As of Oct. 1, Russia had hundreds more nuclear warheads deployed than the United States did. A startling 429 more, in fact, according to the U.S. State Department.

Don’t panic quite yet. The gap is probably temporary. But that doesn’t mean all’s well when it comes to potentially world-ending weaponry.

The reason for the disparity is simple. While the U.S. military has been steadily cutting the number of nukes it loads on submarines and bombers and in missile silos, Russian forces have recently been adding more.

Seemingly more worrying for the United States, Russia’s 1,796 deployed warheads exceed—by a whopping 246 weapons—the cap of 1,550 deployed nuclear weapons that Moscow and Washington agreed to as part of the 2011 New Strategic Arms Reduction Treaty.

The United States, meanwhile, is already well below the New START cap. America’s missile submarines, nuclear-capable heavy bombers, and land-based intercontinental ballistic missiles are armed with just 1,367 warheads, the State Department says.

Both Russia’s nuke surplus and America’s lesser total could change in the next 17 months. Washington and Moscow have agreed on a Feb. 5, 2018, deadline for fully implementing New START. Until then, the countries’ respective nuclear arsenals could fluctuate in size—and often.

“You have to keep in mind that numbers go up and down on a day-to-day basis, so a one-day [snapshot] may mislead about force trends over time,” Jeffrey Lewis, a nuclear expert who blogs at Arms Control Wonk, told The Daily Beast.

Both the United States and Russia have signaled their intention to abide by New START’s terms, meaning Russia will probably start shedding old warheads pretty soon, replacing them with a smaller number of newer atomic munitions and ultimately erasing the current nuclear disparity. “Neither of us is in violation of the agreement,” Lewis stressed.

New START is actually one of the few reasons for optimism amid the U.S.-Russia strategic arms race. For starters, the treaty only covers deployed nukes—meaning those on quick alert aboard subs, on planes, and in silos.

The treaty doesn’t limit how many perfectly functional nuclear weapons the United States and Russia can keep in storage. In many cases, those warheads could go from “stored” to “deployed” with just a few hours’ work.

The State Department told The Daily Beast that the United States possesses 4,717 “deployed and non-deployed” nuclear weapons. Hans Kristensen, director of the Nuclear Information Project at the Federation of American Scientists, has estimated Russia’s stockpile to be around 4,500 warheads. Neither Washington nor Moscow discloses the exact number of its nukes that are totally inactive and awaiting dismantling.

President Obama has called for further nuke cuts—although, in fact, his administration has reduced America’s nuclear stockpile at the slowest rate in a generation. Regardless, the Republican-led Senate, which must approve any treaty, has resisted deeper reductions in the U.S. arsenal. Both the U.S. and Russian governments plan to spend hundreds of billions of dollars in coming decades modernizing their nuclear arsenals with new warheads … and better rockets, bombers, and submarines to carry them.

“Although these programs do not constitute a buildup of the overall nuclear arsenal, they are very comprehensive and reaffirm the determination by both Russia and the United States to retain large offensive nuclear arsenals at high levels of operational readiness,” Kristensen wrote on his blog.

While New START seems to be holding strong, a separate disarmament deal—whereby the United States and Russia agreed to dispose of excess fissile material—has just collapsed. The Plutonium Management and Disposition Agreement, signed in 2000, covered 34 tons of surplus, weapons-grade plutonium in each country.

Under the terms of the agreement, both Russia and the United States would render the plutonium unusable for military purposes—not only to decrease nuclear tensions between the two powers, but also to ensure the excess plutonium didn’t somehow wind up in terrorists’ hands.

Citing a “radically changed environment,” Russian President Vladimir Putin announced Oct. 3 that Russia was pulling out of the deal. Nevertheless, Moscow informally pledged that it wouldn’t use the old plutonium in weapons—agreement or no.

“The decision by the Russians to unilaterally withdraw from this commitment is disappointing,” White House press secretary Josh Earnest said. “The announcement about the Plutonium Management and Disposition Agreement is more in line with those kinds of decisions that have only deepened Russia’s isolation in the international community.”

Meanwhile, the United States has been insisting for at least three years now that Russia is violating the 1987 Intermediate-Range Nuclear Forces Treaty, which bans many types of short-range nuclear weapons.

U.S. officials have not said just how Russia is allegedly violating the treaty, but the purported breach might involve the road-mobile SS-25 ballistic missile.

Earnest expressed cautious optimism that, despite everything, Russia is still committed to reducing the risk of atomic warfare. He pointed to Russia’s cooperation with the United States in negotiating the deal with Iran to end that country’s nuclear-weapons program. “I think that’s an indication of the priority that Russia has placed on nonproliferation,” Earnest said.

But Russia’s and America’s equal commitments to maintaining and modernizing their overall nuclear arsenals—regardless of any agreement to cap the number of deployed warheads—speaks to an underlying atomic distrust that lingers a quarter-century after the Cold War ended.

“How the two countries justify such large arsenals is somewhat of a mystery,” Kristensen noted, “but seems to be mainly determined by the size of the other side’s arsenal.”

Updated Oct. 8, 2016, 9:00 am.