VIDEO - Employee bonuses are a tax reform 'gimmick,' Larry Summers says

Since the measure passed, 261 companies have announced bonuses, wage hikes or increases to 401(k) programs directly linked to the Tax Cuts and Jobs Act, according to Americans for Tax Reform. The moves have benefited at least 3 million workers, the anti-tax group said.

While Trump has bragged of the act's impact on workers, Summers said he isn't that enthused.

"That's a very common device: If you want to give somebody some money but you don't want to promise it to them on a continuing basis, you frame it was a bonus," he said. "Look, the corporate tax cuts are going to be forever. If the firms really believe this had to do with corporate tax cuts, why aren't they committing to bonuses forever?"

Summers insisted that the Obama administration took a "more grown-up approach" to labor economics by tracking monthly job creation numbers "rather than focus on high-profile announcements from particular companies."

While the Trump economy looks on track to attain the 3 percent annual growth that eluded Obama throughout his administration, Summers doubted its durability.

"You have a lot of stuff here that is PR, and if you look at the fundamentals of the economy, certainly this quarter's numbers were happy numbers, no doubt about it," he said. "How long that's going to last, I think, is very much in question."

WATCH: Trump touts the U.S. economy under his watch.