diff --git a/docs/windows-performance.md b/docs/windows-performance.md
index acdf8ad..df23a5f 100644
--- a/docs/windows-performance.md
+++ b/docs/windows-performance.md
@@ -342,8 +342,53 @@ sensor/window and its discrepancy is unresolved. Do not infer a physical CPU
 limit, isolated shader occupancy or a FSR4 speed comparison. Query overhead
 is median 0.094 ms per 500 ms poll, with a roughly 12 ms first query. Results:
 `test-results/silent-hill2-k-telemetry-unprofiled-4k`. The game stability
-summary is still pending its existing ten-minute bound. Remaining K work now
-prioritizes transformer/output-kernel cost; frame scheduling remains measured.
+summary completes 37187 K frames with zero backend failures, CPU image copies,
+previous-frame outputs or recorded crashes, stopping at its ten-minute bound.
+Remaining K work now prioritizes transformer/output-kernel cost; frame
+scheduling remains measured.
+
+### Rejected packed FP16 accumulator experiment
+
+An isolated `D4R_K_F16_WMMA` enc1 build uses gfx12's documented packed FP16
+C/D intrinsic, retaining the current operand/accumulator lane mapping. It
+removes most conversion instructions (1066 static F16/F32 conversions become
+two) and reduces main-kernel VGPRs from 218 to 201; LDS remains 24576 bytes,
+with zero spills. These are compiler/ISA counts, not GPU time or occupancy.
+The candidate is rejected before moving to another layer: its real replay
+changes 1182727 half codes in the output allocation, max absolute difference
+0.0390625 from the validated baseline. All values are finite. Against the
+current twelve-window NumPy reference, PSNR drops from baseline 78.7702 dB
+to 69.2377 dB; max absolute error rises from 0.009765625 to 0.0390625.
+Two independent PTX windows give 70.4022/70.08 dB. These pass the existing
+coarse reference thresholds but do not satisfy this optimization's baseline
+preservation gate. No game installation or performance claim follows.
+
+A public 64-matrix primitive reproducer isolates the difference to direct
+instruction arithmetic. The packed intrinsic and the layout adapter agree
+bit-for-bit. Direct FP16 output differs from FP32 WMMA rounded once to FP16
+even after one K16 step (1674 of 4096 elements, max absolute 0.00390625).
+After eight steps, 2874 elements differ, max absolute 0.0625. This rules out
+the adapter packing as the source of this fixture's difference; the hardware
+internal accumulation/rounding cause is not established. Production K keeps
+its existing FP32-instruction/FP16-rounding baseline and the experimental flag
+is off in every normal build. Results: `test-results/k-f16-wmma-enc1` and
+`test-results/wmma-f16-arithmetic-compare-fixed`.
+The finished `test-wmma-f16.ps1` repeats the same 64-case result. Rebuilding
+every ordinary K/M object leaves all sixteen byte-identical; all seventeen
+CTest gates pass and enc1 still compiles for gfx1101 (compile-only). Logs:
+`test-results/wmma-f16-script-check` and `test-results/k-f16-baseline-ctest.log`.
+
+```powershell
+.\scripts\windows\test-wmma-f16.ps1
+.\scripts\windows\build-native-k-f16-wmma.ps1 -Layer enc1
+```
+
+The first command compiles and runs the public arithmetic diagnostic without
+NVIDIA inputs. Its success means the reproducer executed correctly, not that
+the two instruction paths are equivalent; JSON retains `baselineEquivalent`
+and `gameOptimizationAccepted`. The second compiles the rejected experiment
+in a separate directory and generates no override manifest. Intrinsic API:
+[Clang gfx12 FP16 WMMA](https://clang.llvm.org/docs/AMDGPUBuiltinReference.html#builtin-amdgcn-wmma-f16-16x16x16-f16-w32-gfx12).
 
 Further game coverage (HIP kernel profiling disabled, GPU output checks enabled):
 M at 1920x1080 completes 4833 frames, all finite. K at 3840x2160 completes
diff --git a/docs/windows-rdna4-port.md b/docs/windows-rdna4-port.md
index 3b5f653..789ec35 100644
--- a/docs/windows-rdna4-port.md
+++ b/docs/windows-rdna4-port.md
@@ -140,6 +140,21 @@ metrics as absent and preserving the driver's raw timestamp. See
 The combined capture smoke test passes, followed by the user-confirmed
 1935-present/60-poll measurement recorded at the top of this document. Logs
 and runtime/DLL hashes: `test-results/silent-hill2-k-telemetry-unprofiled-4k`.
