diff --git a/src/cmd/go/internal/modfetch/fetch.go b/src/cmd/go/internal/modfetch/fetch.go
index 9e8d3639a9e..0a84aecd426 100644
--- a/src/cmd/go/internal/modfetch/fetch.go
+++ b/src/cmd/go/internal/modfetch/fetch.go
@@ -35,13 +35,6 @@ import (
 	modzip "golang.org/x/mod/zip"
 )
 
-// The downloadCache is used to cache the operation of downloading a module to disk
-// (if it's not already downloaded) and getting the directory it was downloaded to.
-// It is important that downloadCache must not be accessed by any of the exported
-// functions of this package after they return, because it can be modified by the
-// non-thread-safe SetState function
-var downloadCache = new(par.ErrCache[module.Version, string]) // version → directory;
-
 var ErrToolchain = errors.New("internal error: invalid operation on toolchain module")
 
 // Download downloads the specific module version to the
@@ -56,7 +49,7 @@ func Download(ctx context.Context, mod module.Version) (dir string, err error) {
 	}
 
 	// The par.Cache here avoids duplicate work.
-	return downloadCache.Do(mod, func() (string, error) {
+	return ModuleFetchState.downloadCache.Do(mod, func() (string, error) {
 		dir, err := download(ctx, mod)
 		if err != nil {
 			return "", err
@@ -85,7 +78,7 @@ func Unzip(ctx context.Context, mod module.Version, zipfile string) (dir string,
 		base.Fatal(err)
 	}
 
-	return downloadCache.Do(mod, func() (string, error) {
+	return ModuleFetchState.downloadCache.Do(mod, func() (string, error) {
 		ctx, span := trace.StartSpan(ctx, "modfetch.Unzip "+mod.String())
 		defer span.Done()
 
@@ -444,9 +437,6 @@ func RemoveAll(dir string) error {
 // accessed by any of the exported functions of this package after they return, because
 // they can be modified by the non-thread-safe SetState function.
 
-var GoSumFile string             // path to go.sum; set by package modload
-var WorkspaceGoSumFiles []string // path to module go.sums in workspace; set by package modload
-
 type modSum struct {
 	mod module.Version
 	sum string
@@ -471,11 +461,31 @@ type modSumStatus struct {
 
 // State holds a snapshot of the global state of the modfetch package.
 type State struct {
-	goSumFile           string
-	workspaceGoSumFiles []string
-	lookupCache         *par.Cache[lookupCacheKey, Repo]
-	downloadCache       *par.ErrCache[module.Version, string]
-	sumState            sumState
+	// path to go.sum; set by package modload
+	GoSumFile string
+	// path to module go.sums in workspace; set by package modload
+	WorkspaceGoSumFiles []string
+	// The Lookup cache is used cache the work done by Lookup.
+	// It is important that the global functions of this package that access it do not
+	// do so after they return.
+	lookupCache *par.Cache[lookupCacheKey, Repo]
+	// The downloadCache is used to cache the operation of downloading a module to disk
+	// (if it's not already downloaded) and getting the directory it was downloaded to.
+	// It is important that downloadCache must not be accessed by any of the exported
+	// functions of this package after they return, because it can be modified by the
+	// non-thread-safe SetState function.
+	downloadCache *par.ErrCache[module.Version, string] // version → directory;
+
+	sumState sumState
+}
+
+var ModuleFetchState *State = NewState()
+
+func NewState() *State {
+	s := new(State)
+	s.lookupCache = new(par.Cache[lookupCacheKey, Repo])
+	s.downloadCache = new(par.ErrCache[module.Version, string])
+	return s
 }
 
