diff --git a/src/Marten/Events/EventDocumentStorage.cs b/src/Marten/Events/EventDocumentStorage.cs
index 05da629d31..b28cdeff6c 100644
--- a/src/Marten/Events/EventDocumentStorage.cs
+++ b/src/Marten/Events/EventDocumentStorage.cs
@@ -228,6 +228,22 @@ public IStorageOperation OverwriteProjected(IEvent document, string tenant)
         throw new NotSupportedException();
     }
 
+    // #4667 — events aren't projected through the document write path.
+    public IStorageOperation UpsertProjected(IEvent document, string tenant)
+    {
+        throw new NotSupportedException();
+    }
+
+    public IStorageOperation InsertProjected(IEvent document, string tenant)
+    {
+        throw new NotSupportedException();
+    }
+
+    public IStorageOperation UpdateProjected(IEvent document, string tenant)
+    {
+        throw new NotSupportedException();
+    }
+
     public abstract IStorageOperation AppendEvent(EventGraph events, IMartenSession session, StreamAction stream,
         IEvent e);
 
diff --git a/src/Marten/Events/EventMapping.cs b/src/Marten/Events/EventMapping.cs
index d3a991662a..548839235e 100644
--- a/src/Marten/Events/EventMapping.cs
+++ b/src/Marten/Events/EventMapping.cs
@@ -334,6 +334,22 @@ IStorageOperation IDocumentStorage<T>.OverwriteProjected(T document, string tena
         throw new NotSupportedException();
     }
 
+    // #4667 — events aren't projected through the document write path.
+    IStorageOperation IDocumentStorage<T>.UpsertProjected(T document, string tenant)
+    {
+        throw new NotSupportedException();
+    }
+
+    IStorageOperation IDocumentStorage<T>.InsertProjected(T document, string tenant)
+    {
+        throw new NotSupportedException();
+    }
+
+    IStorageOperation IDocumentStorage<T>.UpdateProjected(T document, string tenant)
+    {
+        throw new NotSupportedException();
+    }
+
     public IDeletion DeleteForDocument(T document, string tenant)
     {
         throw new NotSupportedException();
diff --git a/src/Marten/Internal/ClosedShape/NumericClosedShapeInsertOperation.cs b/src/Marten/Internal/ClosedShape/NumericClosedShapeInsertOperation.cs
index 15446bd497..6db1d9df11 100644
--- a/src/Marten/Internal/ClosedShape/NumericClosedShapeInsertOperation.cs
+++ b/src/Marten/Internal/ClosedShape/NumericClosedShapeInsertOperation.cs
@@ -26,14 +26,14 @@ internal sealed class NumericClosedShapeInsertOperation<TDoc, TId>: ClosedShapeI
     where TDoc : notnull
     where TId : notnull
 {
-    private readonly Dictionary<TId, long> _revisions;
+    private readonly Dictionary<TId, long>? _revisions;
 
     public NumericClosedShapeInsertOperation(
         TDoc document,
         TId id,
         string tenantId,
         DocumentStorageDescriptor<TDoc, TId> descriptor,
-        Dictionary<TId, long> revisions)
+        Dictionary<TId, long>? revisions)
         : base(document, id, tenantId, descriptor)
     {
         _revisions = revisions;
@@ -67,7 +67,13 @@ public override async Task PostprocessAsync(DbDataReader reader, IList<Exception
         }
 
         var newRevision = await reader.GetFieldValueAsync<long>(0, token).ConfigureAwait(false);
-        _revisions[_id] = newRevision;
+        // #4667 — null tracker (the InsertProjected path) skips the tracker
+        // write. RevisionBinder still applies so the document's revision
+        // field is fresh.
+        if (_revisions is not null)
+        {
+            _revisions[_id] = newRevision;
+        }
         _descriptor.RevisionBinder!.ApplyRevisionTo(_document, newRevision);
     }
 
diff --git a/src/Marten/Internal/ClosedShape/NumericClosedShapeUpdateOperation.cs b/src/Marten/Internal/ClosedShape/NumericClosedShapeUpdateOperation.cs
index b109d0bb4c..7e922055ba 100644
--- a/src/Marten/Internal/ClosedShape/NumericClosedShapeUpdateOperation.cs
+++ b/src/Marten/Internal/ClosedShape/NumericClosedShapeUpdateOperation.cs
@@ -24,14 +24,14 @@ internal sealed class NumericClosedShapeUpdateOperation<TDoc, TId>: ClosedShapeU
     where TDoc : notnull
     where TId : notnull
 {
-    private readonly Dictionary<TId, long> _revisions;
+    private readonly Dictionary<TId, long>? _revisions;
 
