications equipment company. The company develops and delivers digital wireless communications products and services based on CDMA digital technology. QUALCOMM Incorporated serves customers worldwide. The underlying shares of QUALCOMM Incorporated are registered under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Information provided to or filed with the SEC by QUALCOMM Incorporated pursuant to the Exchange Act can be located by reference to the SEC file number 000-19528 through the SEC's website at http://www.sec.gov. In addition, information regarding QUALCOMM Incorporated may be obtained from other sources including, but not limited to, press releases, newspaper articles and other publicly disseminated documents. The underlying shares of QUALCOMM Incorporated trade on the NASDAQ Global Select Market under the ticker symbol "QCOM."

This pricing supplement relates only to the securities offered hereby and does not relate to the underlying shares or other securities of the underlying share issuer. We have derived all disclosures contained in this pricing supplement regarding the underlying shares and the underlying share issuer from the publicly available documents described above. In connection with the offering of the securities, none of Citigroup Global Markets Holdings Inc., Citigroup Inc. or CGMI has participated in the preparation of such documents or made any due diligence inquiry with respect to the underlying share issuer.

The securities represent obligations of Citigroup Global Markets Holdings Inc. (guaranteed by Citigroup Inc.) only. The underlying share issuer is not involved in any way in this offering and has no obligation relating to the securities or to holders of the securities.

Neither we nor any of our affiliates make any representation to you as to the performance of the underlying shares.

Historical Information

The closing price of QUALCOMM Incorporated on November 6, 2024 was $172.99.

The graph below shows the closing price of the underlying shares for each day such price was available from January 2, 2014 to November 6, 2024. The table that follows shows the high and low closing prices of, and dividends paid on, the underlying shares for each quarter in that same period. We obtained the closing prices and other information below from Bloomberg L.P., without independent verification. If certain corporate transactions occurred during the historical period shown below, including, but not limited to, spin-offs or mergers, then the closing prices of the underlying shares shown below for the period prior to the occurrence of any such transaction have been adjusted by Bloomberg L.P. as if any such transaction had occurred prior to the first day in the period shown below. You should not take the historical prices of the underlying shares as an indication of future performance.

* The red line indicates the hypothetical downside threshold price of $121.093, assuming the closing price on November 6, 2024 were the initial share price.

We make no representation as to the amount of dividends, if any, that may be paid on the underlying shares in the future. In any event, as an investor in the securities, you will not be entitled to receive dividends, if any, that may be payable on the underlying shares.

United States Federal Tax Considerations

You should read carefully the discussion under "United States Federal Tax Considerations" and "Risk Factors Relating to the Securities" in the accompanying product supplement and "Summary Risk Factors" in this pricing supplement.

Due to the lack of any controlling legal authority, there is substantial uncertainty regarding the U.S. federal tax consequences of an investment in the securities. In connection with any information reporting requirements we may have in respect of the securities under applicable law, we intend (in the absence of an administrative determination or judicial ruling to the contrary) to treat the securities for U.S. federal income tax purposes as prepaid forward contracts with associated coupon payments that will be treated as gross income to you at the time received or accrued in accordance with your regular method of tax accounting. We expect that our counsel will advise us that, based on current market conditions, this treatment of the securities is reasonable under current law, but that it is unable to conclude affirmatively that this treatment is more likely than not to be upheld, and that alternative treatments are possible. The information set forth under this section remains subject to confirmation by our counsel following the pricing of the securities. If that information cannot be confirmed by our counsel, you may be asked to accept revisions to that information in connection with your purchase. Under these circumstances, if you decline to accept revisions to that information, your purchase of the securities will be canceled.

Assuming this treatment of the securities is respected and subject to the discussion in "United States Federal Tax Considerations" in the accompanying product supplement, the following U.S. federal income tax consequences should result under current law:

We do not plan to request a ruling from the IRS regarding the treatment of the securities. An alternative characterization of the securities could materially and adversely affect the tax consequences of ownership and disposition of the securities, including the timing and character of income recognized. In addition, the U.S. Treasury Department and the IRS have requested comments on various issues regarding the U.S. federal income tax treatment of "prepaid forward contracts" and similar financial instruments and have indicated that such transactions may be the subject of future regulations or other guidance. Furthermore, members of Congress have proposed legislative changes to the tax treatment of derivative contracts. Any legislation, Treasury regulations or other guidance promulgated after consideration of these issues could materially and adversely affect the tax consequences of an investment in the securities, possibly with retroactive effect. You should consult your tax adviser regarding possible alternative tax treatments of the securities and potential changes in applicable law.

Withholding Tax on Non-U.S. Holders. Because significant aspects of the tax treatment of the securities are uncertain, persons having withholding responsibility in respect of the securities may withhold on any coupon payment paid to Non-U.S. Holders (as defined in the accompanying product supplement), generally at a rate of 30%. To the extent that we have (or an affiliate of ours has) withholding responsibility in respect of the securities, we intend to so withhold. In order to claim an exemption from, or a reduction in, the 30% withholding, you may need to comply with certification requirements to establish that you are not a U.S. person and are eligible for such an exemption or reduction under an applicable tax treaty. You should consult your tax adviser regarding the tax treatment of the securities, including the possibility of obtaining a refund of any amounts withheld and the certification requirement described above.

