diff --git a/.github/workflows/build-posix-latest.yml b/.github/workflows/build-posix-latest.yml
index 13ac881ab..8f9320e57 100644
--- a/.github/workflows/build-posix-latest.yml
+++ b/.github/workflows/build-posix-latest.yml
@@ -47,3 +47,14 @@ jobs:
       continue-on-error: true
     - name: Test ${{ matrix.os }} ${{ matrix.config }}
       run: ./build-tests.sh ${{ matrix.config }}
+
+  public-headers:
+    name: Public header gate (GCC/Clang)
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Install clang
+      run: sudo apt-get update && sudo apt-get install -y clang
+    - name: Compile each public header standalone under strict flags
+      run: bash tests/headers/check_public_headers.sh
diff --git a/.github/workflows/test-win-latest.yml b/.github/workflows/test-win-latest.yml
index 255868a88..4928fc71f 100644
--- a/.github/workflows/test-win-latest.yml
+++ b/.github/workflows/test-win-latest.yml
@@ -54,3 +54,13 @@ jobs:
     - name: Test ${{ matrix.arch }} ${{ matrix.build }}
       shell: cmd
       run: build-tests.cmd ${{ matrix.arch }} ${{ matrix.build }}
+
+  public-headers:
+    name: Public header gate (MSVC)
+    runs-on: windows-2022
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Compile each public header standalone under /W4 /WX
+      shell: cmd
+      run: tests\headers\check_public_headers.cmd
diff --git a/lib/include/public/CompliantByDefaultFilterApi.hpp b/lib/include/public/CompliantByDefaultFilterApi.hpp
index 642aa4c9e..85e779c3f 100644
--- a/lib/include/public/CompliantByDefaultFilterApi.hpp
+++ b/lib/include/public/CompliantByDefaultFilterApi.hpp
@@ -7,6 +7,7 @@
 
 #include "ctmacros.hpp"
 
+#include <cstdint>
 #include <vector>
 
 namespace MAT_NS_BEGIN { namespace Modules { namespace Filtering
diff --git a/tests/headers/check_public_headers.cmd b/tests/headers/check_public_headers.cmd
new file mode 100644
index 000000000..53860422c
--- /dev/null
+++ b/tests/headers/check_public_headers.cmd
@@ -0,0 +1,129 @@
+@echo off
+REM Copyright (c) Microsoft Corporation. All rights reserved.
+REM SPDX-License-Identifier: Apache-2.0
+REM
+REM Public header gate (MSVC). Compiles each public SDK header on its own under
+REM /W4 /WX, mirroring how ONNX Runtime / Foundry Local compile their own C++
+REM translation units on Windows. STL/Windows SDK headers are treated as external
+REM (/external:W0) so only the SDK's headers are gated. Exits non-zero if any
+REM header fails to compile or emits a warning. Also compiles mat.h as C11 (/TC).
+setlocal enabledelayedexpansion
+
+set "SCRIPT_DIR=%~dp0"
+set "REPO_ROOT=%SCRIPT_DIR%..\.."
+set "PUB=%REPO_ROOT%\lib\include\public"
+set "C_API_HEADER=mat.h"
+
+REM Fail fast if the public header directory is missing or miscomputed, otherwise
+REM the header loop below would run zero times and the gate would silently "pass"
+REM without compiling anything -- a false negative.
+if not exist "%PUB%" (
+  echo error: public header directory not found: %PUB% 1>&2
+  exit /b 2
+)
+
+REM Enter the MSVC x64 developer environment via vswhere (portable across runners).
