diff --git a/go.env b/go.env
index 9bab8ffd73d..6ff2b921d46 100644
--- a/go.env
+++ b/go.env
@@ -8,5 +8,5 @@ GOPROXY=https://proxy.golang.org,direct
 GOSUMDB=sum.golang.org
 
 # Automatically download newer toolchains as directed by go.mod files.
-# See https://go.dev/s/gotoolchain for details.
+# See https://go.dev/doc/toolchain for details.
 GOTOOLCHAIN=auto
diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 7ef763d6be6..05ee094ea74 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -671,6 +671,14 @@
 //
 //	go get example.com/mod@none
 //
+// To upgrade the minimum required Go version to the latest released Go version:
+//
+//	go get go@latest
+//
+// To upgrade the Go toolchain to the latest patch release of the current Go toolchain:
+//
+//	go get toolchain@patch
+//
 // See https://golang.org/ref/mod#go-get for details.
 //
 // In earlier versions of Go, 'go get' was used to build and install packages.
@@ -705,6 +713,9 @@
 //
 // For more about modules, see https://golang.org/ref/mod.
 //
+// For more about using 'go get' to update the minimum Go version and
+// suggested Go toolchain, see https://go.dev/doc/toolchain.
+//
 // For more about specifying packages, see 'go help packages'.
 //
 // This text describes the behavior of get using modules to manage source
diff --git a/src/cmd/go/internal/gover/mod.go b/src/cmd/go/internal/gover/mod.go
index 18e5635cdf7..d3cc17068de 100644
--- a/src/cmd/go/internal/gover/mod.go
+++ b/src/cmd/go/internal/gover/mod.go
@@ -84,6 +84,9 @@ func ModIsValid(path, vers string) bool {
 // The caller is assumed to have checked that ModIsValid(path, vers) is true.
 func ModIsPrefix(path, vers string) bool {
 	if IsToolchain(path) {
+		if path == "toolchain" {
+			return IsLang(FromToolchain(vers))
+		}
 		return IsLang(vers)
 	}
 	// Semver
@@ -110,3 +113,15 @@ func ModIsPrerelease(path, vers string) bool {
 	}
 	return semver.Prerelease(vers) != ""
 }
+
+// ModMajorMinor returns the "major.minor" truncation of the version v,
+// for use as a prefix in "@patch" queries.
+func ModMajorMinor(path, vers string) string {
+	if IsToolchain(path) {
+		if path == "toolchain" {
+			return "go" + Lang(FromToolchain(vers))
+		}
+		return Lang(vers)
+	}
+	return semver.MajorMinor(vers)
+}
diff --git a/src/cmd/go/internal/gover/toolchain.go b/src/cmd/go/internal/gover/toolchain.go
index bd0d52ad840..efa2de46a51 100644
--- a/src/cmd/go/internal/gover/toolchain.go
+++ b/src/cmd/go/internal/gover/toolchain.go
@@ -14,20 +14,17 @@ import (
 
 // FromToolchain returns the Go version for the named toolchain,
 // derived from the name itself (not by running the toolchain).
-// A toolchain is named "goVERSION" or "anything-goVERSION".
+// A toolchain is named "goVERSION".
 // A suffix after the VERSION introduced by a +, -, space, or tab is removed.
 // Examples:
 //
 //	FromToolchain("go1.2.3") == "1.2.3"
 //	FromToolchain("go1.2.3-bigcorp") == "1.2.3"
-//	FromToolchain("gccgo-go1.23rc4") == "1.23rc4"
 //	FromToolchain("invalid") == ""
 func FromToolchain(name string) string {
 	var v string
 	if strings.HasPrefix(name, "go") {
 		v = name[2:]
-	} else if i := strings.Index(name, "-go"); i >= 0 {
-		v = name[i+3:]
 	} else {
 		return ""
 	}
diff --git a/src/cmd/go/internal/gover/toolchain_test.go b/src/cmd/go/internal/gover/toolchain_test.go
index 7d05f1d0c39..d1c22fbc37c 100644
--- a/src/cmd/go/internal/gover/toolchain_test.go
+++ b/src/cmd/go/internal/gover/toolchain_test.go
@@ -14,6 +14,6 @@ var fromToolchainTests = []testCase1[string, string]{
 	{"go1.2.3+bigcorp", ""},
 	{"go1.2.3-bigcorp", "1.2.3"},
 	{"go1.2.3-bigcorp more text", "1.2.3"},
-	{"gccgo-go1.23rc4", "1.23rc4"},
-	{"gccgo-go1.23rc4-bigdwarf", "1.23rc4"},
+	{"gccgo-go1.23rc4", ""},
+	{"gccgo-go1.23rc4-bigdwarf", ""},
 }
diff --git a/src/cmd/go/internal/modfetch/sumdb.go b/src/cmd/go/internal/modfetch/sumdb.go
index 492b03bd84a..6e60e7d9764 100644
--- a/src/cmd/go/internal/modfetch/sumdb.go
+++ b/src/cmd/go/internal/modfetch/sumdb.go
@@ -33,6 +33,14 @@ import (
 
 // useSumDB reports whether to use the Go checksum database for the given module.
 func useSumDB(mod module.Version) bool {
+	if mod.Path == "golang.org/toolchain" {
+		// Downloaded toolchains cannot be listed in go.sum,
+		// so we require checksum database lookups even if
+		// GOSUMDB=off or GONOSUMDB matches the pattern.
+		// If GOSUMDB=off, then the eventual lookup will fail
+		// with a good error message.
+		return true
+	}
 	return cfg.GOSUMDB != "off" && !module.MatchPrefixPatterns(cfg.GONOSUMDB, mod.Path)
 }
 
