Compass Therapeutics (CMPX) 424B5 Prospectus supplement for primary offering

Filed pursuant to Rule 424(b)(5)
Registration No. 333-257821

PROSPECTUS

$75,000,000

Common Stock

We have entered into a sales agreement, or the sales agreement, with B. Riley Securities, Inc., or B. Riley Securities, relating to shares of our common stock offered by this prospectus. In accordance with the terms of the sales agreement, we may offer and sell shares of our common stock having an aggregate offering price of up to $75,000,000 from time to time through or to B. Riley Securities acting as our agent or principal.

Our common stock is currently trading on the OTCQB Market under the stock symbol CMPX. On July 2, 2021, the closing price for our common stock, as reported on the OTCQB Market, was $4.90 per share. No offers or sales shall occur pursuant to this prospectus until such time as our common stock is listed on a national securities exchange.

Sales of our common stock, if any, under this prospectus may be made in sales deemed to be an “at-the-market” equity offering as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or the Securities Act. B. Riley Securities is not required to sell any specific number or dollar amount of securities, but will act as a sales agent using commercially reasonable efforts consistent with its normal trading and sales practices, on mutually agreed terms between B. Riley Securities and us. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

The compensation to B. Riley Securities for sales of common stock sold pursuant to the sales agreement will be an amount up to 3.0% of the gross proceeds of any shares of common stock sold under the sales agreement. In connection with the sale of the common stock on our behalf, B. Riley Securities will be deemed to be an “underwriter” within the meaning of the Securities Act and the compensation of B. Riley Securities will be deemed to be underwriting commissions or discounts. We have also agreed to provide indemnification and contribution to B. Riley Securities with respect to certain liabilities, including liabilities under the Securities Act or the Securities Exchange Act of 1934, as amended, or the Exchange Act.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” on page 4 of this prospectus and under similar headings in the other documents that are incorporated by reference into this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

B. Riley Securities

The date of this prospectus is July 20, 2021.

TABLE OF CONTENTS

Prospectus

	Page
ABOUT THIS PROSPECTUS	i
SUMMARY	1
THE OFFERING	3
RISK FACTORS	4
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	6
USE OF PROCEEDS	8
DILUTION	9
DESCRIPTION OF CAPITAL STOCK	10
PLAN OF DISTRIBUTION	14
LEGAL MATTERS	16
EXPERTS	16
WHERE YOU CAN FIND MORE INFORMATION	16
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	16

ABOUT THIS PROSPECTUS

This prospectus relates to part of a registration statement on Form S-3 that we have filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under this shelf registration process, we may sell any combination of the securities described in our base prospectus included in the shelf registration statement in one or more offerings. In connection with such offers and when accompanied by the base prospectus included in the registration statement of which this prospectus forms a part, this prospectus will be deemed a prospectus supplement to such base prospectus.

This prospectus relates to the offering of our common stock. Before buying any of the common stock that we are offering, we urge you to carefully read this prospectus, together with the information incorporated by reference as described under the headings “Where You Can Find More Information” and “Incorporation of Certain Information by Reference” in this prospectus. These documents contain important information that you should consider when making your investment decision.

This prospectus describes the terms of this offering of common stock and also adds to and updates information contained in the documents incorporated by reference into this prospectus. To the extent there is a conflict between the information contained in this prospectus, on the one hand, and the information contained in any document incorporated by reference into this prospectus that was filed with the SEC before the date of this prospectus, on the other hand, you should rely on the information in this prospectus. If any statement in one of these documents is inconsistent with a statement in another document having a later date (for example, a document incorporated by reference into this prospectus) the statement in the document having the later date modifies or supersedes the earlier statement.

You should rely only on the information contained in or incorporated by reference in this prospectus and in any free writing prospectus that we have authorized for use in connection with this offering. We have not, and the sales agent has not, authorized anyone to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not, and the sales agent is not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus, the documents incorporated by reference in this prospectus, and in any free writing prospectus that we have authorized for use in connection with this offering, is accurate only as of the date of those respective documents. Our business, financial condition, results of operations and prospects may have changed since those dates. You should read this prospectus, the documents incorporated by reference in this prospectus, and any free writing prospectus that we have authorized for use in connection with this offering, in their entirety before making an investment decision.

All references to “Compass OpCo” refer to Compass Therapeutics LLC, a privately held Delaware limited liability company and our direct, wholly owned subsidiary. Unless otherwise stated or the context otherwise indicates, references to the “Company”, “we”, “our”, “us” or similar terms refer to Compass Therapeutics, Inc. (formerly named Olivia Ventures, Inc.) together with its wholly-owned subsidiary, Compass OpCo. Compass OpCo holds all material assets and conducts all business activities and operations of Compass Therapeutics, Inc.

