diff --git a/doc/go1.16.html b/doc/go1.16.html
index 0ffaecc..95e63d0 100644
--- a/doc/go1.16.html
+++ b/doc/go1.16.html
@@ -52,7 +52,7 @@
   TODO: write and link to tutorial or blog post
 </p>
 
-<p><!-= golang.org/issue/29062 -->
+<p><!-- golang.org/issue/29062 -->
   When using <code>go test</code>, a test that
   calls <code>os.Exit(0)</code> during execution of a test function
   will now be considered to fail.
@@ -62,6 +62,18 @@
   that is still considered to be a passing test.
 </p>
 
+<h4 id="all-pattern">The <code>all</code> pattern</h4>
+
+<p><!-- golang.org/cl/240623 -->
+  When the main module's <code>go.mod</code> file
+  declares <code>go</code> <code>1.16</code> or higher, the <code>all</code>
+  package pattern now matches only those packages that are transitively imported
+  by a package or test found in the main module. (Packages imported by <em>tests
+  of</em> packages imported by the main module are no longer included.) This is
+  the same set of packages retained
+  by <code>go</code> <code>mod</code> <code>vendor</code> since Go 1.11.
+</p>
+
 <p>
   TODO
 </p>
diff --git a/src/cmd/go/internal/modcmd/tidy.go b/src/cmd/go/internal/modcmd/tidy.go
index c7c53d7..4dcb62e 100644
--- a/src/cmd/go/internal/modcmd/tidy.go
+++ b/src/cmd/go/internal/modcmd/tidy.go
@@ -40,6 +40,18 @@
 		base.Fatalf("go mod tidy: no arguments allowed")
 	}
 
+	// Tidy aims to make 'go test' reproducible for any package in 'all', so we
+	// need to include test dependencies. For modules that specify go 1.15 or
+	// earlier this is a no-op (because 'all' saturates transitive test
+	// dependencies).
+	//
+	// However, with lazy loading (go 1.16+) 'all' includes only the packages that
+	// are transitively imported by the main module, not the test dependencies of
+	// those packages. In order to make 'go test' reproducible for the packages
+	// that are in 'all' but outside of the main module, we must explicitly
+	// request that their test dependencies be included.
+	modload.LoadTests = true
+
 	modload.LoadALL(ctx)
 	modload.TidyBuildList()
 	modload.TrimGoSum()
diff --git a/src/cmd/go/internal/modcmd/why.go b/src/cmd/go/internal/modcmd/why.go
index b16887d..30b15fc 100644
--- a/src/cmd/go/internal/modcmd/why.go
+++ b/src/cmd/go/internal/modcmd/why.go
@@ -65,6 +65,8 @@
 	loadALL := modload.LoadALL
 	if *whyVendor {
 		loadALL = modload.LoadVendor
+	} else {
+		modload.LoadTests = true
 	}
 	if *whyM {
 		listU := false
diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index 2096dfb..9cedc21 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -231,7 +231,7 @@
 	loaded = loadFromRoots(loaderParams{
 		tags:               tags,
 		allPatternIsRoot:   allPatternIsRoot,
-		allClosesOverTests: true, // until lazy loading in Go 1.16+
+		allClosesOverTests: index.allPatternClosesOverTests(),
 
 		listRoots: func() (roots []string) {
 			updateMatches(nil)
@@ -450,7 +450,7 @@
 			roots = append(roots, testImports...)
 			return roots
 		},
-		allClosesOverTests: true, // until lazy loading.
+		allClosesOverTests: index.allPatternClosesOverTests(),
 	})
 	WriteGoMod()
 }
@@ -501,7 +501,7 @@
 	loaded = loadFromRoots(loaderParams{
 		tags:               imports.Tags(),
 		listRoots:          func() []string { return nil },
-		allClosesOverTests: true, // until lazy loading, but doesn't matter because the root list is empty.
+		allClosesOverTests: index.allPatternClosesOverTests(), // but doesn't matter because the root list is empty.
 	})
 	return buildList
 }
@@ -512,9 +512,13 @@
 // It adds modules to the build list as needed to satisfy new imports.
 // This set is useful for deciding whether a particular import is needed
 // anywhere in a module.
+//
+// In modules that specify "go 1.16" or higher, ALL follows only one layer of
+// test dependencies. In "go 1.15" or lower, ALL follows the imports of tests of
+// dependencies of tests.
 func LoadALL(ctx context.Context) []string {
 	InitMod(ctx)
-	return loadAll(ctx, true)
+	return loadAll(ctx, index.allPatternClosesOverTests())
 }
 
