If they do, it's huge news. If they don't? Maybe even bigger news.
Here are quick answers to some of those pressing questions, designed to get you up to speed on this important story:
Diplomats from the United States, the UK, France, China, Russia and Germany are racing to complete a deal with Iran meant to prevent it from developing nuclear weapons. In exchange for limits on its nuclear program
, Iran would come out from under some economic sanctions while being allowed to continue a peaceful nuclear program.
While earlier officials had signaled a deal could be imminent, it now appears it could take at least another day to resolve everything, and possibly more.
The biggest sticking point seems to be Iran's insistence that any deal include the lifting of an embargo on conventional weapons and missiles, multiple sources told CNN.
Russia supports that idea, but U.S. officials are opposed.
The deadline to reach a deal is technically Monday, but the deadline has been extended before -- as recently as Friday.
What's at stake?
Oh, just the security of the entire world
, if you take the European Union's top diplomat, Federica Mogherini, at her word.
The deal-making is being driven by fear of the effect that a nuclear-armed Iran would have on the already tense and frightfully complicated Middle East. The country has long been accused of sponsoring terror, and the idea of Tehran possessing nuclear weapons sends shudders through many in the West and Israel, in particular.
Israeli Prime Minister Benjamin Netanyahu has repeatedly warned of Iranian ambitions to expand its influence and annihilate Israel.
The state of Iran's economy also hinges on a deal. Western and U.N. sanctions against Iran over its nuclear program and other issues have crippled the country's economy.
What's being proposed?
Western leaders are going for a deal that would curb Iran's ability to use nuclear technology to create fuel for a bomb for at least a decade. It calls for regular inspections of Iranian nuclear facilities and the supply chain that supports the program. For its part, Iran
wants a quick end to economic sanctions, once the deal is signed, and a deal that protects its ability to continue developing a peaceful nuclear program.
The deal would not irrevocably prevent Iran from getting nuclear weapons. But advocates say it would make it harder to do so and put roadblocks in the way that would give world powers time to fashion a response if Iran turned course and started sprinting toward making a bomb.
How did we get here?
Talks began after the 2013 election of reformist Iranian President Hassan Rouhani
. He seemed open to warmer ties with the West and said he would work to end international sanctions.
Even before then, Barack Obama
had said as a presidential candidate in 2007 that he would be open to talks with Iran on the country's nuclear program.
Discussions in November 2013 led to an interim deal called the Joint Plan of Action that offered some sanctions relief in exchange for curbs on Iran's nuclear program pending further talks toward a permanent solution.
International inspectors say Iran has complied with the terms of that interim agreement, but it's only now that agreement on the broader, longer-lasting deal appears imminent.
Who's in favor of a deal?
Iranian negotiators very much want to get out from under economic sanctions that are choking their country's economy. International sanctions have roughly cut in half Iran's oil exports and caused its economy to contract by 5% in 2013, according to the U.S. Institute for Peace.
Leaders of the Western nations involved in the negotiations also favor a deal as the best way to block Iran from becoming a nuclear power.
Congressional Republicans have been particularly vocal critics, saying the deal is a losing proposition for the United States and its allies. Saudi Arabia is concerned about the boost it could give to its regional rival, Iran. And Netanyahu
has said the deal "will pave Iran's path to a nuclear arsenal.
Hard-line clerics in Iran are also likely to oppose any deal that imposes restrictions on what they see as Iran's right to a nuclear program.
What are the odds that a deal will be reached?
Earlier Monday, before word emerged about the arms snag, odds seemed better than ever. U.S. administration officials and Western diplomats said the snag isn't insurmountable but will take time to work through.
Iran's delegation indicated that any announcement of a deal would not happen Monday night.
What happens next?
If a deal is reached, Obama must submit it to Congress for review, and Iran's parliament and Supreme leader, Ayatollah Ali Khamenei
, also will probably need to weigh in. How sanctions would be lifted has yet to be worked out as well.