     public NumericClosedShapeUpdateOperation(
         TDoc document,
         TId id,
         string tenantId,
         DocumentStorageDescriptor<TDoc, TId> descriptor,
-        Dictionary<TId, long> revisions)
+        Dictionary<TId, long>? revisions)
         : base(document, id, tenantId, descriptor)
     {
         _revisions = revisions;
@@ -66,7 +66,13 @@ public override async Task PostprocessAsync(DbDataReader reader, IList<Exception
         }
 
         var newRevision = await reader.GetFieldValueAsync<long>(0, token).ConfigureAwait(false);
-        _revisions[_id] = newRevision;
+        // #4667 — null tracker (the UpdateProjected path) skips the tracker
+        // write. RevisionBinder still applies so the document's revision
+        // field is fresh.
+        if (_revisions is not null)
+        {
+            _revisions[_id] = newRevision;
+        }
         _descriptor.RevisionBinder!.ApplyRevisionTo(_document, newRevision);
     }
 
diff --git a/src/Marten/Internal/ClosedShape/NumericClosedShapeUpsertOperation.cs b/src/Marten/Internal/ClosedShape/NumericClosedShapeUpsertOperation.cs
index 9e9ef81666..1ae8f37a6f 100644
--- a/src/Marten/Internal/ClosedShape/NumericClosedShapeUpsertOperation.cs
+++ b/src/Marten/Internal/ClosedShape/NumericClosedShapeUpsertOperation.cs
@@ -27,7 +27,7 @@ internal sealed class NumericClosedShapeUpsertOperation<TDoc, TId>: ClosedShapeU
     where TDoc : notnull
     where TId : notnull
 {
-    private readonly Dictionary<TId, long> _revisions;
+    private readonly Dictionary<TId, long>? _revisions;
 
     public NumericClosedShapeUpsertOperation(
         TDoc document,
@@ -35,7 +35,7 @@ public NumericClosedShapeUpsertOperation(
         string tenantId,
         DocumentStorageDescriptor<TDoc, TId> descriptor,
         OperationRole role,
-        Dictionary<TId, long> revisions)
+        Dictionary<TId, long>? revisions)
         : base(document, id, tenantId, descriptor, role)
     {
         _revisions = revisions;
@@ -68,7 +68,13 @@ public override async Task PostprocessAsync(DbDataReader reader, IList<Exception
         }
 
         var newRevision = await reader.GetFieldValueAsync<long>(0, token).ConfigureAwait(false);
-        _revisions[_id] = newRevision;
+        // #4667 — null tracker (the UpsertProjected path) skips the tracker
+        // write. RevisionBinder still applies so the document's revision
+        // field is fresh.
+        if (_revisions is not null)
+        {
+            _revisions[_id] = newRevision;
+        }
         _descriptor.RevisionBinder!.ApplyRevisionTo(_document, newRevision);
     }
 
diff --git a/src/Marten/Internal/ClosedShape/NumericDirtyCheckedClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/NumericDirtyCheckedClosedShapeStorage.cs
index f55487a283..e0e03154c6 100644
--- a/src/Marten/Internal/ClosedShape/NumericDirtyCheckedClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/NumericDirtyCheckedClosedShapeStorage.cs
@@ -33,6 +33,16 @@ public override IStorageOperation Overwrite(TDoc document, IMartenSession sessio
     public override IStorageOperation OverwriteProjected(TDoc document, string tenant)
         => new NumericClosedShapeOverwriteOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
 
+    // #4667 — null revision tracker; see Lightweight peer for semantics.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => new NumericClosedShapeUpsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, OperationRole.Upsert, null);
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => new NumericClosedShapeInsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => new NumericClosedShapeUpdateOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
     public override ISelector BuildSelector(IMartenSession session)
         => _descriptor.HierarchyMapping is not null
             ? new HierarchicalNumericClosedShapeDirtyTrackingSelector<TDoc, TId>(session, _descriptor)
diff --git a/src/Marten/Internal/ClosedShape/NumericIdentityMapClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/NumericIdentityMapClosedShapeStorage.cs
index 8862e489b5..9c3b15bfc1 100644
--- a/src/Marten/Internal/ClosedShape/NumericIdentityMapClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/NumericIdentityMapClosedShapeStorage.cs
@@ -33,6 +33,16 @@ public override IStorageOperation Overwrite(TDoc document, IMartenSession sessio
     public override IStorageOperation OverwriteProjected(TDoc document, string tenant)
         => new NumericClosedShapeOverwriteOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
 
