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

Date of Report (Date of earliest event reported): March 23, 2016 (March 22, 2016)

CENTENE CORPORATION

(Exact Name of Registrant as Specified in Charter)

Registrant’s telephone number, including area code: (314) 725-4477

(Former Name or Former Address, if Changed Since Last Report): N/A

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 (see General Instruction A.2. below):

Item 8.01. Other Events

As previously disclosed, Centene Corporation (“Centene”) entered into an Agreement and Plan of Merger, dated as of July 2, 2015 (the “Merger Agreement”), by and among Centene, Health Net, Inc., a Delaware corporation (“Health Net”), Chopin Merger Sub I, Inc., a Delaware corporation and a direct wholly owned subsidiary of Centene (“Merger Sub I”), and Chopin Merger Sub II, Inc., a Delaware corporation and a direct wholly owned subsidiary of Centene (“Merger Sub II” and, together with Centene and Merger Sub I, the “Applicant”), pursuant to which Merger Sub I will merge with and into Health Net (the “Merger”), with Health Net surviving the Merger as the surviving corporation (the “Surviving Corporation”) and, immediately following the Merger, the Surviving Corporation will merge with and into Merger Sub II (the “Second Merger” and, together with the Merger, the “Mergers”), with Merger Sub II surviving the Second Merger as the final surviving corporation, subject to the terms and conditions set forth in the Merger Agreement.

CDI Approval

On March 22, 2016, the California Department of Insurance (“CDI”) announced that it had issued an order approving the change in control of Health Net Life Insurance Company (“HNLIC”), a wholly owned subsidiary of Health Net (the “CDI Approval Order”). This change of control will occur upon the completion of the Mergers. The CDI Approval Order was issued in connection with the Applicant’s application (known as a “Form A”) that the Applicant previously filed with CDI in connection with the Mergers.

In connection with the Form A, Centene, Health Net, HNLIC and, with respect to select provisions, Health Net of California, Inc. (collectively, the “Companies”) executed a “Stipulation and Undertakings” with CDI (the “CDI Undertakings”). A copy of the CDI Undertakings, excluding the Confidential Appendix thereto which modifies and supplements certain of the undertakings, is attached hereto as Exhibit 99.1 and is incorporated by reference herein. The CDI Undertakings contain various commitments by the Companies that will be effective upon completion of the Mergers, including, but not limited to, the following:

The commitments set forth in the CDI Undertakings are subject to the enforcement mechanisms established in Undertaking 21 of the CDI Undertakings.

The CDI Undertakings will become effective on the closing date of the Merger and, except as expressly set forth otherwise with respect to one or more particular undertakings or provisions, will remain in full force and effect until the earlier of (i) five (5) years ending on the fifth anniversary of the closing date of the Merger, (ii) the date on which Centene ceases to maintain a majority of voting power, direct or indirect, over HNLIC, as established by CDI approving a Form A authorizing a change of control or a divestiture or (iii) the date terminated with the written consent of the California Insurance Commissioner.

DMHC Approval

On March 22, 2016, the California Department of Managed Health Care (“DMHC”) announced that it had issued orders approving the change of control of Health Net of California, Inc. (“HNCA”), Health Net Community Solutions, Inc. (“HNCS”) and Managed Health Network (“MHN” and, together with HNCA and HNCS, the “Knox-Keene Entities”), each a wholly owned subsidiary of Health Net (the “DMHC Approval Orders”). This change of control will occur upon the completion of the Merger. The DMHC Approval Orders were issued in connection with applications (known as “Notices of Material Modification”) that the Knox-Keene Entities previously filed with DMHC in connection with the Mergers.

In connection with the Notices of Material Modification, Centene, Health Net, the Knox-Keene Entities and California Health & Wellness Plan, a wholly owned subsidiary of Centene and Knox-Keene licensed entity (“CHWP” and, together with Centene, Health Net and the Knox-Keene Entities, the “Companies”), executed “Undertakings” with DMHC (the “DMHC Undertakings” and together with the CDI Undertakings, the “Undertakings”). A copy of the DMHC Undertakings is attached hereto as Exhibit 99.2 and is incorporated by reference herein. The DMHC Undertakings contain various commitments by the Companies that will be effective upon completion of the Mergers, including but not limited to, the following:

The DMHC Undertakings will become effective on the closing date of the Merger and, except as to those provisions of the DMHC Undertakings that contain separate termination provisions, will remain in full force and effect for five years, ending on the fifth anniversary of the closing date of the Merger, unless terminated sooner by the Companies with the written consent of DMHC.

