diff --git a/src/cmd/compile/internal/importer/iimport.go b/src/cmd/compile/internal/importer/iimport.go
index cbc7853..d04ef5c 100644
--- a/src/cmd/compile/internal/importer/iimport.go
+++ b/src/cmd/compile/internal/importer/iimport.go
@@ -43,12 +43,12 @@
 
 // Keep this in sync with constants in iexport.go.
 const (
-	iexportVersionGo1_11 = 0
-	iexportVersionPosCol = 1
-	// TODO: before release, change this back to 2.
-	iexportVersionGenerics = iexportVersionPosCol
+	iexportVersionGo1_11   = 0
+	iexportVersionPosCol   = 1
+	iexportVersionGenerics = 1 // probably change to 2 before release
+	iexportVersionGo1_18   = 2
 
-	iexportVersionCurrent = iexportVersionGenerics
+	iexportVersionCurrent = 2
 )
 
 type ident struct {
@@ -99,13 +99,9 @@
 
 	version = int64(r.uint64())
 	switch version {
-	case /* iexportVersionGenerics, */ iexportVersionPosCol, iexportVersionGo1_11:
+	case iexportVersionGo1_18, iexportVersionPosCol, iexportVersionGo1_11:
 	default:
-		if version > iexportVersionGenerics {
-			errorf("unstable iexport format version %d, just rebuild compiler and std library", version)
-		} else {
-			errorf("unknown iexport format version %d", version)
-		}
+		errorf("unknown iexport format version %d", version)
 	}
 
 	sLen := int64(r.uint64())
@@ -374,7 +370,19 @@
 		id := ident{r.currPkg.Name(), name}
 		r.p.tparamIndex[id] = t
 
-		t.SetConstraint(r.typ())
+		var implicit bool
+		if r.p.exportVersion >= iexportVersionGo1_18 {
+			implicit = r.bool()
+		}
+		constraint := r.typ()
+		if implicit {
+			iface, _ := constraint.(*types2.Interface)
+			if iface == nil {
+				errorf("non-interface constraint marked implicit")
+			}
+			iface.MarkImplicit()
+		}
+		t.SetConstraint(constraint)
 
 	case 'V':
 		typ := r.typ()
@@ -392,6 +400,10 @@
 
 func (r *importReader) value() (typ types2.Type, val constant.Value) {
 	typ = r.typ()
+	if r.p.exportVersion >= iexportVersionGo1_18 {
+		// TODO: add support for using the kind
+		_ = constant.Kind(r.int64())
+	}
 
 	switch b := typ.Underlying().(*types2.Basic); b.Info() & types2.IsConstType {
 	case types2.IsBoolean:
diff --git a/src/cmd/compile/internal/typecheck/iexport.go b/src/cmd/compile/internal/typecheck/iexport.go
index 46865ba..6057000 100644
--- a/src/cmd/compile/internal/typecheck/iexport.go
+++ b/src/cmd/compile/internal/typecheck/iexport.go
@@ -254,15 +254,16 @@
 // Current indexed export format version. Increase with each format change.
 // 0: Go1.11 encoding
 // 1: added column details to Pos
-// 2: added information for generic function/types (currently unstable)
+// 2: added information for generic function/types.  The export of non-generic
+// functions/types remains largely backward-compatible.  Breaking changes include:
+//    - a 'kind' byte is added to constant values
 const (
-	iexportVersionGo1_11 = 0
-	iexportVersionPosCol = 1
-	// TODO: before release, change this back to 2.  Kept at previous version
-	// for now (for testing).
-	iexportVersionGenerics = iexportVersionPosCol
+	iexportVersionGo1_11   = 0
+	iexportVersionPosCol   = 1
+	iexportVersionGenerics = 1 // probably change to 2 before release
+	iexportVersionGo1_18   = 2
 
-	iexportVersionCurrent = iexportVersionGenerics
+	iexportVersionCurrent = 2
 )
 
