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A new report warns that the world’s nine nuclear-armed states are modernizing and expanding their arsenals, which is creating “new risks.”

Getting into it: The study, published Monday by the Stockholm International Peace Research Institute, found that most of the nine powers fielded new nuclear-capable systems last year, reversing decades of post-Cold War disarmament. As of January, the world held an estimated 12,187 warheads, with about 9,745 in stockpiles available for use, roughly 4,012 deployed on missiles and aircraft, and as many as 2,200 kept on high alert and launchable within minutes. While that total marked a slight dip from a year earlier, SIPRI warned the long decline is poised to reverse as dismantlement slows and deployment speeds up, with researcher Hans Kristensen saying states are “flexing their nuclear muscles.”

The US and Russia still dominate, holding almost 85% of usable warheads with more than 5,000 each. Both kept their stockpiles relatively stable but are pursuing sweeping modernization. Notably, the US program is facing funding delays and the added strain of the roughly $1.2 trillion Golden Dome missile-defense plan, while Russia’s effort has been dogged by failed Sarmat ICBM tests, sanctions, and the demands of the Ukraine war. Despite this, SIPRI expects both countries to deploy more warheads in the years ahead.

The report also said that Israel (estimated to have about 90 nuclear warheads) is modernizing its weapons while still not acknowledging it has them.

China is expanding faster than anyone, growing to roughly 620 warheads and building new missile silo fields that could give it as many ICBMs as the US or Russia by 2030, though even surpassing 1,000 warheads would leave it at about a quarter of either rival’s stockpile.

Elsewhere, the UK held steady near 225 but plans to grow its arsenal, buy nuclear-capable F-35A jets for NATO nuclear sharing, and stop disclosing its size, while France (which has about 300) is doing the same after Macron ordered an increase. India (about 200) and Pakistan (about 170) both kept building after their brief clash in May 2025.

This all comes as researchers said the most concerning thing is the collapse of arms-control agreements, the failure of the latest Nuclear Non-Proliferation Treaty review conference to produce an outcome for a third straight time, and intensifying great-power rivalry.

SIPRI’s Matt Korda added that a “drift towards authoritarianism” in some nuclear states makes their behavior harder to predict, warning that leaders may not receive accurate information or act rationally during a crisis.