Pausanias on Achaean armament, ca. 200 BCE

[Paralus]

As for passages in which they are clearly shown wielding the sarissa, there's the already-mentioned passage in Plutarch for the battle of Pydna, which finds parallel in the remnants of Livy's description of the failed attack of the Paeligni against the hasta-armed caetrati. In fact, the Paeligni who in Livy suffer losses against the caetrati, are the same Paeligni who attack the agema (=(or include) caetrati/peltastai) and suffer such heavy losses trying to break through the sarissa ranks…

The Livy narrative at Cynoscephalae has both the caetrati and the phalanx abandon their hasta, which were so long that they were an impediment. I'm conflicted over how to use this passage, since Livy and all the other sources clearly understand a cohesive, sarissa-armed phalanx in combat with the Romans, thus I don't think they threw aside their sarissa. On the other hand, it does show that he considers them, like Polybius, to be sarissa-armed soldiers comparable to the phalanx.

Going with the last first, I suspect the passage in Livy is the following:

Livy, 33.8
Then, as the enemy were approaching, and especially as his own men were being cut down as they fled and could not be saved unless they were defended by fresh troops, and also as retreat was no longer safe, he found himself compelled to take the supreme risk, though half his force had not yet come up. The cavalry and light infantry who had been in action he stationed on his right; the caetrati and the men of the phalanx were ordered to lay aside their spears, the length of which only embarrassed them, and make use of their swords. To prevent his line from being quickly broken he halved the front and gave twice the depth to the files, so that the depth might be greater than the width. He also ordered the ranks to close up so that man might be in touch with man and arms with arms.

Livy is following Polybius in his account. This is immediately apparent when one reads both together. That agreed, I can only hypothesise that Livy has corrupted his account in conflating the attack of the Macedonian right and the incontinent departure from the field of the yet to form up left.

Polybius is rather more lucid in his reconstruction. He describes the Macedonian light troops, skirmishers and mercenaries falling back – after initial success – as the Roman “heavy infantryâ€