+Its ten-minute game summary completes **37187 K/4K frames**, zero backend
+errors/CPU image copies/previous-frame outputs or recorded crashes.
+
+The next isolated K enc1 experiment replaces FP32 WMMA + FP16 rounding with
+gfx12's packed FP16 accumulator instruction. ISA conversions and VGPRs fall,
+but the real output changes and reference PSNR falls. A 64-matrix public GPU
+reproducer shows the direct instruction differs from FP32 + FP16 rounding
+already at a single K16 step while the adapter is exact against the packed
+instruction. The experiment is rejected at enc1; no subsequent layer or game
+uses it. Baseline preservation takes priority over the instruction reduction.
+`D4R_K_F16_WMMA` remains disabled in every normal build. Reproducer/results and
+exact metrics are in `windows-performance.md`.
+All sixteen ordinary K/M objects remain byte-identical after rebuilding with
+the disabled experimental code. All seventeen CTest gates pass; gfx1101 enc1
+compile-only compatibility and the ready-made public WMMA script also pass.
 
 The public prerelease `windows-rdna4-dev-20261002-a346d76` is published to
 `xdfnx-dev/d4r`, containing source commit `a346d76` and ZLUDA `a1c506f`.
diff --git a/kernels/common/wmma_layout.h b/kernels/common/wmma_layout.h
index e417b0c..6335874 100644
--- a/kernels/common/wmma_layout.h
+++ b/kernels/common/wmma_layout.h
@@ -229,6 +229,20 @@ WM_FN wm_f8v wm_mma(const wm_op& a, const wm_op& b, wm_f8v c)
 {
     return __builtin_amdgcn_wmma_f32_16x16x16_f16_w32_gfx12(__builtin_bit_cast(wm_h8, a), __builtin_bit_cast(wm_h8, b), c);
 }
+#ifdef D4R_K_F16_WMMA
+// Rejected K experiment: direct packed F16 changes the arithmetic on gfx1201.
+// The public WMMA reproducer and enc1 replay are in tools/windows and docs.
+// Experimental gfx12 packed FP16 C/D. K's strict baseline enters each K16
+// step with an already FP16-rounded accumulator. Keep the existing logical
+// eight-row contract; only this instruction/register representation changes.
+WM_FN wm_f8v wm_mma_f16_step(const wm_op& a, const wm_op& b, wm_f8v c)
+{
+    const wm_h8 hc = __builtin_convertvector(c, wm_h8);
+    const wm_h8 hd = __builtin_amdgcn_wmma_f16_16x16x16_f16_w32_gfx12(
+        __builtin_bit_cast(wm_h8, a), __builtin_bit_cast(wm_h8, b), hc);
+    return __builtin_convertvector(hd, wm_f8v);
+}
+#endif
 #else
 WM_FN wm_f8v wm_mma11(const wm_u8v& a, const wm_u8v& b, wm_f8v c)
 {
diff --git a/kernels/k/pwin_common.h b/kernels/k/pwin_common.h
index 3867fa1..78cae77 100644
--- a/kernels/k/pwin_common.h
+++ b/kernels/k/pwin_common.h
@@ -80,6 +80,12 @@ __device__ __forceinline__ half_t l2_sum(const half_t* row)
 // PWIN_F32ACC: keep the accumulator in f32 through the chain (rounded to f16 where the values are used)
 __device__ __forceinline__ f8v mma16(const op_t& a, const op_t& b, f8v c)
 {
+#ifdef D4R_K_F16_WMMA
+#if !defined(__GFX12__) || D4R_WMMA_LAYOUT != 12 || !defined(D4R_K_FP16_BASELINE)
+#error "experimental packed F16 WMMA requires gfx12 native layout and strict K baseline"
+#endif
+    return wm_mma_f16_step(a, b, c);
+#else
     f8v d = wm_mma(a, b, c);
 #if !defined(PWIN_F32ACC) || defined(D4R_K_FP16_BASELINE)
 #pragma unroll
@@ -87,6 +93,7 @@ __device__ __forceinline__ f8v mma16(const op_t& a, const op_t& b, f8v c)
         d[i] = (float)(half_t)d[i];
 #endif
     return d;
+#endif
 }
 
 __device__ __forceinline__ f8v splat8(float v)
diff --git a/scripts/windows/build-native-k-f16-wmma.ps1 b/scripts/windows/build-native-k-f16-wmma.ps1
new file mode 100644
index 0000000..56b02bf
--- /dev/null
+++ b/scripts/windows/build-native-k-f16-wmma.ps1
@@ -0,0 +1,40 @@
+[CmdletBinding()]
+param([ValidateSet('enc0','enc1','enc2','enc3','enc4','dec5','dec4','dec3','dec2','dec1','dec0')]
+    [string]$Layer='enc1', [string]$HipRoot, [string]$OutputDirectory)
+$ErrorActionPreference='Stop'
+$repo=[IO.Path]::GetFullPath((Join-Path $PSScriptRoot '../..'))
