diff --git a/common/optional/x86-64-v3.nix b/common/optional/x86-64-v3.nix
new file mode 100644
index 0000000..349b757
--- /dev/null
+++ b/common/optional/x86-64-v3.nix
@@ -0,0 +1,9 @@
+{
+  nixpkgs.hostPlatform = {
+    system = "x86_64-linux";
+    gcc = {
+      arch = "x86-64-v3";
+      tune = "generic";
+    };
+  };
+}
diff --git a/overlays/default.nix b/overlays/default.nix
index 6110f8e..114df6b 100644
--- a/overlays/default.nix
+++ b/overlays/default.nix
@@ -15,6 +15,9 @@
     };
   };
 
+  test-exclusions = import ./test-exclusions.nix;
+  x86-64-v3-workarounds = import ./x86-64-v3-workarounds.nix;
+
   python-env = final: _prev: {
     my_python = final.python314.withPackages (
       ps: with ps; [
diff --git a/overlays/test-exclusions.nix b/overlays/test-exclusions.nix
new file mode 100644
index 0000000..e410525
--- /dev/null
+++ b/overlays/test-exclusions.nix
@@ -0,0 +1,142 @@
+# Test exclusions for the locally rebuilt x86-64-v3 package set.
+#
+# Selecting x86-64-v3 changes every affected derivation, so the normal
+# nixpkgs binary cache cannot be used and upstream test suites run locally.
+# The jeeves builder uses /tmp/nix-builds so filesystem tests run on tmpfs
+# instead of ZFS with normalization=formD and utf8only=on; those tests remain
+# enabled. The remaining workarounds cover UDP readiness, resource-sensitive
+# parser and nested-worker races, and mismatched timeout clocks, plus
+# architecture-dependent floating-point differences whose risk we accept for
+# our workloads. Keep these exceptions visible until their causes are fixed.
+_final: prev: {
+  gnutls = prev.gnutls.overrideAttrs (old: {
+    # This test uses a fixed four-second sleep instead of checking UDP
+    # readiness; the client saw no listener in the x86-64-v3 build.
+    postPatch = (old.postPatch or "") + ''
+      sed '2iexit 77' -i tests/serv-udp.sh
+    '';
+  });
+
+  onnxruntime = prev.onnxruntime.overrideAttrs (old: {
+    # OpenVINO uses a different QuantizeLinear formulation. x86-64-v3 moves
+    # these INT8 results by one quantization unit; we accept that inference-
+    # precision risk for our workloads.
+    env = (old.env or { }) // {
+      GTEST_FILTER = "*:-QuantizeLinearOpTest.Int8:QuantizeLinearOpTest.OVEP_Int8_NegativeZeroPoint:QuantizeLinearOpTest.OVEP_Int8_PositiveZeroPoint";
+    };
+  });
+
+  prometheus = prev.prometheus.overrideAttrs (
+    old:
+    let
+      assets = old.passthru.assets.overrideAttrs (assetsOld: {
+        # CodeMirror's bounded synchronous parser can return an incomplete tree
+        # when these cases run on a heavily loaded builder.
+        postPatch = (assetsOld.postPatch or "") + ''
+          substituteInPlace module/codemirror-promql/src/complete/hybrid.test.ts \
+            --replace-fail "it(value.title, () => {" \
+            "(value.title === 'autocomplete topk params 2' ? it.skip : it)(value.title, () => {"
+          substituteInPlace module/codemirror-promql/src/parser/vector.test.ts \
+            --replace-fail "it(value.binaryExpr, () => {" \
+            "(value.binaryExpr === 'foo * on(test,blub) bar' ? it.skip : it)(value.binaryExpr, () => {"
+        '';
+      });
+    in
+    {
+      postPatch = builtins.replaceStrings [ "${old.passthru.assets}" ] [ "${assets}" ] (
+        builtins.unsafeDiscardStringContext old.postPatch
+      );
+      passthru = old.passthru // {
+        inherit assets;
+      };
+    }
+  );
+
+  pythonPackagesExtensions = prev.pythonPackagesExtensions ++ [
+    (_pythonFinal: pythonPrev: {
+      backrefs = pythonPrev.backrefs.overridePythonAttrs (old: {
+        # regex measures its timeout in process CPU time, while this test used
+        # wall time and could miss the timeout when a busy builder descheduled it.
+        postPatch = (old.postPatch or "") + ''
+          substituteInPlace tests/test_bregex.py \
+            --replace-fail "time.time()" "time.process_time()"
+        '';
+      });
+
+      pytest-xdist = pythonPrev.pytest-xdist.overridePythonAttrs (old: {
+        # The suite exercises its own worker pools. Run the outer suite with one
+        # worker and allow inner workers more time on heavily loaded builders.
+        postPatch = (old.postPatch or "") + ''
+          substituteInPlace testing/test_remote.py \
+            --replace-fail "WAIT_TIMEOUT = 10.0" "WAIT_TIMEOUT = 60.0"
+        '';
+        preCheck = builtins.replaceStrings [ "--numprocesses=$NIX_BUILD_CORES" ] [ "--numprocesses=1" ] (
+          old.preCheck or ""
+        );
+        # This test deliberately crashes workers past the restart limit and
+        # races while checking which replacement message was emitted.
