Westworld season 2 revealed a dark truth: every hat contained an embedded scanner, constantly reading the wearer's cognitive functions and brain activity.
In Westworld season 4's Golden Age park - built by the Charlotte Hale host that evolved from a Dolores copy - those scanners got upgraded. Rather than secreting the tech inside fedoras, Hale constructed much larger scanners behind each and every park mirror. Human guests would be processed much faster this way, but that's not the real reason Westworld season 4 swaps suspicious stetsons for malicious mirrors. The twist is actually a perfect representation of the new relationship between mankind and its robotic creations.
Charlotte Hale is, quite literally, holding up a mirror to humanity as part of her quest for global domination. It's an eerie metaphor for how Earth's flesh-and-blood population have become enslaved in Westworld season 4, while hosts are now the dominant species. The new reality is an exact mirror image of the landscape from Westworld's earlier seasons, and gives humans a bitter taste of their own sadistic medicine. That Hale achieved her cyborg conquest by making Golden Age guests look themselves in mirrors is beautifully poetic justice. Westworld's mirror twist also speaks to mankind's greatest weakness: vanity. According to Jeffrey Wright's Bernard Lowe, Hale picked mirrors as her weapon to exploit our natural vain tendencies. That very same vanity is why hosts were first built in humanity's image, and now Hale has exploited her race's likeness by creating near-perfect copies such as Jay, the Man in Black, Senator Whitney and his wife, etc. It's like they're looking at themselves in a mirror...
Westworld's Hats & Mirrors Purpose Explained
The official, outward purpose of Westworld's scanner hats was data collection - an industrial scale privacy violation. By understanding the inner workings of guests, Delos effectively made traditional market research obsolete, and this data was highly coveted by Rehoboam, who wanted the information to improve its predictive algorithms for Earth's future in Westworld season 3. The true, secret reason Delos slipped mini-MRI machines into WestWorld headgear was the immortality project happening in Section 16's Forge facility. Delos sought to create human-host hybrids - an authentic consciousness existing inside an artificial body. For that, the company needed human minds mapped out in forensic detail.
Charlotte Hale has little use for marketing, nor immortality, but her Golden Age mirror scanners serve a very different purpose. As Bernard explains, Hale learned about her enemy by reading guests' minds, gaining a crucial tactical advantage ahead of her quest for global domination. By gathering data on humans and understanding what makes them tick, Hale could also create profiles on every person inside her jurisdiction. If we assume Hale has scan-mirrors planted in her city too, this might explain how the host version of Daniel Wu's Jay knows his counterpart had a brother and broadly acts similar to the original (even if Frankie is smart enough to tell the difference).
Just like WestWorld's hats, however, Charlotte Hale's mirrors may hold a deeper, as-yet-unseen purpose. With Caleb, Hale is desperately trying to iron out the remaining kinks in Delos' immortality project. Back in Westworld season 4's premiere, she also secured Hoover Dam, where all that Section 16 Forge data on the human mind is stored. Hale's endgame could be turning every single human into a hybrid, thereby creating a world in which the two species are indistinguishable.
Westworld continues Sunday on HBO.