The tribunal's rules stipulate that the suspects and their lawyers will be allowed to address the court via videoconference if the judge decides to keep them in jail after the hearing starts at 1200 GMT.
The special tribunal for Lebanon, which began work on March 1 and is based in The Hague, Netherlands, said three weeks ago that Lebanon had supplied a list of those detained over Hariri's assassination to the tribunal charged with trying the suspects.
But a Lebanese investigating judge earlier this month lifted arrest warrants against the four generals jailed since 2005 in connection with the killing.
However, the judge also ordered that the four remain in jail pending a decision by the tribunal on their fate.
Hariri was killed along with 22 others in a bomb blast on the Beirut seafront on February 14, 2005, stirring a political crisis and leading to the withdrawal of Syrian troops in Lebanon after a 29-year presence.
A UN investigative commission has said there was evidence that Syrian and Lebanese intelligence services were linked to Hariri's killing.
Damascus has denied any involvement.