> This is official firmware which turns the ESP into a "radio co-processor", so you can treat it like a SPI or UART Wi-Fi/BLE chip.

Kinda funny because the ESP8266 basically started off as a WiFi "co-processor" with AT commands sent over UART. People quickly discovered it had a good amount of power and you could run your entire application on the ESP8266 instead of using it as a co-processor. That led to an explosion in popularity for "makers" because the chip was so cheap and capable for projects at the time, and I think that led to the ESP32 becoming so widely known.

Interestingly, Espressif nowadays does something similar on the ESP32-P4 which is RiscV but doesn't have builtin Wifi/BT. So they tend to pair it with an ESP32-C6 which runs the WiFi stack and firmware that communicates with the P4 using SDIO. Not bare metal though, but similar dual-mcu setup for wifi/bt.

I didn’t know about hosted-MCU! I just started using the ESP-AT firmware for an ESP acting as a radio co-processor on a project at work - do you know how hosted-MCU differs?

I did glance at the readme and get the impression that hosted-MCU works for all compatible ESPs and seems more flexible and powerful, where ESP-AT is for select ESP chips and is more limited.