The particular chat.svg file in the linked post is (hopefully) not the way that the data will truly be "redacted". This file feels more like an export from a design mockup, as I cannot imagine SVG being the default output format for interacting with OpenAI models.

But I also have extreme doubts that proper redaction can be done robustly. The design mockup image suggests that this will all be done as a step subsequent to response generation. Given the abundance of "prompt jailbreaks", a determined adversary is going to get around this.