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PROSPECTUS SUMMARY

This summary highlights certain information about us, this offering and selected information contained elsewhere in this prospectus. This summary is not complete and does not contain all of the information that you should consider before deciding whether to invest in the securities covered by this prospectus. For a more complete understanding of the Company and this offering, we encourage you to read and consider carefully the more detailed information in this prospectus, any related prospectus supplement and any related free writing prospectus, including the information set forth in the section titled “Risk Factors” in this prospectus, any related prospectus supplement, any related free writing prospectus and our Annual Report on Form 10-K for the fiscal year ended December 31, 2020, and any amendment or update thereto reflected in subsequent filings with the SEC and incorporated by reference in this prospectus in their entirety before making an investment decision.

Overview

We are a clinical-stage, oncology-focused biopharmaceutical company developing proprietary antibody-based therapeutics to treat multiple human diseases. Our scientific focus is on the relationship between angiogenesis and the immune system. Our pipeline includes novel product candidates that leverage our understanding of the tumor microenvironment, including both angiogenesis-targeted agents and immune-oncology focused agents. These product candidates are designed to optimize critical components required for an effective anti-tumor response to cancer. These include modulation of the microvasculature via angiogenesis-targeted agents; induction of a potent immune response via activators on effector cells in the tumor microenvironment; and alleviation of immunosuppressive mechanisms used by tumors to evade immune surveillance. We plan to advance our product candidates through clinical development as both standalone therapies and in combination with our proprietary drug candidates as long as their continued development is supported by clinical and nonclinical data.

Recent Developments

TRIGR Acquisition

On May 13, 2021, we and TRIGR Therapeutics, Inc., or TRIGR, a private biotechnology company, entered into a definitive merger agreement, or the TRIGR Merger Agreement. On June 28, 2021, pursuant to the TRIGR Merger Agreement, we, through our wholly owned subsidiaries and a two-step merger structure, acquired all of the outstanding shares of TRIGR, or the TRIGR Merger. Consideration payable to TRIGR shareholders at closing totaled an aggregate of 10,265,145 shares of our common stock, issued as unregistered shares in a private placement. In addition, TRIGR shareholders are eligible to receive up to $9 million, representing earnout payments which are dependent on certain events, including $5 million which is dependent on biologics license application approval of a product candidate acquired in the transaction, renamed CTX-009.

Emerging Growth Company

We are an “emerging growth company” as defined in the JOBS Act. We could be an emerging growth company for up to five years, although circumstances could cause us to lose that status earlier, including if the market value of our common stock held by non-affiliates exceeds $700.0 million as of the prior June 30, if we have total annual gross revenue of approximately $1.1 billion or more during any fiscal year, or if we issue more than $1.0 billion in non-convertible debt during any three-year period.

As an emerging growth company, we may take advantage of specified reduced disclosure and other requirements that are otherwise generally applicable to public companies. These provisions include:

• only two years of audited financial statements in addition to any required unaudited interim financial statements with correspondingly reduced “Management’s Discussion and Analysis of Financial Condition and Results of Operations” disclosure;

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• reduced disclosure about our executive compensation arrangements;

• no requirement that we hold non-binding advisory votes on executive compensation or golden parachute arrangements; and

• exemption from the auditor attestation requirement in the assessment of our internal control over financial reporting.

We have taken advantage of some of these reduced disclosure and other requirements, and thus the information we provide stockholders may be different than you might receive or obtain from other public companies in which you hold shares.

In addition, Section 107 of the JOBS Act provides that an emerging growth company can use the extended transition period provided in Section 7(a)(2)(B) of the Securities Act for complying with new or revised accounting standards. This permits an emerging growth company to delay the adoption of certain accounting standards until those standards would otherwise apply to private companies. We have irrevocably elected not to avail ourselves of this extended transition period and, as a result, we will adopt new or revised accounting standards on the relevant dates on which adoption of such standards is required for other companies. Section 107 of the JOBS Act provides that our decision to opt out of the extended transition period for complying with new or revised accounting standards is irrevocable.

Corporate Information

We were originally incorporated in the State of Delaware on March 20, 2018 under the name Olivia Ventures, Inc. Olivia Ventures, Inc. was a “shell” company registered under the Exchange Act, with no specific business plan or purpose until it began operating the business of Compass OpCo following the closing of the merger of our wholly-owned subsidiary, Compass Acquisitions, with and into Compass OpCo, with Compass OpCo continuing as the surviving entity and our wholly owned subsidiary, or the Merger, on June 17, 2020. Compass OpCo, a clinical-stage biotechnology company developing proprietary antibody therapeutics intended to engage the immune system to treat both solid tumors and hematological malignancies, was originally formed as a private limited liability company under the name Compass Therapeutics, LLC in the State of Delaware on January 29, 2014. As a result of the Merger, we acquired the business of Compass OpCo, and we will continue the existing business operations of Compass OpCo as a public reporting company under the name Compass Therapeutics, Inc.