@@ -70,6 +78,10 @@ func dbDial() (dbName string, db *sumdb.Client, err error) {
 		gosumdb = "sum.golang.org https://sum.golang.google.cn"
 	}
 
+	if gosumdb == "off" {
+		return "", nil, fmt.Errorf("checksum database disabled by GOSUMDB=off")
+	}
+
 	key := strings.Fields(gosumdb)
 	if len(key) >= 1 {
 		if k := knownGOSUMDB[key[0]]; k != "" {
diff --git a/src/cmd/go/internal/modget/get.go b/src/cmd/go/internal/modget/get.go
index 43708a3cab6..5d9eb70489e 100644
--- a/src/cmd/go/internal/modget/get.go
+++ b/src/cmd/go/internal/modget/get.go
@@ -72,6 +72,14 @@ To remove a dependency on a module and downgrade modules that require it:
 
 	go get example.com/mod@none
 
+To upgrade the minimum required Go version to the latest released Go version:
+
+	go get go@latest
+
+To upgrade the Go toolchain to the latest patch release of the current Go toolchain:
+
+	go get toolchain@patch
+
 See https://golang.org/ref/mod#go-get for details.
 
 In earlier versions of Go, 'go get' was used to build and install packages.
@@ -106,6 +114,9 @@ from a repository.
 
 For more about modules, see https://golang.org/ref/mod.
 
+For more about using 'go get' to update the minimum Go version and
+suggested Go toolchain, see https://go.dev/doc/toolchain.
+
 For more about specifying packages, see 'go help packages'.
 
 This text describes the behavior of get using modules to manage source
diff --git a/src/cmd/go/internal/modload/query.go b/src/cmd/go/internal/modload/query.go
index 945b6e1642d..81c32d27a19 100644
--- a/src/cmd/go/internal/modload/query.go
+++ b/src/cmd/go/internal/modload/query.go
@@ -393,7 +393,7 @@ func newQueryMatcher(path string, query, current string, allowed AllowedFunc) (*
 			qm.mayUseLatest = true
 		} else {
 			qm.mayUseLatest = module.IsPseudoVersion(current)
-			qm.prefix = semver.MajorMinor(current) + "."
+			qm.prefix = gover.ModMajorMinor(qm.path, current) + "."
 			qm.filter = func(mv string) bool { return gover.ModCompare(qm.path, mv, current) >= 0 }
 		}
 
diff --git a/src/cmd/go/internal/toolchain/toolchain.go b/src/cmd/go/internal/toolchain/select.go
similarity index 73%
rename from src/cmd/go/internal/toolchain/toolchain.go
rename to src/cmd/go/internal/toolchain/select.go
index e6ff584480a..6aac8c1eaad 100644
--- a/src/cmd/go/internal/toolchain/toolchain.go
+++ b/src/cmd/go/internal/toolchain/select.go
@@ -81,11 +81,12 @@ func FilterEnv(env []string) []string {
 	return out
 }
 
-// Switch invokes a different Go toolchain if directed by
+// Select invokes a different Go toolchain if directed by
 // the GOTOOLCHAIN environment variable or the user's configuration
 // or go.mod file.
 // It must be called early in startup.
-func Switch() {
+// See https://go.dev/doc/toolchain#select.
+func Select() {
 	log.SetPrefix("go: ")
 	defer log.SetPrefix("")
 
@@ -93,6 +94,21 @@ func Switch() {
 		return
 	}
 
+	// As a special case, let "go env GOTOOLCHAIN" and "go env -w GOTOOLCHAIN=..."
+	// be handled by the local toolchain, since an older toolchain may not understand it.
+	// This provides an easy way out of "go env -w GOTOOLCHAIN=go1.19" and makes
+	// sure that "go env GOTOOLCHAIN" always prints the local go command's interpretation of it.
+	// We look for these specific command lines in order to avoid mishandling
+	//
+	//	GOTOOLCHAIN=go1.999 go env -newflag GOTOOLCHAIN
+	//
+	// where -newflag is a flag known to Go 1.999 but not known to us.
+	if (len(os.Args) == 3 && os.Args[1] == "env" && os.Args[2] == "GOTOOLCHAIN") ||
+		(len(os.Args) == 4 && os.Args[1] == "env" && os.Args[2] == "-w" && strings.HasPrefix(os.Args[3], "GOTOOLCHAIN=")) {
+		return
+	}
+
+	// Interpret GOTOOLCHAIN to select the Go toolchain to run.
 	gotoolchain := cfg.Getenv("GOTOOLCHAIN")
 	gover.Startup.GOTOOLCHAIN = gotoolchain
 	if gotoolchain == "" {
@@ -105,77 +121,70 @@ func Switch() {
 		return
 	}
 
