We have few Roman swords dating from the 1st century BC, though what we do have would appear to support the hispaniensis type swords being the norm until the end of the century. Meaning that if you had to put a sword in the hand of a Roman soldier heading off to the Gallic war with Caesar, it would most likely be this type.

We have a rather solidly dated example of such a sword from the Island of Delos in Greece, which was a pirate/slaver base attacked and destroyed by Roman forces in 69 BC. The sword is associated with the destruction phase and therefore comfortably belongs in the decade prior to Caesar's Gaulish campaigns. It is very much of the longer hispaniensis type, with a 64cm long blade. An even longer sword from Soknopaiou Nesos/Naukratis in Egypt dates from between 50 BC to 0 AD and was found with a pommel that matches the type from the rare depiction of a sword on the tombstone of the centurion Minucius from Padua in Italy (mid-1st century BC).

Swords dated to the last few decades BC such as those from Fontillet in France and Giubiasco in Switzerland still have blades in excess of 60cm and can still be placed in the Hispaniensis category as opposed to the Mainz/Fulham type, though these swords are not strictly from Roman contexts.

However, it is in these last few decades BC that we find the Ljubljanica sword from Slovenia, a Mainz-type sword found in its scabbard from the river Ljubljanica.

Whether there was a true break or a slow evolution from long hispaniensis swords into shorter Mainz/Fulham types is hard to pin down. However, its quite possible, or even likely, that both types were in use simultaneously in the 1st century BC.

Sources:

Bishop, M. C. 2016. The Gladius. Osprey. Oxford.

Bishop, M. C. & Coulston, J.C.N. 2006. Roman military equipment from the Punic wars to the fall of Rome. Oxbow. Oxford