Our corporate headquarters are located at 80 Guest Street, Suite 601, Boston, Massachusetts 02135, and our telephone number is (617) 500-8099. We maintain a website at www.compasstherapeutics.com, where we regularly post copies of our press releases as well as additional information about our company. Our filings with the SEC are available free of charge through the website as soon as reasonably practicable after being electronically filed with or furnished to the SEC. Information contained in our website is not a part of, nor incorporated by reference into, this prospectus or our other filings with the SEC, and should not be relied upon.

All trademarks, service marks and trade names appearing in this prospectus are the property of their respective holders. Use or display by us of other parties’ trademarks, trade dress, or products in this prospectus is not intended to, and does not, imply a relationship with, or endorsements or sponsorship of, us by the trademark or trade dress owners

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THE OFFERING

Common Stock Offered By Us	Shares of our common stock having an aggregate offering price of up to $75,000,000.
Common Stock to be Outstanding After This Offering	Up to 77,629,269 shares (as more fully described in the notes following this table), assuming sales of 15,306,122 shares of our common stock in this offering at an offering price of $4.90 per share, which was the last reported sale price of our common stock on the OTCQB Market on July 2, 2021. The actual number of shares issued will vary depending on the sales price under this offering.
Manner of Offering	“At-the-market” offering that may be made from time to time through our sales agent, B. Riley Securities. See “Plan of Distribution” on page 14.
Use of Proceeds	We currently intend to use the net proceeds from this offering primarily to fund the research and development of our product candidates, acquire or invest in businesses, products or technologies that are complementary to our own, although we have no current plans, commitments or agreements with respect to any acquisitions as of the date of this prospectus, and for working capital and general corporate purposes. See “Use of Proceeds” on page 8 of this prospectus.
Risk Factors	Investing in our common stock involves significant risks. See “Risk Factors” on page 4 of this prospectus, and under similar headings in other documents incorporated by reference into this prospectus.
OTCQB Market symbol	“CMPX”

The number of shares of common stock outstanding is based on an aggregate of 62,323,147 shares outstanding as of June 30, 2021 and excludes 5,015,513 shares of common stock reserved under the 2020 Incentive Plan, from which options to purchase an aggregate of 3,372,083 shares of common stock, at a weighted-average exercise price of $5.15 per share, have been granted and remain unexercised.

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RISK FACTORS

Investing in our securities involves a high degree of risk. You should carefully review the risks and uncertainties described below and under the section titled “Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2020, and in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2021, as updated by our subsequent filings, which are incorporated by reference into this prospectus, before deciding whether to purchase any of the securities being registered pursuant to the registration statement of which this prospectus is a part. Each of the risk factors could adversely affect our business, results of operations, financial condition and cash flows, as well as adversely affect the value of an investment in our securities, and the occurrence of any of these risks might cause you to lose all or part of your investment. Additional risks not presently known to us or that we currently believe are immaterial may also significantly impair our business operations. Please also read carefully the section below titled “Special Note Regarding Forward-Looking Statements.”

Risks Related to this Offering

You may experience immediate and substantial dilution.

The offering price per share in this offering may exceed the net tangible book value per share of our common stock outstanding prior to this offering. Assuming that an aggregate of 15,306,122 shares of our common stock are sold at a price of $4.90 per share, the last reported sale price of our common stock on the OTCQB Market on July 2, 2021, for aggregate gross proceeds of $75,000,000 million, and after deducting commissions and estimated offering expenses payable by us, you would experience immediate dilution of $3.53 per share, representing our as adjusted net tangible book value as of March 31, 2021, after giving effect to this offering. See the section titled “Dilution” below for a more detailed illustration of the dilution you would incur if you participate in this offering.

In addition, we have a significant number of stock options and pre-funded warrants outstanding. To the extent that these have been or may be exercised, investors purchasing in this offering may experience further dilution. In addition, we may choose to raise additional capital due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. To the extent that additional capital is raised through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our stockholders or result in downward pressure on the price of our common stock.

Because the sales of the shares offered hereby will be made directly into the market or in negotiated transactions, the prices at which we sell these shares will vary and these variations may be significant. Purchasers of the shares we sell, as well as our existing stockholders, will experience significant dilution if we sell shares at prices significantly below the price at which they invested.

Our management might apply the net proceeds from this offering in ways with which you do not agree and in ways that may impair the value of your investment.

We currently intend to use the net proceeds from this offering primarily to fund the research and development, acquire or invest in businesses, products or technologies that are complementary to our own, although we have no current plans, commitments or agreements with respect to any acquisitions as of the date of this prospectus, and for working capital and general corporate purposes. Pending the use of net proceeds, we intend to invest the net proceeds in short-term, investment-grade, interest bearing obligations, certificates of deposit or direct or guaranteed obligations of the United States government. Our management has broad discretion as to the use of these proceeds and you will be relying on the judgment of our management regarding the application of these proceeds. We might apply these proceeds in ways with which you do not agree, or in ways that do not yield a favorable return. If our management applies these proceeds in a manner that does not yield a significant return, if any, on our investment of these net proceeds, it could compromise our ability to pursue our growth strategy and adversely affect the market price of our common stock.