+if (!$HipRoot) { $HipRoot=Join-Path $repo '.tools/therock-10.2.0a20260929/_rocm_sdk_core' }
+if (!$OutputDirectory) { $OutputDirectory=Join-Path $repo 'build/native-k-f16-wmma-experimental' }
+$OutputDirectory=[IO.Path]::GetFullPath($OutputDirectory)
+if ($OutputDirectory -eq [IO.Path]::GetFullPath((Join-Path $repo 'build/native-k-gfx1201'))) {
+    throw 'Keep the validated baseline separate from this experimental build.'
+}
+$compiler=Join-Path $HipRoot 'lib/llvm/bin/clang++.exe'
+if (!(Test-Path -LiteralPath $compiler)) { $compiler=Join-Path $HipRoot 'bin/clang++.exe' }
+if (!(Test-Path -LiteralPath $compiler)) { throw "HIP compiler missing under $HipRoot" }
+$name="dltss_pwin_${Layer}_layer"
+$source=Join-Path $repo "kernels/k/$name.hip"
+$flags=@()
+if ((Get-Content -LiteralPath $source -Raw) -match '// d4r-build-flags: ([^\r\n]+)') { $flags=$Matches[1].Trim().Split(' ') }
+New-Item -ItemType Directory -Force $OutputDirectory | Out-Null
+$object=Join-Path $OutputDirectory "$name.hsaco"
+$ErrorActionPreference='Continue'
+& $compiler -x hip -std=c++17 --offload-arch=gfx1201 --offload-device-only --no-gpu-bundle-output `
+    -mno-wavefrontsize64 -nogpuinc -nogpulib -O3 -DD4R_DEVICE_ONLY_MINIMAL `
+    -DD4R_K_FP16_BASELINE -DD4R_K_F16_WMMA @flags $source -o $object `
+    > (Join-Path $OutputDirectory "$name.build.stdout.log") 2> (Join-Path $OutputDirectory "$name.build.stderr.log")
+$ErrorActionPreference='Stop'
+if ($LASTEXITCODE) { throw "Experimental K FP16 WMMA compile failed: $Layer" }
+$isa=Join-Path $OutputDirectory "$name.isa.txt"
+& (Join-Path (Split-Path $compiler) 'llvm-objdump.exe') --disassemble --mcpu=gfx1201 $object > $isa
+if ($LASTEXITCODE -or !(Select-String -LiteralPath $isa -Pattern 'v_wmma_f16_16x16x16_f16')) {
+    throw 'Packed FP16 WMMA is absent from ISA; no alternative instruction is accepted.'
+}
+& (Join-Path (Split-Path $compiler) 'llvm-readobj.exe') --notes $object `
+    > (Join-Path $OutputDirectory "$name.metadata.txt")
+if ($LASTEXITCODE) { throw 'Native object metadata extraction failed.' }
+@{layer=$Layer; architecture='gfx1201'; experimental=$true; numericalValidation='pending';
+    compiler=$compiler; sha256=(Get-FileHash -LiteralPath $object -Algorithm SHA256).Hash} |
+    ConvertTo-Json | Set-Content -LiteralPath (Join-Path $OutputDirectory "$name.build-info.json") -Encoding UTF8
+Write-Host "Compiled experimental gfx1201 packed FP16 WMMA: $Layer. Validate before selecting another layer."
+# This script does not generate an override manifest or install into the game.
diff --git a/scripts/windows/test-wmma-f16.ps1 b/scripts/windows/test-wmma-f16.ps1
new file mode 100644
index 0000000..0a6c2da
--- /dev/null
+++ b/scripts/windows/test-wmma-f16.ps1
@@ -0,0 +1,24 @@
+[CmdletBinding()]
+param([string]$HipRoot, [string]$PackageRoot, [string]$OutputDirectory)
+$ErrorActionPreference='Stop'
+$repo=[IO.Path]::GetFullPath((Join-Path $PSScriptRoot '../..'))
