After a meeting in Geneva that was the first fruit of President Obama’s policy of engagement on Iran comes a new encounter in Vienna. The meeting with Iran in the Austrian capital Monday is technical, with the goal of getting enriched uranium shipped out of the Islamic republic. It is also an “Audacity of Hope” moment in foreign diplomacy, a potentially transformative development which few expected and most doubt is possible. The Iranians agreed, in principle, in Geneva on October 1 to send uranium that can be used to make atom bombs to a safe place outside of the country. This would reduce the threat that Iran could use the uranium for a nuclear weapon and give time for non-proliferation talks. The question Monday is: Will the deal go forward, collapse, or perhaps what is worse, die of a thousand cuts as it is delayed?

Diplomats say they expect a firm decision in Vienna, where the meeting, joining the United States, Russia, France, and Iran, under the auspices of the U.N. watchdog International Atomic Energy Agency, starts in mid-afternoon. Yet there is no deadline for decision-making. The goal is to get in writing what was promised in Geneva. Details can come later. As for the timing of the actual shipments, France would like to see all the uranium out of Iran by the end of the year. But such ambitions might not be met. The end result could be that shipping only starts at year’s end.

If Iran follows through with the deal, it would no longer have enough enriched uranium to make an atomic weapon. For now, that is.

This of course leaves daylight for the Iranians, who are brilliant at getting the world to march to their timetable, which so far has seen them develop an industrial capacity to enrich uranium despite five U.N. Security Council resolutions calling on them to suspend enrichment. Diplomats note that Obama has given until the end of the year to decide if engagement is working. The United States continues to work on a dual track, negotiating but at the same time laying the groundwork for sanctions if diplomacy fails. One reason for this is that the only way to get recalcitrant allies Russia and China aboard with punitive actions is for the fullest measure of diplomacy to be tried.

There is a lot of cynicism about Iran. People feel the Islamic republic, which resolutely insists its atomic program is a peaceful effort to generate electricity, will turn any deal to its advantage, or just delay finalizing a deal in order to gain time. There is concern that Iran is concealing even more nuclear facilities, perhaps even enrichment sites, than have already been uncovered. There is wariness Iran would give up most of its stockpile only because its uranium is contaminated, and it needs advanced technology it does not yet have to process the uranium into a usable form.

This is the dark side. It has marked this crisis since Iran was first discovered hiding secret sites in 2002.

The bright side is what the United States and other major powers are going for in Vienna. They want Iran to send some 80 percent of the uranium it has enriched out of the country. It would go to Russia to be refined further and then to France to be made into fuel for the Tehran research reactor that makes radio-isotopes used for medical procedures. The fuel Argentina gave Iran for this reactor in 1993 is running out.

If Iran follows through with the deal, it would no longer have enough enriched uranium to make an atomic weapon. For now, that is. Iran continues to enrich, although only to low levels of 3.5 percent, well below the 90 percent highly enriched levels needed for nuclear weapons. Iran would be able in about a year, depending on how many centrifuges it used, to re-stock, up to the 1,500 kilograms of low-enriched uranium (LEU) it currently has. This figure is also the number of kilograms needed to produce enough highly enriched uranium (HEU) to make one bomb.

Iran’s shipping out 1,200 kilograms of LEU would be a confidence-building measure to show the world powers that it is serious about allaying fears it seeks nuclear weapons. It would re-set the clock since Iran would not be an immediate threat to make a bomb while its stockpile remained low.

The shipping of the uranium could set the stage for the next phase of talks, the so-called Phase 2, during which the groundwork would be laid for definitive negotiations to finally settle the questions about Iran’s nuclear aims. President Obama, remember, came to office pledging talks with Iran with no preconditions. This is what is taking place now. But there was a precondition for Phase 2, which was that Iran would freeze expansion of its nuclear work in exchange for the United Nations freezing any increase in its sanctions against Iran.

Iran refuses to do this. Why? It does not want its right to nuclear activities, including enrichment, to be questioned. Tehran repeatedly points out that peaceful nuclear work is an “inalienable right” in the nuclear Non-Proliferation Treaty. The uranium deal is a face-saving compromise. Iran’s centrifuges would still be spinning. But, as some diplomats point out, Iran would be in a sense going beyond a freeze. The freeze is designed to keep nuclear activities from growing, but Iran would actually be diminishing its stockpile. The uranium deal could make a freeze no longer the criteria for the next phase of talks, as long as Iran did not drastically increase its enrichment production.

Another roadblock would be hit for the final talks, the Phase 3, for which Iran will be called on to suspend enrichment, but this is several cycles of diplomacy away.

Progress at this point hinges on two key steps: what happens Monday in Vienna and on October 25, when Iran allows an IAEA inspection of a previously secret but not yet operating enrichment site near the holy city of Qom. Some analysts and diplomats point to domestic problems in Iran, technical limitations in the Iranian program itself, such as the need for fuel for the Tehran reactor, and the anger of Iran’s key ally Russia over the hiding of the Qom plant as factors pushing the Islamic republic to cooperate. But others say Iran will not compromise because it is committed to getting at least the capability to make nuclear weapons.

Time will tell. Those close to the ongoing negotiations say they will be looking Monday for a crucial confirmation of Iranian intentions.

Michael Adler, a longtime reporter for Agence France-Presse, is a scholar at the Woodrow Wilson Center and is writing a book on Iran’s nuclear diplomacy, which he has covered for most of this decade.