Filed by the Registrant

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Filed by a Party other than the Registrant

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Preliminary Proxy Statement

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Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

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Definitive Proxy Statement

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Definitive Additional Materials

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Soliciting Material Pursuant to § 240.14a-12

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No fee required.

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Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.

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Title of each class of securities to which transaction applies:

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Proposed maximum aggregate value of transaction:

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Total fee paid:

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Fee paid previously with preliminary materials.

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Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously.  Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

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Amount Previously Paid:

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Form, Schedule or Registration Statement No.:

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Filing Party:

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Date Filed:

MMMMMMMMMMMM + MMMMMMM C 1234567890 The Sample Company 000004 ENDORSEMENT_LINE______________ SACKPACK_____________ MR A SAMPLE DESIGNATION (IF ANY) ADD 1 ADD 2 ADD 3 ADD 4 ADD 5 ADD 6 Online Go to www.envisionreports.com/XNCR or scan the QR code — login details are located in the shaded bar below. Important Notice Regarding the Availability of Proxy Materials for the Xencor, Inc. Shareholder Meeting to be Held on June 25, 2020 Under Securities and Exchange Commission rules, you are receiving this notice that the proxy materials for the annual shareholders’ meeting are available on the Internet. Follow the instructions below to view the materials and vote online or request a copy. The items to be voted on and location of the annual meeting are on the reverse side. Your vote is important! This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. The 2020 proxy statement and annual report to shareholders are available at: www.envisionreports.com/XNCR Easy Online Access — View your proxy materials and vote. Step 1: Step 2: Step 3: Step 4: Step 5: Go to www.envisionreports.com/XNCR. Click on Cast Your Vote or Request Materials. Follow the instructions on the screen to log in. Make your selections as instructed on each screen for your delivery preferences. Vote your shares. When you go online, you can also help the environment by consenting to receive electronic delivery of future materials. Obtaining a Copy of the Proxy Materials – If you want to receive a copy of the proxy materials, you must request one. There is no charge to you for requesting a copy. Please make your request as instructed on the reverse side on or before June 12, 2020 to facilitate timely delivery. + 2 N O T C O Y 0386EB MMMMMMMMM Shareholder Meeting Notice 1234 5678 9012 345

Xencor’s Annual Meeting of Shareholders will be held on Thursday, June 25, 2020 at 2:30 p.m. Pacific Time, virtually via the Internet at www.meetingcenter.io/264465325. To access the virtual meeting, you must have the 15 digit number that is printed in the shaded bar located on the reverse side of this form. The password for the meeting is XNCR2020. Proposals to be voted on at the meeting are listed below along with the Board of Directors’ recommendations. The Board of Directors recommend a vote FOR all the nominees listed and FOR Proposals 2 and 3: 1. 2. 3. Election of Directors. Proposal to ratify RSM US LLP as the independent registered public accounting firm for 2020. Proposal to approve, on an advisory basis, the compensation of the Company’s named executive officers as disclosed in the proxy materials. PLEASE NOTE – YOU CANNOT VOTE BY RETURNING THIS NOTICE. To vote your shares you must go online or request a paper copy of the proxy materials to receive a proxy card. Here’s how to order a copy of the proxy materials and select delivery preferences: Current and future delivery requests can be submitted using the options below. If you request an email copy, you will receive an email with a link to the current meeting materials. PLEASE NOTE: You must use the number in the shaded bar on the reverse side when requesting a copy of the proxy materials. — — — Internet – Go to www.envisionreports.com/XNCR. Click Cast Your Vote or Request Materials. Phone – Call us free of charge at 1-866-641-4276. Email – Send an email to investorvote@computershare.com with “Proxy Materials Xencor, Inc.” in the subject line. Include your full name and address, plus the number located in the shaded bar on the reverse side, and state that you want a paper copy of the meeting materials. To facilitate timely delivery, all requests for a paper copy of proxy materials must be received by June 12, 2020. Shareholder Meeting Notice

MMMMMMMMMMMM Using a black ink pen, mark your votes with an X as shown in this example. Please do not write outside the designated areas. q IF VOTING BY MAIL, SIGN, DETACH AND RETURN THE BOTTOM PORTION IN THE ENCLOSED ENVELOPE. q + 1. Election of Directors: For Withhold For Withhold For Withhold 01 - Bassil I. Dahiyat 02 - Ellen G. Feigal 03 - Kevin C. Gorman 04 - Kurt A. Gustafson 05 - Yujiro S. Hata 06 - A. Bruce Montgomery 07 - Richard J. Ranieri 08 - Dagmar Rosa-Bjorkeson ForAgainst Abstain ForAgainst Abstain 2. Proposal to ratify RSM US LLP as the independent registered public accounting firm for 2020 3. Proposal to approve, on an advisory basis, the compensation of the Company’s named executive officers as disclosed in the proxy materials Please sign exactly as name(s) appears hereon. Joint owners should each sign. When signing as attorney, executor, administrator, corporate officer, trustee, guardian, or custodian, please give full title. Date (mm/dd/yyyy) — Please print date below. Signature 1 — Please keep signature within the box. Signature 2 — Please keep signature within the box. + 1 U P X 4 5 8 5 9 9 0386DC MMMMMMMMM B Authorized Signatures — This section must be completed for your vote to count. Please date and sign below. A Proposals — The Board of Directors recommend a vote FOR all the nominees listed and FOR Proposals 2 and 3. Xencor, Inc. Annual Meeting Proxy Card

q IF VOTING BY MAIL, SIGN, DETACH AND RETURN THE BOTTOM PORTION IN THE ENCLOSED ENVELOPE. q Notice of 2020 Annual Meeting of Shareholders Proxy Solicited by Board of Directors for Annual Meeting — June 25, 2020 Bassil I. Dahiyat, John J. Kuch or Celia E. Eckert, or any of them, each with the power of substitution, are hereby authorized to represent and vote the shares of the undersigned, with all the powers which the undersigned would possess if personally present, at the Annual Meeting of Shareholders of Xencor, Inc. to be held on June 25, 2020 or at any postponement or adjournment thereof. Shares represented by this proxy will be voted by the stockholder. If no such directions are indicated, the Proxies will have authority to vote FOR all nominees, and FOR Proposals 2 and 3. In their discretion, the Proxies are authorized to vote upon such other business as may properly come before the meeting. (Items to be voted appear on reverse side) Proxy — Xencor, Inc.