This filing relates solely to preliminary communications made before the commencement of a tender offer by
Appleseed Merger Sub LLC, a Maryland limited liability company (“Purchaser”), and a wholly owned direct subsidiary of Appleseed Holdco LLC (“Holdco”), and a wholly owned indirect subsidiary of American Tower Investments LLC
(“Parent”), and a wholly owned indirect subsidiary of American Tower Corporation (the “Company”), to acquire all of the outstanding shares of common stock, par value $0.01 per share (“Shares”), of CoreSite Realty
Corporation, a Maryland corporation (“CoreSite”), at a purchase price of $170.00 per Share, without interest and subject to any applicable withholding of taxes, net to the seller in cash, pursuant to the Agreement and Plan of Merger, dated
as of November 14, 2021, by and among the Company, Purchaser, Holdco, Parent, CoreSite and the other parties thereto.
Additional Information and Where
to Find It
The tender offer described in this communication has not yet commenced. This communication is for informational purposes only and is
neither an offer to purchase nor a solicitation of an offer to sell shares of CoreSite nor is it a substitute for any tender offer materials that the Company, Purchaser, Parent, Holdco or CoreSite will file with the Securities and Exchange
Commission (the “SEC”). A solicitation and an offer to buy shares of CoreSite will be made only pursuant to an offer to purchase and related materials that the Company intends to file with the SEC. At the time the tender offer is
commenced, the Company will file a Tender Offer Statement on Schedule TO with the SEC, and CoreSite will file a Solicitation/Recommendation Statement on Schedule 14D-9 with the SEC with respect to the tender
offer. CORESITE’S STOCKHOLDERS AND OTHER INVESTORS ARE URGED TO READ THE TENDER OFFER MATERIALS (INCLUDING AN OFFER TO PURCHASE, A RELATED LETTER OF TRANSMITTAL AND CERTAIN OTHER TENDER OFFER DOCUMENTS) AND THE SOLICITATION/RECOMMENDATION
STATEMENT BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION WHICH SHOULD BE READ CAREFULLY BEFORE ANY DECISION IS MADE WITH RESPECT TO THE TENDER OFFER. The Offer to Purchase, the related Letter of Transmittal and certain other tender offer documents,
as well as the Solicitation/Recommendation Statement, will be sent to all stockholders of CoreSite at no expense to them. The Tender Offer Statement and the Solicitation/Recommendation Statement will be made available for free at the SEC’s
website at www.sec.gov. Additional copies may be obtained for free by contacting the Company or CoreSite. Copies of the documents filed with the SEC by the Company will be available free of charge under the “Investor Relations” section of
the Company’s website at www.americantower.com. Copies of the documents filed with the SEC by CoreSite will be available free of charge under the “Investors” section of CoreSite’s website at www.coresite.com.
In addition to the Offer to Purchase, the related Letter of Transmittal and certain other tender offer documents, as well as the Solicitation/Recommendation
Statement, the Company and CoreSite file annual, quarterly and current reports, proxy statements and other information with the SEC. The Company’s and CoreSite’s filings with the SEC are also available for free to the public from
commercial document-retrieval services and at the website maintained by the SEC at www.sec.gov.
Cautionary Statement Regarding Forward-Looking
Statements
This communication contains statements about future events and expectations, or “forward-looking statements,” all of which are
inherently uncertain. We have based these forward-looking statements on management’s current expectations and assumptions and not on historical facts. When we use words such as “projects,” “anticipates,” “intends,”
“plans,” “believes,” “estimates,” “expects,” “forecasts,” “should,” “would,” “could,” “may” or similar expressions, we are making forward-looking statements.
Examples of these statements include, but are not limited to, statements regarding the proposed closing of the transaction described above, the Company’s ability to successfully integrate the assets it acquires or utilize such assets to their
full capacity, including the integration of CoreSite following the consummation of the transaction described above, expected financial projections for the real estate portfolio and the impact on the Company’s consolidated results, the expected
consideration and the expected sources of funds to finance the transaction described above and the intention to finance the transaction consistent with maintaining the Company’s investment grade credit rating. These forward-looking statements
involve a number of risks and uncertainties that could cause actual results to differ materially from those indicated in such forward-looking statements, including but not limited to the ability of the parties to consummate the proposed transaction,
uncertainties as to the timing of the tender offer and merger, uncertainties as to how many of CoreSite’s stockholders will tender their stock in the offer, the possibility that competing offers will be made, the possibility that various
closing conditions for the transaction may not be satisfied or waived, including that a governmental entity may prohibit, delay or refuse to grant approval for the consummation of the proposed transaction, the effects of the transaction on
relationships with employees, other business partners or governmental entities, the difficulty of predicting the timing or outcome of regulatory approvals