diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.csproj b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.csproj
index c8d2716..d33a446 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.csproj
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.csproj
@@ -15,10 +15,36 @@
     <ItemGroup>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Abstractions\ZB.MOM.WW.OtOpcUa.Core.Abstractions.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core\ZB.MOM.WW.OtOpcUa.Core.csproj"/>
-        <!-- mxaccessgw .NET client. Path-based ProjectReference because both repos sit
-             side-by-side on the dev box; long-term we'll consume MxGateway.Client as a
-             NuGet package. PR 4.W revisits the dependency shape before parity gating. -->
-        <ProjectReference Include="..\..\..\..\mxaccessgw\clients\dotnet\MxGateway.Client\MxGateway.Client.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <!-- Vendored mxaccessgw .NET client. Originally consumed via path-based
+             ProjectReference to the sibling repo, but the sibling repo restructured
+             and the MxGateway.Client.csproj path no longer exists. The DLLs in
+             libs/ are the last known-good build (May 2026); they reference proto
+             types from MxGateway.Contracts.dll using the pre-restructure namespace
+             (MxGateway.Contracts.Proto). See libs/README.md for the unwinding plan
+             once the sibling repo restores a client library or we migrate to the
+             new ZB.MOM.WW.MxGateway.Contracts.Proto namespace. -->
+        <Reference Include="MxGateway.Client">
+            <HintPath>libs\MxGateway.Client.dll</HintPath>
+            <Private>true</Private>
+        </Reference>
+        <Reference Include="MxGateway.Contracts">
+            <HintPath>libs\MxGateway.Contracts.dll</HintPath>
+            <Private>true</Private>
+        </Reference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <!-- Transitive deps the vendored DLLs need exposed at consumer level
+             (versions match the sibling mxaccessgw repo's
+             ZB.MOM.WW.MxGateway.Contracts.csproj so binary-compat is preserved). -->
+        <PackageReference Include="Google.Protobuf" Version="3.34.1" />
+        <PackageReference Include="Grpc.Core.Api" Version="2.76.0" />
+        <PackageReference Include="Grpc.Net.Client" Version="2.71.0" />
+        <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.0" />
+        <PackageReference Include="Polly" Version="8.5.2" />
     </ItemGroup>
 
     <ItemGroup>
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/libs/MxGateway.Client.dll b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/libs/MxGateway.Client.dll
new file mode 100644
index 0000000..6fc124b
Binary files /dev/null and b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/libs/MxGateway.Client.dll differ
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/libs/MxGateway.Contracts.dll b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/libs/MxGateway.Contracts.dll
new file mode 100644
index 0000000..f918a73
Binary files /dev/null and b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/libs/MxGateway.Contracts.dll differ
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/libs/README.md b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/libs/README.md
new file mode 100644
index 0000000..63400e8
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/libs/README.md
@@ -0,0 +1,63 @@
+# Vendored MxGateway client DLLs
+
+This directory holds binary copies of `MxGateway.Client.dll` and
+`MxGateway.Contracts.dll` from the sibling `mxaccessgw` repo's last known-good
+build (May 2026). The DLLs are referenced from the driver's csproj as
+`<Reference HintPath="…" />` items rather than `ProjectReference`.
+
+## Why
+
+The sibling `mxaccessgw` repo restructured: the `clients/dotnet/MxGateway.Client`
+project the driver previously referenced via path-based `ProjectReference` no
+longer exists, and the proto contracts moved from the `MxGateway.Contracts.Proto`
+namespace to `ZB.MOM.WW.MxGateway.Contracts.Proto`. The driver's source still
+expects the pre-restructure namespace, so re-pointing at the new contracts would
+require a global namespace rename across ~19 driver files PLUS reimplementing
+the `MxGatewayClient` / `MxGatewaySession` / `GalaxyRepositoryClient` types the
+old client library provided (the sibling repo dropped the client library
+entirely, keeping only the contracts).
+
+Vendoring the binaries unblocks the build in minutes instead of hours, freezes
+the gateway contract surface at a known-good version, and preserves the option
+to migrate properly later without an emergency rewrite.
+
+## What's vendored
+
+| File | Source | Built against |
+|---|---|---|
+| `MxGateway.Client.dll` | mxaccessgw repo, `clients/dotnet/MxGateway.Client/` (pre-restructure) | net10.0, `MxGateway.Contracts.dll` |
+| `MxGateway.Contracts.dll` | mxaccessgw repo, `src/MxGateway.Contracts/` (pre-restructure) | net10.0, proto namespace `MxGateway.Contracts.Proto[.Galaxy]` |
+
+The NuGet packages the vendored DLLs need transitively (Google.Protobuf,
+Grpc.Core.Api, Grpc.Net.Client, Microsoft.Extensions.Logging.Abstractions,
+Polly) are declared as direct `PackageReference` in the driver csproj — when
+the dropped `ProjectReference` was in place those packages were transitively
+provided; with binary references the consumer must declare them explicitly.
+Versions match what the sibling repo's `ZB.MOM.WW.MxGateway.Contracts.csproj`
+uses so the gRPC + proto runtime stays binary-compatible.
+
+## Decompiled-source archive
+
+The vendored DLLs are byte-for-byte the build output. The full source can be
+recovered with `ilspycmd MxGateway.Client.dll > MxGateway.Client.cs` if a code
+review or audit needs it. There is no proprietary code in either DLL — they
+are the OtOpcUa team's own client implementation against the gateway's open
+proto contracts.
+
+## How to unwind
+
+Either path closes the vendored-binary debt:
+
+1. **Sibling repo restores `MxGateway.Client.csproj`** (or publishes a NuGet
+   package). Switch the csproj back to a `ProjectReference` / `PackageReference`,
+   delete this directory.
+2. **Driver migrates to the new `ZB.MOM.WW.MxGateway.Contracts.Proto`
+   namespace.** Global namespace rename across the ~19 consuming source files,
+   plus re-implementing `MxGatewayClient` / `MxGatewaySession` /
+   `GalaxyRepositoryClient` (≈2,200 LoC of behavioural client code) either
+   inlined into this driver or as a fresh sibling library. Delete this
+   directory.
+
+Either way: when unwinding, also drop the five `PackageReference` lines added
+to the csproj alongside the `<Reference>` items — the new ProjectReference /
+PackageReference will provide them transitively again.
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests.csproj b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests.csproj
index eaf17ef..dd2b9df 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests.csproj
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests.csproj
@@ -21,9 +21,19 @@
 
     <ItemGroup>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Galaxy\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.csproj"/>
-        <!-- Pulled in transitively via Driver.Galaxy → MxGateway.Client → MxGateway.Contracts;
-             explicit reference lets tests construct GalaxyObject / GalaxyAttribute fixtures. -->
-        <ProjectReference Include="..\..\..\..\mxaccessgw\src\MxGateway.Contracts\MxGateway.Contracts.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <!-- Vendored mxaccessgw contracts DLL. The driver under test holds the same
+             binary reference; this explicit duplicate lets tests construct
+             GalaxyObject / GalaxyAttribute / MxCommand / MxEvent fixtures directly
+             rather than only via the driver's public surface. See
+             ..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Galaxy\libs\README.md for
+             the unwinding plan. -->
+        <Reference Include="MxGateway.Contracts">
+            <HintPath>..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Galaxy\libs\MxGateway.Contracts.dll</HintPath>
+            <Private>true</Private>
+        </Reference>
     </ItemGroup>
 
 </Project>