Temp DB space allocated- will it be reclaimed ever? I have observed that the tempdb in the production environment has grown over to 100 GB after initializing it.

I understand that due to server load and some expensive queries have resulted to the growth of tempdb in a span of just two days. I have been observing this over a week now and find this size did not grow further and remains the same.

I have one mdf file configured for tempdb on the server having 8 logical cores. Though I could add multiple mdf files based on the logical cores.

I observe that the free page size and the physical size of temp db data file are the same in my case

SELECT SUM(unallocated_extent_page_count) AS [free pages], 
(SUM(unallocated_extent_page_count)*1.0/128) AS [free space in MB]
FROM sys.dm_db_file_space_usage;


Help me understand if this physical space would ever be reclaimed automatically without we explicitly executing script to shrink the space or by restarting the server to reset the temp db allocation??
Like all databases, free (unallocated) space in tempdb is reused for new objects.  No action is needed for this space to be reused.  

The physical size of tempdb files will reflect the high-water mark of growth since the instance was last started.  The size will revert back to the initial file size after an instance restart, freeing space on the disk volume if growth occurred.  It is also possible to release unused file space using DBCC SHRINKFILE.  That should not be done routinely but may be desirable if the growth was an anomaly, such as due to a bad query.  It is best to size files to accommodate expected space requirements and provide growth as a safety net for unexpected needs.

Multiple tempdb data files of equal size and growth can improve performance by reducing allocation page contention for some workloads.  However, that is unrelated to space reclamation.