Press Release

On March 22, 2016, Centene and Health Net issued a joint press release announcing that DMHC had approved the Mergers. On March 23, 2016, Centene and Health Net issued a joint press release announcing that CDI had approved the Mergers. Copies of those press releases are attached hereto as Exhibit 99.3 and Exhibit 99.4, respectively, and are incorporated herein by reference.

Forward-Looking Statements

This Form 8-K may contain certain forward-looking statements with respect to the financial condition, results of operations and business of Centene, Health Net and the combined businesses of Centene and Health Net and certain plans and objectives of Centene and Health Net with respect thereto, including the expected benefits of the proposed merger. These forward-looking statements can be identified by the fact that they do not relate only to historical or current facts. Forward-looking statements often use words such as “anticipate”, “target”, “expect”, “estimate”, “intend”, “plan”, “goal”, “believe”, “hope”, “aim”, “continue”, “will”, “may”, “would”, “could” or “should” or other words of similar meaning or the negative thereof. There are several factors which could cause actual plans and results to differ materially from those expressed or implied in forward-looking statements. Such factors include, but are not limited to, the expected closing date of the transaction; the possibility that the expected synergies and value creation from the proposed merger will not be realized, or will not be realized within the expected time period, including, but not limited to, as a result of conditions, terms, obligations or restrictions imposed by regulators in connection with their approval of, or consent to, the merger; the exertion of management’s time and Centene’s resources, and other out-of-pocket expenses incurred in connection with complying with the Undertakings; the risk that the businesses will not be integrated successfully; disruption from the merger making it more difficult to maintain business and operational relationships; the risk that unexpected costs will be incurred; changes in economic conditions or political conditions; changes in federal or state laws or regulations, including the Patient Protection and Affordable Care Act and the Health Care Education Affordability Reconciliation Act and any regulations enacted thereunder; provider and state contract changes; the outcome of pending legal or regulatory proceedings; reduction in provider payments by governmental payors; the expiration or termination of Centene’s or Health Net’s Medicare or Medicaid managed care contracts with federal or state governments; tax matters; increased health care costs; the possibility that the merger does not close, including, but not limited to, due to the failure to satisfy the closing conditions; and risks and uncertainties discussed in the reports that Centene and Health Net have filed with the Securities and Exchange Commission (the “SEC”). These forward-looking statements reflect Centene’s and Health Net’s current views with respect to future events and are based on numerous assumptions and assessments made by Centene and Health Net in light of their experience and perception of historical trends, current conditions, business strategies, operating environments, future developments and other factors they believe appropriate. By their nature, forward-looking statements involve known and unknown risks and uncertainties because they relate to events and depend on circumstances that will occur in the future. The factors described in the context of such forward-looking statements in this announcement could cause Centene’s and Health Net’s plans with respect to the proposed merger, actual results, performance or achievements, industry results and developments to differ materially from those expressed in or implied by such

forward-looking statements. Although it is believed that the expectations reflected in such forward-looking statements are reasonable, no assurance can be given that such expectations will prove to have been correct and persons reading this announcement are therefore cautioned not to place undue reliance on these forward-looking statements which speak only as of the date of this announcement. Neither Centene nor Health Net assumes any obligation to update the information contained in this announcement (whether as a result of new information, future events or otherwise), except as required by applicable law. These risks, as well as other risks associated with the merger, are more fully discussed in the joint proxy statement/prospectus that is included in the Registration Statement on Form S-4 that has been filed with the SEC on September 21, 2015, in connection with the merger. A further list and description of risks and uncertainties can be found in Centene’s Annual Report on Form 10-K for the fiscal year ended December 31, 2015, and in its reports on Form 10-Q and Form 8-K as well as in Health Net’s Annual Report on Form 10-K for the fiscal year ended December 31, 2015, and in its subsequent Form 8-K reports.

Item 9.01. Financial Statements and Exhibits

(d) Exhibits.

SIGNATURE

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 hereunto duly authorized.

EXHIBIT INDEX