+if (!$HipRoot) { $HipRoot=Join-Path $repo '.tools/therock-10.2.0a20260929/_rocm_sdk_core' }
+if (!$PackageRoot) { $PackageRoot=Join-Path $repo 'dist/windows-rdna4-command-list' }
+if (!$OutputDirectory) { $OutputDirectory=Join-Path $repo ('test-results/wmma-f16-' + (Get-Date -Format 'yyyyMMdd-HHmmss-fff')) }
+$compiler=Join-Path $HipRoot 'lib/llvm/bin/clang++.exe'
+if (!(Test-Path -LiteralPath $compiler)) { $compiler=Join-Path $HipRoot 'bin/clang++.exe' }
+New-Item -ItemType Directory -Force $OutputDirectory | Out-Null
+$module=Join-Path $OutputDirectory 'wmma_f16_compare.hsaco'
+& $compiler -x hip -std=c++17 --offload-arch=gfx1201 --offload-device-only --no-gpu-bundle-output `
+    -mno-wavefrontsize64 -nogpuinc -nogpulib -O3 (Join-Path $repo 'tools/windows/wmma_f16_compare.hip') -o $module
+if ($LASTEXITCODE) { throw 'WMMA arithmetic probe compilation failed.' }
+$previousPython=$env:PYTHONPATH
+try {
+    $env:PYTHONPATH="$(Join-Path $repo '.tools/python/vendor');$previousPython"
+    & python.exe (Join-Path $repo 'tools/windows/wmma_f16_compare.py') `
+        --probe (Join-Path $PackageRoot 'bin/d4r_native_replay_probe.exe') --module $module `
+        --hip-root $HipRoot --output-dir $OutputDirectory
+    if ($LASTEXITCODE) { throw "WMMA arithmetic diagnostic failed; logs: $OutputDirectory" }
+} finally { $env:PYTHONPATH=$previousPython }
+# A successful diagnostic is not acceptance of native FP16 accumulators for K.
+# Read baselineEquivalent/gameOptimizationAccepted in validation.json.
diff --git a/tools/windows/wmma_f16_compare.hip b/tools/windows/wmma_f16_compare.hip
new file mode 100644
index 0000000..79a357f
--- /dev/null
+++ b/tools/windows/wmma_f16_compare.hip
@@ -0,0 +1,40 @@
+// Public synthetic reproducer: compare packed F16 WMMA with F32 WMMA followed
+// by one FP16 rounding after each K16 step. Never part of game packaging.
+#define D4R_K_F16_WMMA
+#include "../../kernels/common/wmma_layout.h"
+
+// The replay utility passes a single by-value parameter block, like K/M.
+struct CompareParams { const _Float16* a; const _Float16* b; const float* c; float* output; };
+extern "C" __attribute__((global)) void d4r_wmma_f16_compare(CompareParams params)
+{
+    const _Float16* a = params.a;
+    const _Float16* b = params.b;
+    const float* c = params.c;
+    float* output = params.output;
+    const unsigned test = __builtin_amdgcn_workgroup_id_x();
+    const unsigned token = wm_lane() & 15;
+    const unsigned base = test * 256;
+    const wm_op aa = wm_op_load(a + base + token * 16);
+    const wm_op bb = wm_op_load(b + base + token * 16);
+    wm_f8v baseline, adapted;
+    wm_h8 packed;
+    for (unsigned i = 0; i < 8; ++i) {
+        baseline[i] = c[base + wm_acc_row(i) * 16 + token];
+        packed[i] = (_Float16)baseline[i];
+    }
+    adapted = baseline;
+    const unsigned steps = 1u << (test / 16);
+    for (unsigned step = 0; step < steps; ++step) {
+        baseline = wm_mma(aa, bb, baseline);
+        for (unsigned i = 0; i < 8; ++i) baseline[i] = (float)(_Float16)baseline[i];
+        packed = __builtin_amdgcn_wmma_f16_16x16x16_f16_w32_gfx12(
+            __builtin_bit_cast(wm_h8, aa), __builtin_bit_cast(wm_h8, bb), packed);
+        adapted = wm_mma_f16_step(aa, bb, adapted);
+    }
+    for (unsigned i = 0; i < 8; ++i) {
+        const unsigned index = wm_acc_row(i) * 16 + token;
+        output[test * 768 + index] = baseline[i];
+        output[test * 768 + 256 + index] = (float)packed[i];
+        output[test * 768 + 512 + index] = adapted[i];
+    }
+}
diff --git a/tools/windows/wmma_f16_compare.py b/tools/windows/wmma_f16_compare.py
new file mode 100644
index 0000000..9f2ddef
--- /dev/null
+++ b/tools/windows/wmma_f16_compare.py
@@ -0,0 +1,67 @@
+"""Public gfx1201 WMMA arithmetic comparison; does not load DLSS or weights."""