 // LoadVendor is like LoadALL but only follows test dependencies
@@ -523,7 +527,9 @@
 // This set is useful for identifying the which packages to include in a vendor directory.
 func LoadVendor(ctx context.Context) []string {
 	InitMod(ctx)
-	return loadAll(ctx, false)
+	// 'go mod vendor' has never followed test dependencies since Go 1.11.
+	const closeOverTests = false
+	return loadAll(ctx, closeOverTests)
 }
 
 func loadAll(ctx context.Context, closeOverTests bool) []string {
diff --git a/src/cmd/go/internal/modload/modfile.go b/src/cmd/go/internal/modload/modfile.go
index a45c4a6..18dd293 100644
--- a/src/cmd/go/internal/modload/modfile.go
+++ b/src/cmd/go/internal/modload/modfile.go
@@ -25,6 +25,11 @@
 	"golang.org/x/mod/semver"
 )
 
+// lazyLoadingVersion is the Go version (plus leading "v") at which lazy module
+// loading takes effect.
+const lazyLoadingVersionV = "v1.16"
+const go116EnableLazyLoading = true
+
 var modFile *modfile.File
 
 // A modFileIndex is an index of data corresponding to a modFile
@@ -249,6 +254,23 @@
 	return i
 }
 
+// allPatternClosesOverTests reports whether the "all" pattern includes
+// dependencies of tests outside the main module (as in Go 1.11–1.15).
+// (Otherwise — as in Go 1.16+ — the "all" pattern includes only the packages
+// transitively *imported by* the packages and tests in the main module.)
+func (i *modFileIndex) allPatternClosesOverTests() bool {
+	if !go116EnableLazyLoading {
+		return true
+	}
+	if i != nil && semver.Compare(i.goVersionV, lazyLoadingVersionV) < 0 {
+		// The module explicitly predates the change in "all" for lazy loading, so
+		// continue to use the older interpretation. (If i == nil, we not in any
+		// module at all and should use the latest semantics.)
+		return true
+	}
+	return false
+}
+
 // modFileIsDirty reports whether the go.mod file differs meaningfully
 // from what was indexed.
 // If modFile has been changed (even cosmetically) since it was first read,
diff --git a/src/cmd/go/testdata/script/mod_all.txt b/src/cmd/go/testdata/script/mod_all.txt
index 9f4b0a4..aac6629 100644
--- a/src/cmd/go/testdata/script/mod_all.txt
+++ b/src/cmd/go/testdata/script/mod_all.txt
@@ -187,16 +187,104 @@
 stdout '^example.com/main/testonly.test$'
 stdout '^example.com/main/testonly_test \[example.com/main/testonly.test\]$'
 
