diff --git a/vector/type.go b/vector/type.go
index 997ce8fe2..acba379e0 100644
--- a/vector/type.go
+++ b/vector/type.go
@@ -59,6 +59,10 @@ func (t *TypeValue) Value(slot uint32) super.Type {
 	return t.Types()[slot]
 }
 
+func (t *TypeValue) Sctx() *super.Context {
+	return t.sctx
+}
+
 func (t *TypeValue) TypeIDs() (*super.TypeDefs, []uint32) {
 	t.mu.Lock()
 	defer t.mu.Unlock()
diff --git a/vector/vbuild/fusion.go b/vector/vbuild/fusion.go
index 0108e00bd..ff8faa2da 100644
--- a/vector/vbuild/fusion.go
+++ b/vector/vbuild/fusion.go
@@ -8,7 +8,7 @@ import (
 type fusionBuilder struct {
 	typ      *super.TypeFusion
 	vals     Builder
-	subtypes []super.Type
+	subtypes fusionTypeBuilder
 }
 
 func newFusionBuilder(typ *super.TypeFusion) *fusionBuilder {
@@ -25,17 +25,107 @@ func (f *fusionBuilder) Write(vec vector.Any) {
 	if view, ok := vec.(*vector.View); ok {
 		fusion := view.Any.(*vector.Fusion)
 		f.vals.Write(vector.Pick(fusion.Values, view.Index))
-		types := fusion.Subtypes.Types()
-		for _, idx := range view.Index {
-			f.subtypes = append(f.subtypes, types[idx])
-		}
+		f.subtypes.Write(vector.Pick(fusion.Subtypes, view.Index))
 		return
 	}
 	fusion := vec.(*vector.Fusion)
 	f.vals.Write(fusion.Values)
-	f.subtypes = append(f.subtypes, fusion.Subtypes.Types()...)
+	f.subtypes.Write(fusion.Subtypes)
 }
 
 func (f *fusionBuilder) Build() vector.Any {
-	return vector.NewFusion(f.typ, f.vals.Build(), f.subtypes)
+	return &vector.Fusion{
+		Typ:      f.typ,
+		Values:   f.vals.Build(),
+		Subtypes: f.subtypes.Build().(*vector.TypeValue),
+	}
+}
+
+type fusionTypeBuilder struct {
+	sctx  *super.Context
+	defs  *super.TypeDefs
+	ids   []uint32
+	types *genericFlatWriter[super.Type]
+}
+
+func (t *fusionTypeBuilder) Write(vec vector.Any) {
+	if t.sctx != nil || (t.types == nil && typeSctx(vec) != nil) {
+		if t.sctx == nil {
+			t.sctx = typeSctx(vec)
+			t.defs = super.NewTypeDefs()
+		}
+		t.writeTypeIDs(vec)
+		return
+	}
+	if t.types == nil {
+		t.types = &genericFlatWriter[super.Type]{
+			valuesOf: func(vec vector.Any) []super.Type { return vec.(*vector.TypeValue).Types() },
+			build: func(vals []super.Type) vector.Any {
+				return vector.NewTypeValue(vals)
+			},
+		}
+	}
+	t.types.Write(vec)
+}
+
+func (t *fusionTypeBuilder) writeTypeIDs(vec vector.Any) {
+	switch vec := vec.(type) {
+	case *vector.Const:
+		types := vec.Any.(*vector.TypeValue)
+		defs, ids := types.TypeIDs()
+		id := super.NewTypeDefsMerger(t.defs, defs).LookupID(ids[0])
+		for range vec.Len() {
+			t.ids = append(t.ids, id)
+		}
+	case *vector.Dict:
+		index := vec.Index
+		types := vec.Any.(*vector.TypeValue)
+		defs, ids := types.TypeIDs()
+		merger := super.NewTypeDefsMerger(t.defs, defs)
+		for _, slot := range index {
+			t.ids = append(t.ids, merger.LookupID(ids[slot]))
+		}
+	case *vector.View:
+		index := vec.Index
+		types := vec.Any.(*vector.TypeValue)
+		defs, ids := types.TypeIDs()
+		merger := super.NewTypeDefsMerger(t.defs, defs)
+		for _, slot := range index {
+			t.ids = append(t.ids, merger.LookupID(ids[slot]))
+		}
+	case *vector.TypeValue:
+		defs, ids := vec.TypeIDs()
+		merger := super.NewTypeDefsMerger(t.defs, defs)
+		for _, id := range ids {
+			t.ids = append(t.ids, merger.LookupID(id))
+		}
+	default:
+		panic(vec)
+	}
+}
+
+func (t *fusionTypeBuilder) Build() vector.Any {
+	if t.types != nil {
+		return t.types.Build()
+	}
+	return vector.NewTypeValueWithLoader(t.sctx, t)
+}
+
+func (t *fusionTypeBuilder) Load() (*super.TypeDefs, []uint32) {
+	return t.defs, t.ids
+}
+
+func typeSctx(vec vector.Any) *super.Context {
+	switch vec := vec.(type) {
+	case *vector.Const:
+		return typeSctx(vec.Any)
+	case *vector.Dict:
+		return typeSctx(vec.Any)
+	case *vector.View:
+		return typeSctx(vec.Any)
+	case *vector.TypeValue:
+		return vec.Sctx()
+	default:
+		panic(vec)
+	}
 }