diff --git a/src/cmd/go/script_test.go b/src/cmd/go/script_test.go
index 1f38be8..c353a9c 100644
--- a/src/cmd/go/script_test.go
+++ b/src/cmd/go/script_test.go
@@ -165,7 +165,7 @@
 		"GOCACHE=" + testGOCACHE,
 		"GODEBUG=" + os.Getenv("GODEBUG"),
 		"GOEXE=" + cfg.ExeSuffix,
-		"GOEXPSTRING=" + objabi.Expstring()[2:],
+		"GOEXPERIMENT=" + objabi.GOEXPERIMENT(),
 		"GOOS=" + runtime.GOOS,
 		"GOPATH=" + filepath.Join(ts.workdir, "gopath"),
 		"GOPROXY=" + proxyURL,
diff --git a/src/cmd/go/testdata/script/README b/src/cmd/go/testdata/script/README
index d658ceb..b4dcb1f 100644
--- a/src/cmd/go/testdata/script/README
+++ b/src/cmd/go/testdata/script/README
@@ -29,7 +29,7 @@
 	GOARCH=<target GOARCH>
 	GOCACHE=<actual GOCACHE being used outside the test>
 	GOEXE=<executable file suffix: .exe on Windows, empty on other systems>
-	GOEXPSTRING=<value of objabi.Expstring(), from GOEXPERIMENT when toolchain built>
+	GOEXPERIMENT=<value of objabi.GOEXPERIMENT>
 	GOOS=<target GOOS>
 	GOPATH=$WORK/gopath
 	GOPROXY=<local module proxy serving from cmd/go/testdata/mod>
diff --git a/src/cmd/go/testdata/script/build_tag_goexperiment.txt b/src/cmd/go/testdata/script/build_tag_goexperiment.txt
index 26ad029..dfda3d2 100644
--- a/src/cmd/go/testdata/script/build_tag_goexperiment.txt
+++ b/src/cmd/go/testdata/script/build_tag_goexperiment.txt
@@ -1,6 +1,6 @@
 # compile_ext will fail if the buildtags that are enabled (or not enabled) for the
 # framepointer and fieldtrack experiments are not consistent with the value of
-# GOEXPSTRING (which comes from objabi.Expstring()).
+# objabi.GOEXPERIMENT.
 
 [short] skip
 go run m
@@ -19,10 +19,8 @@
 }
 
 func hasExpEntry(s string) bool {
-	// script_test.go defines GOEXPSTRING to be the value of
-	// objabi.Expstring(), which gives the enabled experiments baked into the
-	// toolchain.
-	g := os.Getenv("GOEXPSTRING")
+	// script_test.go defines GOEXPERIMENT to be the enabled experiments.
+	g := os.Getenv("GOEXPERIMENT")
 	for _, f := range strings.Split(g, ",") {
 		if f == s {
 			return true
@@ -43,7 +41,7 @@
 
 func fp() {
 	if hasExpEntry("framepointer") {
-		fmt.Println("in !framepointer build, but objabi.Expstring() has 'framepointer'")
+		fmt.Println("in !framepointer build, but objabi.GOEXPERIMENT has 'framepointer'")
 		os.Exit(1)
 	}
 }
@@ -60,7 +58,7 @@
 
 func fp() {
 	if !hasExpEntry("framepointer") {
-		fmt.Println("in framepointer build, but objabi.Expstring() does not have 'framepointer', is", os.Getenv("GOEXPSTRING"))
+		fmt.Println("in framepointer build, but objabi.GOEXPERIMENT does not have 'framepointer', is", os.Getenv("GOEXPERIMENT"))
 		os.Exit(1)
 	}
 }
@@ -77,7 +75,7 @@
 
 func ft() {
 	if hasExpEntry("fieldtrack") {
-		fmt.Println("in !fieldtrack build, but objabi.Expstring() has 'fieldtrack'")
+		fmt.Println("in !fieldtrack build, but objabi.GOEXPERIMENT has 'fieldtrack'")
 		os.Exit(1)
 	}
 }
@@ -94,7 +92,7 @@
 
 func ft() {
 	if !hasExpEntry("fieldtrack") {
-		fmt.Println("in fieldtrack build, but objabi.Expstring() does not have 'fieldtrack', is", os.Getenv("GOEXPSTRING"))
+		fmt.Println("in fieldtrack build, but objabi.GOEXPERIMENT does not have 'fieldtrack', is", os.Getenv("GOEXPERIMENT"))
 		os.Exit(1)
 	}
 }
diff --git a/src/cmd/internal/objabi/exp.go b/src/cmd/internal/objabi/exp.go
index 21a70d5..eaa8620 100644
--- a/src/cmd/internal/objabi/exp.go
+++ b/src/cmd/internal/objabi/exp.go
@@ -20,8 +20,6 @@
 // was built with.)
 var Experiment goexperiment.Flags
 
-var defaultExpstring string // Set by package init
-
 // FramePointerEnabled enables the use of platform conventions for
 // saving frame pointers.
 //
@@ -32,13 +30,15 @@
 var FramePointerEnabled = GOARCH == "amd64" || GOARCH == "arm64"
 
 func init() {
-	// Capture "default" experiments.
-	defaultExpstring = Expstring()
+	// Start with the baseline configuration.
+	Experiment = goexperiment.BaselineFlags
 
-	goexperiment := envOr("GOEXPERIMENT", defaultGOEXPERIMENT)
+	// Pick up any changes to the baseline configuration from the
+	// GOEXPERIMENT environment. This can be set at make.bash time
+	// and overridden at build time.
+	env := envOr("GOEXPERIMENT", defaultGOEXPERIMENT)
 