+set "VSWHERE=%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe"
+if not exist "%VSWHERE%" (
+  echo error: vswhere.exe not found 1>&2
+  exit /b 2
+)
+set "VSPATH="
+for /f "usebackq tokens=*" %%i in (`"%VSWHERE%" -latest -products * -property installationPath`) do set "VSPATH=%%i"
+if not defined VSPATH (
+  echo error: no Visual Studio installation found 1>&2
+  exit /b 2
+)
+call "%VSPATH%\VC\Auxiliary\Build\vcvars64.bat" >nul
+if errorlevel 1 (
+  echo error: failed to initialize the MSVC environment 1>&2
+  exit /b 2
+)
+
+REM Unique work directory under the repository so concurrent invocations on the
+REM same machine do not clobber each other's temporary translation units.
+set "WORK=%REPO_ROOT%\.public-header-gate_%RANDOM%_%RANDOM%"
+if exist "%WORK%" rmdir /s /q "%WORK%"
+mkdir "%WORK%"
+if errorlevel 1 (
+  echo error: failed to create work directory %WORK% 1>&2
+  exit /b 2
+)
+
+REM /W4 /WX matches ORT; /external:W0 suppresses platform/STL warnings so only our headers gate.
+set "CXX_COMMON=/nologo /permissive- /W4 /WX /EHsc /experimental:external /external:anglebrackets /external:W0"
+set "C_COMMON=/nologo /std:c11 /TC /W4 /WX /experimental:external /external:anglebrackets /external:W0"
+set "FAIL=0"
+set "TOTAL=0"
+
+REM MSVC does not expose a /std:c++11 switch; /std:c++14 is its lowest selectable mode.
+call :RunCxxHeaders c++14 /std:c++14 "cl (c++14, /W4 /WX)"
+call :RunCxxHeaders c++17 /std:c++17 "cl (c++17, /W4 /WX)"
+call :RunCHeader
+
+rmdir /s /q "%WORK%" 2>nul
+
+if "%FAIL%"=="1" (
+  echo Public header gate FAILED.
+  exit /b 1
+)
+echo Public header gate passed. ^(!TOTAL! checks^)
+exit /b 0
+
+:RunCxxHeaders
+set "STD_NAME=%~1"
+set "STD_FLAG=%~2"
+set "LABEL=%~3"
+set "OKC=0"
+set "FAILC=0"
+echo == %LABEL% ==
+for %%h in ("%PUB%\*.hpp" "%PUB%\*.h") do (
+  set "NAME=%%~nxh"
+  REM Skip implementation-fragment headers not meant to be included standalone
+  REM (VariantType.hpp is included by Variant.hpp, which defines VariantMap/VariantArray first).
+  if /I not "!NAME!"=="VariantType.hpp" (
+    > "%WORK%\tu_!STD_NAME!.cpp" echo #include "!NAME!"
+    >> "%WORK%\tu_!STD_NAME!.cpp" echo int main^(^){return 0;}
+    cl %CXX_COMMON% %STD_FLAG% /I "%PUB%" /I "%REPO_ROOT%\lib\include" /Zs "%WORK%\tu_!STD_NAME!.cpp" > "%WORK%\err.txt" 2>&1
+    if errorlevel 1 (
+      echo   FAIL: !NAME!
+      type "%WORK%\err.txt"
+      set "FAIL=1"
+      set /a FAILC+=1
+    ) else (
+      set /a OKC+=1
+      set /a TOTAL+=1
+    )
+  )
+)
+REM No headers compiled means PUB matched nothing -- treat it as a failure rather
+REM than a silent pass.
