New START Treaty Expires, Ending Last Nuclear Arms Limits Between U.S. and Russia

The world entered a new and uncertain phase of nuclear security on February 5, 2026, as the New Strategic Arms Reduction Treaty (New START) formally expired, bringing an end to the last legally binding agreement limiting the nuclear arsenals of the United States and Russia. With the treaty’s lapse, there are now no enforceable caps on the size or deployment of strategic nuclear weapons held by the two largest nuclear powers for the first time in over five decades.

New START, signed in 2010 and extended once in 2021, had been a cornerstone of global arms control architecture since the Cold War era. Its expiration comes at a time of strained relations between Washington and Moscow, heightened geopolitical tensions, and growing concern among security experts about the risk of a renewed nuclear arms race.

What the Treaty Did

The New START treaty placed strict numerical limits on the strategic nuclear forces of both countries. It capped deployed intercontinental and submarine-launched ballistic missiles and nuclear-capable heavy bombers at 700, limited total deployed nuclear warheads to 1,550, and restricted total launchers to 800, including both deployed and non-deployed systems. These reductions were fully implemented by 2018.

Beyond numerical limits, the treaty established a verification regime that included regular data exchanges, notifications about the movement of strategic forces, and short-notice on-site inspections. These mechanisms were widely seen as critical confidence-building measures, helping each side understand the other’s nuclear posture and reducing the risk of miscalculation.

Breakdown Before Expiry

Although the treaty remained legally in force until February 2026, its practical functioning had already weakened. In February 2023, Russia suspended its participation in verification activities, citing tensions related to the Ukraine conflict. Inspections and data exchanges were halted, though Moscow stated it would continue to respect the treaty’s numerical limits.

Despite the suspension, analysts say the treaty’s framework still provided a degree of restraint and predictability. Its final expiration removes even that remaining structure.

Global Alarm Over Nuclear Risks

The end of New START has intensified warnings from international security experts and scientific institutions. The Bulletin of the Atomic Scientists recently moved its symbolic Doomsday Clock closer to midnight, reflecting what it described as rising global risks. The clock now stands at 85 seconds to midnight, the closest it has ever been, signaling concern over nuclear threats, emerging technologies such as artificial intelligence, biological risks, and climate change.

Experts associated with the Bulletin have warned that nuclear weapons are playing a more prominent role in national security strategies worldwide. Several nuclear-armed states are modernising their arsenals, while some non-nuclear states are reassessing their security options amid global instability.

Potential for Rapid Arsenal Expansion

With New START no longer in force, both the U.S. and Russia technically have the capacity to significantly increase their deployed nuclear warheads in a relatively short period. Analysts estimate that Russia could raise its deployed warheads by around 60%, while the United States could increase its numbers by more than 100%, simply by loading more warheads onto existing missiles and bombers.

Such moves would not require new weapons development, making the risk of escalation more immediate. Security specialists caution that even without an explicit decision to expand arsenals, the absence of legal limits increases uncertainty and mistrust.

Strategic Developments Add Complexity

The treaty’s expiration coincides with major strategic developments on both sides. The United States is moving ahead with advanced missile defence initiatives, while Russia has announced new strategic weapons systems designed to bypass existing defences. These parallel developments have raised concerns that defensive measures by one side could be perceived as offensive threats by the other, further destabilising the strategic balance.

Impact on Global Non-Proliferation

The timing of New START’s expiry has also raised concerns ahead of the 2026 Review Conference of the Nuclear Non-Proliferation Treaty (NPT). The absence of progress on arms control between the world’s largest nuclear powers could weaken the credibility of the NPT and deepen divisions between nuclear-armed and non-nuclear states.

Non-nuclear countries have long argued that disarmament commitments by nuclear powers are essential to maintaining the legitimacy of the global non-proliferation regime. The lapse of New START may complicate diplomatic efforts to reinforce that framework.

Is There Still Room for Restraint?

Despite the bleak outlook, some diplomatic space remains. Russian President Vladimir Putin has proposed that both countries voluntarily continue observing New START’s numerical limits beyond the treaty’s expiration. Moscow has indicated willingness to extend this arrangement at least temporarily, even without a formal treaty.

U.S. President Donald Trump has previously stated that he did not want the treaty to lapse but has also argued that any future arms control framework should include China. Beijing, however, has consistently resisted trilateral negotiations, pointing out that its nuclear arsenal is significantly smaller than those of the U.S. and Russia.

There is currently no precedent for a three-way nuclear arms control agreement, and experts say insisting on such a format could delay or derail efforts to prevent an unconstrained arms buildup.

An Uncertain Path Ahead

With New START now expired, the responsibility for avoiding a new nuclear arms race rests largely on political decisions rather than legal obligations. Analysts stress that even informal or temporary arrangements could help maintain stability while broader negotiations are explored.

As global attention turns to how Washington and Moscow respond in the coming weeks, many experts argue that the lessons of the Cold War remain relevant: transparency, communication, and restraint are essential to reducing nuclear risks. Whether those principles will guide policy in the post-New START era remains an open question.