Wary of sharing its most effective technologies with potential foes - this is a big step for Russia
To understand the significance of this story you must know two things.
One is that the air defense system in question is the most advanced in Russia's own military arsenal.
The second is that so far Moscow has been reluctant to transfer its most state of the art weapons systems to China.
That now it does so points to a new-found proximity between the two.
This article originally appeared at Russia Beyond the Headlines
The first-ever contract for exports of the S-400 Triumf air defense missile system has been signed.
"A contract between Rosoboronexport and the Chinese Defense Ministry was signed at the beginning of this fall for the delivery of at least six battalions of S-400 air defense missile systems worth of more than $3 billion," Vedomosti reported on Wednesday.
Negotiations on the delivery of S-400 systems to China had been in progress for several years and the Russian Defense Ministry said in 2011 that exports might begin no earlier than 2016 because the Russian Armed Forces would have to be provided for first, the newspaper said.
The S-400 Triumf air defense missile system is a product of the Almaz-Antei Concern and is based on the S-300 long-range air defense system, one of whose major buyers was the People's Liberation Army of China.
Rosoboronexport fulfilled the most recent contract for 15 battalions of the S-300PMU-2 air defense missile system in 2010.
Following the breakup of the former Soviet Union, S-300P systems were exported to Vietnam, Algeria, Azerbaijan and Cyprus and systems from the Russian Armed Forces' stock were supplied to Kazakhstan and Belarus.
The S-300 contract with Iran was cancelled for political reasons in 2010 and the delivery of the air defense missile system to Syria was suspended due to the ongoing civil war.
S-300V systems, another modification of S-300P designed for air defense units of the Ground Forces rather than area air defense, were supplied to Venezuela and Egypt.