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It is not possible to predict the actual number of shares we will sell under the sales agreement, or the gross proceeds resulting from those sales.

Subject to certain limitations in the sales agreement and compliance with applicable law, we have the discretion to deliver a placement notice to the sales agent at any time throughout the term of the sales agreement. The number of shares that are sold through the sales agent after delivering a placement notice will fluctuate based on a number of factors, including the market price of the common stock during the sales period, the limits we set with the sales agent in any applicable placement notice, and the demand for our common stock during the sales period. Because the price per share of each share sold will fluctuate during the sales period, it is not currently possible to predict the number of shares that will be sold or the gross proceeds to be raised in connection with those sales, if any.

The common stock offered hereby will be sold in “at the market offerings,” and investors who buy shares at different times will likely pay different prices.

Investors who purchase shares in this offering at different times will likely pay different prices, and so they may experience different levels of dilution and different outcomes in their investment results. We will have discretion, subject to market demand, to vary the timing, prices, and numbers of shares sold in this offering. In addition, there is no minimum or maximum sales price for shares to be sold in this offering. Investors may experience a decline in the value of the shares they purchase in this offering as a result of sales made at prices lower than the prices they paid.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, including the documents that we incorporate by reference, includes forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. Forward-looking statements relate to, among others, our plans, objectives and expectations for our business, operations and financial performance and condition, and can be identified by terminology such as “may”, “should”, “expect”, “intend”, “plan”, “anticipate”, “believe”, “estimate”, “predict”, “potential”, “continue” and similar expressions that do not relate solely to historical matters. Forward-looking statements are based on management’s belief and assumptions and on information currently available to management. Although we believe that the expectations reflected in forward-looking statements are reasonable, such statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by forward-looking statements.

Forward-looking statements include, but are not limited to, statements about:

• our expectations regarding the timing, progress and results of preclinical studies and clinical trials for CTX-009, CTX-471, CTX-8371 and any other product candidates we develop, including statements regarding the timing of initiation and completion of studies or trials and related preparatory work, the period during which the results of the trials will become available and our research and development programs;

• the sufficiency of our existing cash and cash equivalents to fund our future operating expenses and capital expenditure requirements;

• the timing or likelihood of regulatory filings for CTX-009, CTX-471, CTX-8371 and any other product candidates we develop and our ability to obtain and maintain regulatory approvals for such product candidates for any indication;

• our expectations regarding the potential benefits, activity, effectiveness and safety of CTX-009, CTX-471, CTX-8371 and any other product candidates we develop;

• our intentions and ability to successfully commercialize our product candidates;

• our expectations regarding the nature of the biological pathways we are targeting;

• our estimates regarding the use of proceeds from this offering, expenses, future revenues,

• capital requirements and our need for or ability to obtain additional financing, together with our current cash, cash equivalents and marketable securities, to fund our operations;

• our intended reliance on and the performance of third parties, including collaborators, contract research organizations and third-party manufacturers;

• our ability to protect and enforce our intellectual property protection and the scope and duration of such protection;

• developments and projections relating to our competitors and our industry, including competing therapies;

• the impact of current and future laws and regulations;

• the impact of the COVID-19 pandemic on our business, results of operations and future growth prospects; and

• other risks and uncertainties, including those listed under the caption “Risk Factors”.

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These statements relate to future events or our future operational or financial performance, and involve known and unknown risks, uncertainties and other factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by these forward-looking statements. Factors that may cause actual results to differ materially from current expectations include, among other things, those listed under the section titled “Risk Factors” and elsewhere in this prospectus, in any applicable prospectus supplement and in any related free writing prospectus.

Any forward-looking statement in this prospectus, in any applicable prospectus supplement and in any related free writing prospectus reflects our current view with respect to future events and is subject to these and other risks, uncertainties and assumptions relating to our business, results of operations, industry and future growth. Given these uncertainties, you should not place undue reliance on these forward-looking statements. No forward-looking statement is a guarantee of future performance. You should read this prospectus, any applicable prospectus supplement and any related free writing prospectus and the documents that we reference therein and have filed with the SEC as exhibits thereto completely and with the understanding that our actual future results may be materially different from any future results expressed or implied by these forward-looking statements. Except as required by law, we assume no obligation to update or revise these forward-looking statements for any reason, even if new information becomes available in the future.

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USE OF PROCEEDS

We may issue and sell shares of our common stock having aggregate sales proceeds of up to $75,000,000 million from time to time. Because there is no minimum offering amount required as a condition to close this offering, the actual total public offering amount, commissions and proceeds to us, if any, are not determinable at this time. There can be no assurance that we will sell any shares under or fully utilize the sales agreement with B. Riley Securities as a source of financing.

