The Russians have called for such a move for years. and the move will no doubt be seen as a victory for Russia and a gift from the US. The program was begun under Obama in 2013.However, stopping the program will not end US involvement in Syria by any stretch of the imagination as the US is deeply involved in funding and arming the Syrian Democratic Forces dominated by Kurds. The Kurds are regarded as terrorists by Turkey and there have been clashes with them.
The US was recently angered as Turkey revealed the location of its numerous bases in Kurdish-controlled areas. There are reports of US armored vehicles pouring into Kurdish-held areas in Syria suggesting that US involvement in Syria is actually increasing even though the CIA program has been jettisoned.
The aid seems to have been frozen in February after the groups suffered from a major Islamist attack in January. There were complicated relations and conflict among groups. Apparently, Trump made the decision after talking with CIA director Mike Pompeo and national security adviser H.R. McMaster. Trump and Russian President Putin also made a deal for a partial cease-fire during their recent meeting at the G-20 summit. The ceasefire includes the area where rebels supported by the CIA are stationed. While this may be seen as helping Russia it also help all those living the areas as they will not suffer the effects of being in a battle zone.
The development is a stark change from the situation last month when the US shot down a Syrian plane and Russia in response said that US planes flying over the area would be regarded as potential targets. Earlier still, the US had hit a Syrian base with Tomahawk missiles in response to an alleged chemical attack by Assad. No doubt there will be an outpouring of articles describing the cessation of the program as a sellout to Russia even though there is plenty of evidence the program was not working well. It is unlikely to have made any significant difference to the progress of the war.