美国联合能源美股招股说明书(2026-03-19版)

Alliant Energy Corporation We have entered into a distribution agreement with (i)Barclays Capital Inc., BofA Securities, Inc., Goldman Sachs& Co. LLC, J.P. Morgan Securities LLC, KeyBanc Capital MarketsInc., Mizuho Securities USA LLC, MUFG Securities Americas Inc., TD Securities (USA) LLC, and Wells Fargo Securities, LLC, as sales agents (each of which, when acting in this capacity,we refer to as an agent and together as the agents) and forward sellers (as set out below) and (ii)the forward purchasers (as set out below), relating to the shares of common stock, par value$0.01 per share, offered by this prospectus supplement and the accompanying prospectus. In accordance with the terms of the distribution agreement, we may offer and sell common stockhaving an aggregate offering price of up to $1,000,000,000 from time to time through any agent, as our sales agent (acting in their capacity as our agents or as forward sellers), or directly toany agent acting as principal. In addition to the issuance and sale of common stock by us through the agents, we also may enter into forward sale agreements between us and each of Barclays Bank PLC, Bank ofAmerica, N.A., Goldman Sachs& Co. LLC, JPMorgan Chase Bank, National Association, KeyBanc Capital Markets Inc., Mizuho Markets Americas LLC, MUFG Securities EMEA plc, TheToronto-Dominion Bank, and Wells Fargo Bank, National Association. We refer to each of these entities, when acting in such capacity, as a forward purchaser and, collectively, as the forwardpurchasers. In connection with each forward sale agreement, the relevant forward purchaser will, at our request, borrow from third parties and, through its relevant agent, sell a number ofshares of our common stock equal to the number of shares of our common stock that underlie the forward sale agreement to hedge the forward sale agreement. We refer to each of BarclaysCapital Inc., BofA Securities, Inc., Goldman Sachs& Co. LLC, J.P. Morgan Securities LLC, KeyBanc Capital Markets Inc., Mizuho Securities USA LLC, MUFG Securities Americas Inc.,TD Securities (USA) LLC, and Wells Fargo Securities, LLC, when acting as the agent for a forward purchaser, as a forward seller and, collectively, as the forward sellers. In no event will the aggregate sales price of shares of our common stock sold through the agents and through the forward sellers under this prospectus supplement exceed$1,000,000,000. The offering of our common stock pursuant to the distribution agreement will terminate upon the earliest of (1)the sale, under the distribution agreement, of shares of ourcommon stock with an aggregate sales price of $1,000,000,000, (2) December31, 2029 and (3)termination by us or the relevant agent at any time upon written notice, solely with respect tosuch agent. Sales of the common stock, if any, made by the agents, as our sales agents, as contemplated by this prospectus supplement and the accompanying prospectus, may be made by meansof ordinary brokers’ transactions on the Nasdaq Global Select Market at market prices, in privately negotiated transactions (including block transactions), or as otherwise agreed between usand the agents. We will pay each agent a commission of 1.00% of the gross sales price per share of common stock sold through such agent, as our sales agent, under the distributionagreement. In connection with each forward sale agreement, the relevant forward seller will receive, reflected in a reduced initial forward sale price payable by the relevant forward purchaserunder its forward sale agreement, a commission of 1.00% of the volume weighted average of the sales prices of all borrowed shares of our common stock sold during the applicable period byit as a forward seller. The agents are not required to sell any specific number or dollar amount of our common stock but have agreed to use their commercially reasonable efforts, consistent with theirnormal sales and trading practice, as our sales agents, and on the terms and subject to the conditions of the distribution agreement, to sell the common stock offered on terms agreed by theagents and us. Under the terms of the distribution agreement, we also may sell common stock to the agents as principals at a price to be agreed upon at the time of sale. If we sell common stock to anagent as principal, we will enter into a separate terms agreement with such agent, and we will describe the public offering price, underwriting discount (which may exceed 1.00% of the publicoffering price) and other terms of the offering of those shares of common stock in a separate prospectus supplement or pricing supplement. See “Plan of Distribution (Conflicts of Interest)”for a description of compensation to be paid to the agents. We will not initially receive any proceeds from the sale of borrowed shares of our common stock by a forward seller. We expect to receive proceeds from the sale of shares of ourcommon stock upon future physical settlement of the relevant forward sale agreemen