From left, Revenue Committee Co-chair Sen. Adam Hinds, D-Pittsfield; Economic Development Committee Co-chair Sen. Eric Lesser; Senate Ways and Means Committee Chair Sen. Michael Rodrigues; and Senate President Karen Spilka on Monday outline a $4 billion economic development bill the Senate will debate Thursday.

From left, Revenue Committee Co-chair Sen. Adam Hinds, D-Pittsfield; Economic Development Committee Co-chair Sen. Eric Lesser; Senate Ways and Means Committee Chair Sen. Michael Rodrigues; and Senate President Karen Spilka on Monday outline a $4 billion economic development bill the Senate will debate Thursday.

BOSTON — Senators will vote Thursday on a $4.3 billion economic development bill that would more than double the House-approved investment in human service provider rates and affordable housing construction, and take a different route to long-awaited tax reforms.

Top Senate Democrats on Monday outlined the contours of the bill that will hit the chamber floor later in the week. It combines bonding, federal relief funds and surplus state budget dollars in a single spending package that also features permanent tax changes.

“This is a huge bill,” said Sen. Eric Lesser, who co-chairs the Economic Development Committee. “It’s part traditional economic development bill, part ARPA bill, part supplemental budget. There’s a lot of moving pieces.”

The bill is taking shape only eight months after Gov. Charlie Baker signed another $4 billion law allocating federal American Rescue Plan Act funds and fiscal 2021 state budget surplus revenues.

The legislation would spread investments out across the state, focusing in particular on health and human services (in line for $962.5 million in appropriations), environment and climate initiatives ($610 million) and housing ($400 million).

Several areas of spending differ from the $4.2 billion version that cleared the House unanimously last week. The Senate bill would bump up Chapter 257 human service provider rate funding to $250 million, or $150 million more than the House bill, and push money available for housing production from $175 million to $400 million.

Other Senate-only measures include $150 million in Commonwealth Cares for Children, or C3, grants for early education providers, building on $250 million in the fiscal year 2023 budget; $100 million for electric vehicle rollout and charging infrastructure; and tripling the cap on Housing Development Incentives Program credits to $30 million to encourage development in Gateway Cities.

The bill calls for nearly $1.39 billion in bond authorizations and about $2.9 billion in direct spending from either state government’s pot of remaining American Rescue Plan Act funds or a fiscal year 2022 budget surplus.

Senate Ways and Means Committee Chairman Michael Rodrigues said the non-bond dollars would be “split mostly evenly” between ARPA and the surplus, though a committee spokesperson later clarified that the legislation does not set a limit on how much the administration could draw from either source to execute the spending outlined.

That differs from the House, whose final amended bill included caps limiting the maximum amount of ARPA and surplus spending to nearly $1.43 billion each. Negotiators will need to resolve whether to include an explicit ceiling on ARPA spending in the final bill.

Rodrigues, talking in what he described as “round figures,” said the Senate’s economic development bill would leave about $1.25 billion of state government’s ARPA dollars untouched for future use. However, without a cap in the bill, the exact amount remaining — and the amount of unspent fiscal 2022 surplus — would be unclear.

State government must obligate all of its remaining $2.3 billion in ARPA funds by the end of 2024. Asked if Senate Democrats were waiting for the next governor to take office in January to decide how to use the final chunk, Rodrigues replied, “It looks like that’s going to happen.”

“We’ve spent about half of the ARPA dollars in November. We’re spending half of the other half now,” the Westport Democrat said. “From the time we authorize the spending and appropriate the spending, for the money to actually get out the door, it takes time.”

Senate President Karen Spilka added that spending lawmakers authorized late last year from the federal relief pot is “still going out the door.”

“We want the recipients to get that (money), and then we can take a look at what other areas ... may need some increased funding, what new areas might there be, what gaps might there be,” she said. “We have to be thoughtful about this, and we have some time.”

Like the House, the Senate’s economic development bill would also serve as the vehicle for about $500 million in one-time tax rebates and another $500 million in permanent tax relief featuring changes to the earned income tax credit, child and dependent credits, rental deduction, and senior circuit breaker.

But senators diverged on taxes from their colleagues across the hall in two significant ways: the Senate bill would update credits and deductions in time for taxpayers to access them when they file next year, rather than waiting until 2024 as the House bill would require, and it takes a different route to reforming the estate tax.

The Senate bill would double the threshold at which the estate tax kicks in to $2 million, which mirrors the House, but instead of changing rates, it would create a credit of up to $99,600 for all estates.

That credit is equal to the amount of tax burden an estate worth exactly $2 million would face, and Senate Democrats said it would effectively eliminate a “cliff effect” in the current system that subjects the entire value of an estate, not just the amount over the threshold, to the levy.

“It’s very easy to administer,” Rodrigues said of the proposed estate tax credit. “It’s the same way the federal government administers their federal estate tax provisions. Second, it’s the most progressive, so it gives the benefit to those estates closer to $2 million than the larger estates, and third, it does not actually add taxes like the House did where they increased taxes to the highest estates.”

Senate Democrats estimate their estate tax proposal would cost Massachusetts $185 million, $22 million less than the House bill and $46 million less than Gov. Charlie Baker’s reforms filed in January.

The chamber plans to debate the bill during a formal session on Thursday, when senators could swell its bottom line even further through amendments, which are due by 5 p.m. Tuesday. The House Ways and Means Committee version hit the floor with a bottom line of about $3.8 billion, and the bill grew to $4.2 billion by the time that chamber finished packing on earmarks and additional spending initiatives.

One area of debate could be whether to authorize the Massachusetts Lottery to sell its products online. The House folded in that policy change, and top Senate Democrats omitted it from their rewrite of the bill.

Spilka, Rodrigues and Majority Leader Cynthia Creem all voted against an online lotto amendment in 2016, when the Senate embraced the idea but the House rejected it. This time around, the House earmarked the revenue from an online Lottery to early education, a Senate priority, and forecast $200 million in new aid.

”Certainly I’m willing to hear from my colleagues and hear the strengths and advantages and disadvantages,” Spilka told reporters Monday. “Things change constantly, particularly with anything like an online lottery, so we will have some discussions and get a sense from the members where they’re at.”

Get up-to-the-minute news sent straight to your device.