+    // #4667 — null revision tracker; see Lightweight peer for semantics.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => new NumericClosedShapeUpsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, OperationRole.Upsert, null);
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => new NumericClosedShapeInsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => new NumericClosedShapeUpdateOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
     public override ISelector BuildSelector(IMartenSession session)
         => _descriptor.HierarchyMapping is not null
             ? new HierarchicalNumericClosedShapeIdentityMapSelector<TDoc, TId>(session, _descriptor)
diff --git a/src/Marten/Internal/ClosedShape/NumericLightweightClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/NumericLightweightClosedShapeStorage.cs
index 630ab69a45..2a770c0f71 100644
--- a/src/Marten/Internal/ClosedShape/NumericLightweightClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/NumericLightweightClosedShapeStorage.cs
@@ -38,6 +38,19 @@ public override IStorageOperation OverwriteProjected(TDoc document, string tenan
         // the session's numeric-revision map for the projected doc.
         => new NumericClosedShapeOverwriteOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
 
+    // #4667 — null revision tracker. Numeric ops bind the IRevisionedOperation
+    // `Revision` property (default 0) in ConfigureCommand, so the WHERE guard
+    // `? = 0 OR table.mt_version < ?` always passes when the caller leaves
+    // Revision at the default.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => new NumericClosedShapeUpsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, OperationRole.Upsert, null);
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => new NumericClosedShapeInsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => new NumericClosedShapeUpdateOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
     public override ISelector BuildSelector(IMartenSession session)
         => _descriptor.HierarchyMapping is not null
             ? new HierarchicalNumericClosedShapeLightweightSelector<TDoc, TId>(session, _descriptor)
diff --git a/src/Marten/Internal/ClosedShape/OptimisticClosedShapeInsertOperation.cs b/src/Marten/Internal/ClosedShape/OptimisticClosedShapeInsertOperation.cs
index 6ce0426f71..2cc24e246a 100644
--- a/src/Marten/Internal/ClosedShape/OptimisticClosedShapeInsertOperation.cs
+++ b/src/Marten/Internal/ClosedShape/OptimisticClosedShapeInsertOperation.cs
@@ -25,7 +25,7 @@ internal sealed class OptimisticClosedShapeInsertOperation<TDoc, TId>: ClosedSha
     where TDoc : notnull
     where TId : notnull
 {
-    private readonly Dictionary<TId, Guid> _versions;
+    private readonly Dictionary<TId, Guid>? _versions;
     private readonly Guid _newVersion;
 
     public OptimisticClosedShapeInsertOperation(
@@ -33,7 +33,7 @@ public OptimisticClosedShapeInsertOperation(
         TId id,
         string tenantId,
         DocumentStorageDescriptor<TDoc, TId> descriptor,
-        Dictionary<TId, Guid> versions)
+        Dictionary<TId, Guid>? versions)
         : base(document, id, tenantId, descriptor)
     {
         _versions = versions;
@@ -69,6 +69,12 @@ public override async Task PostprocessAsync(DbDataReader reader, IList<Exception
             return;
         }
 
-        _versions[_id] = _newVersion;
+        // #4667 — null tracker (the InsertProjected path) just skips the
+        // tracker write. The fresh version is still applied to the document
+        // via VersionBinder during command configuration.
+        if (_versions is not null)
+        {
+            _versions[_id] = _newVersion;
+        }
     }
 }
diff --git a/src/Marten/Internal/ClosedShape/OptimisticClosedShapeUpdateOperation.cs b/src/Marten/Internal/ClosedShape/OptimisticClosedShapeUpdateOperation.cs
index cdaed99fd3..09b6b12434 100644
--- a/src/Marten/Internal/ClosedShape/OptimisticClosedShapeUpdateOperation.cs
+++ b/src/Marten/Internal/ClosedShape/OptimisticClosedShapeUpdateOperation.cs
@@ -26,7 +26,7 @@ internal sealed class OptimisticClosedShapeUpdateOperation<TDoc, TId>: ClosedSha
     where TDoc : notnull
     where TId : notnull
 {
-    private readonly Dictionary<TId, Guid> _versions;
+    private readonly Dictionary<TId, Guid>? _versions;
     private readonly Guid _newVersion;
 
