In 2004, a group of rabbis in Israel attempted to begin the process of re-establishing the Sanhedrin using the Rambam's method of universal consensus to re-establish the line of semikha. Rabbi Moshe Halberstam was selected as the first musmakh and he proceeded to confer semikha on others until enough rabbis had been granted semikha to establish a Sanhedrin, which R' Adin Steinsaltz, as Nasi, referred to as the "Nascent Sanhedrin".
As far as I can tell, this new Nascent Sanhedrin is still active; albeit quietly. Rambam, whose opinion was relied upon to re-establish semikha, also holds that whenever a Sanhedrin exists, new months must be established through testimony (Hilkhos Kiddush HaChodesh 5:2). Does this new Sanhedrin sanctify the new month through witnesses? Is there any record of this happening?