+	// Note: minToolchain is what https://go.dev/doc/toolchain#select calls the default toolchain.
 	minToolchain := gover.LocalToolchain()
 	minVers := gover.Local()
-	if min, mode, ok := strings.Cut(gotoolchain, "+"); ok { // go1.2.3+auto
-		v := gover.FromToolchain(min)
-		if v == "" {
-			base.Fatalf("invalid GOTOOLCHAIN %q: invalid minimum toolchain %q", gotoolchain, min)
+	var mode string
+	if gotoolchain == "auto" {
+		mode = "auto"
+	} else if gotoolchain == "path" {
+		mode = "path"
+	} else {
+		min, suffix, plus := strings.Cut(gotoolchain, "+") // go1.2.3+auto
+		if min != "local" {
+			v := gover.FromToolchain(gotoolchain)
+			if v == "" {
+				if plus {
+					base.Fatalf("invalid GOTOOLCHAIN %q: invalid minimum toolchain %q", gotoolchain, min)
+				}
+				base.Fatalf("invalid GOTOOLCHAIN %q", gotoolchain)
+			}
+			minToolchain = min
+			minVers = v
 		}
-		minToolchain = min
-		minVers = v
-		if mode != "auto" && mode != "path" {
+		if plus && suffix != "auto" && suffix != "path" {
 			base.Fatalf("invalid GOTOOLCHAIN %q: only version suffixes are +auto and +path", gotoolchain)
 		}
-		gotoolchain = mode
+		mode = suffix
 	}
 
-	if gotoolchain == "auto" || gotoolchain == "path" {
-		gotoolchain = minToolchain
-
-		// Locate and read go.mod or go.work.
-		// For go install m@v, it's the installed module's go.mod.
-		if m, goVers, ok := goInstallVersion(); ok {
-			if gover.Compare(goVers, minVers) > 0 {
-				// Always print, because otherwise there's no way for the user to know
-				// that a non-default toolchain version is being used here.
-				// (Normally you can run "go version", but go install m@v ignores the
-				// context that "go version" works in.)
-				var err error
-				gotoolchain, err = NewerToolchain(context.Background(), goVers)
-				if err != nil {
-					fmt.Fprintf(os.Stderr, "go: %v\n", err)
-					gotoolchain = "go" + goVers
-				}
-				fmt.Fprintf(os.Stderr, "go: using %s for %v\n", gotoolchain, m)
-			}
+	gotoolchain = minToolchain
+	if (mode == "auto" || mode == "path") && !goInstallVersion() {
+		// Read go.mod to find new minimum and suggested toolchain.
+		file, goVers, toolchain := modGoToolchain()
+		gover.Startup.AutoFile = file
+		if toolchain == "default" {
+			// "default" means always use the default toolchain,
+			// which is already set, so nothing to do here.
+			// Note that if we have Go 1.21 installed originally,
+			// GOTOOLCHAIN=go1.30.0+auto or GOTOOLCHAIN=go1.30.0,
+			// and the go.mod  says "toolchain default", we use Go 1.30, not Go 1.21.
+			// That is, default overrides the "auto" part of the calculation
+			// but not the minimum that the user has set.
+			// Of course, if the go.mod also says "go 1.35", using Go 1.30
+			// will provoke an error about the toolchain being too old.
+			// That's what people who use toolchain default want:
+			// only ever use the toolchain configured by the user
+			// (including its environment and go env -w file).
+			gover.Startup.AutoToolchain = toolchain
 		} else {
-			file, goVers, toolchain := modGoToolchain()
-			gover.Startup.AutoFile = file
-			if toolchain == "local" {
-				// Local means always use the default local toolchain,
-				// which is already set, so nothing to do here.
-				// Note that if we have Go 1.21 installed originally,
-				// GOTOOLCHAIN=go1.30.0+auto or GOTOOLCHAIN=go1.30.0,
-				// and the go.mod  says "toolchain local", we use Go 1.30, not Go 1.21.
-				// That is, local overrides the "auto" part of the calculation
-				// but not the minimum that the user has set.
-				// Of course, if the go.mod also says "go 1.35", using Go 1.30
-				// will provoke an error about the toolchain being too old.
-				// That's what people who use toolchain local want:
-				// only ever use the toolchain configured in the local system
-				// (including its environment and go env -w file).
-				gover.Startup.AutoToolchain = toolchain
-				gotoolchain = "local"
-			} else {
-				if toolchain != "" {
-					// Accept toolchain only if it is >= our min.
-					toolVers := gover.FromToolchain(toolchain)
-					if toolVers == "" || (!strings.HasPrefix(toolchain, "go") && !strings.Contains(toolchain, "-go")) {
-						base.Fatalf("invalid toolchain %q in %s", toolchain, base.ShortPath(file))
-					}
-					if gover.Compare(toolVers, minVers) >= 0 {
-						gotoolchain = toolchain
-						minVers = toolVers
-						gover.Startup.AutoToolchain = toolchain
-					}
+			if toolchain != "" {
+				// Accept toolchain only if it is >= our min.
+				toolVers := gover.FromToolchain(toolchain)
+				if toolVers == "" || (!strings.HasPrefix(toolchain, "go") && !strings.Contains(toolchain, "-go")) {
+					base.Fatalf("invalid toolchain %q in %s", toolchain, base.ShortPath(file))
 				}
-				if gover.Compare(goVers, minVers) > 0 {
-					gotoolchain = "go" + goVers
-					gover.Startup.AutoGoVersion = goVers
-					gover.Startup.AutoToolchain = "" // in case we are overriding it for being too old
+				if gover.Compare(toolVers, minVers) >= 0 {
+					gotoolchain = toolchain
+					minVers = toolVers
+					gover.Startup.AutoToolchain = toolchain
 				}
 			}
+			if gover.Compare(goVers, minVers) > 0 {
+				gotoolchain = "go" + goVers
+				gover.Startup.AutoGoVersion = goVers
+				gover.Startup.AutoToolchain = "" // in case we are overriding it for being too old
+			}
 		}
 	}
 
@@ -219,11 +228,12 @@ func Switch() {
 		base.Fatalf("invalid GOTOOLCHAIN %q", gotoolchain)
 	}
 