We currently intend to use the net proceeds from the sale of any securities offered under this prospectus for general corporate purposes unless otherwise indicated in the applicable prospectus supplement. General corporate purposes may include research and development and clinical development costs to support the advancement of our product candidates and the expansion of our product candidate pipeline; repayment and refinancing of debt; working capital; and capital expenditures. We may also use a portion of the net proceeds to acquire or invest in businesses, products and technologies that are complementary to our own, although we have no commitments or agreements with respect to any acquisitions as of the date of this prospectus. Pending these uses, we may invest the net proceeds in a variety of capital preservation instruments, including short-term, investment-grade, interest-bearing instruments and U.S. government securities, or may hold such proceeds as cash, until they are used for their stated purpose. We have not determined the amount of net proceeds to be used specifically for such purposes. As a result, management will retain broad discretion over the allocation of net proceeds.

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DILUTION

Our historical net tangible book value as of March 31, 2021 was $33.5 million, or $0.54 per share. Net tangible book value per share is determined by dividing our total tangible assets, less total liabilities, by the number of shares of our common stock outstanding as of June 30, 2021.

After giving effect to the sale of 15,306,122 shares of our common stock in this offering at an assumed offering price of $4.90 per share, the last reported sale price of our common stock on the OTCQB Market on July 2, 2021, and after deducting estimated offering commissions and offering expenses payable by us, our as adjusted net tangible book value as of March 31, 2021 (with shares adjusted for June 30, 2021) would have been $106.2 million, or $1.37 per share. This represents an immediate increase in net tangible book value of $0.83 per share to existing stockholders and immediate dilution of $3.53 per share to investors purchasing our common stock in this offering at the public offering price. The following table illustrates this dilution on a per share basis:

Assumed public offering price per share			$	4.90
Historical net tangible book value per share of as March 31, 2021	$	0.54
Increase in net tangible book value per share attributable to new investors purchasing shares of common stock in this offering		0.83
As adjusted net tangible book value per share as of March 31, 2021, after giving effect to this offering				1.37
Dilution per share to investors purchasing our common stock in this offering			$	3.53

The number of shares of common stock outstanding is based on an aggregate of 62,323,147 shares outstanding as of June 30, 2021 and excludes 5,015,513 shares of common stock reserved under the 2020 Incentive Plan, from which options to purchase an aggregate of 3,372,083 shares of common stock, at a weighted-average exercise price of $5.15 per share, have been granted and remain unexercised.

The table above assumes for illustrative purposes that an aggregate of 15,306,122 shares of our common stock are sold during the term of the sales agreement with B. Riley Securities at a price of $4.90 per share, the last reported sale price of our common stock on the OTCQB Market on July 2, 2021, for aggregate gross proceeds of $75 million. The shares subject to the sales agreement with B. Riley Securities are being sold from time to time at various prices. An increase of $1.00 per share in the price at which the shares are sold from the assumed offering price of $4.90 per share shown in the table above, assuming all of our common stock in the aggregate amount of $75 million during the term of the sales agreement with B. Riley Securities is sold at that price, would increase our pro forma as adjusted net tangible book value per share to $1.42 per share and would change the dilution in net tangible book value per share to new investors in this offering to $3.48 per share, after deducting commissions and estimated aggregate offering expenses payable by us. A decrease of $1.00 per share in the price at which the shares are sold from the assumed offering price of $3.90 per share shown in the table above, assuming all of our common stock in the aggregate amount of $75 million during the term of the sales agreement with B. Riley Securities is sold at that price, would decrease our pro forma as adjusted net tangible book value per share to $1.30 per share and would change the dilution in net tangible book value per share to new investors in this offering to $3.60 per share, after deducting commissions and estimated aggregate offering expenses payable by us. This information is supplied for illustrative purposes only and assumes no exercise of the options or warrants outstanding as of June 30, 2021. For more information, see “Description of Capital Stock.”

To the extent that options and warrants outstanding as of June 30, 2021 have been or may be exercised or other shares issued, investors purchasing our common stock in this offering may experience further dilution. In addition, we may choose to raise additional capital due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. To the extent that additional capital is raised through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our stockholders.

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DESCRIPTION OF CAPITAL STOCK

The following description of our capital stock and provisions of our amended and restated certificate of incorporation and amended and restated bylaws are summaries. You should also refer to the amended and restated certificate of incorporation and the amended and restated bylaws, which are filed as exhibits to the registration statement of which this prospectus is part.

We have authorized capital stock consisting of 300,000,000 shares of common stock and 10,000,000 shares of preferred stock, each of par value $0.0001 per share. Except as otherwise provided in the certificate of designation of any series of preferred stock we may issue, the number of authorized shares of common stock or preferred stock may from time to time be increased or decreased (but not below the number of shares of such class outstanding) by the affirmative vote of the holders of a majority in voting power of the outstanding shares of our capital stock.

As of June 30, 2021, we had 62,323,147 shares of common stock issued and outstanding, and no shares of preferred stock issued and outstanding. Unless stated otherwise, the following discussion summarizes the term and provisions of our amended and restated certificate of incorporation and our amended and restated bylaws.

