The RP2354 has the flash stacked inside the chip; https://www.raspberrypi.com/news/rp2350-a4-rp2354-and-a-new-hacking-challenge/ https://www.raspberrypi.com/new

The RP2354 has the flash stacked inside the chip; https://www.raspberrypi.com/news/rp2350-a4-rp2354-and-a-new-hacking-challenge/ https://www.raspberrypi.com/news/rp2350-a4-rp2354-and-a-new-... Still can be reflashed if you have access to the right pins, but I believe there are more security features built into the later generations of these chips (plus some security fixed from the original 2350 design).