 // Reset resets globals in the modfetch package, so previous loads don't affect
@@ -500,20 +510,20 @@ func SetState(newState State) (oldState State) {
 	defer goSum.mu.Unlock()
 
 	oldState = State{
-		goSumFile:           GoSumFile,
-		workspaceGoSumFiles: WorkspaceGoSumFiles,
-		lookupCache:         lookupCache,
-		downloadCache:       downloadCache,
+		GoSumFile:           ModuleFetchState.GoSumFile,
+		WorkspaceGoSumFiles: ModuleFetchState.WorkspaceGoSumFiles,
+		lookupCache:         ModuleFetchState.lookupCache,
+		downloadCache:       ModuleFetchState.downloadCache,
 		sumState:            goSum.sumState,
 	}
 
-	GoSumFile = newState.goSumFile
-	WorkspaceGoSumFiles = newState.workspaceGoSumFiles
+	ModuleFetchState.GoSumFile = newState.GoSumFile
+	ModuleFetchState.WorkspaceGoSumFiles = newState.WorkspaceGoSumFiles
 	// Uses of lookupCache and downloadCache both can call checkModSum,
 	// which in turn sets the used bit on goSum.status for modules.
 	// Set (or reset) them so used can be computed properly.
-	lookupCache = newState.lookupCache
-	downloadCache = newState.downloadCache
+	ModuleFetchState.lookupCache = newState.lookupCache
+	ModuleFetchState.downloadCache = newState.downloadCache
 	// Set, or reset all fields on goSum. If being reset to empty, it will be initialized later.
 	goSum.sumState = newState.sumState
 
@@ -525,7 +535,7 @@ func SetState(newState State) (oldState State) {
 // use of go.sum is now enabled.
 // The goSum lock must be held.
 func initGoSum() (bool, error) {
-	if GoSumFile == "" {
+	if ModuleFetchState.GoSumFile == "" {
 		return false, nil
 	}
 	if goSum.m != nil {
@@ -536,7 +546,7 @@ func initGoSum() (bool, error) {
 	goSum.status = make(map[modSum]modSumStatus)
 	goSum.w = make(map[string]map[module.Version][]string)
 
-	for _, f := range WorkspaceGoSumFiles {
+	for _, f := range ModuleFetchState.WorkspaceGoSumFiles {
 		goSum.w[f] = make(map[module.Version][]string)
 		_, err := readGoSumFile(goSum.w[f], f)
 		if err != nil {
@@ -544,7 +554,7 @@ func initGoSum() (bool, error) {
 		}
 	}
 
-	enabled, err := readGoSumFile(goSum.m, GoSumFile)
+	enabled, err := readGoSumFile(goSum.m, ModuleFetchState.GoSumFile)
 	goSum.enabled = enabled
 	return enabled, err
 }
@@ -790,7 +800,7 @@ func checkModSum(mod module.Version, h string) error {
 // goSum.mu must be locked.
 func haveModSumLocked(mod module.Version, h string) bool {
 	sumFileName := "go.sum"
-	if strings.HasSuffix(GoSumFile, "go.work.sum") {
+	if strings.HasSuffix(ModuleFetchState.GoSumFile, "go.work.sum") {
 		sumFileName = "go.work.sum"
 	}
 	for _, vh := range goSum.m[mod] {
@@ -934,7 +944,7 @@ Outer:
 	if readonly {
 		return ErrGoSumDirty
 	}
-	if fsys.Replaced(GoSumFile) {
+	if fsys.Replaced(ModuleFetchState.GoSumFile) {
 		base.Fatalf("go: updates to go.sum needed, but go.sum is part of the overlay specified with -overlay")
 	}
 
