This depends on your views on the authenticity of the early sutras. Some Buddhist scholars think that just about of all of them have been memorized, just as the ancient Vedas were, by monks with excellent memories from the time of the first great council shortly after Buddha died. If so, then it’s actually possible to get more accurate transmission by memory and passing on through speech than by written word copied by scribes, if the original texts don’t survive - as copies of written texts often have errors.

In support of this view, the early Buddhist sutras when collected from widely separated geographical regions that weren’t in contact when the texts were written down, are essentially the same texts with only minor changes. That suggest they were preserved unchanged for centuries.

If that’s correct, then much of the Pali Canon dates from that time, soon after the Buddha died. Now that doesn’t mean that it’s all the words of the Buddha. The later sutras were memorized by monks as he taught and they checked their understanding with him. But the earlier ones were remembered many years later. Especially the accounts of his birth and his early years as a prince are stories retold many years after the actual events.

Also they didn’t have the same idea of what counts as historical accuracy as us. And they worked out their consensus for the canon after he died. And the sutras are clearly organized to be easier to memorize, and are surely not “transcriptions” of his speeches as we’d understand it.

Still on this view, much of the Pali canon then consists of the teachings of the Buddha as he taught them and it may well record many of the actual words and phrases he used. Many renowned Buddhist scholars actually hold this view including the famous Buddhist scholar Richard Gombrich and Prayudh Payutto amongst others, so it’s certainly an academically respectable view to hold. There’s a lot of evidence in support of this view. See my Origins of the Buddhist Sutras - were they the Teachings of the Buddha?

The Mahayana canon is much later and some Buddhist teachings, e.g. Zen and some Tibetan teachings which in those traditions are said to carry the inspiration of enlightenment, continue to arise as new teachings to this day.