+import argparse
+import json
+import os
+import pathlib
+import struct
+import subprocess
+
+import numpy as np
+
+
+def main():
+    p = argparse.ArgumentParser(description=__doc__)
+    p.add_argument('--probe', type=pathlib.Path, required=True)
+    p.add_argument('--module', type=pathlib.Path, required=True)
+    p.add_argument('--hip-root', type=pathlib.Path, required=True)
+    p.add_argument('--output-dir', type=pathlib.Path, required=True)
+    args = p.parse_args()
+    root = args.output_dir.resolve()
+    root.mkdir(parents=True, exist_ok=True)
+    fixture = root / 'fixture'
+    fixture.mkdir(exist_ok=True)
+    rng = np.random.default_rng(90701201)
+    a = rng.uniform(-1, 1, (64, 16, 16)).astype(np.float16)
+    b = rng.uniform(-1, 1, a.shape).astype(np.float16)
+    c = rng.uniform(-.25, .25, a.shape).astype(np.float16).astype(np.float32)
+    initial_output = np.full((64, 3, 16, 16), np.nan, np.float32)
+    arrays = (a, b, c, initial_output)
+    bases = [0x10000000 * (i + 1) for i in range(4)]
+    (fixture / 'args.bin').write_bytes(struct.pack('<4Q', *bases))
+    lines = ['kernel d4r_wmma_f16_compare', 'launch 64 1 1 32 1 1 0', 'args 32']
+    for i, data in enumerate(arrays):
+        data.tofile(fixture / f'alloc-{i}.bin')
+        lines += [f'alloc {i} {bases[i]:#x} {data.nbytes}', f'pointer {i * 8} {i} 0']
+    (fixture / 'manifest.txt').write_text('\n'.join(lines) + '\n', encoding='utf-8')
+    env = os.environ.copy()
+    env['D4R_DIAG_DIR'] = str(root)
+    with (root / 'gpu.stdout.log').open('wb') as out, (root / 'gpu.stderr.log').open('wb') as err:
+        status = subprocess.run([str(args.probe.resolve()), '--hip-root', str(args.hip_root.resolve()),
+            '--module', str(args.module.resolve()), '--fixture-dir', str(fixture), '--output-dir',
+            str(root / 'output'), '--iterations', '1'], env=env, stdout=out, stderr=err, timeout=120)
+    if status.returncode:
+        raise RuntimeError(f'GPU probe exit {status.returncode}; see {root}')
+    output = np.fromfile(root / 'output/alloc-3.bin', np.float32).reshape(64, 3, 16, 16)
+    if not np.isfinite(output).all():
+        raise RuntimeError('Nonfinite/unwritten WMMA output')
+    rows = []
+    for group, steps in enumerate((1, 2, 4, 8)):
+        values = output[group * 16:(group + 1) * 16]
+        difference = np.abs(values[:, 0].astype(np.float64) - values[:, 1].astype(np.float64))
+        row = dict(steps=steps, elements=difference.size, differing=int(np.count_nonzero(difference)),
+            maxAbsoluteError=float(difference.max()), rms=float(np.sqrt(np.mean(difference ** 2))))
+        rows.append(row)
+        print('WMMA_F16_COMPARE ' + json.dumps(row), flush=True)
+    adapter_exact = np.array_equal(output[:, 1].view(np.uint32), output[:, 2].view(np.uint32))
+    if not adapter_exact:
+        raise RuntimeError('Direct packed instruction and layout adapter differ')
+    result = dict(passed=True, architecture='gfx1201', publicSynthetic=True, adapterExact=adapter_exact,
+        baselineEquivalent=all(row['differing'] == 0 for row in rows), cases=rows,
+        gameOptimizationAccepted=False)
+    (root / 'validation.json').write_text(json.dumps(result, indent=2) + '\n', encoding='utf-8')
+    print('PASS WMMA_F16_ARITHMETIC_DIAGNOSTIC adapter_exact=1 baseline_equivalent=' +
+        str(int(result['baselineEquivalent'])), flush=True)
+
+
+if __name__ == '__main__':
+    main()