+if "!OKC!"=="0" if "!FAILC!"=="0" (
+  echo error: no public headers found under %PUB% 1>&2
+  set "FAIL=1"
+)
+echo   %LABEL%: !OKC! passed, !FAILC! failed
+exit /b 0
+
+:RunCHeader
+set "LABEL=cl (C11 mat.h, /TC, /W4 /WX)"
+echo == !LABEL! ==
+if not exist "%PUB%\%C_API_HEADER%" (
+  echo error: C API header not found: %PUB%\%C_API_HEADER% 1>&2
+  set "FAIL=1"
+  echo   !LABEL!: 0 passed, 1 failed
+  exit /b 0
+)
+> "%WORK%\tu_mat_c11.c" echo #include "%C_API_HEADER%"
+>> "%WORK%\tu_mat_c11.c" echo int main^(void^){return 0;}
+cl %C_COMMON% /I "%PUB%" /I "%REPO_ROOT%\lib\include" /Zs "%WORK%\tu_mat_c11.c" > "%WORK%\err.txt" 2>&1
+if errorlevel 1 (
+  echo   FAIL: %C_API_HEADER%
+  type "%WORK%\err.txt"
+  set "FAIL=1"
+  echo   !LABEL!: 0 passed, 1 failed
+) else (
+  set /a TOTAL+=1
+  echo   !LABEL!: 1 passed, 0 failed
+)
+exit /b 0
diff --git a/tests/headers/check_public_headers.sh b/tests/headers/check_public_headers.sh
new file mode 100644
index 000000000..79724e588
--- /dev/null
+++ b/tests/headers/check_public_headers.sh
@@ -0,0 +1,158 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+#
+# Public header gate (GCC/Clang).
+#
+# Verifies that every public SDK header is self-contained (compiles on its own,
+# in any include order) and warning-clean under strict, consumer-representative
+# warning flags. Downstream consumers such as ONNX Runtime / Foundry Local
+# compile their own translation units -- which include these headers -- with
+# -Wall -Wextra -Werror (plus -Wshorten-64-to-32 on Clang). This gate compiles
+# each public header on its own as both C++11 and C++17, with no -isystem
+# suppression, so any header issue surfaces here instead of at integration time.
+# It also compiles the ABI-stable C API header (mat.h) as C11.
+#
+# Exits non-zero if any header fails to compile or emits a warning.
+
+set -uo pipefail
+shopt -s nullglob
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+PUB="$REPO_ROOT/lib/include/public"
+
+# Fail fast if the public header directory is missing or miscomputed. With
+# nullglob on, a bad PUB would make the header globs below expand to nothing and
+# the gate would silently "pass" without compiling anything -- a false negative.
+if [ ! -d "$PUB" ]; then
+  echo "error: public header directory not found: $PUB" >&2
+  exit 2
+fi
+
+# Implementation-fragment headers: intentionally included by another public
+# header (which supplies their dependencies first) and not meant to be included
+# standalone. They are exercised through their public entry point instead.
+EXCLUDES=(
+  "VariantType.hpp"   # included by Variant.hpp, which defines VariantMap/VariantArray first
+)
+
+# Mirror the strict warning flags third-party consumers build with
+# (-Wall -Wextra -Werror, matching this repo's pipeline and ORT). Unused
+# parameters are deliberately NOT suppressed: intentional ones use the
+# UNREFERENCED_PARAMETER macro, which expands to (void)(...) on GCC/Clang, so the
+# headers stay warning-clean without a blanket -Wno-unused-parameter that would
+# hide a real consumer break (e.g. an override that leaves a parameter unused).
