diff --git a/config_src/drivers/nuopc_cap/mom_cap.F90 b/config_src/drivers/nuopc_cap/mom_cap.F90
index e0e618c76e..2c8271a028 100644
--- a/config_src/drivers/nuopc_cap/mom_cap.F90
+++ b/config_src/drivers/nuopc_cap/mom_cap.F90
@@ -1943,12 +1943,14 @@ subroutine ModelAdvance(gcomp, rc)
                  msg=subname//' ERROR opening '//rpointer_filename, line=__LINE__, file=u_FILE_u, rcToReturn=rc)
             return
           endif
-          if (len_trim(inst_suffix) == 0) then
-            write(writeunit,'(a)') trim(restartname)//'.nc'
-          else
-            write(writeunit,'(a)') trim(restartname)//'.'//trim(inst_suffix)//'.nc'
+
+          ! update restart file name to include the instance suffix
+          if (len_trim(inst_suffix) > 0) then
+            write(restartname, '(A,".mom6",A,".r",A)') trim(casename), trim(inst_suffix), timestamp
           endif
 
+          write(writeunit,'(a)') trim(restartname)//'.nc'
+
           if (num_rest_files > 1) then
             ! append i.th restart file name to rpointer
             do i=1, num_rest_files-1
diff --git a/src/framework/MOM_restart.F90 b/src/framework/MOM_restart.F90
index b99cd3f184..ce47e3b0fa 100644
--- a/src/framework/MOM_restart.F90
+++ b/src/framework/MOM_restart.F90
@@ -132,6 +132,7 @@ module MOM_restart
   type(p4d), pointer :: var_ptr4d(:) => NULL()
   !>@}
   integer :: max_fields !< The maximum number of restart fields
+  character(len=32) :: restartfile_appx_prefix !< The prefix for the restart file appendix (i.e., ensemble id)
 end type MOM_restart_CS
 
 !> Register fields for restarts
@@ -1613,6 +1614,8 @@ subroutine save_restart(directory, time, G, CS, time_stamped, filename, GV, num_
   integer :: turns                      ! Number of quarter turns from input to model domain
   integer, parameter :: nmax_extradims = 5
   type(axis_info), dimension(:), allocatable :: extra_axes
+  integer :: prefix_index    ! The index of the first occurrence of prefix in the restart filename.
+  integer :: prefix_length   ! The length of the prefix string.
 
   turns = CS%turns
 
@@ -1654,10 +1657,26 @@ subroutine save_restart(directory, time, G, CS, time_stamped, filename, GV, num_
   call get_filename_appendix(filename_appendix)
   if (len_trim(filename_appendix) > 0) then
     length = len_trim(restartname)
-    if (restartname(length-2:length) == '.nc') then
-      restartname = restartname(1:length-3)//'.'//trim(filename_appendix)//'.nc'
-    else
-      restartname = restartname(1:length)  //'.'//trim(filename_appendix)
+
+    ! Determine if a valid prefix for appendix is provided.
+    prefix_index = 0
+    prefix_length = len_trim(CS%restartfile_appx_prefix)
+    if (prefix_length > 0) prefix_index = index(restartname, trim(CS%restartfile_appx_prefix))
+
+    if (prefix_index == 0) then ! No prefix is found
+      if (restartname(length-2:length) == '.nc') then
+        restartname = restartname(1:length-3)//'.'//trim(filename_appendix)//'.nc'
+      else
+        restartname = restartname(1:length)  //'.'//trim(filename_appendix)
+      endif
+    else ! Prefix is found
+      if (restartname(length-2:length) == '.nc') then
+        restartname = restartname(1:prefix_index-1+prefix_length) // &
+                  trim(filename_appendix) // restartname(prefix_index+prefix_length:length-3) // '.nc'
+      else
+        restartname = restartname(1:prefix_index-1+prefix_length) // &
+                  trim(filename_appendix) // restartname(prefix_index+prefix_length:)
+      endif
     endif
   endif
 
@@ -2304,6 +2323,12 @@ subroutine restart_init(param_file, CS, restart_root)
                  "made from a run with a different mask_table than the current run, "//&
                  "in which case the checksums will not match and cause crash.",&
                  default=.true.)
+  call get_param(param_file, mdl, "RESTARTFILE_APPENDIX_PREFIX", CS%restartfile_appx_prefix, &
+                 "The prefix for the restart file appendix (i.e., ensemble id for ensemble runs). "// &
+                 "If this prefix is found in the restart file name, the appendix is added right after the "// &
+                 "first occurrence of the prefix. If not found, the appendix is added to the end of the "// &
+                 "file name. This parameter is ignored for non-ensemble runs.", &
+                 default="")
   call get_param(param_file, mdl, "RESTART_SYMMETRIC_CHECKSUMS", CS%symmetric_checksums, &
                  "If true, do the restart checksums on all the edge points for a non-reentrant "//&
                  "grid.  This requires that SYMMETRIC_MEMORY_ is defined at compile time.", &