+rm vendor
+
+# Convert all modules to go 1.16 to enable lazy loading.
+go mod edit -go=1.16 a/go.mod
+go mod edit -go=1.16 b/go.mod
+go mod edit -go=1.16 c/go.mod
+go mod edit -go=1.16 d/go.mod
+go mod edit -go=1.16 q/go.mod
+go mod edit -go=1.16 r/go.mod
+go mod edit -go=1.16 s/go.mod
+go mod edit -go=1.16 t/go.mod
+go mod edit -go=1.16 u/go.mod
+go mod edit -go=1.16 w/go.mod
+go mod edit -go=1.16 x/go.mod
+go mod edit -go=1.16
+
+# With lazy loading, 'go list all' with neither -mod=vendor nor -test should
+# match -mod=vendor without -test in 1.15.
+
+go list -f $PKGFMT all
+stdout -count=8 '^.'
+stdout '^example.com/a$'
+stdout '^example.com/b$'
+stdout '^example.com/main$'
+stdout '^example.com/main/testonly$'
+stdout '^example.com/q$'
+stdout '^example.com/r$'
+stdout '^example.com/t$'
+stdout '^example.com/u$'
+
+# 'go list -test all' should expand that to include the test variants of the
+# packages in 'all', but not the dependencies of outside tests.
+
+go list -test -f $PKGFMT all
+stdout -count=25 '^.'
+stdout '^example.com/a$'
+stdout '^example.com/b$'
+stdout '^example.com/main$'
+stdout '^example.com/main/testonly$'
+stdout '^example.com/q$'
+stdout '^example.com/r$'
+stdout '^example.com/t$'
+stdout '^example.com/u$'
+stdout '^example.com/a.test$'
+stdout '^example.com/a_test \[example.com/a.test\]$'
+stdout '^example.com/b.test$'
+stdout '^example.com/b_test \[example.com/b.test\]$'
+stdout '^example.com/main.test$'
+stdout '^example.com/main \[example.com/main.test\]$'
+stdout '^example.com/main_test \[example.com/main.test\]$'
+stdout '^example.com/main/testonly.test$'
+stdout '^example.com/main/testonly_test \[example.com/main/testonly.test\]$'
+stdout '^example.com/q.test$'
+stdout '^example.com/q_test \[example.com/q.test\]$'
+stdout '^example.com/r.test$'
+stdout '^example.com/r_test \[example.com/r.test\]$'
+stdout '^example.com/t.test$'
+stdout '^example.com/t_test \[example.com/t.test\]$'
+stdout '^example.com/u.test$'
+stdout '^example.com/u_test \[example.com/u.test\]$'
+
+# 'go list -test -deps all' should include the dependencies of those tests,
+# but not the tests of the dependencies of outside tests.
+
+go list -test -deps -f $PKGFMT all
+stdout -count=28 '^.'
+stdout '^example.com/a$'
+stdout '^example.com/b$'
+stdout '^example.com/c$'
+stdout '^example.com/main$'
+stdout '^example.com/main/testonly$'
+stdout '^example.com/q$'
+stdout '^example.com/r$'
+stdout '^example.com/s$'
+stdout '^example.com/t$'
+stdout '^example.com/u$'
+stdout '^example.com/w$'
+stdout '^example.com/a.test$'
+stdout '^example.com/a_test \[example.com/a.test\]$'
+stdout '^example.com/b.test$'
+stdout '^example.com/b_test \[example.com/b.test\]$'
+stdout '^example.com/main.test$'
+stdout '^example.com/main \[example.com/main.test\]$'
+stdout '^example.com/main_test \[example.com/main.test\]$'
+stdout '^example.com/main/testonly.test$'
+stdout '^example.com/main/testonly_test \[example.com/main/testonly.test\]$'
+stdout '^example.com/q.test$'
+stdout '^example.com/q_test \[example.com/q.test\]$'
+stdout '^example.com/r.test$'
+stdout '^example.com/r_test \[example.com/r.test\]$'
+stdout '^example.com/t.test$'
+stdout '^example.com/t_test \[example.com/t.test\]$'
+stdout '^example.com/u.test$'
+stdout '^example.com/u_test \[example.com/u.test\]$'
+
+
 # TODO(#36460):
-
-# With lazy loading, 'go list all' without -mod=vendor should match
-# 'go mod vendor'.
-
-# 'go list -test all' should expand that to cover test dependencies
-# of packages imported by the main module.
-
-# 'go list -m all' should cover the packages in 'go list -test all'.
-
+# 'go list -m all' should exactly cover the packages in 'go list -test all'.
 
 -- go.mod --
 module example.com/main