Common Stock

The holders of outstanding shares of common stock are entitled to receive dividends out of assets or funds legally available for the payment of dividends at such times and in such amounts as the board of directors from time to time may determine. Holders of common stock are entitled to one vote for each share held on all matters submitted to a vote of stockholders. There is no cumulative voting of the election of directors then standing for election. The common stock is not entitled to pre-emptive rights and is not subject to conversion or redemption. Upon liquidation, dissolution or winding up of our company, the assets legally available for distribution to stockholders are distributable ratably among the holders of the common stock after payment of liquidation preferences, if any, on any outstanding payment of other claims of creditors. Each outstanding share of common stock is duly and validly issued, fully paid and non-assessable.

Preferred Stock

Shares of preferred stock may be issued from time to time in one or more series, each of which will have such distinctive designation or title as may be determined by our board of directors prior to the issuance of any shares thereof. Preferred stock will have such voting powers, full or limited, or no voting powers, and such preferences and relative, participating, optional or other special rights and such qualifications, limitations or restrictions thereof, as shall be stated in such resolution or resolutions providing for the issue of such class or series of preferred stock as may be adopted from time to time by the board of directors prior to the issuance of any shares thereof.

While we do not currently have any plans for the issuance of additional preferred stock, the issuance of such preferred stock could adversely affect the rights of the holders of common stock and, therefore, reduce the value of the common stock. It is not possible to state the actual effect of the issuance of any shares of preferred stock on the rights of holders of the common stock until the board of directors determines the specific rights of the holders of the preferred stock; however, these effects may include:

• Restricting dividends on the common stock;

• Diluting the voting power of the common stock;

• Impairing the liquidation rights of the common stock; or

• Delaying or preventing a change in control of our company without further action by the stockholders.

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Other than in connection with shares of preferred stock, which preferred stock is not currently designated nor contemplated by us, and the division of our board of directors into three classes with staggered three-year terms, we do not believe that any provision of our amended and restated certificate of incorporation or amended and restated bylaws would delay, defer or prevent a change in control.

Other Convertible Securities

As of the date hereof, other than the securities described above, we do not have any outstanding convertible securities.

Anti-Takeover Effects of Provisions of our Amended and Restated Certificate of Incorporation, our Amended and Restated Bylaws and Delaware Law

Some provisions of Delaware law, our amended and restated certificate of incorporation and our amended and restated bylaws contain provisions that could make the following transactions more difficult: (i) acquisition of us by means of a tender offer (ii) acquisition of us by means of a proxy contest or otherwise, or (iii) removal of our incumbent officers and directors. It is possible that these provisions could make it more difficult to accomplish or could deter transactions that stockholders may otherwise consider to be in their best interest or in our best interests, including transactions that might result in a premium over the price of our common stock.

These provisions, summarized below, are expected to discourage coercive takeover practices and inadequate takeover bids. These provisions are also designed to encourage persons seeking to acquire control of us to first negotiate with our board of directors. We believe that the benefits of increased protection of our potential ability to negotiate with the proponent of an unfriendly or unsolicited proposal to acquire or restructure us outweigh the disadvantages of discouraging these proposals because negotiation of these proposals could result in an improvement of their terms.

Delaware Anti-Takeover Statute

We are subject to Section 203 of the DGCL, which prohibits a person deemed an “interested stockholder” from engaging in a “business combination” with a publicly held Delaware corporation for three years following the date such person becomes an interested stockholder unless the business combination is, or the transaction in which the person became an interested stockholder was, approved in a prescribed manner or another prescribed exception applies. Generally, an “interested stockholder” is a person who, together with affiliates and associates, owns, or within three years prior to the determination of interested stockholder status did own, 15% or more of a corporation’s voting stock. Generally, a “business combination” includes a merger, asset or stock sale, or other transaction resulting in a financial benefit to the interested stockholder. The existence of this provision may have an anti-takeover effect with respect to transactions not approved in advance by the board of directors, such as discouraging takeover attempts that might result in a premium over the price of our common stock.

Undesignated Preferred Stock

The ability to authorize undesignated preferred stock makes it possible for our board of directors to issue preferred stock with voting or other rights or preferences that could impede the success of any attempt to change control of our company. These and other provisions may have the effect of deterring hostile takeovers or delaying changes in control or management of our company.

Special Stockholder Meetings

Our amended and restated bylaws provide that a special meeting of stockholders may be called only by a majority of our board of directors then in office.

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Requirements for Advance Notification of Stockholder Nominations and Proposals

Our amended and restated bylaws establish advance notice procedures with respect to stockholder proposals and the nomination of candidates for election as directors, other than nominations made by or at the direction of the board of directors or a committee of the board of directors.

Elimination of Stockholder Action by Written Consent

Our amended and restated certificate of incorporation will eliminate the right of stockholders to act by written consent without a meeting.

