The onstat -g act option prints active threads.
Following is sample output from the onstat -g act command. For a description of the output, see The onstat -g ath Option.
IBM Informix Dynamic Server Version 10.00.UC1 -- On-Line -- Up 18:47:42 -- 101376 Kbytes Running threads: tid tcb rstcb prty status vp-class #scheds name *2 b3132d8 0 2 running 2adm 0 adminthd *40 c5384d0 0 2 running 1cpu 102630 tlitcppoll