     public OptimisticClosedShapeUpdateOperation(
@@ -34,7 +34,7 @@ public OptimisticClosedShapeUpdateOperation(
         TId id,
         string tenantId,
         DocumentStorageDescriptor<TDoc, TId> descriptor,
-        Dictionary<TId, Guid> versions)
+        Dictionary<TId, Guid>? versions)
         : base(document, id, tenantId, descriptor)
     {
         _versions = versions;
@@ -46,8 +46,12 @@ public override void ConfigureCommand(ICommandBuilder builder, IMartenSession se
         var parameters = builder.AppendWithParameters(_descriptor.UpdateSql, '?');
         var slot = BindPreConcurrencyParameters(parameters, session);
 
-        // Trailing WHERE mt_version = ? guard.
-        if (_versions.TryGetValue(_id, out var expected))
+        // Trailing WHERE mt_version = ? guard. #4667 — null tracker (the
+        // UpdateProjected path) treats expected version as DBNull, which the
+        // SQL WHERE never matches. Callers that go through UpdateProjected
+        // should also set IgnoreConcurrencyViolation = true to suppress the
+        // resulting "no row" exception.
+        if (_versions is not null && _versions.TryGetValue(_id, out var expected))
         {
             parameters[slot].Value = expected;
         }
@@ -69,7 +73,13 @@ public override async Task PostprocessAsync(DbDataReader reader, IList<Exception
             return;
         }
 
-        _versions[_id] = _newVersion;
+        // #4667 — null tracker (the UpdateProjected path) just skips the
+        // tracker write. The fresh version is still applied to the document
+        // via VersionBinder during command configuration.
+        if (_versions is not null)
+        {
+            _versions[_id] = _newVersion;
+        }
     }
 
     protected override int BindClientSideBinder(NpgsqlParameter[] parameters, int slot, IDocumentMetadataBinder<TDoc> binder, IMartenSession session)
diff --git a/src/Marten/Internal/ClosedShape/OptimisticClosedShapeUpsertOperation.cs b/src/Marten/Internal/ClosedShape/OptimisticClosedShapeUpsertOperation.cs
index 95accfa033..63edd63564 100644
--- a/src/Marten/Internal/ClosedShape/OptimisticClosedShapeUpsertOperation.cs
+++ b/src/Marten/Internal/ClosedShape/OptimisticClosedShapeUpsertOperation.cs
@@ -27,7 +27,7 @@ internal sealed class OptimisticClosedShapeUpsertOperation<TDoc, TId>: ClosedSha
     where TDoc : notnull
     where TId : notnull
 {
-    private readonly Dictionary<TId, Guid> _versions;
+    private readonly Dictionary<TId, Guid>? _versions;
     private readonly Guid _newVersion;
 
     public OptimisticClosedShapeUpsertOperation(
@@ -36,7 +36,7 @@ public OptimisticClosedShapeUpsertOperation(
         string tenantId,
         DocumentStorageDescriptor<TDoc, TId> descriptor,
         OperationRole role,
-        Dictionary<TId, Guid> versions)
+        Dictionary<TId, Guid>? versions)
         : base(document, id, tenantId, descriptor, role)
     {
         _versions = versions;
@@ -48,8 +48,12 @@ public override void ConfigureCommand(ICommandBuilder builder, IMartenSession se
         var parameters = builder.AppendWithParameters(_descriptor.UpsertSql, '?');
         var slot = BindPreOnConflictParameters(parameters, session);
 
-        // Trailing WHERE table.mt_version = ? guard.
-        if (_versions.TryGetValue(_id, out var expected))
+        // Trailing WHERE table.mt_version = ? guard. #4667 — null tracker
+        // (the UpsertProjected path) treats expected version as DBNull. On
+        // the ON CONFLICT branch the WHERE will never match, so existing
+        // rows in Optimistic mode are left untouched. The INSERT branch
+        // still fires for new rows.
+        if (_versions is not null && _versions.TryGetValue(_id, out var expected))
         {
             parameters[slot].Value = expected;
         }
@@ -71,7 +75,13 @@ public override async Task PostprocessAsync(DbDataReader reader, IList<Exception
             return;
         }
 