Classified Board; Election and Removal of Directors

Our board of directors is divided into three classes. The directors in each class will serve for a three-year term, one class being elected each year by our stockholders, with staggered three-year terms. Only one class of directors will be elected at each annual meeting of our stockholders, with the other classes continuing for the remainder of their respective three-year terms. Because our stockholders do not have cumulative voting rights, our stockholders holding a majority of the shares of our common stock outstanding will be able to elect all of our directors. In addition, our directors may not be removed without cause, and removal of our directors for cause will require a supermajority (66 2/3%) stockholder vote. For more information on the classified board of directors, see the section titled “Management—Board Composition”. This system of electing and removing directors may tend to discourage a third party from making a tender offer or otherwise attempting to obtain control of us, because it generally makes it more difficult for stockholders to replace a majority of the directors.

Choice of Forum

Our amended and restated bylaws provide that the Court of Chancery of the State of Delaware shall be the sole and exclusive forum for any state law claims for: (i) any derivative action or proceeding brought on behalf of our company, (ii) any action asserting a claim of breach of a fiduciary duty owed by any of our directors or officers to the company or our stockholders, (iii) any action asserting a claim against our company arising pursuant to any provision of the DGCL or our certificate of incorporation or bylaws, (iv) any action to interpret, apply, enforce, or determine the validity of our certificate of incorporation or bylaws, or (v) any action asserting a claim against our company governed by the internal affairs doctrine. This exclusive forum provision will not apply to any causes of action arising under the Securities Act or the Exchange Act or any other claim for which the federal courts have exclusive jurisdiction. Unless we consent in writing to the selection of an alternate forum, the United States District Court for the District of Massachusetts is the sole and exclusive forum for resolving any complaint asserting a cause of action arising under the Securities Act, as our principal executive office is located Cambridge, Massachusetts. Although our amended and restated bylaws contain the choice of forum provision described above, it is possible that a court could rule that such provisions are inapplicable for a particular claim or action or that such provisions are unenforceable.

Amendment of Charter and Bylaw Provisions

The amendment of any of the above provisions in our amended and restated certificate of incorporation and amended and restated bylaws, except for the provision making it possible for our board of directors to issue convertible preferred stock, would require a supermajority (66 2/3% and majority of the minority, if applicable) stockholder vote.

The provisions of the DGCL, our amended and restated certificate of incorporation and amended and restated bylaws could have the effect of discouraging others from attempting hostile takeovers and, as a consequence, they may also inhibit temporary fluctuations in the price of our common stock that often result from actual or rumored hostile takeover attempts. These provisions may also have the effect of preventing changes in our management. It is possible that these provisions could make it more difficult to accomplish transactions that stockholders may otherwise deem to be in their best interests.

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Limitations of Liability and Indemnification Matters

For a discussion of liability and indemnification, see the section titled “Directors, Executive Officers, Promoters and Control Persons—Limitation on Liability and Indemnification Matters”.

Transfer Agent

We have appointed American Stock Transfer & Trust Company to serve as transfer agent and registrar for our common stock.

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PLAN OF DISTRIBUTION

We have entered into a sales agreement with B. Riley Securities, under which we may issue and sell from time to time up to $75,000,000 of our common stock through or to B. Riley Securities as our sales agent or principal. Sales of our common stock, if any, will be made at market prices by any method that is deemed to be “at the market” as defined in Rule 415(a)(4) under the Securities Act, including sales made directly on any trading market for our common stock. No offers or sales shall occur pursuant to this prospectus until such time as our common stock is listed on a national securities exchange. If authorized by us in writing, B. Riley Securities may purchase shares of our common stock as principal.

B. Riley Securities will offer our common stock subject to the terms and conditions of the sales agreement on a daily basis or as otherwise agreed upon by us and B. Riley Securities. We will designate the maximum amount of common stock to be sold through B. Riley Securities on a daily basis or otherwise determine such maximum amount together with B. Riley Securities. Subject to the terms and conditions of the sales agreement, B. Riley Securities will use its commercially reasonable efforts to sell on our behalf all of the shares of common stock requested to be sold by us. We may instruct B. Riley Securities not to sell common stock if the sales cannot be effected at or above the price designated by us in any such instruction. B. Riley Securities or we may suspend the offering of our common stock being made through B. Riley Securities under the sales agreement upon proper notice to the other party. B. Riley Securities and we each have the right, by giving written notice as specified in the sales agreement, to terminate the sales agreement in each party’s sole discretion at any time.

The aggregate compensation payable to B. Riley Securities as sales agent up to 3.0% of the gross sales price of the shares sold through it pursuant to the sales agreement. We have also agreed to reimburse B. Riley Securities up to $50,000 of B. Riley Securities’ actual outside legal expenses incurred by B. Riley Securities in connection with this offering. We estimate that the total expenses of the offering payable by us, excluding commissions payable to B. Riley Securities under the sales agreement, will be approximately $70,000.

The remaining sales proceeds, after deducting any expenses payable by us and any transaction fees imposed by any governmental, regulatory, or self-regulatory organization in connection with the sales, will equal our net proceeds for the sale of such common stock.

