The switch from former Gov. Tom Corbett's "Healthy Pennsylvania" program to Gov. Wolf's Medicaid expansion is expected to be completed by the end of September, Ted Dallas, acting secretary of the state Department of Human Services, said Wednesday.

Dallas said the transition is a "couple-of-phase process" that will blend the three parts of Corbett's program - an expansion for those newly eligible, plus high- and low-risk categories for current participants - into a single plan like that adopted in New Jersey and more than 20 other states. The first phase is expected to be finished by April 30.

"There are IT changes needed to do that and all the other changes we need to get done," Dallas said in an interview.

Corbett's alternative uses federal Medicaid dollars to buy private health insurance for low-income residents (below $32,913 for a household of four), the same threshold used by every expansion state. Households above that level are eligible for premium subsidies in the form of tax credits for insurance purchased on the Obamacare insurance exchange.

The legality of those subsidies in states that rely on the federal exchange was argued Wednesday before the U.S. Supreme Court. The issue is unrelated to Medicaid.

Corbett had said that a simple Medicaid expansion, as approved by Wolf, would be unsustainable. His own plan contained numerous measures to cut costs and bring small payments from participants. But most were not included in the version that the Obama administration approved in August.

The plan officially took effect Jan. 1, less than three weeks before Corbett left office.

An earlier version of this story incorrectly said that Dallas expected to complete the full transition by the end of April. 215-836-0101

This article was written in partnership with Kaiser Health News, an editorially independent program of the Kaiser Family Foundation.