-        _versions[_id] = _newVersion;
+        // #4667 — null tracker (the UpsertProjected path) just skips the
+        // tracker write. The fresh version is still applied to the document
+        // via VersionBinder during command configuration.
+        if (_versions is not null)
+        {
+            _versions[_id] = _newVersion;
+        }
     }
 
     protected override int BindClientSideBinder(NpgsqlParameter[] parameters, int slot, IDocumentMetadataBinder<TDoc> binder, IMartenSession session)
diff --git a/src/Marten/Internal/ClosedShape/OptimisticDirtyCheckedClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/OptimisticDirtyCheckedClosedShapeStorage.cs
index e7922d16a7..50c0441e54 100644
--- a/src/Marten/Internal/ClosedShape/OptimisticDirtyCheckedClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/OptimisticDirtyCheckedClosedShapeStorage.cs
@@ -33,6 +33,16 @@ public override IStorageOperation Overwrite(TDoc document, IMartenSession sessio
     public override IStorageOperation OverwriteProjected(TDoc document, string tenant)
         => new OptimisticClosedShapeOverwriteOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
 
+    // #4667 — null version tracker; see Lightweight peer for semantics.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => new OptimisticClosedShapeUpsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, OperationRole.Upsert, null);
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => new OptimisticClosedShapeInsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => new OptimisticClosedShapeUpdateOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
     public override ISelector BuildSelector(IMartenSession session)
         => _descriptor.HierarchyMapping is not null
             ? new HierarchicalOptimisticClosedShapeDirtyTrackingSelector<TDoc, TId>(session, _descriptor)
diff --git a/src/Marten/Internal/ClosedShape/OptimisticIdentityMapClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/OptimisticIdentityMapClosedShapeStorage.cs
index 5d2cab781d..034c9789ea 100644
--- a/src/Marten/Internal/ClosedShape/OptimisticIdentityMapClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/OptimisticIdentityMapClosedShapeStorage.cs
@@ -33,6 +33,16 @@ public override IStorageOperation Overwrite(TDoc document, IMartenSession sessio
     public override IStorageOperation OverwriteProjected(TDoc document, string tenant)
         => new OptimisticClosedShapeOverwriteOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
 
+    // #4667 — null version tracker; see Lightweight peer for semantics.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => new OptimisticClosedShapeUpsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, OperationRole.Upsert, null);
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => new OptimisticClosedShapeInsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => new OptimisticClosedShapeUpdateOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
     public override ISelector BuildSelector(IMartenSession session)
         => _descriptor.HierarchyMapping is not null
             ? new HierarchicalOptimisticClosedShapeIdentityMapSelector<TDoc, TId>(session, _descriptor)
diff --git a/src/Marten/Internal/ClosedShape/OptimisticLightweightClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/OptimisticLightweightClosedShapeStorage.cs
index a96c6f25f0..4d544baabe 100644
--- a/src/Marten/Internal/ClosedShape/OptimisticLightweightClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/OptimisticLightweightClosedShapeStorage.cs
@@ -38,6 +38,21 @@ public override IStorageOperation OverwriteProjected(TDoc document, string tenan
         // the session's optimistic-version map for the projected doc.
         => new OptimisticClosedShapeOverwriteOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
 
+    // #4667 — projection write paths pass null tracker (no session-shared
+    // dict access). Optimistic Upsert/Update with null tracker bind DBNull
+    // for the WHERE-guard; existing rows are left untouched on the ON CONFLICT
+    // branch. Callers in the projection runtime set IgnoreConcurrencyViolation
+    // = true (see ProjectionStorage.StoreProjection / Store flows) to suppress
+    // the resulting "no row" exception.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => new OptimisticClosedShapeUpsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, OperationRole.Upsert, null);
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => new OptimisticClosedShapeInsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => new OptimisticClosedShapeUpdateOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, null);
+
     public override ISelector BuildSelector(IMartenSession session)
         => _descriptor.HierarchyMapping is not null
             ? new HierarchicalOptimisticClosedShapeLightweightSelector<TDoc, TId>(session, _descriptor)
diff --git a/src/Marten/Internal/ClosedShape/QueryOnlyClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/QueryOnlyClosedShapeStorage.cs
index 3a4cc1b669..aad3f7c992 100644
--- a/src/Marten/Internal/ClosedShape/QueryOnlyClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/QueryOnlyClosedShapeStorage.cs
@@ -61,6 +61,16 @@ public override IStorageOperation Overwrite(TDoc document, IMartenSession sessio
     public override IStorageOperation OverwriteProjected(TDoc document, string tenant)
         => throw new NotSupportedException("QueryOnly storage doesn't support OverwriteProjected.");
 
