Efforts to end the war are now proceeding along two rival tracks: the formal political peace process hosted at United Nations headquarters in Geneva and, since January, parallel talks in Kazakhstan brokered by Russia, Iran and Turkey.
Observers say the UN appears to be scrambling to match Astana's momentum after a landmark deal signed in Kazakhstan on May 4 that would create four "de-escalation" zones across some of Syria's bloodiest battlegrounds.
Since the deal came into effect a week ago, fighting has slowed across swathes of the country.
But in Damascus, which is not included in the deal, the government has secured the evacuation of three rebel-held districts, bringing it closer to exerting full control over the capital for the first time since 2012.
Briefing journalists last week in Geneva, UN special envoy Staffan de Mistura stressed the "rather business-like, rather short" nature of the upcoming talks, expected to last just four days in order to "hit the iron while it's hot".
"After the Astana meeting which took place and which we attended proactively, there has been some outcomes that we find extremely, potentially, promising and we want to connect, as much as possible, that outcome with some political horizon," de Mistura said.
Numerous rounds of UN-backed talks have fallen short of producing concrete results, although during the last round in March the sides finally began discussing four separate "baskets" of issues: governance, a new constitution, elections and combating "terrorism" in the war-ravaged country.
Aron Lund, a fellow at The Century Foundation, said that despite Geneva's important "symbolic value, it isn't moving forward in any visible way."
"In practice, the Geneva track has largely been sidelined by the Astana track, at least for now," Lund said.
- 'Dead-end demand' -
Delegations are expected to arrive in Geneva on Monday, a day before the talks start.
The Syrian government team will be headed once again by its ambassador to the United Nations, Bashar al-Jaafari.
The opposition delegation will be represented by the Riyadh-based High Negotiations Committee and led again by Nasr al-Hariri and Mohammad Sabra.
The HNC has continued to call for the ouster of President Bashar al-Assad as part of a political transition, a demand seen as a non-starter by the Syrian regime.
"By design, the Geneva process revolves around this dead-end demand for a negotiated transition," Lund told AFP.
"In terms of actually trying to stabilise Syria, the main effect of pegging peace to transition has been to marginalise the UN in Geneva and shift attention to Astana instead," he said.
Rebel backer Turkey and government allies Russia and Iran sponsored the first talks in Astana in late January to reinforce a faltering ceasefire.
They have since returned for several meetings, culminating this month in the safe zones deal.
"The Astana process doesn't carry the same baggage and is run more on Russia's terms. That means it is more in tune with battlefield realities," Lund said.
Assad has brushed off the upcoming Geneva negotiations as "merely a meeting for the media".
"There is nothing substantial in all the Geneva meetings. Not even one per million. It is null," Assad said in a recent interview with Belarus's ONT channel.
"As to Astana, the situation is different... This started to produce results through more than one attempt to achieve ceasefire, the most recent of which is what's called the de-escalation areas," Assad said.
Syrian peace efforts have also been marked in recent months by Washington's all-but withdrawal from the process under President Donald Trump.
The previous US administration, in particular then-secretary of state John Kerry, was deeply involved in the Geneva process but since Trump took office Washington has played little apparent role.
-----------------------------------------------------------------------------------------------------------------