13D Filing: Abdiel Qualified Master Fund LP and Appian Corp (APPN)

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

SCHEDULE 13D

(Rule 13d-101)

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 3)*

Appian
Corporation

(Name of Issuer)

Class A Common Stock, $0.001 par value per share

(Title of Class of Securities)

03782L101

(CUSIP Number)

Abdiel Capital

410 Park Avenue, Suite 930

New York, NY 10022

Attn:
Colin T. Moran

Tel: (646) 496-9202

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

June 30, 2017

(Date of
Event Which Requires Filing of This Statement)

If the filing person has
previously filed a statement on Schedule 13G to report the acquisition which is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box.  ☐

Note. Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for
other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be
deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act
(however, see the Notes).

AMENDMENT NO. 3 TO SCHEDULE 13D

This Amendment No. 3 (Amendment No. 3) amends and supplements the Schedule 13D filed on June 12, 2017 (the Original
Schedule 13D) as amended by Amendment No. 1 thereto on June 27, 2017 (Amendment No. 1) and Amendment No. 2 thereto on June 29, 2017 (Amendment No. 2 and, together with the Original
Schedule 13D and Amendment No. 1, the Schedule 13D), relating to the shares of Class A common stock, $0.001 par value per share (the Common Stock), of Appian Corporation (the Issuer). Each Item below
amends and supplements the information disclosed under the corresponding Item of the Schedule 13D. Except as specifically provided herein, this Amendment No. 3 does not modify any of the information previously reported in the Schedule 13D.
Capitalized terms used but not defined in this Amendment No. 3 shall have the same meanings herein as are ascribed to such terms in the Schedule 13D.

Item 3 of the Schedule 13D is hereby
supplemented by adding the following:

In a series of transactions completed through July 3, 2017, the Reporting Persons acquired an aggregate amount of
129,893 shares of the Common Stock for the accounts of Abdiel Qualified Master Fund, LP and Abdiel Capital, LP for aggregate consideration of approximately $2.4 million (including commissions). The source of funds used to acquire the 129,893 shares
of Common Stock was the working capital of Abdiel Qualified Master Fund, LP and Abdiel Capital, LP.

Item 5 of the Schedule 13D is hereby amended by amending and
restating paragraphs (a) and (b) thereof as follows:

(a) The information requested by this paragraph is incorporated herein by reference to the
information provided on the cover pages to this Amendment No. 3.

(b) The information requested by this paragraph is incorporated herein by reference
to the information provided on the cover pages to this Amendment No. 3 and Item 2(c) of the Schedule 13D.

Item 5(c) of the Schedule 13D is
hereby supplemented by adding the following:

(c) Information with respect to all transactions in the Common Stock which were effected by each of the
Reporting Persons since the filing of Amendment No. 3 is set forth on Exhibit E attached hereto and incorporated herein by reference.

Item 7 of the Schedule 13D is hereby amended by amending and
restating it as follows:

Exhibit A Joint Filing Agreement (filed as Exhibit A to the Schedule 13D on June 12, 2017)

Exhibit B Information with respect to Transactions Effected During the Past Sixty Days (filed as Exhibit B to the Schedule 13D on June 12, 2017)

Exhibit C Information with respect to Transactions Effected Since the Filing of the Schedule 13D (filed as Exhibit C to Amendment No. 1 on
June 27, 2017)

Exhibit D Information with respect to Transactions Effected Since the Filing of Amendment No. 1 (filed as Exhibit D to
Amendment No. 2 on June 29, 2017)

Exhibit E Information with respect to Transactions Effected Since the Filing of Amendment No. 2*

SIGNATURES

After reasonable inquiry and to the best of their knowledge and belief, the undersigned certify that the information set forth in this statement is true,
complete and correct.

Dated: July 3, 2017