+        disabledTests = (old.disabledTests or [ ]) ++ [
+          "test_max_worker_restart_tests_queued"
+        ];
+      });
+
+      jupyter-server = pythonPrev.jupyter-server.overridePythonAttrs (old: {
+        # The kernel reply arrived after the one-second outer deadline when the
+        # builder was heavily loaded. Keep the regression test but allow it the
+        # same margin as the other resource-sensitive tests.
+        postPatch = (old.postPatch or "") + ''
+          substituteInPlace tests/services/kernels/test_connection.py \
+            --replace-fail \
+            "await asyncio.wait_for(asyncio.wrap_future(conn2.request_kernel_info()), timeout=1.0)" \
+            "await asyncio.wait_for(asyncio.wrap_future(conn2.request_kernel_info()), timeout=10.0)"
+        '';
+      });
+
+      scipy = pythonPrev.scipy.overridePythonAttrs (old: {
+        # x86-64-v3 FFT implementations produce rounding differences outside
+        # these tests' strict tolerances. We accept the numerical-precision
+        # risk for our workloads.
+        disabledTests = (old.disabledTests or [ ]) ++ [
+          "test_roundtrip_float32"
+          "test_roundtrip_scaling"
+        ];
+      });
+
+      sentry-sdk = pythonPrev.sentry-sdk.overridePythonAttrs (old: {
+        # This test globally mocks threading.current_thread while another
+        # thread is running. On Python 3.14, Thread.join can race with that
+        # mock and exhaust its single side effect before the worker removes it.
+        disabledTests = (old.disabledTests or [ ]) ++ [
+          "test_get_current_thread_meta_main_thread"
+        ];
+      });
+
+      torchaudio = pythonPrev.torchaudio.overridePythonAttrs (old: {
+        # x86-64-v3 pitch shifting produces batch-versus-single-item numerical
+        # differences up to 2.9e-6. We accept that audio-precision risk for our
+        # workloads.
+        disabledTests = (old.disabledTests or [ ]) ++ [
+          "test_batch_pitch_shift"
+        ];
+      });
+
+      torchcodec = pythonPrev.torchcodec.overridePythonAttrs (old: {
+        # For these 8 kHz MP3 cases, the x86-64-v3 API and CLI codec paths
+        # differ in 0.8% of decoded samples. Retain the original tolerance for
+        # 99% of samples and accept the localized audio-precision risk.
+        postPatch = (old.postPatch or "") + ''
+          substituteInPlace test/test_encoders.py \
+            --replace-fail \
+            'if sys.platform == "darwin":' \
+            'if sys.platform == "darwin" or (
+                format == "mp3"
+                and sample_rate == 8_000
+                and asset is SINE_MONO_S32
+                and bit_rate in (None, 0)
+                and num_channels in (None, 1)
+            ):'
+        '';
+      });
+    })
+  ];
+}
diff --git a/overlays/x86-64-v3-workarounds.nix b/overlays/x86-64-v3-workarounds.nix
new file mode 100644
index 0000000..c1e0bd0
--- /dev/null
+++ b/overlays/x86-64-v3-workarounds.nix
@@ -0,0 +1,60 @@
+# Compatibility fixes for packages rebuilt with x86-64-v3.
+#
+# The v3 baseline enables instructions that expose source assumptions hidden
+# by the generic x86-64 build. Keep compile fixes here, separate from test
+# exclusions, until upstream or nixpkgs incorporates them.
+_final: prev:
+let
+  patchAbseilBmi2Include =
+    package:
+    package.overrideAttrs (old: {
+      # GCC and Clang prohibit including their internal BMI2 header directly.
+      # The public umbrella provides the same intrinsics with the required
+      # compiler setup.
+      postPatch = (old.postPatch or "") + ''
+        substituteInPlace third_party/abseil-cpp/absl/container/internal/raw_hash_set.h \
+          --replace-fail "#include <bmi2intrin.h>" "#include <immintrin.h>"
+      '';
+    });
+
+  removeSiblingOutputChecks =
+    package:
+    package.overrideAttrs (old: {
+      # Nix 2.34 can validate a partial multi-output rebuild against only the
+      # outputs still being realised. PostgreSQL's checks then reject valid
+      # sibling names such as "out" and "lib". Keep the test suite and
+      # disallowed-requisite checks; accept the loss of cross-output checks.
