256
Google's next-gen reCAPTCHA system could spell trouble for de-Googled phones - Android Authority
(www.androidauthority.com)
This is a most excellent place for technology news and articles.
According to the support page (found here: https://support.google.com/recaptcha/answer/16609652) if you are browsing on a phone it will prompt you to click a link to open some kind of Captcha app on the device rather than scanning a QR code.