-	// GOEXPERIMENT=none overrides all experiments enabled at dist time.
-	if goexperiment != "none" {
+	if env != "" {
 		// Create a map of known experiment names.
 		names := make(map[string]reflect.Value)
 		rv := reflect.ValueOf(&Experiment).Elem()
@@ -49,10 +49,16 @@
 		}
 
 		// Parse names.
-		for _, f := range strings.Split(goexperiment, ",") {
+		for _, f := range strings.Split(env, ",") {
 			if f == "" {
 				continue
 			}
+			if f == "none" {
+				// GOEXPERIMENT=none restores the baseline configuration.
+				// (This is useful for overriding make.bash-time settings.)
+				Experiment = goexperiment.BaselineFlags
+				continue
+			}
 			val := true
 			if strings.HasPrefix(f, "no") {
 				f, val = f[2:], false
@@ -93,40 +99,45 @@
 	}
 }
 
-// expList returns the list of enabled GOEXPERIMENTs names.
-func expList(flags *goexperiment.Flags) []string {
+// expList returns the list of lower-cased experiment names for
+// experiments that differ from base. base may be nil to indicate no
+// experiments.
+func expList(exp, base *goexperiment.Flags) []string {
 	var list []string
-	rv := reflect.ValueOf(&Experiment).Elem()
+	rv := reflect.ValueOf(exp).Elem()
+	var rBase reflect.Value
+	if base != nil {
+		rBase = reflect.ValueOf(base).Elem()
+	}
 	rt := rv.Type()
 	for i := 0; i < rt.NumField(); i++ {
+		name := strings.ToLower(rt.Field(i).Name)
 		val := rv.Field(i).Bool()
-		if val {
-			field := rt.Field(i)
-			list = append(list, strings.ToLower(field.Name))
+		baseVal := false
+		if base != nil {
+			baseVal = rBase.Field(i).Bool()
+		}
+		if val != baseVal {
+			if val {
+				list = append(list, name)
+			} else {
+				list = append(list, "no"+name)
+			}
 		}
 	}
 	return list
 }
 
-// Expstring returns the GOEXPERIMENT string that should appear in Go
-// version signatures. This always starts with "X:".
-func Expstring() string {
-	list := expList(&Experiment)
-	if len(list) == 0 {
-		return "X:none"
-	}
-	return "X:" + strings.Join(list, ",")
-}
-
-// GOEXPERIMENT returns a comma-separated list of enabled experiments.
-// This is derived from the GOEXPERIMENT environment variable if set,
-// or the value of GOEXPERIMENT when make.bash was run if not.
+// GOEXPERIMENT is a comma-separated list of enabled or disabled
+// experiments that differ from the baseline experiment configuration.
+// GOEXPERIMENT is exactly what a user would set on the command line
+// to get the set of enabled experiments.
 func GOEXPERIMENT() string {
-	return strings.Join(expList(&Experiment), ",")
+	return strings.Join(expList(&Experiment, &goexperiment.BaselineFlags), ",")
 }
 
 // EnabledExperiments returns a list of enabled experiments, as
 // lower-cased experiment names.
 func EnabledExperiments() []string {
-	return expList(&Experiment)
+	return expList(&Experiment, nil)
 }
diff --git a/src/cmd/internal/objabi/flag.go b/src/cmd/internal/objabi/flag.go
index 25b0185..6a8a691 100644
--- a/src/cmd/internal/objabi/flag.go
+++ b/src/cmd/internal/objabi/flag.go
@@ -91,16 +91,12 @@
 	name = name[strings.LastIndex(name, `\`)+1:]
 	name = strings.TrimSuffix(name, ".exe")
 
-	// If there's an active experiment, include that,
-	// to distinguish go1.10.2 with an experiment
-	// from go1.10.2 without an experiment.
-	p := Expstring()
-	if p == defaultExpstring {
-		p = ""
-	}
-	sep := ""
-	if p != "" {
-		sep = " "
+	p := ""
+
+	// If the enabled experiments differ from the defaults,
+	// include that difference.
+	if goexperiment := GOEXPERIMENT(); goexperiment != "" {
+		p = " X:" + goexperiment
 	}
 
 	// The go command invokes -V=full to get a unique identifier
@@ -114,7 +110,7 @@
 		}
 	}
 
-	fmt.Printf("%s version %s%s%s\n", name, Version, sep, p)
+	fmt.Printf("%s version %s%s\n", name, Version, p)
 	os.Exit(0)
 	return nil
 }
diff --git a/src/cmd/internal/objabi/util.go b/src/cmd/internal/objabi/util.go
index c2c05bd..5a7a74c 100644
--- a/src/cmd/internal/objabi/util.go
+++ b/src/cmd/internal/objabi/util.go
@@ -128,5 +128,5 @@
 // or link object files that are incompatible with each other. This
 // string always starts with "go object ".
 func HeaderString() string {
-	return fmt.Sprintf("go object %s %s %s %s\n", GOOS, GOARCH, Version, Expstring())
+	return fmt.Sprintf("go object %s %s %s X:%s\n", GOOS, GOARCH, Version, strings.Join(EnabledExperiments(), ","))
 }
diff --git a/src/internal/goexperiment/flags.go b/src/internal/goexperiment/flags.go
index c5e3d2c..1c513d5 100644
--- a/src/internal/goexperiment/flags.go
+++ b/src/internal/goexperiment/flags.go
@@ -75,3 +75,8 @@
 	// register arguments to defer/go).
 	RegabiArgs bool
 }
+
+// BaselineFlags specifies the experiment flags that are enabled by
+// default in the current toolchain. This is, in effect, the "control"
+// configuration and any variation from this is an experiment.
+var BaselineFlags = Flags{}