diff --git a/local/AGENTS.md b/local/AGENTS.md
index cd2b779ead..abe76db26a 100644
--- a/local/AGENTS.md
+++ b/local/AGENTS.md
@@ -556,6 +556,29 @@ a live ISO for each:
 
 Desktop/graphics are available only on `redbear-full`.
 
+### SUPPORTED CPU PLATFORM — amd64 ONLY (ABSOLUTE)
+
+**Red Bear OS supports exactly one CPU platform: `amd64` (x86-64,
+`x86_64-unknown-redox`).** We do **NOT** support 32-bit x86, AArch64, RISC-V,
+or any other CPU architecture. There is one `TARGET`: `x86_64-unknown-redox`.
+
+Practical consequences:
+
+- Recipes must not carry, gate on, or build for non-amd64 CPU targets. Multi-arch
+  `case "$ARCH" in …` ladders are vestigial — only the `x86`/`x86_64` arm is ever
+  taken; do not add `aarch64`/`riscv64gc` handling for new work.
+- **LLVM naming caveat:** LLVM's CPU *target name* for amd64 is **`X86`** (the
+  LLVM `X86` backend emits x86-64/amd64 code — there is no separate "amd64" or
+  "X86_64" LLVM target). So `LLVM_TARGETS_TO_BUILD="X86"` is the CORRECT amd64
+  setting; it is not "32-bit x86 support". Do not read a bare `X86` in an LLVM
+  build as a policy violation.
+- GPU backends are a SEPARATE axis from the CPU platform: e.g. `AMDGPU` is an
+  LLVM GPU codegen backend needed by Mesa's radeonsi/radv (AMD GPU) drivers.
+  Enabling `AMDGPU` (or R600) alongside `X86` does not contradict amd64-only —
+  it adds GPU shader codegen for the (amd64) host/target, it does not add a
+  second CPU platform.
+- Build only the amd64 ISO. There are no cross-arch ISOs.
+
 ## RELEASE MODEL (FORK — NOT OVERLAY)
 
 Red Bear OS is a FULL FORK, not an overlay. The repository diverges from upstream Redox through local/sources/<comp>/ forks (see "LOCAL FORK SUPREMACY POLICY" below) rather than through per-package overlay patches.