More than 1,500 delegates have been taking part in the Syrian National Dialogue Congress in Sochi, with most coming from the war-torn country itself.
The opposition umbrella group, the High Negotiations Committee, said they would not attend.
Syria's main Kurdish group also stayed away from the Russian-brokered peace talks because of the Turkish offensive in Afrin.
But the Moscow platform, which claims to represent some Syrian opposition groups, will be present in Sochi. Their leader is Qadri Jamil.
“Here we will discuss the future content of the Constitution," he said. "Different sides represented here have different opinions, and we all have to learn how to reach a consensus.
"Syrians for a long time have not experienced any political freedom, in order to talk to discuss and to find a solution through a compromise.”
Many Syrian activists do not recognise the Moscow Platform and are sceptical of Qadri Jamil, who was a former member of Assad’s government.
But Jamil insists he just wants to kick start the peace talks.
He said: “Now in Sochi we are trying to start the inter-Syrian dialogue, which will provide the political support to the Geneva process.”
Euronews reporter, Galina Polonskaya explained what the delegates are hoping to achieve.
“One of the major goals of the Congress in Sochi is to select candidates for the Commission of the Constitutional Reform in Syria," she said. There will be other, difficult - considered for now to be the dead-end - questions discussed. What is clear is that the main result of this Congress is a process which could begin this Tuesday.”