As discussed under "United States Federal Tax Considerations-Tax Consequences to Non-U.S. Holders" in the accompanying product supplement, Section 871(m) of the Code and Treasury regulations promulgated thereunder ("Section 871(m)") generally impose a 30% withholding tax on dividend equivalents paid or deemed paid to Non-U.S. Holders with respect to certain financial instruments linked to U.S. equities ("U.S. Underlying Equities") or indices that include U.S. Underlying Equities. Section 871(m) generally applies to instruments that substantially replicate the economic performance of one or more U.S. Underlying Equities, as determined based on tests set forth in the applicable Treasury regulations. However, the regulations, as modified by an IRS notice, exempt financial instruments issued prior to January 1, 2027 that do not have a "delta" of one. Based on the terms of the securities and market conditions as of the date of this preliminary pricing supplement, we expect that the securities will not be treated as transactions that have a "delta" of one within the meaning of the regulations with respect to any U.S. Underlying Equity and, therefore, should not be subject to withholding tax under Section 871(m). However, the final determination regarding the treatment of the securities under Section 871(m) will be made as of the pricing date for the securities, and it is possible that the securities will be subject to withholding tax under Section 871(m) based on the circumstances as of that date.

A determination that the securities are not subject to Section 871(m) is not binding on the IRS, and the IRS may disagree with this treatment. Moreover, Section 871(m) is complex and its application may depend on your particular circumstances, including your other transactions. You should consult your tax adviser regarding the potential application of Section 871(m) to the securities.

We will not be required to pay any additional amounts with respect to amounts withheld.

You should read the section entitled "United States Federal Tax Considerations" in the accompanying product supplement.

You should also consult your tax adviser regarding all aspects of the U.S. federal income and estate tax consequences of an investment in the securities and any tax consequences arising under the laws of any state, local or non-U.S. taxing jurisdiction.

Supplemental Plan of Distribution

CGMI, an affiliate of Citigroup Global Markets Holdings Inc. and the underwriter of the sale of the securities, is acting as principal and will receive an underwriting fee of $22.50 for each $1,000.00 security sold in this offering. From this underwriting fee, CGMI will pay selected dealers not affiliated with CGMI, including Morgan Stanley Wealth Management, and their financial advisors collectively a fixed selling concession of $17.50 for each $1,000.00 security they sell. In addition, Morgan Stanley Wealth Management will receive a structuring fee of $5.00 for each security they sell. For the avoidance of doubt, the fees and selling concessions described in this pricing supplement will not be rebated if the securities are automatically redeemed prior to maturity.

The costs included in the original issue price of the securities will include a fee paid by CGMI to LFT Securities, LLC, an entity in which an affiliate of Morgan Stanley Wealth Management has an ownership interest, for providing certain electronic platform services with respect to this offering.

See "Plan of Distribution; Conflicts of Interest" in the accompanying product supplement and "Plan of Distribution" in each of the accompanying prospectus supplement and prospectus for additional information.

Valuation of the Securities

CGMI calculated the estimated value of the securities set forth on the cover page of this pricing supplement based on proprietary pricing models. CGMI's proprietary pricing models generated an estimated value for the securities by estimating the value of a hypothetical package of financial instruments that would replicate the payout on the securities, which consists of a fixed-income bond (the "bond component") and one or more derivative instruments underlying the economic terms of the securities (the "derivative component"). CGMI calculated the estimated value of the bond component using a discount rate based on our internal funding rate. CGMI calculated the estimated value of the derivative component based on a proprietary derivative-pricing model, which generated a theoretical price for the instruments that constitute the derivative component based on various inputs, including the factors described under "Summary Risk Factors-The value of the securities prior to maturity will fluctuate based on many unpredictable factors" in this pricing supplement, but not including our or Citigroup Inc.'s creditworthiness. These inputs may be market-observable or may be based on assumptions made by CGMI in its discretionary judgment.

The estimated value of the securities is a function of the terms of the securities and the inputs to CGMI's proprietary pricing models. As of the date of this preliminary pricing supplement, it is uncertain what the estimated value of the securities will be on the pricing date because it is uncertain what the values of the inputs to CGMI's proprietary pricing models will be on the pricing date.

For a period of approximately three months following issuance of the securities, the price, if any, at which CGMI would be willing to buy the securities from investors, and the value that will be indicated for the securities on any brokerage account statements prepared by CGMI or its affiliates (which value CGMI may also publish through one or more financial information vendors), will reflect a temporary upward adjustment from the price or value that would otherwise be determined. This temporary upward adjustment represents a portion of the hedging profit expected to be realized by CGMI or its affiliates over the term of the securities. The amount of this temporary upward adjustment will decline to zero on a straight-line basis over the three-month temporary adjustment period. However, CGMI is not obligated to buy the securities from investors at any time. See "Summary Risk Factors-The securities will not be listed on any securities exchange and you may not be able to sell them prior to maturity."

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