The current 15th season of CSI will consist of 18 episodes, the first time the long-running crime drama has produced fewer than a full-season 22 episodes outside of the writers strike-impacted 2007-08 season. The order trim, first reported by TVLine, was part of a flex plan put in place in May, with the network now triggering the option to go down to 18 episodes. The rationale is understandable — none of CBS’ new fall dramas failed, and the network has three 13-episode hourlong series to accommodate for midseason, including the latest CSI offshoot, CSI: Cyber, which will share the Sunday 10 PM slot with the mothership series, reducing the number of originals needed. (The other CBS midseason dramas are Vince Gilligan and David Shore’s Battle Creek and the seventh and likely final season of The Mentalist).

CBS sources insist that the order reduction in no way reflects a decline in confidence in the veteran series as the network brass appear happy with CSI creatively and ratings-wise (the series has been delivering numbers on par with The Mentalist last fall in the Sunday 10 PM hour, though it is down double digits from its performance in its previous Wednesday 10 PM slot). Still, if history is any indication, CSI fans have a reason for concern.

CSI: Miami’s order was reduced for the first time in Season Ten, to 19 episodes. That turned out to be the series’ final season as it was followed by a cancellation. The second CSI spinoff, CSI: NY, got its first reduction in Season Eight, to 18 episodes. It lived to see Season 9, also partial, at 17 episodes, before getting cancelled.

Even if both new midseason dramas crash and The Mentalist ends its run as expected, CBS still will have an inventory problem in May, putting pressure on long-running series like CSI, which, despite its lower ratings and high cost, remains a revenue generator for CBS, which owns it, because it has an off-network deal and remains popular around the world. So, even if this is not the end, it most likely is the final chapter for the venerable drama, with its seasons numbered.