-	SwitchTo(gotoolchain)
+	Exec(gotoolchain)
 }
 
 // NewerToolchain returns the name of the toolchain to use when we need
-// to reinvoke a newer toolchain that must support at least the given Go version.
+// to switch to a newer toolchain that must support at least the given Go version.
+// See https://go.dev/doc/toolchain#switch.
 //
 // If the latest major release is 1.N.0, we use the latest patch release of 1.(N-1) if that's >= version.
 // Otherwise we use the latest 1.N if that's allowed.
@@ -345,14 +355,14 @@ func HasPath() bool {
 //
 //	"switch" - simulate version switches by reinvoking the test go binary with a different TESTGO_VERSION.
 //	"mismatch" - like "switch" but forget to set TESTGO_VERSION, so it looks like we invoked a mismatched toolchain
-//	"loop" - like "switch" but
+//	"loop" - like "mismatch" but forget the target check, causing a toolchain switching loop
 var TestVersionSwitch string
 
-// SwitchTo invokes the specified Go toolchain or else prints an error and exits the process.
-// If $GOTOOLCHAIN is set to path or min+path, SwitchTo only considers the PATH
-// as a source of Go toolchains. Otherwise SwitchTo tries the PATH but then downloads
+// Exec invokes the specified Go toolchain or else prints an error and exits the process.
+// If $GOTOOLCHAIN is set to path or min+path, Exec only considers the PATH
+// as a source of Go toolchains. Otherwise Exec tries the PATH but then downloads
 // a toolchain if necessary.
-func SwitchTo(gotoolchain string) {
+func Exec(gotoolchain string) {
 	log.SetPrefix("go: ")
 
 	count, _ := strconv.Atoi(os.Getenv(countEnv))
@@ -496,28 +506,32 @@ func modGoToolchain() (file, goVers, toolchain string) {
 	return file, gover.GoModLookup(data, "go"), gover.GoModLookup(data, "toolchain")
 }
 
-// goInstallVersion looks at the command line to see if it is go install m@v or go run m@v.
-// If so, it returns the m@v and the go version from that module's go.mod.
-func goInstallVersion() (m module.Version, goVers string, found bool) {
+// goInstallVersion reports whether the command line is go install m@v or go run m@v.
+// If so, Select must not read the go.mod or go.work file in "auto" or "path" mode.
+func goInstallVersion() bool {
 	// Note: We assume there are no flags between 'go' and 'install' or 'run'.
 	// During testing there are some debugging flags that are accepted
 	// in that position, but in production go binaries there are not.
 	if len(os.Args) < 3 || (os.Args[1] != "install" && os.Args[1] != "run") {
-		return module.Version{}, "", false
+		return false
 	}
 
+	// Check for pkg@version.
 	var arg string
 	switch os.Args[1] {
+	default:
+		return false
 	case "install":
-		// Cannot parse 'go install' command line precisely, because there
-		// may be new flags we don't know about. Instead, assume the final
-		// argument is a pkg@version we can use.
+		// We would like to let 'go install -newflag pkg@version' work even
+		// across a toolchain switch. To make that work, assume the pkg@version
+		// is the last argument and skip the flag parsing.
 		arg = os.Args[len(os.Args)-1]
 	case "run":
-		// For run, the pkg@version can be anywhere on the command line.
-		// We don't know the flags, so we can't strictly speaking do this correctly.
-		// We do the best we can by interrogating the CmdRun flags and assume
-		// that any unknown flag does not take an argument.
+		// For run, the pkg@version can be anywhere on the command line,
+		// because it is preceded by run flags and followed by arguments to the
+		// program being run. To handle that precisely, we have to interpret the
+		// flags a little bit, to know whether each flag takes an optional argument.
+		// We can still allow unknown flags as long as they have an explicit =value.
 		args := os.Args[2:]
 		for i := 0; i < len(args); i++ {
 			a := args[i]
@@ -526,19 +540,21 @@ func goInstallVersion() (m module.Version, goVers string, found bool) {
 				break
 			}
 			if a == "-" {
-				break
+				// non-flag but also non-pkg@version
+				return false
 			}
 			if a == "--" {
-				if i+1 < len(args) {
-					arg = args[i+1]
+				if i+1 >= len(args) {
+					return false
 				}
+				arg = args[i+1]
 				break
 			}
 			a = strings.TrimPrefix(a, "-")
 			a = strings.TrimPrefix(a, "-")
 			if strings.HasPrefix(a, "-") {
-				// non-flag but also non-m@v
-				break
+				// non-flag but also non-pkg@version
+				return false
 			}
 			if strings.Contains(a, "=") {
 				// already has value
@@ -546,8 +562,8 @@ func goInstallVersion() (m module.Version, goVers string, found bool) {
 			}
 			f := run.CmdRun.Flag.Lookup(a)
 			if f == nil {
-				// Unknown flag. Assume it doesn't take a value: best we can do.
-				continue
+				// Unknown flag. Give up. The command is going to fail in flag parsing.
+				return false
 			}
 			if bf, ok := f.Value.(interface{ IsBoolFlag() bool }); ok && bf.IsBoolFlag() {
 				// Does not take value.
@@ -557,13 +573,24 @@ func goInstallVersion() (m module.Version, goVers string, found bool) {
 		}
 	}
 	if !strings.Contains(arg, "@") || build.IsLocalImport(arg) || filepath.IsAbs(arg) {
-		return module.Version{}, "", false
+		return false
 	}
-	m.Path, m.Version, _ = strings.Cut(arg, "@")
-	if m.Path == "" || m.Version == "" || gover.IsToolchain(m.Path) {
-		return module.Version{}, "", false
+	path, version, _ := strings.Cut(arg, "@")
+	if path == "" || version == "" || gover.IsToolchain(path) {
+		return false
 	}
 
