For 2025-09, delivered foundational ARM64 Pointer Authentication Code (PAC) support in the Go project (golang/go), strengthening defense against control-flow attacks and aligning with ELF ABI requirements. Implemented PAC instruction support in cmd/internal/obj/arm64 to enable signing and verification of the link register during function calls, paving the way for the compiler to emit PAC sequences. This work establishes the groundwork for PAC-aware binaries and reduces ROP risk in ARM64 builds. The main commit (11d3d2f77d8293fe14638e74cbf52d1241b60e78) adds PAC instructions with a path for future compiler integration. Review context and references were captured in the commit metadata to support follow-up changes. Impact: improved security posture, better reliability against return-oriented attacks, and alignment with external ARMv8.3+ PAC guidance; sets foundations for broader hardening across the Go toolchain.