Argentina: "autito"
Colombia: "autico"
Spain: "autillo" but last time I posted it, anthk said it's more complicated https://news.ycombinator.com/item?id=44490096
They sound quite different, and all are accepted and understood, but it's very unusual to use the "wrong" one. Only if you are a tourist or immigrant or something.
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For the GP: the idea is that a few variants/dialects are accepted. When the pronunciation changes, it slowly is introduced in the written text as a literally recourse, and then it the new spelling may get popular in some area, and then accepted as a regional variant. If the new variant gets everywhere it becomes the official one. So the spelling slowly changes to accommodate the changes in the local or global variants and the old spelling get's deprecated.
So the spelling is keep somewhat in sync with the oral version.