@@ -944,7 +954,7 @@ Outer:
 		defer unlock()
 	}
 
-	err := lockedfile.Transform(GoSumFile, func(data []byte) ([]byte, error) {
+	err := lockedfile.Transform(ModuleFetchState.GoSumFile, func(data []byte) ([]byte, error) {
 		tidyGoSum := tidyGoSum(data, keep)
 		return tidyGoSum, nil
 	})
@@ -963,7 +973,7 @@ Outer:
 func TidyGoSum(keep map[module.Version]bool) (before, after []byte) {
 	goSum.mu.Lock()
 	defer goSum.mu.Unlock()
-	before, err := lockedfile.Read(GoSumFile)
+	before, err := lockedfile.Read(ModuleFetchState.GoSumFile)
 	if err != nil && !errors.Is(err, fs.ErrNotExist) {
 		base.Fatalf("reading go.sum: %v", err)
 	}
@@ -980,7 +990,7 @@ func tidyGoSum(data []byte, keep map[module.Version]bool) []byte {
 		// truncated the file to remove erroneous hashes, and we shouldn't restore
 		// them without good reason.
 		goSum.m = make(map[module.Version][]string, len(goSum.m))
-		readGoSum(goSum.m, GoSumFile, data)
+		readGoSum(goSum.m, ModuleFetchState.GoSumFile, data)
 		for ms, st := range goSum.status {
 			if st.used && !sumInWorkspaceModulesLocked(ms.mod) {
 				addModSumLocked(ms.mod, ms.sum)
diff --git a/src/cmd/go/internal/modfetch/repo.go b/src/cmd/go/internal/modfetch/repo.go
index 5d4d679e832..bb5dfc4655d 100644
--- a/src/cmd/go/internal/modfetch/repo.go
+++ b/src/cmd/go/internal/modfetch/repo.go
@@ -184,11 +184,6 @@ type RevInfo struct {
 // To avoid version control access except when absolutely necessary,
 // Lookup does not attempt to connect to the repository itself.
 
-// The Lookup cache is used cache the work done by Lookup.
-// It is important that the global functions of this package that access it do not
-// do so after they return.
-var lookupCache = new(par.Cache[lookupCacheKey, Repo])
-
 type lookupCacheKey struct {
 	proxy, path string
 }
@@ -210,7 +205,7 @@ func Lookup(ctx context.Context, proxy, path string) Repo {
 		defer logCall("Lookup(%q, %q)", proxy, path)()
 	}
 
-	return lookupCache.Do(lookupCacheKey{proxy, path}, func() Repo {
+	return ModuleFetchState.lookupCache.Do(lookupCacheKey{proxy, path}, func() Repo {
 		return newCachingRepo(ctx, path, func(ctx context.Context) (Repo, error) {
 			r, err := lookup(ctx, proxy, path)
 			if err == nil && traceRepo {
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 3d6f9a4a65a..bbdd0e95b5c 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -928,9 +928,9 @@ func loadModFile(loaderstate *State, ctx context.Context, opts *PackageOpts) (*R
 		}
 		for _, modRoot := range loaderstate.modRoots {
 			sumFile := strings.TrimSuffix(modFilePath(modRoot), ".mod") + ".sum"
-			modfetch.WorkspaceGoSumFiles = append(modfetch.WorkspaceGoSumFiles, sumFile)
+			modfetch.ModuleFetchState.WorkspaceGoSumFiles = append(modfetch.ModuleFetchState.WorkspaceGoSumFiles, sumFile)
 		}
-		modfetch.GoSumFile = loaderstate.workFilePath + ".sum"
+		modfetch.ModuleFetchState.GoSumFile = loaderstate.workFilePath + ".sum"
 	} else if len(loaderstate.modRoots) == 0 {
 		// We're in module mode, but not inside a module.
 		//
@@ -950,7 +950,7 @@ func loadModFile(loaderstate *State, ctx context.Context, opts *PackageOpts) (*R
 		//
 		// See golang.org/issue/32027.
 	} else {
-		modfetch.GoSumFile = strings.TrimSuffix(modFilePath(loaderstate.modRoots[0]), ".mod") + ".sum"
+		modfetch.ModuleFetchState.GoSumFile = strings.TrimSuffix(modFilePath(loaderstate.modRoots[0]), ".mod") + ".sum"
 	}
 	if len(loaderstate.modRoots) == 0 {
 		// TODO(#49228): Instead of creating a fake module with an empty modroot,