diff --git a/flashduty_test.go b/flashduty_test.go
index 828992b..6a01336 100644
--- a/flashduty_test.go
+++ b/flashduty_test.go
@@ -97,6 +97,38 @@ func TestOptionalObjectRequestFieldOmitsWhenUnset(t *testing.T) {
 	}
 }
 
+// TestDashboardVariableOmitsUnsetVariableQuery guards the flattened-oneOf case
+// of the rule above: DashboardVariable is one struct for the datasource,
+// custom, and query arms, and only the query arm carries variable_query. The
+// backend rejects unknown fields per arm, so a datasource variable sent with
+// `"variable_query":{"kind":""}` fails the whole dashboard create, update, or
+// panel preview.
+func TestDashboardVariableOmitsUnsetVariableQuery(t *testing.T) {
+	body, err := json.Marshal(DashboardVariable{
+		Kind:           "datasource",
+		Name:           "metrics_ds",
+		DatasourceType: "prometheus",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.Contains(string(body), `"variable_query"`) {
+		t.Fatalf("unset VariableQuery must be omitted from the wire, got %s", body)
+	}
+
+	body, err = json.Marshal(DashboardVariable{
+		Kind:          "query",
+		Name:          "service",
+		VariableQuery: DashboardVariableQuery{Kind: "prometheus", Metric: "up", Label: "job"},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(string(body), `"variable_query":{`) {
+		t.Fatalf("set VariableQuery must be present on the wire, got %s", body)
+	}
+}
+
 // TestResetPostMortemContentSendsZeroExpectedRevision guards a codegen
 // contract: expected_revision is a required field where 0 is a valid value
 // (first write to a never-saved document, per the spec's minimum: 0), so it
diff --git a/internal/cmd/gen/main.go b/internal/cmd/gen/main.go
index 1c0d96b..60f97f1 100644
--- a/internal/cmd/gen/main.go
+++ b/internal/cmd/gen/main.go
@@ -1170,8 +1170,9 @@ func pointerizableScalar(gt string) bool {
 // isStructSchema reports whether property schema s is emitted as a Go struct
 // (as opposed to a scalar, enum, alias, slice, or map). It resolves s the same
 // way emitModels' top-level classification switch does (following $ref and
-// allOf). Callers use this both to emit `,omitzero` for request values and to
-// pointer-wrap nullable or absence-preserving fields.
+// allOf, and flattening a named oneOf of object arms into one struct). Callers
+// use this both to emit `,omitzero` for request values and to pointer-wrap
+// nullable or absence-preserving fields.
 func (g *Gen) isStructSchema(s map[string]any) bool {
 	if s == nil {
 		return false
@@ -1180,7 +1181,12 @@ func (g *Gen) isStructSchema(s map[string]any) bool {
 		if g.skip[ref] {
 			return false
 		}
-		return g.isStructSchema(asMap(g.schemas[ref]))
+		// emitModels queues a named schema as g.resolveObject(name), which
+		// flattens a oneOf of object arms into a single struct. Classify that
+		// emitted shape, not the raw oneOf, or an optional field of such a type
+		// gets `,omitempty` — a no-op on a struct value — and an unset field
+		// goes on the wire as an object holding only its zero discriminator.
+		return g.isStructSchema(g.resolveObject(ref))
 	}
 	if len(asSlice(s["allOf"])) > 0 {
 		s = g.mergeAllOf(s)
diff --git a/internal/cmd/gen/main_test.go b/internal/cmd/gen/main_test.go
index fb85e86..1ba387f 100644
--- a/internal/cmd/gen/main_test.go
+++ b/internal/cmd/gen/main_test.go
@@ -351,6 +351,51 @@ func TestEmitStructPreserveAbsenceRequestObjectPointerWraps(t *testing.T) {
 	}
 }
 
+// TestEmitStructOptionalFlattenedOneOfRequestFieldOmitsZero covers an optional
+// request field whose $ref target is a oneOf of object arms. emitModels
+// flattens that oneOf into one struct, so the field is a bare struct value and
+// needs `,omitzero`: `,omitempty` never drops a struct, and the unset field
+// would reach the wire as an object holding only an empty discriminator.
+func TestEmitStructOptionalFlattenedOneOfRequestFieldOmitsZero(t *testing.T) {
+	g := newTestGen(map[string]any{
+		"PromQuery": map[string]any{
+			"type":     "object",
+			"required": []any{"kind"},
+			"properties": map[string]any{
+				"kind":   map[string]any{"type": "string"},
+				"metric": map[string]any{"type": "string"},
+			},
+		},
+		"LogsQuery": map[string]any{
+			"type":     "object",
+			"required": []any{"kind"},
+			"properties": map[string]any{
+				"kind":  map[string]any{"type": "string"},
+				"field": map[string]any{"type": "string"},
+			},
+		},
+		"VariableQuery": map[string]any{
+			"oneOf": []any{
+				map[string]any{"$ref": "#/components/schemas/PromQuery"},
+				map[string]any{"$ref": "#/components/schemas/LogsQuery"},
+			},
+		},
+	})
+	g.reqGoNames["Variable"] = true
+
+	schema := map[string]any{
+		"type": "object",
+		"properties": map[string]any{
+			"variable_query": map[string]any{"$ref": "#/components/schemas/VariableQuery"},
+		},
+	}
+
+	src := g.emitStruct("Variable", schema)
+	if !strings.Contains(src, "VariableQuery VariableQuery `json:\"variable_query,omitzero\"") {
+		t.Fatalf("optional flattened-oneOf request field must use omitzero; got:\n%s", src)
+	}
+}
+
 // TestOpClassificationPredicates pins the three-way split of non-standard
 // operations: ndjson streams and non-JSON request bodies are hand-written,
 // while bounded binary downloads generate ordinary raw methods.
diff --git a/models_gen.go b/models_gen.go
index 8c34cf6..3a672e7 100644
--- a/models_gen.go
+++ b/models_gen.go
@@ -3696,7 +3696,7 @@ type DashboardVariable struct {
 	// When the candidates are recomputed: `on_dashboard_load` = once when the dashboard loads; `on_time_range_change` = every time the time range changes.
 	Refresh       string                   `json:"refresh,omitempty" toon:"refresh,omitempty"`
 	Selection     DashboardSelectionConfig `json:"selection,omitzero" toon:"selection,omitempty"`
-	VariableQuery DashboardVariableQuery   `json:"variable_query,omitempty" toon:"variable_query,omitempty"`
+	VariableQuery DashboardVariableQuery   `json:"variable_query,omitzero" toon:"variable_query,omitempty"`
 }
 
 // DashboardVariableQuery is generated from the Flashduty OpenAPI schema.