 // predeclReserved is the number of type offsets reserved for types
@@ -561,6 +562,10 @@
 			// A typeparam has a name, and has a type bound rather
 			// than an underlying type.
 			w.pos(n.Pos())
+			if iexportVersionCurrent >= iexportVersionGo1_18 {
+				implicit := n.Type().Bound().IsImplicit()
+				w.bool(implicit)
+			}
 			w.typ(n.Type().Bound())
 			break
 		}
@@ -1137,17 +1142,24 @@
 
 func (w *exportWriter) value(typ *types.Type, v constant.Value) {
 	w.typ(typ)
+
+	if iexportVersionCurrent >= iexportVersionGo1_18 {
+		w.int64(int64(v.Kind()))
+	}
+
 	var kind constant.Kind
 	var valType *types.Type
 
 	if typ.IsTypeParam() {
-		// A constant will have a TYPEPARAM type if it appears in a place
-		// where it must match that typeparam type (e.g. in a binary
-		// operation with a variable of that typeparam type). If so, then
-		// we must write out its actual constant kind as well, so its
-		// constant val can be read in properly during import.
 		kind = v.Kind()
-		w.int64(int64(kind))
+		if iexportVersionCurrent < iexportVersionGo1_18 {
+			// A constant will have a TYPEPARAM type if it appears in a place
+			// where it must match that typeparam type (e.g. in a binary
+			// operation with a variable of that typeparam type). If so, then
+			// we must write out its actual constant kind as well, so its
+			// constant val can be read in properly during import.
+			w.int64(int64(kind))
+		}
 
 		switch kind {
 		case constant.Int:
diff --git a/src/cmd/compile/internal/typecheck/iimport.go b/src/cmd/compile/internal/typecheck/iimport.go
index fcfadc1..7c6c23e 100644
--- a/src/cmd/compile/internal/typecheck/iimport.go
+++ b/src/cmd/compile/internal/typecheck/iimport.go
@@ -118,13 +118,9 @@
 
 	version := ird.uint64()
 	switch version {
-	case /* iexportVersionGenerics, */ iexportVersionPosCol, iexportVersionGo1_11:
+	case iexportVersionGo1_18, iexportVersionPosCol, iexportVersionGo1_11:
 	default:
-		if version > iexportVersionGenerics {
-			base.Errorf("import %q: unstable export format version %d, just recompile", pkg.Path, version)
-		} else {
-			base.Errorf("import %q: unknown export format version %d", pkg.Path, version)
-		}
+		base.Errorf("import %q: unknown export format version %d", pkg.Path, version)
 		base.ErrorExit()
 	}
 
@@ -408,8 +404,15 @@
 		sym.Def = nname
 		nname.SetType(t)
 		t.SetNod(nname)
-
-		t.SetBound(r.typ())
+		implicit := false
+		if r.p.exportVersion >= iexportVersionGo1_18 {
+			implicit = r.bool()
+		}
+		bound := r.typ()
+		if implicit {
+			bound.MarkImplicit()
+		}
+		t.SetBound(bound)
 		return nname
 
 	case 'V':
@@ -429,10 +432,17 @@
 	var kind constant.Kind
 	var valType *types.Type
 
