The Current count for concurrent hosts is an indication of how many host addresses have been learned by the system, that is, the number of entries currently in the host database. Entries in the host database are not periodically aged out or cleared from memory — instead, they are reused when needed for new hosts. Therefore a value of 0 in the Remaining column does not mean your unit can't accommodate any more hosts — new hosts will simply replace hosts that are no longer active. It is normal and expected to see the number of concurrent hosts at its limit.
PacketShaper# sys limit
Statically allocated objects Current Remaining Total
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Traffic classes 697 1351 2048
Partitions 6 1018 1024
Dynamic Partitions 0 1024 1024
Policies 9 2039 2048
Matching rules 1759 3363 5122
Classes with worst clients/servers 0 16 16
Classes with top talkers/listeners 0 12 12
TCP flows 9 39991 40000
Other IP flows 44 19956 20000
Legacy flows 4 1996 2000
Concurrent Hosts 20000 0 20000
MAC Cache Entries 5 7495 7500
Fragment Cache Entries 0 4000 4000
Command Contexts 7 23 30
Compression tunnels 0 0 0
Compression entries 0 0 0
Tunnels 0 30 30