+	// It would be correct to simply return true here, bypassing use
+	// of the current go.mod or go.work, and let "go run" or "go install"
+	// do the rest, including a toolchain switch.
+	// Our goal instead is, since we have gone to the trouble of handling
+	// unknown flags to some degree, to run the switch now, so that
+	// these commands can switch to a newer toolchain directed by the
+	// go.mod which may actually understand the flag.
+	// This was brought up during the go.dev/issue/57001 proposal discussion
+	// and may end up being common in self-contained "go install" or "go run"
+	// command lines if we add new flags in the future.
+
 	// Set up modules without an explicit go.mod, to download go.mod.
 	modload.ForceUseModules = true
 	modload.RootMode = modload.NoRoot
@@ -573,21 +600,17 @@ func goInstallVersion() (m module.Version, goVers string, found bool) {
 	// See internal/load.PackagesAndErrorsOutsideModule
 	ctx := context.Background()
 	allowed := modload.CheckAllowed
-	if modload.IsRevisionQuery(m.Path, m.Version) {
+	if modload.IsRevisionQuery(path, version) {
 		// Don't check for retractions if a specific revision is requested.
 		allowed = nil
 	}
 	noneSelected := func(path string) (version string) { return "none" }
-	_, err := modload.QueryPackages(ctx, m.Path, m.Version, noneSelected, allowed)
-	if tooNew := (*gover.TooNewError)(nil); errors.As(err, &tooNew) {
-		m.Path, m.Version, _ = strings.Cut(tooNew.What, "@")
-		return m, tooNew.GoVersion, true
+	_, err := modload.QueryPackages(ctx, path, version, noneSelected, allowed)
+	if errors.Is(err, gover.ErrTooNew) {
+		// Run early switch, same one go install or go run would eventually do,
+		// if it understood all the command-line flags.
+		SwitchOrFatal(ctx, err)
 	}
 
-	// QueryPackages succeeded, or it failed for a reason other than
-	// this Go toolchain being too old for the modules encountered.
-	// Either way, we identified the m@v on the command line,
-	// so return found == true so the caller does not fall back to
-	// consulting go.mod.
-	return m, "", true
+	return true // pkg@version found
 }
diff --git a/src/cmd/go/internal/toolchain/reqs.go b/src/cmd/go/internal/toolchain/switch.go
similarity index 98%
rename from src/cmd/go/internal/toolchain/reqs.go
rename to src/cmd/go/internal/toolchain/switch.go
index e5ca8d0eb4c..b35198748d4 100644
--- a/src/cmd/go/internal/toolchain/reqs.go
+++ b/src/cmd/go/internal/toolchain/switch.go
@@ -22,6 +22,8 @@ import (
 // *gover.TooNewErrors (potentially wrapped) and switching is
 // permitted by GOTOOLCHAIN, Switch switches to a new toolchain.
 // Otherwise Switch prints all the errors using base.Error.
+//
+// See https://go.dev/doc/toolchain#switch.
 type Switcher struct {
 	TooNew *gover.TooNewError // max go requirement observed
 	Errors []error            // errors collected so far
@@ -91,7 +93,7 @@ func (s *Switcher) Switch(ctx context.Context) {
 	}
 
 	fmt.Fprintf(os.Stderr, "go: %v requires go >= %v; switching to %v\n", s.TooNew.What, s.TooNew.GoVersion, tv)
-	SwitchTo(tv)
+	Exec(tv)
 	panic("unreachable")
 }
 
diff --git a/src/cmd/go/main.go b/src/cmd/go/main.go
index af13f01240c..d050792998a 100644
--- a/src/cmd/go/main.go
+++ b/src/cmd/go/main.go
@@ -92,7 +92,7 @@ var _ = go11tag
 
 func main() {
 	log.SetFlags(0)
-	toolchain.Switch()
+	toolchain.Select()
 
 	flag.Usage = base.Usage
 	flag.Parse()
diff --git a/src/cmd/go/testdata/script/gotoolchain_local.txt b/src/cmd/go/testdata/script/gotoolchain_local.txt
index 18b4faabde7..313c5415015 100644
--- a/src/cmd/go/testdata/script/gotoolchain_local.txt
+++ b/src/cmd/go/testdata/script/gotoolchain_local.txt
@@ -70,15 +70,15 @@ go mod edit -go=1.700 -toolchain=go1.300
 go version
 stdout go1.700 # toolchain too old, ignored
 
-go mod edit -go=1.300 -toolchain=local
+go mod edit -go=1.300 -toolchain=default
 go version
 stdout go1.500
 
-go mod edit -go=1.700 -toolchain=local
+go mod edit -go=1.700 -toolchain=default
 go version
 stdout go1.500 # toolchain local is like GOTOOLCHAIN=local and wins
 ! go build
-stderr '^go: go.mod requires go >= 1.700 \(running go 1.500; go.mod sets toolchain local\)'
+stderr '^go: go.mod requires go >= 1.700 \(running go 1.500; go.mod sets toolchain default\)'
 
 # GOTOOLCHAIN=path does the same.
 env GOTOOLCHAIN=path
@@ -94,25 +94,33 @@ go mod edit -go=1.700 -toolchain=go1.300
 go version
 stdout go1.700 # toolchain too old, ignored
 
-go mod edit -go=1.300 -toolchain=local
+go mod edit -go=1.300 -toolchain=default
 go version
 stdout go1.500
 