-	if typ.IsTypeParam() {
-		// If a constant had a typeparam type, then we wrote out its
-		// actual constant kind as well.
+	if r.p.exportVersion >= iexportVersionGo1_18 {
+		// TODO: add support for using the kind in the non-typeparam case.
 		kind = constant.Kind(r.int64())
+	}
+
+	if typ.IsTypeParam() {
+		if r.p.exportVersion < iexportVersionGo1_18 {
+			// If a constant had a typeparam type, then we wrote out its
+			// actual constant kind as well.
+			kind = constant.Kind(r.int64())
+		}
 		switch kind {
 		case constant.Int:
 			valType = types.Types[types.TINT64]
diff --git a/src/cmd/compile/internal/typecheck/subr.go b/src/cmd/compile/internal/typecheck/subr.go
index 9ebd8f1..96e120f 100644
--- a/src/cmd/compile/internal/typecheck/subr.go
+++ b/src/cmd/compile/internal/typecheck/subr.go
@@ -1390,7 +1390,7 @@
 		}
 	}
 	if newfields != nil {
-		return types.NewInterface(t.Pkg(), newfields, false)
+		return types.NewInterface(t.Pkg(), newfields, t.IsImplicit())
 	}
 	return t
 }
diff --git a/src/cmd/compile/internal/types/type.go b/src/cmd/compile/internal/types/type.go
index ec17fe8..c3efbc9 100644
--- a/src/cmd/compile/internal/types/type.go
+++ b/src/cmd/compile/internal/types/type.go
@@ -1884,6 +1884,12 @@
 	return t.extra.(*Interface).implicit
 }
 
+// MarkImplicit marks the interface as implicit.
+func (t *Type) MarkImplicit() {
+	t.wantEtype(TINTER)
+	t.extra.(*Interface).implicit = true
+}
+
 // NewUnion returns a new union with the specified set of terms (types). If
 // tildes[i] is true, then terms[i] represents ~T, rather than just T.
 func NewUnion(terms []*Type, tildes []bool) *Type {
diff --git a/src/go/internal/gcimporter/iimport.go b/src/go/internal/gcimporter/iimport.go
index 0771fa3..49ea643 100644
--- a/src/go/internal/gcimporter/iimport.go
+++ b/src/go/internal/gcimporter/iimport.go
@@ -44,12 +44,12 @@
 
 // Keep this in sync with constants in iexport.go.
 const (
-	iexportVersionGo1_11 = 0
-	iexportVersionPosCol = 1
-	// TODO: before release, change this back to 2.
-	iexportVersionGenerics = iexportVersionPosCol
+	iexportVersionGo1_11   = 0
+	iexportVersionPosCol   = 1
+	iexportVersionGenerics = 1 // probably change to 2 before release
+	iexportVersionGo1_18   = 2
 
-	iexportVersionCurrent = iexportVersionGenerics
+	iexportVersionCurrent = 2
 )
 
 type ident struct {
@@ -98,13 +98,9 @@
 
 	version = int64(r.uint64())
 	switch version {
-	case /* iexportVersionGenerics, */ iexportVersionPosCol, iexportVersionGo1_11:
+	case iexportVersionGo1_18, iexportVersionPosCol, iexportVersionGo1_11:
 	default:
-		if version > iexportVersionGenerics {
-			errorf("unstable iexport format version %d, just rebuild compiler and std library", version)
-		} else {
-			errorf("unknown iexport format version %d", version)
-		}
+		errorf("unknown iexport format version %d", version)
 	}
 
 	sLen := int64(r.uint64())
@@ -367,7 +363,19 @@
 		id := ident{r.currPkg.Name(), name}
 		r.p.tparamIndex[id] = t
 
-		t.SetConstraint(r.typ())
+		var implicit bool
+		if r.p.exportVersion >= iexportVersionGo1_18 {
+			implicit = r.bool()
+		}
+		constraint := r.typ()
+		if implicit {
+			iface, _ := constraint.(*types.Interface)
+			if iface == nil {
+				errorf("non-interface constraint marked implicit")
+			}
+			iface.MarkImplicit()
+		}
+		t.SetConstraint(constraint)
 
 	case 'V':
 		typ := r.typ()
@@ -385,6 +393,10 @@
 
 func (r *importReader) value() (typ types.Type, val constant.Value) {
 	typ = r.typ()
+	if r.p.exportVersion >= iexportVersionGo1_18 {
+		// TODO: add support for using the kind
+		_ = constant.Kind(r.int64())
+	}
 
 	switch b := typ.Underlying().(*types.Basic); b.Info() & types.IsConstType {
 	case types.IsBoolean: