As filed with the Securities and Exchange Commission on or about September 21, 2021

Registration Statement File No. 333-45039

Registration Statement File No. 811-08619

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-4

REGISTRATION STATEMENT

UNDER THE SECURITIES ACT OF 1933

¨   Pre-Effective Amendment No.

x   Post-Effective Amendment No. 30

and/or

REGISTRATION STATEMENT

UNDER THE INVESTMENT COMPANY ACT OF 1940

x   Amendment No. 206

(Check appropriate box or boxes.)

Massachusetts Mutual Variable Annuity Separate Account 4

(Exact Name of Registrant)

Massachusetts Mutual Life Insurance Company

(Name of Depositor)

1295 State Street, Springfield, Massachusetts 01111

(Address of Depositor’s Principal Executive Offices)

(413) 788-8411

(Depositor’s Telephone Number, Including Area Code)

John E. Deitelbaum

Head of MMUS Law

Massachusetts Mutual Life Insurance Company

1295 State Street

Springfield, Massachusetts 01111

(Name and Address of Agent for Service)

Approximate Date of Proposed Public Offering: Continuous.

It is proposed that this filing will become effective (check appropriate box)

If appropriate, check the following box:

EXPLANATORY NOTE

Designation of New Effective Date for Previously Filed Post-Effective Amendment

Post-Effective Amendment No. 28 was filed pursuant to Rule 485(a)(1) under the Securities Act of 1933 and Amendment No. 203 was filed under the Investment Company Act of 1940 on June 25, 2021 (collectively, the “Amendments”), and pursuant to Rule 485(a)(1) would have become effective on August 24, 2021. Post-Effective Amendment No. 29 and Amendment No. 204 (collectively, the “Subsequent Amendments”) were filed pursuant to Rule 485(b)(1)(iii) for the sole purpose of designating September 22, 2021 as the new date upon which the Amendments shall become effective. This Post-Effective Amendment No. 30 and Amendment No. 206 are being filed pursuant to Rule 485(b)(1)(iii) for the sole purpose of designating October 21, 2021 as the new date upon which the Amendments shall become effective.

PARTS A, B, AND C

The Prospectus dated May 1, 2021 is incorporated into Part A of this Post-Effective Amendment No. 30 by reference to Registrant’s filings under Rule 485(b) as filed on April 28, 2021 and Rule 485(a) as filed on June 25, 2021.

The Statement of Additional Information dated May 1, 2021 is incorporated into Part B of this Post-Effective Amendment No. 30 by reference to Registrant’s filings under Rule 485(b) as filed on April 28, 2021 and Rule 485(a) as filed on June 25, 2021.

The Other Information section is incorporated into Part C of this Post-Effective Amendment No. 30 by reference to Registrant’s filing under Rule 485(a) as filed on June 25, 2021.

SIGNATURES

Pursuant to the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this Registration Statement under Rule 485(b) under the Securities Act and has duly caused this Registration Statement to be signed on its behalf, duly authorized, in the town of Ellington, and the State of Connecticut on this 21st day of September, 2021.

MASSACHUSETTS MUTUAL VARIABLE ANNUITY SEPARATE ACCOUNT 4

(Registrant)

MASSACHUSETTS MUTUAL LIFE INSURANCE COMPANY

(Depositor)

As required by the Securities Act of 1933, this Post-Effective Amendment to the Registration Statement has been signed by the following persons in the capacities and on the dates indicated.