UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

September 30, 2015

Date of Report (Date of earliest event reported)

SYCAMORE NETWORKS, INC.

(Exact name of registrant as specified in its charter)

300 Brickstone Square, Suite 201

Andover, MA 01810

(Address of principal executive offices)

(Zip code)

Registrant’s telephone number, including area code: (978) 662-5245

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Item 1.01: Entry into a Material Definitive Agreement

As previously reported, on October 10, 2014, Sycamore Networks, Inc. (the “Company”) entered into a Purchase and Sale Agreement, as amended on each of February 24, 2015, March 27, 2015, March 30, 2015, July 30, 2015 and September 15, 2015, relating to the sale of approximately 102 acres of undeveloped land located in Tyngsborough, Massachusetts (the “Tyngsborough Land”) to Princeton Tyngsborough Commons LLC (“Buyer”) for a total purchase price of $2.5 million (the “Purchase Agreement”). On September 30, 2015, the Company and Buyer entered into a Sixth Amendment to Purchase and Sale Agreement (the “Sixth Amendment”) providing for, among other things, an extension of the closing date to October 14, 2015. The terms of the Purchase Agreement, as amended, provide that in the event that Buyer defaults on its obligation to complete the transaction, the Company will retain the entire amount of the deposits, which totalled $350,000 as of October 5, 2015.

The closing of the sale is subject to certain conditions and obligations of the parties prior to closing, some of which are outside of the Company’s control and, accordingly, there can be no assurance when or if such closing will occur. If the Purchase Agreement is terminated, there can be no assurance of when, if ever, the Company will be able to sell the Tyngsborough Land. The inability to sell the Tyngsborough Land may delay the completion of the Company’s liquidation and related distributions to its stockholders.

A copy of the Sixth Amendment is attached as Exhibit 10.1 to this Current Report on Form 8-K and is incorporated herein by reference. The descriptions of the Purchase Agreement and the Sixth Amendment in this Current Report are summaries and are qualified in their entirety by reference to the complete text of such agreements. For further information regarding the transaction, please see Item 1.01 of the Company’s Current Report on Form 8-K filed on October 17, 2014 and the terms and conditions of the Purchase Agreement filed as Exhibit 10.1 thereto; Item 1.01 of the Company’s Current Report on Form 8-K filed on February 26, 2015 and the terms and conditions of the first amendment to the Purchase Agreement filed as Exhibit 10.1 thereto; Item 1.01 of the Company’s Current Report on Form 8-K filed on April 1, 2015 and the terms and conditions of the second and third amendments to the Purchase Agreement filed as Exhibit 10.1 and Exhibit 10.2 thereto, respectively; Item 1.01 of the Company’s Current Report on Form 8-K filed on August 4, 2015 and the terms and conditions of the fourth amendment to the Purchase Agreement filed as Exhibit 10.1 thereto; Item 1.01 of the Company’s Current Report on Form 8-K filed on September 17, 2015 and the terms and conditions of the fifth amendment to the Purchase Agreement filed as Exhibit 10.1 thereto; the Company’s Annual Report on Form 10-K for the year ended July 31, 2014 filed on October 27, 2014; the Company’s Quarterly Report on Form 10-Q for the quarterly period ended October 25, 2014 filed on December 4, 2014; the Company’s Quarterly Report on Form 10-Q for the quarterly period ended January 24, 2015 filed on March 9, 2015; and the Company’s Quarterly Report on Form 10-Q for the quarterly period ended April 25, 2015 filed on June 5, 2015.

Item 9.01: Financial Statements and Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

Dated: October 5, 2015