The phrase "ambitious agreement" means a deal or arrangement that sets high goals and aims to achieve significant or challenging outcomes. It suggests a desire to accomplish big or important things. Full definition
Three degrees warming, he says, is achievable in the «most optimistic case» assessed by the report, in which the researchers assume that the Lima agreements are augmented by a more ambitious agreement in the near future. (planet3.org)
We are a G7 country with a recently completed ambitious agreement with the EU. (asiapacific.ca)
The idea was that it is easier to reach ambitious agreements through multilateral trade negotiations dealing with many issues at once than through piecemeal bilateral agreements. (politics.stackexchange.com)