autocomplete=”bday” with MM/DD/YYYY format?

I am using an input mask to enforce MM/DD/YYYY format on a <input type="text">.

I want to use autocomplete="bday", but I do not want to use the designated hyphen format specified by WHATWG.

What can I do about this? Can I just expect the mobile browser (mostly iOS / Android) to properly input the field into this box.