You can check details of a .si top-level domain using the Slovenian National registry for the .si domain – register.si
When the registration period ends, a .si domain first goes into quarantine. During quarantine, only the current domain holder has the right to renew or buy it, which means a .si domain in quarantine isn’t on the open market and can’t be registered by another company or individual. You can check domain information in the article “Where can I check domain information“.
Arnes manages the .si domain registry, and a .si domain stays in quarantine for 30 days after it expires. After quarantine, the domain is released and anyone can register it again. On register.si, the time until the end of quarantine is shown as “Čas do izbrisa” (time until deletion), which in practice means the domain is released for purchase through any provider.