In September, Chinese leader Xi Jinping won plaudits when he pledged to the United Nations that China would reach carbon neutrality before 2060. Earlier this month, Chinese and U.S. climate envoys issued a full-throated statement that climate campaigners applauded as another meaningful step. But given top billing at President Biden’s climate summit on Thursday, Xi did not offer a fresh jolt of momentum. He rehashed some old promises.

As Biden’s virtual summit wraps up this week, it has reinforced the sense that the United States and China, despite fierce and nationalistic rivalry, will seek common ground on the existential issue of climate change. But it’s uncertain how much more ground Xi is willing to cede — and under what circumstances.

Although the United States, Japan and Canada on Thursday unveiled tighter new greenhouse gas emissions targets for 2030, Xi — as well as another key figure, Indian Prime Minister Narendra Modi — refrained from new commitments. After Xi’s speech, Chinese officials tasked with briefing reporters and Chinese state media repeated long-standing lines that developed countries must do more to cut their emissions while developing economies should be allowed more slack.

Xi’s reticence at the summit could be driven by domestic considerations, said Li Shuo, senior adviser at Greenpeace East Asia.

“He needs to balance divergent interests between domestic industrial groups and international expectations, the need to show China’s green image and also not be seen as caving to U.S. diplomatic pressure,” Li said. “It’s precisely because it’s a U.S.-organized event that China might have been more hesitant to put more offers on the table.”

Li said the next venue for a potential Chinese announcement could be the 26th United Nations Climate Change Conference, known as COP26 — a multilateral, rather than Biden-led, forum to take place in Glasgow in November.