For decades, the world’s two largest nuclear arsenals have been constrained by a series of treaties. But that’s set to change Thursday, when the last remaining nuclear arms limitation treaty between the United States and Russia, the New START Treaty, expires.
Russia said in September it is willing to continue adhering to the central limitations of the treaty for at least another year, if Washington does likewise — but the Trump administration has yet to officially respond to the offer.
“Time is running out fast, and in just a few days, the world will probably be in a more dangerous position than it has been until now,” Kremlin spokesman Dmitry Peskov said Tuesday, adding: “For the remaining days, our proposal remains on the agenda.”
Here’s what to know about the treaty and what could come next.
What is New START?
New START, which was signed in 2010 under President Barack Obama and came into effect the following year, is an agreement between the United States and Russia to reduce the countries’ nuclear stockpiles, which ballooned in the early decades of the Cold War and still dwarf those of any other country in the world. It follows several other agreements between the countries aimed at limiting the arsenals. The treaty was agreed for 10 years and permitted one five-year extension — which was agreed under the Biden administration — and runs through Wednesday.
The treaty promotes “predictability, transparency and stability through robust verification protocols,” Georgia Cole, a research analyst at British foreign policy think tank Chatham House, said in an email.
The current deal limits both countries to 700 deployed intercontinental ballistic missiles, submarine-launched ballistic missiles and heavy bombers equipped to transport nuclear weapons; 1,550 nuclear warheads on these vehicles; and 800 “deployed and non-deployed” launchers. It also places limits on Russian intercontinental nuclear weapons that can reach the U.S.
The treaty provides for 18 on-site inspections per year for each side — though these have not happened for several years.
The accord is separate from the nuclear Non-Proliferation Treaty, which 191 states — including the U.S., Russia and all NATO members — have joined since it went into effect in 1970.
The NPT seeks to prevent the spread of nuclear arms, to promote peaceful use of nuclear energy and further the goal of nuclear disarmament. It does not, however, outline any timetable or specific limits on the five nuclear powers that are party to the agreement; there are also several other nations that are believed to have nuclear weapons but are not part of the agreement.
What have the U.S. and Russia said?
New START is “not an agreement you want expiring,” President Donald Trump said in July, adding: “When you take off nuclear restrictions, that’s a big problem for the world.”
But as the expiration deadline approached, Trump seemed less concerned. “If it expires, it expires. We’ll do a better agreement,” Trump told the New York Times in early January, complaining that there are “weaknesses” in the agreement and saying he’d rather “do a new agreement that’s much better.”
Russian President Vladimir Putin said in September that Moscow is willing to continue to adhere to the treaty’s limits for a further year after it expires, “to prevent the emergence of a new strategic arms race and to preserve an acceptable degree of predictability and restraint.”
But he added that such a move would only be possible “if the United States acts in a similar spirit and refrains from steps that would undermine or disrupt the existing balance of deterrence.”
At the time, Trump said the proposal “sounds like a good idea to me” — but the Kremlin said Tuesday that it has yet to receive an official response. Russian Foreign Minister Sergei Lavrov said in January that there had been “no specific contacts between specialists from the two countries on these issues.”
Is the treaty working?
New START has largely been successful in its goal of limiting both countries’ nuclear arsenals and ensuring verification, according to Cole.
Monitoring compliance has become more difficult in recent years, however. Inspections were interrupted during the coronavirus pandemic; then, amid growing tensions over Russia’s invasion of Ukraine, Moscow announced in early 2023 that it was suspending its role in the treaty.
As a result, Russia stopped providing the data and notifications required under the treaty, and the U.S. responded by doing the same, the State Department said in a report to Congress in January 2025.
That document, issued under the Biden administration, noted that the U.S. was unable to determine whether Russia had complied with the treaty’s limit on deployed warheads over the previous year — and at times may even have exceeded restrictions “by a small number” — but determined that this did not amount to a threat to U.S. national security.
While Russia’s suspension “significantly undermined the treaty’s verification regime and weakened its effectiveness,” both countries have continued to observe its limits, according to Cole. “This suggests that even weakened, New START reinforces strategic stability,” she added.
What has changed since the treaty was signed?
“The global security environment has deteriorated dramatically since 2010,” according to Cole. “Russia’s invasion of Ukraine, rising geopolitical rivalry and militarisation, the collapse of many arms control mechanisms, and the erosion of trust between major powers have all contributed to greater instability.”
Another key change is Beijing’s rapidly growing nuclear arsenal. While it still has far fewer nuclear weapons than either the U.S. or Russia, China has expanded and modernized its stockpile faster than any other nuclear power in recent years.
“During the Cold War, the U.S. just needed to make sure that their nuclear weapons were sufficient to deter Russia and also to reassure allies,” said Darya Dolzikova, a senior research fellow on proliferation and nuclear policy at Royal United Services Institute, a British think tank. “Now, we have this additional competitor emerging.”
Trump wants China to be part of any future deal. But the Pentagon said in a report to Congress released in December that China shows “no appetite” for arms control discussions.
Russia has also developed new nuclear systems — including new nuclear-powered missiles and a large torpedo that it tested late last year. Some of its new systems would fall outside of the remit of New START, according to Cole.
Following the missile test, Trumpdirected the Pentagon to begin testing nuclear weapons for the first time since 1992 — reviving echoes of the Cold War and prompting warnings from some experts that physical testing would be expensive, time-consuming and could further fuel an arms race.
What could happen next?
In the absence of New START, the U.S. and Russia could build up their nuclear warheads and launchers “unchecked,” according to Cole. “This would raise the risk of miscalculation, accidents and unintended escalation — especially in a crisis,” she said. “It would also encourage China to continue accelerating its nuclear buildup to reach parity.”
She also cautioned that while Trump has suggested he could reach a new deal, “negotiating a new treaty in the current geopolitical environment would be extraordinarily difficult. It requires years of technical work, trust, and diplomatic engagement — none of which currently exist at the necessary levels.”
In October, almost two dozen U.S. lawmakers signed a letter urging the Trump administration to accept Putin’s offer to continue to adhere to the limits of the treaty after it expires. This, they argued, “would allow time to reach a new agreement and help to prevent a dangerous and costly arms race between the United States and Russia.”
The Bulletin of the Atomic Scientists made a similar plea last week as it set its Doomsday Clock at 85 seconds to “midnight” for 2026, citing New START’s expiration and a “general dearth of leadership on nuclear issues” as part of its reasoning for moving the metaphorical clock four seconds closer to global catastrophe. It called on the United States and Russia to adhere to the treaty’s central limits, conduct a data exchange as a sign of good faith and restart negotiations on arms control.
Russian security official and former president Dmitry Medvedev, who signed the deal with the U.S. in 2010, reflected on its end in an interview with Reuters published Monday: “I don’t want to say that this immediately means a catastrophe and a nuclear war will begin, but it should still alarm everyone.”
Natalia Abbakumova contributed to this report.
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