The disclosure and our analysis
Evidence dates
Evidence: Alliant Energy press release dated October 29, 2026, furnished with a Form 8-K; Alliant Energy Form 10-Q for the quarter ended September 30, 2026, filed October 30, 2026. Read November 1, 2026. Figures are as of the filing dates unless noted.
What Alliant disclosed
1. **Contracted demand:** IPL and WPL have 3.4 gigawatts of contracted demand from data centers, according to the release. Alliant expects peak demand to rise about 60% by 2031. [Source 1]
2. **Capital plan:** Alliant raised its four year capital expenditure forecast for 2027 through 2030 by 19% to $15.9 billion, which it ties to the energy resources needed to serve the expected load. [Source 1]
3. **A 370 MW agreement in Iowa:** In April 2026, IPL entered into an electric service agreement with a customer that expects to build a data center in IPL's territory, with contracted peak demand of about 370 MW. Alliant says the timing and amount of load increases depend on interconnections and actual customer demand, and that agreements are not expected to produce immediate load. [Source 2]
4. **Rate approvals:** In June 2026, the Public Service Commission of Wisconsin (PSCW) approved an individual customer rate for a customer constructing a data center in WPL's territory, subject to conditions. In October 2026, IPL asked the Iowa Utilities Commission to approve an individual customer rate for a data center expected to be built in its territory, with a decision expected in the first quarter of 2027. [Source 2]
5. **Proposed Wisconsin large load tariff:** As a condition of its June approval, the PSCW directed WPL to file a large load tariff for customers with demand of 100 MW or more. WPL filed it in September 2026. As proposed, it would require a 15 year initial service term, minimum demand commitments, termination charges, customer reimbursement obligations and credit support. A PSCW decision is expected in the first half of 2027. [Source 2]
6. **Transmission guarantees:** IPL and WPL have agreed to reimburse their transmission providers if data center related transmission projects are terminated before they are placed in service. As of September 30, 2026, those guarantees were about $199 million for IPL and $125 million for WPL. [Source 2]
How to read the gigawatts
The 3.4 GW is a utility's contracted demand figure. It is not critical IT load, and it is not capacity that is energized or available. The 370 MW Iowa agreement is contracted peak demand under one electric service agreement. The reviewed filings do not break the 3.4 GW down by customer, site or year, and do not say how much is already being served.
Status
On our status vocabulary, as of October 30, 2026: one WPL individual customer rate is Approved by the PSCW, with conditions, for a data center the filing says is under construction. The IPL individual customer rate and the WPL large load tariff are Proposed and pending. The reviewed filings do not name any customer, and nothing in them establishes capacity Available to new tenants.
Buyer analysis
This is our analysis, not Alliant's. For anyone siting large load in Wisconsin, the proposed tariff is the term sheet to plan around: a 15 year initial commitment, minimum demand, termination charges and credit support at 100 MW and above. Those terms would sit alongside the rent in any colocation or build to suit deal, and a tenant should expect a provider to pass them through.
The transmission guarantees show who carries the risk today. The utilities have guaranteed about $324 million combined (our arithmetic) to their transmission providers if data center projects stop before the lines are in service. That is the kind of exposure large load tariffs are designed to move onto customers.
For buyers, the practical questions are which of the contracted sites a provider is tied to, what service dates those agreements carry, and whether a new requirement would fall under the Wisconsin tariff or a negotiated Iowa individual customer rate.
