diff --git a/src/AVEVA.Historian.Client/Wcf/HistorianHistoricalWriteProtocol.cs b/src/AVEVA.Historian.Client/Wcf/HistorianHistoricalWriteProtocol.cs
index f485d0c..c252c48 100644
--- a/src/AVEVA.Historian.Client/Wcf/HistorianHistoricalWriteProtocol.cs
+++ b/src/AVEVA.Historian.Client/Wcf/HistorianHistoricalWriteProtocol.cs
@@ -28,10 +28,12 @@ namespace AVEVA.Historian.Client.Wcf;
 ///     +0x26  UInt32  0                 // value high dword (constant zero)
 ///     +0x2A  value bytes, native width by tag type:
 ///                Float → Float32(4) · Double → Float64(8) · Int2 → Int16(2)
-///                Int4 → Int32(4) · UInt4 → UInt32(4)
+///                Int4 → Int32(4) · UInt4 → UInt32(4) · UInt1 → UInt8(1)
+///                Int8 → Int64(8) · UInt8 → UInt64(8)
 /// </code>
 ///
-/// Captured for the five analog types <c>EnsureTagAsync</c> supports (Float/Double/Int2/Int4/UInt4).
+/// Live-captured for Float/Double/Int2/Int4/UInt4; UInt1/Int8/UInt8 mirror the captured
+/// Double value layout (8 LE bytes for Int8/UInt8, 1 byte for UInt1) pending live round-trip.
 /// Other tag types have no captured value encoding and are rejected.
 /// </remarks>
 internal static class HistorianHistoricalWriteProtocol
@@ -53,6 +55,8 @@ internal static class HistorianHistoricalWriteProtocol
     /// <paramref name="dataType"/> is the tag's declared analog type (selects the value width), and
     /// <paramref name="receivedTimeUtc"/> is the storage/received timestamp the orchestrator stamps.
     /// Throws <see cref="ProtocolEvidenceMissingException"/> for tag types without a captured encoding.
+    /// Int8/UInt8 carry exact magnitude only up to 2^53 — the value API is <see langword="double"/>;
+    /// full 64-bit range is a separate follow-on.
     /// </summary>
     public static byte[] SerializeAddStreamValuesBuffer(
         Guid tagGuid,
@@ -117,10 +121,26 @@ internal static class HistorianHistoricalWriteProtocol
                 BinaryPrimitives.WriteUInt32LittleEndian(b, checked((uint)value));
                 return b;
             }
+            case HistorianDataType.UInt1:
+            {
+                return [checked((byte)value)];
+            }
+            case HistorianDataType.Int8:
+            {
+                byte[] b = new byte[8];
+                BinaryPrimitives.WriteInt64LittleEndian(b, checked((long)value));
+                return b;
+            }
+            case HistorianDataType.UInt8:
+            {
+                byte[] b = new byte[8];
+                BinaryPrimitives.WriteUInt64LittleEndian(b, checked((ulong)value));
+                return b;
+            }
             default:
                 throw new ProtocolEvidenceMissingException(
                     $"AddHistoricalValuesAsync has no captured value encoding for tag data type '{dataType}'. " +
-                    "Captured types: Float, Double, Int2, Int4, UInt4.");
+                    "Captured types: Float, Double, Int2, Int4, UInt4, UInt1, Int8, UInt8.");
         }
     }
 
diff --git a/src/AVEVA.Historian.Client/Wcf/HistorianTagWriteProtocol.cs b/src/AVEVA.Historian.Client/Wcf/HistorianTagWriteProtocol.cs
index a45faf6..f5e2aaa 100644
--- a/src/AVEVA.Historian.Client/Wcf/HistorianTagWriteProtocol.cs
+++ b/src/AVEVA.Historian.Client/Wcf/HistorianTagWriteProtocol.cs
@@ -58,9 +58,10 @@ internal static class HistorianTagWriteProtocol
     ];
 
     /// <summary>
-    /// Native CDataType wire codes per data type — captured 2026-05-04 by probing
-    /// every type via instrument-wcf-writemessage. Matches the codes already documented
-    /// in <see cref="HistorianWcfTagClient"/> MapDataType for the read path.
+    /// Native CDataType wire codes per data type — captured by probing every type via
+    /// instrument-wcf-writemessage. Matches the codes already documented in
+    /// <see cref="HistorianWcfTagClient"/> MapDataType for the read path; UInt1/Int8/UInt8
+    /// reuse the same read-side codes (0x08/0x19/0x39).
     /// </summary>
     public static byte GetAnalogDataTypeCode(Models.HistorianDataType dataType) => dataType switch
     {
@@ -70,8 +71,11 @@ internal static class HistorianTagWriteProtocol
         Models.HistorianDataType.UInt4 => 0x11,
         Models.HistorianDataType.Int2 => 0x29,
         Models.HistorianDataType.Int4 => 0x31,
+        Models.HistorianDataType.UInt1 => 0x08,
+        Models.HistorianDataType.Int8 => 0x19,
+        Models.HistorianDataType.UInt8 => 0x39,
         _ => throw new ProtocolEvidenceMissingException(
-            $"EnsureTagAsync data type {dataType} has no captured CTagMetadata wire code; supported: Float, Double, UInt2, UInt4, Int2, Int4."),
+            $"EnsureTagAsync data type {dataType} has no captured CTagMetadata wire code; supported: Float, Double, UInt2, UInt4, Int2, Int4, UInt1, Int8, UInt8."),
     };
 
     private static readonly byte[] AnalogPadding16 = new byte[16];
@@ -118,7 +122,8 @@ internal static class HistorianTagWriteProtocol
 
     /// <summary>
     /// Serializes a CTagMetadata payload for an analog tag. Live-verified for Float,
-    /// Double, Int2, Int4, UInt4 — see <see cref="GetAnalogDataTypeCode"/> for the
+    /// Double, Int2, Int4, UInt4; UInt1/Int8/UInt8 supported via the read-side type
+    /// codes (pending live round-trip) — see <see cref="GetAnalogDataTypeCode"/> for the
     /// type-code mapping. Output matches the byte-for-byte capture for the same inputs.
     /// When MinEU/MaxEU/MinRaw/MaxRaw are all defaults (0/100/0/100) emits the compact
     /// `1A 03` scaling marker; otherwise emits `1F` + 4 doubles in order.