I don’t think the maximum length is documented anywhere, at least not that I’m aware of. I just ran a test, though, filling a formula field by repeating a single character based on a count set in another field, then converted that to a single line text field. I also added another formula field to confirm that the character sequence wasn’t being truncated. I got up to 10 million characters before things started to bog down, so I didn’t test any further.

Hey, Justin. Clever test! Thanks for your help.

This appears to be an exception to the rule, perhaps to prevent data loss when converting field types. The default maximum for text fields is 100,000 characters, as reported elsewhere: What is the long text character limit?

I ran into this issue when generating JSON data from my Airtable base, if you attempt to go over the limit while using a script, it will return an error similar to <root> is longer than the maxLength: 100000