-go mod edit -go=1.700 -toolchain=local
+go mod edit -go=1.700 -toolchain=default
 go version
-stdout go1.500 # toolchain applies even if older than go line
+stdout go1.500 # toolchain default applies even if older than go line
 ! go build
-stderr '^go: go.mod requires go >= 1.700 \(running go 1.500; GOTOOLCHAIN=path; go.mod sets toolchain local\)'
+stderr '^go: go.mod requires go >= 1.700 \(running go 1.500; GOTOOLCHAIN=path; go.mod sets toolchain default\)'
 
-# GOTOOLCHAIN names can have prefix- or -suffix
+# GOTOOLCHAIN=min+auto with toolchain default uses min, not local
+
+env GOTOOLCHAIN=go1.400+auto
+go mod edit -go=1.300 -toolchain=default
+go version
+stdout 1.400 # not 1.500 local toolchain
+
+env GOTOOLCHAIN=go1.600+auto
+go mod edit -go=1.300 -toolchain=default
+go version
+stdout 1.600 # not 1.500 local toolchain
+
+# GOTOOLCHAIN names can have -suffix
 env GOTOOLCHAIN=go1.800-bigcorp
 go version
 stdout go1.800-bigcorp
 
-env GOTOOLCHAIN=bigcorp-go1.100
-go version
-stdout bigcorp-go1.100
-
 env GOTOOLCHAIN=auto
 go mod edit -go=1.999 -toolchain=go1.800-bigcorp
 go version
@@ -122,14 +130,6 @@ go mod edit -go=1.777 -toolchain=go1.800-bigcorp
 go version
 stdout go1.800-bigcorp
 
-go mod edit -go=1.999 -toolchain=bigcorp-go1.800
-go version
-stdout go1.999
-
-go mod edit -go=1.777 -toolchain=bigcorp-go1.800
-go version
-stdout bigcorp-go1.800
-
 # go.work takes priority over go.mod
 go mod edit -go=1.700 -toolchain=go1.999-wrong
 go work init
@@ -137,13 +137,13 @@ go work edit -go=1.400 -toolchain=go1.600-right
 go version
 stdout go1.600-right
 
-go work edit -go=1.400 -toolchain=local
+go work edit -go=1.400 -toolchain=default
 go version
 stdout go1.500
 
 # go.work misconfiguration does not break go work edit
 # ('go 1.600 / toolchain local' forces use of 1.500 which can't normally load that go.work; allow work edit to fix it.)
-go work edit -go=1.600 -toolchain=local
+go work edit -go=1.600 -toolchain=default
 go version
 stdout go1.500
 
@@ -154,7 +154,7 @@ stdout go1.600
 rm go.work
 
 # go.mod misconfiguration does not break go mod edit
-go mod edit -go=1.600 -toolchain=local
+go mod edit -go=1.600 -toolchain=default
 go version
 stdout go1.500
 
@@ -177,19 +177,6 @@ go mod edit -go=1.501 -toolchain=none
 go version
 stdout go1.501
 
-env TESTGO_VERSION=bigcorp-go1.500
-go mod edit -go=1.499 -toolchain=none
-go version
-stdout bigcorp-go1.500
-
-go mod edit -go=1.500 -toolchain=none
-go version
-stdout bigcorp-go1.500
-
-go mod edit -go=1.501 -toolchain=none
-go version
-stdout go1.501
-
 env TESTGO_VERSION='go1.500 (bigcorp)'
 go mod edit -go=1.499 -toolchain=none
 go version
@@ -208,60 +195,55 @@ env TESTGO_VERSION=go1.2.3
 go mod edit -go=1.999 -toolchain=go1.998
 
 ! go install rsc.io/fortune/nonexist@v0.0.1
-stderr '^go: using go1.22.9 for rsc.io/fortune@v0.0.1'
+stderr '^go: rsc.io/fortune@v0.0.1 requires go >= 1.21rc999; switching to go1.22.9$'
 stderr '^go: rsc.io/fortune/nonexist@v0.0.1: module rsc.io/fortune@v0.0.1 found, but does not contain package rsc.io/fortune/nonexist'
 
 ! go run rsc.io/fortune/nonexist@v0.0.1
-stderr '^go: using go1.22.9 for rsc.io/fortune@v0.0.1'
+stderr '^go: rsc.io/fortune@v0.0.1 requires go >= 1.21rc999; switching to go1.22.9$'
 stderr '^go: rsc.io/fortune/nonexist@v0.0.1: module rsc.io/fortune@v0.0.1 found, but does not contain package rsc.io/fortune/nonexist'
 
 # go install should handle unknown flags to find m@v
 ! go install -unknownflag rsc.io/fortune/nonexist@v0.0.1
-stderr '^go: using go1.22.9 for rsc.io/fortune@v0.0.1'
+stderr '^go: rsc.io/fortune@v0.0.1 requires go >= 1.21rc999; switching to go1.22.9$'
 stderr '^flag provided but not defined: -unknownflag'
 
 ! go install -unknownflag arg rsc.io/fortune/nonexist@v0.0.1
-stderr '^go: using go1.22.9 for rsc.io/fortune@v0.0.1'
+stderr '^go: rsc.io/fortune@v0.0.1 requires go >= 1.21rc999; switching to go1.22.9$'
 stderr '^flag provided but not defined: -unknownflag'
 
-# go run should handle unknown boolean flags and flags with =arg
+# go run cannot handle unknown boolean flags
 ! go run -unknownflag rsc.io/fortune/nonexist@v0.0.1
-stderr '^go: using go1.22.9 for rsc.io/fortune@v0.0.1'
+! stderr switching
 stderr '^flag provided but not defined: -unknownflag'
 