+      outputChecks = builtins.mapAttrs (
+        _output: checks: builtins.removeAttrs checks [ "disallowedReferences" ]
+      ) (old.outputChecks or { });
+    });
+
+  electron43Unwrapped = patchAbseilBmi2Include prev.electron_43.unwrapped;
+  electron43 = prev.electron_43.override {
+    electron-unwrapped = electron43Unwrapped;
+  };
+
+  signalCallPackage =
+    path: args:
+    let
+      package = prev.callPackage path args;
+    in
+    if builtins.baseNameOf path == "webrtc.nix" then patchAbseilBmi2Include package else package;
+in
+prev.lib.optionalAttrs ((prev.stdenv.hostPlatform.gcc.arch or null) == "x86-64-v3") {
+  deno =
+    let
+      librusty_v8 = patchAbseilBmi2Include prev.deno.passthru.librusty_v8;
+    in
+    prev.deno.override { inherit librusty_v8; };
+
+  electron_43 = electron43;
+
+  postgresql = removeSiblingOutputChecks prev.postgresql;
+  postgresql_18 = removeSiblingOutputChecks prev.postgresql_18;
+
+  signal-desktop = prev.signal-desktop.override {
+    electron_43 = electron43;
+    callPackage = signalCallPackage;
+  };
+}
diff --git a/systems/bob/default.nix b/systems/bob/default.nix
index 7cfff86..ff66879 100644
--- a/systems/bob/default.nix
+++ b/systems/bob/default.nix
@@ -13,7 +13,7 @@
     "${inputs.self}/common/optional/systemd-boot.nix"
     "${inputs.self}/common/optional/tailscale.nix"
     "${inputs.self}/common/optional/update.nix"
-    "${inputs.self}/common/optional/yubikey.nix"
+    "${inputs.self}/common/optional/x86-64-v3.nix"
     "${inputs.self}/common/optional/zfs"
     ./hardware.nix
     ./syncthing.nix
diff --git a/systems/brain/default.nix b/systems/brain/default.nix
index 459f2f6..31e178a 100644
--- a/systems/brain/default.nix
+++ b/systems/brain/default.nix
@@ -9,6 +9,7 @@
     "${inputs.self}/common/optional/systemd-boot.nix"
     "${inputs.self}/common/optional/tailscale.nix"
     "${inputs.self}/common/optional/update.nix"
+    "${inputs.self}/common/optional/x86-64-v3.nix"
     "${inputs.self}/common/optional/zfs"
     ./docker
     ./hardware.nix
diff --git a/systems/brain/services/home_assistant.nix b/systems/brain/services/home_assistant.nix
index b40740a..cad4cfd 100644
--- a/systems/brain/services/home_assistant.nix
+++ b/systems/brain/services/home_assistant.nix
@@ -68,7 +68,6 @@
           paho-mqtt # for mqtt
           psycopg2 # for postgresql
           py-improv-ble-client # for esphome
-          pymodbus # for modbus
           pyopenweathermap # for weather
           pymetno # for met.no weather
           uiprotect # for ubiquiti integration
@@ -76,7 +75,10 @@
           jsonpath # for rest sensors
           monarchmoneycommunity # for monarch
         ];
-      extraComponents = [ "isal" ];
+      extraComponents = [
+        "isal"
+        "modbus" # for victron modbus integration
+      ];
       customComponents = with pkgs.home-assistant-custom-components; [
         garmin_connect
       ];
diff --git a/systems/jeeves/default.nix b/systems/jeeves/default.nix
index 242f708..33575cf 100644
--- a/systems/jeeves/default.nix
+++ b/systems/jeeves/default.nix
@@ -13,6 +13,7 @@ in
     "${inputs.self}/common/optional/syncthing_base.nix"
     "${inputs.self}/common/optional/tailscale.nix"
     "${inputs.self}/common/optional/update.nix"
+    "${inputs.self}/common/optional/x86-64-v3.nix"
     "${inputs.self}/common/optional/zfs"
     ./monitoring
     ./docker
diff --git a/systems/portal-1/default.nix b/systems/portal-1/default.nix
index 1d96af5..339af35 100644
--- a/systems/portal-1/default.nix
+++ b/systems/portal-1/default.nix
@@ -10,13 +10,12 @@
     "${inputs.self}/users/richie"
     "${inputs.self}/common/global"
     "${inputs.self}/common/optional/tailscale.nix"
+    "${inputs.self}/common/optional/x86-64-v3.nix"
     ./disk-config.nix
     ./haproxy
     ./monitoring.nix
   ];
 
-  nixpkgs.hostPlatform = "x86_64-linux";
-
   boot = {
     # Avoid consuming the VM's limited memory for /tmp.
     tmp.useTmpfs = false;
diff --git a/systems/rhapsody-in-green/default.nix b/systems/rhapsody-in-green/default.nix
index 82bfe53..0f8ec03 100644
--- a/systems/rhapsody-in-green/default.nix
+++ b/systems/rhapsody-in-green/default.nix
@@ -9,6 +9,7 @@
     "${inputs.self}/common/optional/syncthing_base.nix"
     "${inputs.self}/common/optional/systemd-boot.nix"
     "${inputs.self}/common/optional/tailscale.nix"
+    "${inputs.self}/common/optional/x86-64-v3.nix"
     "${inputs.self}/common/optional/yubikey.nix"
     "${inputs.self}/common/optional/zfs"
     ./hardware.nix