+    // #4667 — projection write paths aren't reachable from query sessions.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => throw new NotSupportedException("QueryOnly storage doesn't support UpsertProjected.");
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => throw new NotSupportedException("QueryOnly storage doesn't support InsertProjected.");
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => throw new NotSupportedException("QueryOnly storage doesn't support UpdateProjected.");
+
     public override ISelector BuildSelector(IMartenSession session)
         // #4659 Phase 2: pick the Flat / Hierarchical selector ONCE per
         // query — neither selector class branches on HierarchyMapping per
diff --git a/src/Marten/Internal/ClosedShape/UnversionedDirtyCheckedClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/UnversionedDirtyCheckedClosedShapeStorage.cs
index de5160eab6..a8b183bf4d 100644
--- a/src/Marten/Internal/ClosedShape/UnversionedDirtyCheckedClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/UnversionedDirtyCheckedClosedShapeStorage.cs
@@ -33,6 +33,16 @@ public override IStorageOperation Overwrite(TDoc document, IMartenSession sessio
     public override IStorageOperation OverwriteProjected(TDoc document, string tenant)
         => new UnversionedClosedShapeOverwriteOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor);
 
+    // #4667 — Unversioned ops have no tracker plumbing; see Lightweight peer.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => new UnversionedClosedShapeUpsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, OperationRole.Upsert);
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => new UnversionedClosedShapeInsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor);
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => new UnversionedClosedShapeUpdateOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor);
+
     public override ISelector BuildSelector(IMartenSession session)
         => _descriptor.HierarchyMapping is not null
             ? new HierarchicalUnversionedClosedShapeDirtyTrackingSelector<TDoc, TId>(session, _descriptor)
diff --git a/src/Marten/Internal/ClosedShape/UnversionedIdentityMapClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/UnversionedIdentityMapClosedShapeStorage.cs
index bcb3fda9d7..a6e9680627 100644
--- a/src/Marten/Internal/ClosedShape/UnversionedIdentityMapClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/UnversionedIdentityMapClosedShapeStorage.cs
@@ -33,6 +33,16 @@ public override IStorageOperation Overwrite(TDoc document, IMartenSession sessio
     public override IStorageOperation OverwriteProjected(TDoc document, string tenant)
         => new UnversionedClosedShapeOverwriteOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor);
 
+    // #4667 — Unversioned ops have no tracker plumbing; see Lightweight peer.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => new UnversionedClosedShapeUpsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, OperationRole.Upsert);
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => new UnversionedClosedShapeInsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor);
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => new UnversionedClosedShapeUpdateOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor);
+
     public override ISelector BuildSelector(IMartenSession session)
         => _descriptor.HierarchyMapping is not null
             ? new HierarchicalUnversionedClosedShapeIdentityMapSelector<TDoc, TId>(session, _descriptor)
diff --git a/src/Marten/Internal/ClosedShape/UnversionedLightweightClosedShapeStorage.cs b/src/Marten/Internal/ClosedShape/UnversionedLightweightClosedShapeStorage.cs
index a748a5b0f1..fcaeb91367 100644
--- a/src/Marten/Internal/ClosedShape/UnversionedLightweightClosedShapeStorage.cs
+++ b/src/Marten/Internal/ClosedShape/UnversionedLightweightClosedShapeStorage.cs
@@ -36,6 +36,18 @@ public override IStorageOperation Overwrite(TDoc document, IMartenSession sessio
     public override IStorageOperation OverwriteProjected(TDoc document, string tenant)
         => new UnversionedClosedShapeOverwriteOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor);
 
+    // #4667 — Unversioned ops have no tracker plumbing to begin with, so
+    // the *Projected factories return the same op as their session-aware
+    // counterparts. They exist for API uniformity across concurrency modes.
+    public override IStorageOperation UpsertProjected(TDoc document, string tenant)
+        => new UnversionedClosedShapeUpsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor, OperationRole.Upsert);
+
+    public override IStorageOperation InsertProjected(TDoc document, string tenant)
+        => new UnversionedClosedShapeInsertOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor);
+
+    public override IStorageOperation UpdateProjected(TDoc document, string tenant)
+        => new UnversionedClosedShapeUpdateOperation<TDoc, TId>(document, Identity(document), tenant, _descriptor);
+
     public override ISelector BuildSelector(IMartenSession session)
         => _descriptor.HierarchyMapping is not null
             ? new HierarchicalUnversionedClosedShapeLightweightSelector<TDoc, TId>(session, _descriptor)
diff --git a/src/Marten/Internal/Sessions/DocumentSessionBase.ProjectionStorage.cs b/src/Marten/Internal/Sessions/DocumentSessionBase.ProjectionStorage.cs
index 766a8cd672..01dd575132 100644
--- a/src/Marten/Internal/Sessions/DocumentSessionBase.ProjectionStorage.cs
+++ b/src/Marten/Internal/Sessions/DocumentSessionBase.ProjectionStorage.cs
@@ -83,7 +83,10 @@ public void UnDelete(TDoc snapshot)
 