+C_API_HEADER="mat.h"
+
+is_excluded() {
+  local n="$1" e
+  for e in "${EXCLUDES[@]}"; do [ "$e" = "$n" ] && return 0; done
+  return 1
+}
+
+fail=0
+tmp=""
+for _ in 1 2 3 4 5; do
+  candidate="$REPO_ROOT/.public-header-gate.$$.$RANDOM"
+  if mkdir "$candidate" 2>/dev/null; then
+    tmp="$candidate"
+    break
+  fi
+done
+if [ -z "$tmp" ]; then
+  echo "error: failed to create work directory under $REPO_ROOT" >&2
+  exit 2
+fi
+trap 'rm -rf "$tmp"' EXIT
+
+run_cxx_compiler() {
+  local cc="$1" std="$2" label="$3"
+  shift 3
+  local n_ok=0 n_fail=0 h name base tu out
+  echo "== $label =="
+  for h in "$PUB"/*.hpp "$PUB"/*.h; do
+    name="$(basename "$h")"
+    is_excluded "$name" && continue
+    base="${name%.*}"
+    tu="$tmp/tu_${base}_${std}.cpp"
+    printf '#include "%s"\nint main() { return 0; }\n' "$name" > "$tu"
+    if out="$("$cc" "-std=$std" -Wall -Wextra -Werror "$@" -I"$PUB" -I"$REPO_ROOT/lib/include" -fsyntax-only "$tu" 2>&1)"; then
+      n_ok=$((n_ok + 1))
+    else
+      n_fail=$((n_fail + 1)); fail=1
+      echo "  FAIL: $name"
+      echo "$out" | grep -E 'error:|warning:' | head -4 | sed 's/^/      /'
+    fi
+  done
+  if [ $((n_ok + n_fail)) -eq 0 ]; then
+    echo "  ERROR: no public headers found under $PUB"
+    fail=1
+  fi
+  echo "  $label: $n_ok passed, $n_fail failed"
+}
+
+run_c_compiler() {
+  local cc="$1" label="$2"
+  shift 2
+  local tu out
+  echo "== $label =="
+  if [ ! -f "$PUB/$C_API_HEADER" ]; then
+    echo "  ERROR: C API header not found: $PUB/$C_API_HEADER"
+    fail=1
+    echo "  $label: 0 passed, 1 failed"
+    return
+  fi
+  tu="$tmp/tu_${C_API_HEADER%.h}_c11.c"
+  printf '#include "%s"\nint main(void) { return 0; }\n' "$C_API_HEADER" > "$tu"
+  if out="$("$cc" -std=c11 -Wall -Wextra -Werror "$@" -I"$PUB" -I"$REPO_ROOT/lib/include" -fsyntax-only "$tu" 2>&1)"; then
+    echo "  $label: 1 passed, 0 failed"
+  else
+    fail=1
+    echo "  FAIL: $C_API_HEADER"
+    echo "$out" | grep -E 'error:|warning:' | head -4 | sed 's/^/      /'
+    echo "  $label: 0 passed, 1 failed"
+  fi
+}
+
+cxx_ran=0
+if command -v g++ >/dev/null 2>&1; then
+  run_cxx_compiler g++ c++11 "g++  (c++11, -Wall -Wextra -Werror)"
+  run_cxx_compiler g++ c++17 "g++  (c++17, -Wall -Wextra -Werror)"
+  cxx_ran=1
+fi
+if command -v clang++ >/dev/null 2>&1; then
+  run_cxx_compiler clang++ c++11 "clang++ (c++11, + -Wshorten-64-to-32)" -Wshorten-64-to-32
+  run_cxx_compiler clang++ c++17 "clang++ (c++17, + -Wshorten-64-to-32)" -Wshorten-64-to-32
+  cxx_ran=1
+fi
+
+if [ "$cxx_ran" -eq 0 ]; then
+  echo "error: neither g++ nor clang++ was found" >&2
+  exit 2
+fi
+
+c_ran=0
+if command -v gcc >/dev/null 2>&1; then
+  run_c_compiler gcc "gcc  (c11 mat.h, -Wall -Wextra -Werror)"
+  c_ran=1
+fi
+if command -v clang >/dev/null 2>&1; then
+  run_c_compiler clang "clang (c11 mat.h, + -Wshorten-64-to-32)" -Wshorten-64-to-32
+  c_ran=1
+fi
+if [ "$c_ran" -eq 0 ] && command -v cc >/dev/null 2>&1; then
+  run_c_compiler cc "cc   (c11 mat.h, -Wall -Wextra -Werror)"
+  c_ran=1
+fi
+
+if [ "$c_ran" -eq 0 ]; then
+  echo "error: no C compiler (gcc, clang, or cc) was found" >&2
+  exit 2
+fi
+
+if [ "$fail" -ne 0 ]; then
+  echo "Public header gate FAILED."
+  exit 1
+fi
+echo "Public header gate passed."