Otherwise privacy and security would be meaning basically nothing.
All of the kernel drivers are open source, which would be the case for Snapdragon too.
Firmware is largely closed source but Pixels do use Trusty OS for the TEE and secure core, littlekernel as the late stage bootloader firmware and OpenTitan as the firmware/hardware basis for the Titan M2 secure element that's holding up much better to attacks than anything but Apple's SEP (see brute force info in https://discuss.grapheneos.org/d/14344-cellebrite-premium-ju... or the newer February 2025 documentation someone posted further down). We still do security research work on the hardware and firmware including reporting vulnerabilities and suggestions. Several firmware and hardware based features we've proposed were implementing including the pinning-based hardware attestation support we used to improve our Auditor app and AttestationServer, reset attack protection and various other things.
There are still shared source libraries and services for certain hardware but Pixels moving away from Snapdragon has led to that approach being on the way out. The move away from Exynos with the Pixel 10 should help.
If we make our own device with an OEM using Snapdragon, we'd have access to most of the sources for their driver libraries/services and a lot of firmware. It's not open source but OEMs have access. That also means a lot of it gets consistently leaked. They stopped sharing their radio firmware sources with OEMs because of those leaks.