diff --git a/files/en-us/mozilla/add-ons/webextensions/api/runtime/index.md b/files/en-us/mozilla/add-ons/webextensions/api/runtime/index.md
index 535788ec174b5b4..98ca1da4702fcc8 100644
--- a/files/en-us/mozilla/add-ons/webextensions/api/runtime/index.md
+++ b/files/en-us/mozilla/add-ons/webextensions/api/runtime/index.md
@@ -26,8 +26,8 @@ It also provides messaging APIs enabling you to:
   - : Identifies the browser's processor architecture.
 - {{WebExtAPIRef("runtime.PlatformInfo")}}
   - : Contains information about the platform the browser is running on.
-- {{WebExtAPIRef("runtime.PlatformNaclArch")}}
-  - : The native client architecture. This may be different from `PlatformArch` on some platforms.
+- {{WebExtAPIRef("runtime.PlatformNaclArch")}} {{deprecated_inline}}
+  - : The deprecated enumeration value representing Google Native Client architecture. Consider migrating to `PlatformArch`, which is supported by Safari and Mozilla, and represents the true CPU architecture and conveys correct bitness information on ARM.
 - {{WebExtAPIRef("runtime.RequestUpdateCheckStatus")}}
   - : Result of a call to {{WebExtAPIRef("runtime.requestUpdateCheck()")}}.
 - {{WebExtAPIRef("runtime.OnInstalledReason")}}
diff --git a/files/en-us/mozilla/add-ons/webextensions/api/runtime/platforminfo/index.md b/files/en-us/mozilla/add-ons/webextensions/api/runtime/platforminfo/index.md
index 9bf8acad7268eb3..959da9e1bafb36d 100644
--- a/files/en-us/mozilla/add-ons/webextensions/api/runtime/platforminfo/index.md
+++ b/files/en-us/mozilla/add-ons/webextensions/api/runtime/platforminfo/index.md
@@ -16,8 +16,8 @@ Values of this type are objects, which contain the following properties:
   - : {{WebExtAPIRef('runtime.PlatformOs')}}. The platform's operating system.
 - `arch`
   - : {{WebExtAPIRef('runtime.PlatformArch')}}. The platform's processor architecture.
-- `nacl_arch`
-  - : {{WebExtAPIRef('runtime.PlatformNaclArch')}}. The native client architecture. This may be different from `arch` on some platforms.
+- `nacl_arch` {{deprecated_inline}}
+  - : {{WebExtAPIRef('runtime.PlatformNaclArch')}}. The Google Native Client architecture. Only Chromium-based browsers support this attribute, and Chromium is removing it. Consider migrating to `arch`, which contains equivalent information and is more descriptive on some platforms (ARM and RISC-V).
 
 {{WebExtExamples}}
 
diff --git a/files/en-us/mozilla/add-ons/webextensions/api/runtime/platformnaclarch/index.md b/files/en-us/mozilla/add-ons/webextensions/api/runtime/platformnaclarch/index.md
index 7f09c2904589b51..aba23b12ecd4ae7 100644
--- a/files/en-us/mozilla/add-ons/webextensions/api/runtime/platformnaclarch/index.md
+++ b/files/en-us/mozilla/add-ons/webextensions/api/runtime/platformnaclarch/index.md
@@ -6,11 +6,23 @@ browser-compat: webextensions.api.runtime.PlatformNaclArch
 sidebar: addonsidebar
 ---
 
-The native client architecture. This may be different from arch on some platforms.
+> [!NOTE]
+> **This type is deprecated** in favor of {{WebExtAPIRef("runtime.PlatformArch")}}. `PlatformArch` is also available in {{WebExtAPIRef("runtime.PlatformInfo")}}, which you obtain using {{WebExtAPIRef("runtime.getPlatformInfo()")}}.
+
+The enumerated value representing the CPU instruction set architecture of Google Native Client used by the browser. This enum is deprecated, following the removal of Google Native Client from Google Chrome. As of 2026, Chromium intends to remove this enum.
 
 ## Type
 
-Values of this type are strings. Possible values are: `"arm"`, `"x86-32"`, `"x86-64"`.
+- `ARM`
+  - : The string literal `"arm"`. Represents all versions of the ARM ISA, including all 32-bit and 64-bit variants. Equivalent to [`PlatformArch.arm`](/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/PlatformArch#arm) (32-bit variant) and `PlatformArch.arm64` combined into one value.
+- `X86_32`
+  - : The string literal `"x86-32"`. Represents the 32-bit variant of the x86 architecture. Equivalent to [`PlatformArch.x86_32`](/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/PlatformArch#x86-32).
+- `X86_64`
+  - : The string literal `"x86-64"`. Represents the 64-bit variant of the x86 architecture. Equivalent to [`PlatformArch.X86_64`](/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/PlatformArch#x86-64).
+- `MIPS`
+  - : The string literal `"mips"`. Represents the 32-bit variant of the MIPS ISA, which was never supported by official releases. Equivalent to `PlatformArch.mips`.
+- `MIPS64`
+  - : The string literal `"mips64"`. Represents the 64-bit variant of the MIPS ISA, which was never supported by official releases. Equivalent to `PlatformArch.mips64`.
 
 {{WebExtExamples}}