"Regime forces, in March 2017, created a buffer zone between the YPG and Turkish-backed FSA in western Manbij, in order to protect the YPG from any possible FSA moves. They did the same in September 2017 in Afrin.
Assad’s stance towards the YPG changed after Daesh was defeated from urban areas of Syria in late 2017. Assad began calling the YPG “the traitors,” and rejected any US-backed forces on Syrian soil.
But it shifted again in January 2018, when Turkey began its operation in YPG-controlled Afrin in Syria. Opposing Turkey’s and the opposition groups' presence in Syria, Assad allowed movement of YPG militias for reinforcement through the regime-controlled areas. Iran-backed Shia militias, who fight along with the regime forces, are also based in those areas.
But it is now unclear how long Assad’s support will continue to the YPG, or if he will support the group’s desire to rule the areas they capture from Daesh in the long term. "
This describes how things look. Sources are mixed as to how the negotiations will go, and Assad has said some pretty strong stuff, but they do have a history of working alongside each other and they are negotiating and it does look like when the choice is between Turks and Kurds Assad choses Kurds, although again, sources are mixed. Putin has suggested that old agreements between Assad and the Turks that the Turks can do cross border operations against the PKK could be re-opened, but has however demanded that the Kurds and Syrians do not attack each other.
Thinking about the hard power in the situation, the Kurds have really quite a lot. They have a large, now battle hardened militia with mass popular support, while Assad is trying to stitch back together a country ravaged by the worst war in the last 10/20 years. At this point it would be incredibly stupid of him to start another civil war and he is not that stupid.