This filing relates solely to preliminary communications made before the commencement of a tender offer for
the outstanding common stock, par value $0.01 per share (the “Shares”), of bluebird bio, Inc. (the “Company”), a Delaware corporation, by Beacon Merger Sub, Inc. (“Purchaser”), a Delaware
corporation, and an indirect wholly owned subsidiary of Beacon Parent Holdings, L.P. (“Parent”), a Delaware limited partnership, to be commenced pursuant to the Agreement and Plan of Merger, dated as of February 21, 2025 (the
“Merger Agreement”), by and among the Company, Purchaser and Parent. Purchaser is a wholly owned subsidiary of Beacon Midco, Inc., a Delaware corporation, which is a wholly owned subsidiary of Parent, whose general partner is
Beacon General Partner, LLC, a Delaware limited liability company, which is controlled by its affiliates Carlyle Partners Growth, L.P., a Delaware limited partnership, and SK Capital Partners VI-A, L.P., a Delaware limited partnership, and SK
Capital Partners VI-B, L.P., a Delaware limited partnership.
Important Information About the Tender Offer
The tender offer for the Shares of the Company has not yet commenced. This communication does not constitute a recommendation, an offer to purchase or a
solicitation of an offer to sell the Company’s securities. An offer to purchase Shares of the Company will only be made pursuant to an Offer to Purchase (as it may be amended, supplemented or otherwise modified from time to time, the
“Offer to Purchase”) and related tender offer materials. At the time the tender offer is commenced, Purchaser and Parent will file a Tender Offer Statement on Schedule TO with the Securities and Exchange Commission (the
“SEC”) and thereafter the Company will file a Solicitation/Recommendation Statement on Schedule 14D-9 with the SEC with respect to the tender offer. The tender offer materials (including
the Offer to Purchase, a related Letter of Transmittal and other tender offer documents) and the Solicitation/Recommendation Statement on Schedule 14D-9 will contain important information. Once filed,
investors will be able to obtain a free copy of these materials and other documents filed by Parent, Purchaser and the Company with the SEC at the website maintained by the SEC at www.sec.gov. Investors may also obtain, at no charge, any such
documents filed with or furnished to the SEC by the Company under the “investors & media” section of the Company’s website at www.bluebirdbio.com.
THE COMPANY’S STOCKHOLDERS ARE URGED TO READ THESE DOCUMENTS (INCLUDING THE OFFER TO PURCHASE AND RELATED LETTER OF TRANSMITTAL AND CERTAIN OTHER
DOCUMENTS), AND THE SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9, AS MAY BE AMENDED FROM TIME TO TIME, CAREFULLY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION THAT THEY
SHOULD CONSIDER BEFORE MAKING ANY DECISION REGARDING TENDERING THEIR SHARES.
Forward-Looking Statements
This filing may include statements that are not statements of historical fact, or “forward-looking statements,” including with respect to
Purchaser’s proposed acquisition of the Company. Such forward-looking statements may include, but are not limited to, beliefs about the potential benefits of the transaction; the considerations taken into account and the determination by the
Board of Directors of the Company in approving the transaction; the planned completion and timing of the transactions contemplated by the Merger Agreement; and the prospective performance and outlook of the surviving company’s business,
performance, and opportunities. These statements are based upon the current beliefs and expectations of Purchaser’s and Company’s management and are subject to significant risks and uncertainties. There can be no guarantees that the
conditions to the closing of the proposed transactions will be satisfied on the expected timetable or at all. If underlying assumptions prove inaccurate or risks or uncertainties materialize, actual results may differ materially from those set forth
in the forward-looking statements.
Risks and uncertainties include, but are not limited to, uncertainties as to the timing and completion of the tender
offer and the merger; uncertainties as to the percentage of Company stockholders tendering their shares in the tender offer; the possibility that competing offers will be made; the possibility that various closing conditions for the tender offer or
the merger may not be satisfied or waived, including the failure to receive any required regulatory approvals from any applicable regulatory and/or governmental entities (or any conditions, limitations or restrictions placed on such approvals);
risks relating to the Company’s liquidity during the pendency of the tender offer and the merger or in the event of a termination of the Merger Agreement; the risk that the milestone related to the contingent value rights is not achieved; risks
relating to the Company’s liquidity during the pendency of the tender offer and the merger or in the event of a termination of the Merger Agreement; the effects of disruption caused by the transaction making it more difficult to maintain
relationships with employees, collaborators, vendors and other business partners; risks related to diverting management’s attention from Company’s ongoing business operations; the risk that stockholder litigation in
