Filing Details

Item 1(a).

Name of Issuer:

Catalyst Biosciences, Inc. (the "Issuer").

Item 1(b).

Address of Issuer's Principal Executive Offices:

260 Littlefield Avenue

South San Francisco, California 94080

Item 2(a).

Name of Persons Filing:

This Statement is filed on behalf of each of the following persons (collectively, the "Reporting Persons"):

Nexthera GP is the general partner of Nexthera Capital. Mr. Malek and Mr. Hershkovitz are the managing members Nexthera GP By virtue of these relationships, each of Nexthera GP, Mr. Malek and Mr. Hershkovitz may be deemed to have voting and dispositive power with respect to the shares of Common Stock (as defined below) beneficially owned by Nexthera Capital.

Item 2(b).

Address of Principal Business Office or, if None, Residence:

The address of the principal business office of each of the Reporting Persons is 900 Third Avenue, Suite 201.1, New York, New York 10022.

Item 2(c).

Citizenship:

Item 2(d).

Title of Class of Securities:

Common Stock, par value $0.001 per share (the "Common Stock")

Item 2(e).

CUSIP Number:

14888D208

Item 3.

If This Statement is Filed Pursuant to Rule 13d 1(b), or 13d-2(b) or (c), Check Whether the Person Filing is a:

Item 4.

Ownership.

Provide the following information regarding the aggregate number and percentage of the class of securities of the Issuer.

(a)

Amount beneficially owned:

As of the close of business on May 24, 2018, the Reporting Persons may be deemed to have  beneficially owned 577,624 shares of Common Stock.

(b)

Percent of class:

The aggregate percentage of Common Stock reported owned by each person named herein is based upon approximately 11,935,169 shares of Common Stock outstanding as of May 1, 2018, which is the total number of Common Stock outstanding as reported in the Issuer's Definitve Proxy Statement on Form DEF 14A filed with the Securities and Exchange Commission on May 11, 2018. As of the close of business on May 24, 2018, the Reporting Persons may be deemed to have beneficially owned approximately 4.8% of the outstanding Common Stock.

(c)

Number of shares as to which such person has:

(i)

Sole power to vote or to direct the vote:

See Cover Pages Items 5-9.

(ii)

Shared power to vote or to direct the vote

See Cover Pages Items 5-9.

(iii)

Sole power to dispose or to direct the disposition of

See Cover Pages Items 5-9.

(iv)

Shared power to dispose or to direct the disposition of

See Cover Pages Items 5-9.

Item 5.

Ownership of Five Percent or Less of a Class.

If this statement is being filed to report the fact that as of the date hereof the Reporting Persons have ceased to be the beneficial owner of more than five percent of the class of securities, check the following [X].

Item 6.

Ownership of More than Five Percent on Behalf of Another Person.

Not applicable.

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company.

Not applicable.

Item 8.

Identification and Classification of Members of the Group.

See Exhibit A to the Schedule 13G filed with the SEC on December 27, 2017.

Item 9.

Notice of Dissolution of Group.

Not applicable.

Item 10.

Certification.

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

SIGNATURES

After reasonable inquiry and to the best of its knowledge and belief, each of the undersigned certifies that the information with respect to it set forth in this statement is true, complete, and correct.