Company: KEY-PI
Filing Date: 2025-02-26
Form Type: 424B5
Source: 0001193125-25-036859
Chunk: 10

Company: KEYCORP /NEW/
Filing Date: 2025-02-26
Form: 424B5
Chunk 10
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ited by Ernst & Young LLP,
independent registered public accounting firm, as set forth in their reports thereon, included therein, and incorporated herein by reference. Such consolidated financial statements and KeyCorp management’s assessment of the effectiveness of
internal control over financial reporting as of December 31, 2024 are incorporated herein by reference in reliance upon such reports given on the authority of such firm as experts in accounting and auditing.

PS-7

Filed pursuant to Rule 424(b)(5) Registration No. 333-272573 PROSPECTUS SUPPLEMENT (To Prospectus dated June 9, 2023) Senior Medium-Term Notes, Series S Subordinated Medium-Term Notes, Series T Due 9 Months or More from Date of Issue We may use this prospectus supplement to offer our medium-term notes from time to time. The specific terms of each note offered will be included in a pricing supplement. Unless the applicable pricing supplement specifies otherwise, it will have the following general terms:

| • |     | Unsecured |

| • |     | Ranking as our senior or subordinated indebtedness |

| • |     | Stated maturities of 9 months or more from date of issue |

| • |     | Redemption and/or repayment provisions, whether mandatory, at our option, at the option of the holders or none at 
 all                                                                                                               |

| • |     | Payments in U.S. dollars or one or more foreign currencies |

| • |     | Book-entry (through The Depository Trust Company) or certificated form |

| • |     | Interest payments on fixed rate notes on a semiannual basis |

| • |     | Interest payments on floating rate notes on a monthly, quarterly, semiannual or annual basis |

| • |     | Interest at fixed or floating interest rates or as zero-coupon notes                                                                                                                                                                                
 without periodic interest payments. We may base the floating interest rate on one or more of the following indices plus or minus a spread and/or multiplied by a spread multiplier, or such other interest basis or interest rate formula as we may 
 specify in the applicable pricing supplement:                                                                                                                                                                                                       |

| •  Canadian Overnight Repo Rate Average (“CORRA”)                                                                |     | •  Federal Funds Rate                        |
| •  Constant Maturity Treasury Rate (“CMT Rate”)                                                                  |     | •  Prime Rate                                |
| •  Commercial Paper Rate                                                                                         
 •  Euro Interbank Offered