     public void Store(TDoc snapshot)
     {
-        var upsert = _storage.Upsert(snapshot, _session, TenantId);
+        // #4667 — UpsertProjected (not Upsert) so we never read or mutate
+        // _session.Versions / _session.Revisions from a daemon worker. The
+        // projection runtime is by-contract not session-state-aware.
+        var upsert = _storage.UpsertProjected(snapshot, TenantId);
         _session.QueueOperation(upsert);
     }
 
@@ -118,19 +121,35 @@ public void Store(TDoc snapshot, TId id, string tenantId)
     {
         _storage.SetIdentity(snapshot, id);
 
-        // The aggregate may already be in the identity map from a prior SaveChangesAsync
-        // on the same session — for example, a FetchForWriting → save → StartStream
-        // sequence. In that case the projection has built a NEW snapshot instance for
-        // this save, and the duplicate-instance guard in IdentityMapDocumentStorage.store
-        // would throw before the underlying event store can surface the real conflict
-        // (ExistingStreamIdCollisionException). Evict the stale entry so the new snapshot
-        // can take its place.
-        _session.EjectAggregateFromIdentityMap<TDoc, TId>(id);
-
-        // Put it in the identity map -- if necessary
-        _storage.Store(_session, snapshot);
+        // #4667 — The ItemMap eject + IdentityMap-storage Store call below is
+        // the GH-3850 fix: inline-projection-rewriting-an-immutable-aggregate
+        // on an IdentitySession needs the freshly-built snapshot instance to
+        // replace the stale identity-map entry so a subsequent FetchLatest on
+        // the same session sees the new state. That ItemMap mutation is a race
+        // source under the async daemon's parallel Block(10, ...) workers
+        // (#4657), but the daemon never opts into UseIdentityMapForAggregates,
+        // so we gate the identity-map maintenance on the same flag. The
+        // default (false) case takes the session-state-free UpsertProjected
+        // path; the opt-in (true) case preserves the GH-3850 semantics and
+        // accepts the documented race risk per the #4667 Phase 3 design note
+        // ("opt-in is not safe for parallel projection workers").
+        if (_session.Options.EventGraph.UseIdentityMapForAggregates)
+        {
+            // The aggregate may already be in the identity map from a prior
+            // SaveChangesAsync on the same session — for example, a
+            // FetchForWriting → save → StartStream sequence. In that case
+            // the projection has built a NEW snapshot instance for this save
+            // and the duplicate-instance guard in IdentityMapDocumentStorage.store
+            // would throw before the underlying event store can surface the
+            // real conflict (ExistingStreamIdCollisionException). Evict the
+            // stale entry so the new snapshot can take its place.
+            _session.EjectAggregateFromIdentityMap<TDoc, TId>(id);
+
+            // Put it in the identity map -- if necessary
+            _storage.Store(_session, snapshot);
+        }
 
-        var upsert = _storage.Upsert(snapshot, _session, tenantId);
+        var upsert = _storage.UpsertProjected(snapshot, tenantId);
         _session.QueueOperation(upsert);
     }
 
diff --git a/src/Marten/Internal/Storage/DocumentStorage.cs b/src/Marten/Internal/Storage/DocumentStorage.cs
index f1325c0b29..7a6f824525 100644
--- a/src/Marten/Internal/Storage/DocumentStorage.cs
+++ b/src/Marten/Internal/Storage/DocumentStorage.cs
@@ -295,6 +295,15 @@ object IDocumentStorage<T>.IdentityFor(T document)
     /// <inheritdoc />
     public abstract IStorageOperation OverwriteProjected(T document, string tenant);
 