+! go run -unknownflag oops rsc.io/fortune/nonexist@v0.0.1
+! stderr switching
+stderr '^flag provided but not defined: -unknownflag'
+
+# go run can handle unknown flag with argument.
 ! go run -unknown=flag rsc.io/fortune/nonexist@v0.0.1
-stderr '^go: using go1.22.9 for rsc.io/fortune@v0.0.1'
+stderr '^go: rsc.io/fortune@v0.0.1 requires go >= 1.21rc999; switching to go1.22.9$'
 stderr '^flag provided but not defined: -unknown'
 
-# go run assumes unknown flags don't take arguments
-! go run -unknownflag rsc.io/fortune/nonexist@v0.0.1
-stderr '^go: using go1.22.9 for rsc.io/fortune@v0.0.1'
-stderr '^flag provided but not defined: -unknownflag'
-
-! go run -unknownflag oops rsc.io/fortune/nonexist@v0.0.1  # lost parse, cannot find m@v
-! stderr go1.22.9
-! stderr '^go: using'
-stderr '^flag provided but not defined: -unknownflag'
-
 # go install m@v should handle queries
 ! go install rsc.io/fortune/nonexist@v0.0
-stderr '^go: using go1.22.9 for rsc.io/fortune@v0.0.1'
+stderr '^go: rsc.io/fortune@v0.0.1 requires go >= 1.21rc999; switching to go1.22.9$'
 stderr '^go: rsc.io/fortune/nonexist@v0.0: module rsc.io/fortune@v0.0 found \(v0.0.1\), but does not contain package rsc.io/fortune/nonexist'
 
 # go run m@v should handle queries
 ! go install rsc.io/fortune/nonexist@v0
-stderr '^go: using go1.22.9 for rsc.io/fortune@v0.0.1'
+stderr '^go: rsc.io/fortune@v0.0.1 requires go >= 1.21rc999; switching to go1.22.9$'
 stderr '^go: rsc.io/fortune/nonexist@v0: module rsc.io/fortune@v0 found \(v0.0.1\), but does not contain package rsc.io/fortune/nonexist'
 
 # go install m@v should use local toolchain if not upgrading
 ! go install rsc.io/fortune/nonexist@v1
 ! stderr go1.22.9
-! stderr '^go: using'
+! stderr switching
 stderr '^go: downloading rsc.io/fortune v1.0.0$'
 stderr '^go: rsc.io/fortune/nonexist@v1: module rsc.io/fortune@v1 found \(v1.0.0\), but does not contain package rsc.io/fortune/nonexist'
 
 # go run m@v should use local toolchain if not upgrading
 ! go run rsc.io/fortune/nonexist@v1
 ! stderr go1.22.9
-! stderr '^go: using'
+! stderr switching
 stderr '^go: rsc.io/fortune/nonexist@v1: module rsc.io/fortune@v1 found \(v1.0.0\), but does not contain package rsc.io/fortune/nonexist'
diff --git a/src/cmd/go/testdata/script/gotoolchain_net.txt b/src/cmd/go/testdata/script/gotoolchain_net.txt
index d04229d2937..72bb2b72526 100644
--- a/src/cmd/go/testdata/script/gotoolchain_net.txt
+++ b/src/cmd/go/testdata/script/gotoolchain_net.txt
@@ -1,8 +1,6 @@
 # This test only checks that basic network lookups work.
 # The full test of toolchain version selection is in gotoolchain.txt.
 
-[short] skip
-
 env TESTGO_VERSION=go1.21actual
 
 # GOTOOLCHAIN from network, does not exist
@@ -16,7 +14,34 @@ env GOTOOLCHAIN=go1.999testmod
 go version
 stderr 'go: downloading go1.999testmod \(.*/.*\)'
 
+# GOTOOLCHAIN cached from network
+go version
+! stderr downloading
+stdout go1.999testmod
+
+# GOTOOLCHAIN with GOSUMDB enabled but at a bad URL should operate in cache and not try badurl
+env oldsumdb=$GOSUMDB
+env GOSUMDB=$oldsumdb' http://badurl'
+go version
+! stderr downloading
+stdout go1.999testmod
+
+# GOTOOLCHAIN with GOSUMB=off should fail, because it cannot access even the cached sumdb info
+# without the sumdb name.
+env GOSUMDB=off
+! go version
+stderr '^go: golang.org/toolchain@v0.0.1-go1.999testmod.[a-z0-9\-]*: verifying module: checksum database disabled by GOSUMDB=off$'
+
+# GOTOOLCHAIN with GOSUMDB enabled but at a bad URL should fail if cache is incomplete
+env GOSUMDB=$oldsumdb' http://badurl'
+rm $GOPATH/pkg/mod/cache/download/sumdb
+! go version
+! stderr downloading
+stderr 'panic: use of network' # test catches network access
+env GOSUMDB=$oldsumdb
+
 # Test a real GOTOOLCHAIN
+[short] skip
 [!net:golang.org] skip
 [!GOOS:darwin] [!GOOS:windows] [!GOOS:linux] skip
 [!GOARCH:amd64] [!GOARCH:arm64] skip
diff --git a/src/cmd/go/testdata/script/mod_edit_toolchain.txt b/src/cmd/go/testdata/script/mod_edit_toolchain.txt
index 525e4dd54a7..bb544be344d 100644
--- a/src/cmd/go/testdata/script/mod_edit_toolchain.txt
+++ b/src/cmd/go/testdata/script/mod_edit_toolchain.txt
@@ -7,8 +7,8 @@ env GO111MODULE=on
 go mod edit -toolchain=go1.9
 grep 'toolchain go1.9' go.mod
 