B. Riley Securities will provide written confirmation to us following the close of trading on the on each day in which common stock is sold through it as sales agent under the sales agreement. Each confirmation will include the number of shares of common stock sold through it as sales agent on that day, the volume weighted average price of the shares sold, the percentage of the daily trading volume and the net proceeds to us.

We will report at least quarterly the number of shares of common stock sold through B. Riley Securities under the sales agreement, the net proceeds to us and the compensation paid by us to B. Riley Securities in connection with the sales of common stock.

Settlement for sales of common stock will occur, unless the parties agree otherwise or otherwise required by law, on the third business day that is also a trading day following the date on which any sales were made in return for payment of the net proceeds to us. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

In connection with the sales of our common stock on our behalf, B. Riley Securities will be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation paid to B. Riley Securities will be deemed to be underwriting commissions or discounts. We have agreed in the sales agreement to provide indemnification and contribution to B. Riley Securities against certain liabilities, including liabilities under the Securities Act. As sales agent, B. Riley Securities will not engage in any transactions that stabilizes our common stock.

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Our common stock is currently listed on the OTCQB Market and trades under the symbol “CMPX.” The transfer agent of our common stock is American Stock Transfer & Trust Company.

B. Riley Securities and/or its affiliates have provided, and may in the future provide, various investment banking and other financial services for us for which services they have received and, may in the future receive, customary fees.

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LEGAL MATTERS

Certain legal matters in connection with this offering will be passed upon for us by Goodwin Procter LLP, Boston, Massachusetts. B. Riley Securities is being represented in connection with this offering by Duane Morris LLP, New York, New York.

EXPERTS

The consolidated financial statements of Compass Therapeutics, Inc. and subsidiaries as of December 31, 2020 and 2019 incorporated in this registration statement by reference from the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 have been audited by CohnReznick LLP, an independent registered public accounting firm, as set forth in their report thereon, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC this registration statement on Form S-3 under the Securities Act with respect to the shares of common stock being offered by this prospectus. This prospectus, which constitutes a part of this registration statement, does not contain all of the information in this registration statement and its exhibits. For further information with respect to us and the common stock offered by this prospectus, you should refer to this registration statement and the exhibits filed as part of this document. Statements contained in this prospectus as to the contents of any contract or any other document referred to are not necessarily complete, and in each instance, we refer you to the copy of the contract or other document filed as an exhibit to this registration statement. Each of these statements is qualified in all respects by this reference.

We are subject to the informational requirements of the Exchange Act and file annual, quarterly and current reports, proxy statements and other information with the SEC. You can read our SEC filings, including this registration statement, over the Internet on the SEC’s website at http://www.sec.gov. You may also request a copy of these filings, at no cost, by writing or telephoning us at: 80 Guest Street, Suite 601, Boston, Massachusetts 02135, (617) 500-8099

INCORPORATION BY REFERENCE

We have elected to incorporate the following documents into this prospectus, together with all exhibits filed therewith or incorporated therein by reference, to the extent not otherwise amended or superseded by the contents of this prospectus:

• our Annual Report on Form 10-K for the fiscal year ended December 31, 2020, as filed with the SEC on March 5, 2021;

• our Quarterly Report on Form 10-Q for the quarter ended March 31, 2021, as filed with the SEC on April 30, 2021;

• our definitive proxy statement on Schedule 14A, as filed with the SEC on April 29, 2021; and

• our Current Reports on Form 8-K filed with the SEC on April 19, 2021, May 13, 2021, June 4, 2021 and June 30, 2021 (other than any reports or portions thereof that are furnished under Item 2.02 or Item 7.01 and any exhibits included with such Items).

The information incorporated by reference is an important part of this prospectus. In addition, we incorporate by reference in this prospectus any future filings we make with the SEC under Sections 13(a), 13(c), 14, or 15(d) of the Exchange Act (excluding any information furnished and not filed with the SEC) after the date on which the

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registration statement that includes this prospectus was initially filed with the SEC (including all such documents we may file with the SEC after the date of the initial registration statement and prior to the effectiveness of the registration statement) and until all offerings under this prospectus are terminated.

Any statement contained in a document incorporated by reference herein shall be deemed to be modified or superseded for all purposes to the extent that a statement contained in this prospectus or in any other subsequently filed document which is also incorporated or deemed to be incorporated by reference, modifies or supersedes such statement. Any statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus. You may request a copy of these filings (other than an exhibit to a filing unless that exhibit is specifically incorporated by reference into that filing) at no cost by writing, telephoning or e-mailing us at the following address or telephone number:

Compass Therapeutics, Inc.

80 Guest Street

Suite 601

Boston, Massachusetts 02135

(617) 500-8099

You may also access these documents, free of charge on the SEC’s website at www.sec.gov or on our website at www.compasstherapeutics.com. Information contained on our website is not incorporated by reference into this prospectus, and you should not consider any information on, or that can be accessed from, our website as part of this prospectus or any accompanying prospectus supplement.

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$75,000,000

Common Stock

PROSPECTUS

B. Riley Securities

July 20, 2021