+    /// <inheritdoc />
+    public abstract IStorageOperation UpsertProjected(T document, string tenant);
+
+    /// <inheritdoc />
+    public abstract IStorageOperation InsertProjected(T document, string tenant);
+
+    /// <inheritdoc />
+    public abstract IStorageOperation UpdateProjected(T document, string tenant);
+
     public IDeletion DeleteForDocument(T document, string tenant)
     {
         var id = Identity(document);
diff --git a/src/Marten/Internal/Storage/IDocumentStorage.cs b/src/Marten/Internal/Storage/IDocumentStorage.cs
index 58a8e68037..d3f233b5fc 100644
--- a/src/Marten/Internal/Storage/IDocumentStorage.cs
+++ b/src/Marten/Internal/Storage/IDocumentStorage.cs
@@ -120,6 +120,26 @@ public interface IDocumentStorage<T>: IDocumentStorage where T : notnull
     /// </summary>
     IStorageOperation OverwriteProjected(T document, string tenantId);
 
+    /// <summary>
+    /// Session-free Upsert for projection storage (#4667 Phase 1). Builds the same Upsert
+    /// operation as <see cref="Upsert"/> but passes a null version/revision tracker so the
+    /// projection path never touches <see cref="IMartenSession.Versions"/>. Safe to call
+    /// from parallel async-daemon slice handlers that share an <see cref="IMartenSession"/>.
+    /// </summary>
+    IStorageOperation UpsertProjected(T document, string tenantId);
+
+    /// <summary>
+    /// Session-free Insert for projection storage (#4667 Phase 1). See
+    /// <see cref="UpsertProjected"/>.
+    /// </summary>
+    IStorageOperation InsertProjected(T document, string tenantId);
+
+    /// <summary>
+    /// Session-free Update for projection storage (#4667 Phase 1). See
+    /// <see cref="UpsertProjected"/>.
+    /// </summary>
+    IStorageOperation UpdateProjected(T document, string tenantId);
+
     IDeletion DeleteForDocument(T document, string tenantId);
 
 
diff --git a/src/Marten/Internal/Storage/SubClassDocumentStorage.cs b/src/Marten/Internal/Storage/SubClassDocumentStorage.cs
index 37def2d102..5bae400c1b 100644
--- a/src/Marten/Internal/Storage/SubClassDocumentStorage.cs
+++ b/src/Marten/Internal/Storage/SubClassDocumentStorage.cs
@@ -172,6 +172,23 @@ public IStorageOperation OverwriteProjected(T document, string tenant)
         return _parent.OverwriteProjected(document, tenant);
     }
 
+    // #4667 — delegate the new projection write entry points to the parent
+    // hierarchy storage just like Overwrite/OverwriteProjected do.
+    public IStorageOperation UpsertProjected(T document, string tenant)
+    {
+        return _parent.UpsertProjected(document, tenant);
+    }
+
+    public IStorageOperation InsertProjected(T document, string tenant)
+    {
+        return _parent.InsertProjected(document, tenant);
+    }
+
+    public IStorageOperation UpdateProjected(T document, string tenant)
+    {
+        return _parent.UpdateProjected(document, tenant);
+    }
+
     public IDeletion DeleteForDocument(T document, string tenant)
     {
         return _parent.DeleteForDocument(document, tenant);
diff --git a/src/Marten/Internal/ValueTypeIdentifiedDocumentStorage.cs b/src/Marten/Internal/ValueTypeIdentifiedDocumentStorage.cs
index 58e9ce0756..f63e660941 100644
--- a/src/Marten/Internal/ValueTypeIdentifiedDocumentStorage.cs
+++ b/src/Marten/Internal/ValueTypeIdentifiedDocumentStorage.cs
@@ -141,6 +141,16 @@ public IStorageOperation Overwrite(TDoc document, IMartenSession session, string
     public IStorageOperation OverwriteProjected(TDoc document, string tenantId)
         => Inner.OverwriteProjected(document, tenantId);
 
+    // #4667 — delegate the projection write entry points.
+    public IStorageOperation UpsertProjected(TDoc document, string tenantId)
+        => Inner.UpsertProjected(document, tenantId);
+
+    public IStorageOperation InsertProjected(TDoc document, string tenantId)
+        => Inner.InsertProjected(document, tenantId);
+
+    public IStorageOperation UpdateProjected(TDoc document, string tenantId)
+        => Inner.UpdateProjected(document, tenantId);
+
     public IDeletion DeleteForDocument(TDoc document, string tenantId)
         => Inner.DeleteForDocument(document, tenantId);