-go mod edit -toolchain=local
-grep 'toolchain local' go.mod
+go mod edit -toolchain=default
+grep 'toolchain default' go.mod
 
 go mod edit -toolchain=none
 ! grep toolchain go.mod
diff --git a/src/cmd/go/testdata/script/mod_get_toolchain.txt b/src/cmd/go/testdata/script/mod_get_toolchain.txt
new file mode 100644
index 00000000000..143ad32a4e1
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_get_toolchain.txt
@@ -0,0 +1,102 @@
+# setup
+env TESTGO_VERSION=go1.99.0
+env TESTGO_VERSION_SWITCH=switch
+
+# go get go should use the latest Go 1.23
+cp go.mod.orig go.mod
+go get go
+stderr '^go: upgraded go 1.21 => 1.23.9$'
+grep 'go 1.23.9' go.mod
+grep 'toolchain go1.99.0' go.mod
+
+# go get go@1.23 should use the latest Go 1.23
+cp go.mod.orig go.mod
+go get go@1.23
+stderr '^go: upgraded go 1.21 => 1.23.9$'
+grep 'go 1.23.9' go.mod
+grep 'toolchain go1.99.0' go.mod
+
+# go get go@1.22 should use the latest Go 1.22
+cp go.mod.orig go.mod
+go get go@1.22
+stderr '^go: upgraded go 1.21 => 1.22.9$'
+grep 'go 1.22.9' go.mod
+grep 'toolchain go1.99.0' go.mod
+
+# go get go@patch should use the latest patch release
+go get go@1.22.1
+go get go@patch
+stderr '^go: upgraded go 1.22.1 => 1.22.9$'
+grep 'go 1.22.9' go.mod
+grep 'toolchain go1.99.0' go.mod
+
+# go get go@1.24 does NOT find the release candidate
+cp go.mod.orig go.mod
+! go get go@1.24
+stderr '^go: go@1.24: no matching versions for query "1.24"$'
+
+# go get go@1.24rc1 works
+cp go.mod.orig go.mod
+go get go@1.24rc1
+stderr '^go: upgraded go 1.21 => 1.24rc1$'
+grep 'go 1.24rc1' go.mod
+grep 'toolchain go1.99.0' go.mod
+
+# go get go@latest finds the latest Go 1.23
+cp go.mod.orig go.mod
+go get go@latest
+stderr '^go: upgraded go 1.21 => 1.23.9$'
+grep 'go 1.23.9' go.mod
+grep 'toolchain go1.99.0' go.mod
+
+# Again, with toolchains.
+
+# go get toolchain should find go1.999testmod.
+go get toolchain
+stderr '^go: upgraded toolchain go1.99.0 => go1.999testmod$'
+grep 'go 1.23.9' go.mod
+grep 'toolchain go1.999testmod' go.mod
+
+# go get toolchain@go1.23 should use the latest Go 1.23
+go get toolchain@go1.23
+stderr '^go: removed toolchain go1.999testmod$'
+grep 'go 1.23.9' go.mod
+! grep 'toolchain go1.23.9' go.mod  # implied
+
+# go get toolchain@go1.22 should use the latest Go 1.22 and downgrade go.
+go get toolchain@go1.22
+stderr '^go: downgraded go 1.23.9 => 1.22.9$'
+grep 'go 1.22.9' go.mod
+! grep 'toolchain go1.22.9' go.mod # implied
+
+# go get toolchain@patch should use the latest patch release
+go get toolchain@go1.22.1
+go get toolchain@patch
+stderr '^go: added toolchain go1.22.9$'
+grep 'go 1.22.1' go.mod
+grep 'toolchain go1.22.9' go.mod
+go get go@1.22.9 toolchain@none
+grep 'go 1.22.9' go.mod
+! grep 'toolchain go1.22.9' go.mod
+
+# go get toolchain@go1.24 does NOT find the release candidate
+! go get toolchain@go1.24
+stderr '^go: toolchain@go1.24: no matching versions for query "go1.24"$'
+
+# go get toolchain@go1.24rc1 works
+go get toolchain@go1.24rc1
+stderr '^go: added toolchain go1.24rc1$'
+grep 'go 1.22.9' go.mod  # no longer implied
+grep 'toolchain go1.24rc1' go.mod
+
+# go get toolchain@latest finds go1.999testmod.
+cp go.mod.orig go.mod
+go get toolchain@latest
+stderr '^go: added toolchain go1.999testmod$'
+grep 'go 1.21' go.mod
+grep 'toolchain go1.999testmod' go.mod
+
+-- go.mod.orig --
+module m
+
+go 1.21
diff --git a/src/cmd/go/testdata/script/work_edit_toolchain.txt b/src/cmd/go/testdata/script/work_edit_toolchain.txt
index a171296707b..b4e260d2387 100644
--- a/src/cmd/go/testdata/script/work_edit_toolchain.txt
+++ b/src/cmd/go/testdata/script/work_edit_toolchain.txt
@@ -7,8 +7,8 @@ env GO111MODULE=on
 go work edit -toolchain=go1.9
 grep 'toolchain go1.9' go.work
 
-go work edit -toolchain=local
-grep 'toolchain local' go.work
+go work edit -toolchain=default
+grep 'toolchain default' go.work
 
 go work edit -toolchain=none
 ! grep toolchain go.work