diff --git a/aetest/instance_vm.go b/aetest/instance_vm.go
index 48aa5d48..e1647fdb 100644
--- a/aetest/instance_vm.go
+++ b/aetest/instance_vm.go
@@ -18,7 +18,6 @@ import (
 	"regexp"
 	"time"
 
-	"golang.org/x/net/context"
 	"google.golang.org/appengine/internal"
 )
 
@@ -61,7 +60,6 @@ type instance struct {
 	appDir         string
 	appID          string
 	startupTimeout time.Duration
-	relFuncs       []func() // funcs to release any associated contexts
 }
 
 // NewRequest returns an *http.Request associated with this instance.
@@ -72,21 +70,11 @@ func (i *instance) NewRequest(method, urlStr string, body io.Reader) (*http.Requ
 	}
 
 	// Associate this request.
-	req, release := internal.RegisterTestRequest(req, i.apiURL, func(ctx context.Context) context.Context {
-		ctx = internal.WithAppIDOverride(ctx, "dev~"+i.appID)
-		return ctx
-	})
-	i.relFuncs = append(i.relFuncs, release)
-
-	return req, nil
+	return internal.RegisterTestRequest(req, i.apiURL, "dev~"+i.appID), nil
 }
 
 // Close kills the child api_server.py process, releasing its resources.
 func (i *instance) Close() (err error) {
-	for _, rel := range i.relFuncs {
-		rel()
-	}
-	i.relFuncs = nil
 	child := i.child
 	if child == nil {
 		return nil
diff --git a/appengine_vm.go b/appengine_vm.go
index 78d2575a..6e1d041c 100644
--- a/appengine_vm.go
+++ b/appengine_vm.go
@@ -8,12 +8,13 @@
 package appengine
 
 import (
-	"golang.org/x/net/context"
-
-	"google.golang.org/appengine/internal"
+	"context"
 )
 
 // BackgroundContext returns a context not associated with a request.
+//
+// Deprecated: App Engine no longer has a special background context.
+// Just use context.Background().
 func BackgroundContext() context.Context {
-	return internal.BackgroundContext()
+	return context.Background()
 }
diff --git a/internal/api.go b/internal/api.go
index 750a0077..2339da39 100644
--- a/internal/api.go
+++ b/internal/api.go
@@ -24,8 +24,9 @@ import (
 	"sync/atomic"
 	"time"
 
+	netcontext "context"
+
 	"github.com/golang/protobuf/proto"
-	netcontext "golang.org/x/net/context"
 
 	basepb "google.golang.org/appengine/internal/base"
 	logpb "google.golang.org/appengine/internal/log"
@@ -33,8 +34,7 @@ import (
 )
 
 const (
-	apiPath             = "/rpc_http"
-	defaultTicketSuffix = "/default.20150612t184001.0"
+	apiPath = "/rpc_http"
 )
 
 var (
@@ -66,21 +66,22 @@ var (
 			IdleConnTimeout:     90 * time.Second,
 		},
 	}
-
-	defaultTicketOnce     sync.Once
-	defaultTicket         string
-	backgroundContextOnce sync.Once
-	backgroundContext     netcontext.Context
 )
 
-func apiURL() *url.URL {
+func apiURL(ctx netcontext.Context) *url.URL {
 	host, port := "appengine.googleapis.internal", "10001"
 	if h := os.Getenv("API_HOST"); h != "" {
 		host = h
 	}
+	if hostOverride := ctx.Value(apiHostOverrideKey); hostOverride != nil {
+		host = hostOverride.(string)
+	}
 	if p := os.Getenv("API_PORT"); p != "" {
 		port = p
 	}
+	if portOverride := ctx.Value(apiPortOverrideKey); portOverride != nil {
+		port = portOverride.(string)
+	}
 	return &url.URL{
 		Scheme: "http",
 		Host:   host + ":" + port,
@@ -98,7 +99,6 @@ func handleHTTPMiddleware(next http.Handler) http.Handler {
 		c := &context{
 			req:       r,
 			outHeader: w.Header(),
-			apiURL:    apiURL(),
 		}
 		r = r.WithContext(withContext(r.Context(), c))
 		c.req = r
@@ -235,8 +235,6 @@ type context struct {
 		lines   []*logpb.UserAppLogLine
 		flushes int
 	}
-
-	apiURL *url.URL
 }
 
 var contextKey = "holds a *context"
@@ -304,59 +302,19 @@ func WithContext(parent netcontext.Context, req *http.Request) netcontext.Contex
 	}
 }
 
-// DefaultTicket returns a ticket used for background context or dev_appserver.
-func DefaultTicket() string {
-	defaultTicketOnce.Do(func() {
-		if IsDevAppServer() {
-			defaultTicket = "testapp" + defaultTicketSuffix
-			return
-		}
-		appID := partitionlessAppID()
-		escAppID := strings.Replace(strings.Replace(appID, ":", "_", -1), ".", "_", -1)
-		majVersion := VersionID(nil)
-		if i := strings.Index(majVersion, "."); i > 0 {
-			majVersion = majVersion[:i]
-		}
-		defaultTicket = fmt.Sprintf("%s/%s.%s.%s", escAppID, ModuleName(nil), majVersion, InstanceID())
-	})
-	return defaultTicket
-}
-
-func BackgroundContext() netcontext.Context {
-	backgroundContextOnce.Do(func() {
-		// Compute background security ticket.
-		ticket := DefaultTicket()
-
-		c := &context{
-			req: &http.Request{
-				Header: http.Header{
-					ticketHeader: []string{ticket},
-				},
-			},
-			apiURL: apiURL(),
-		}
-		backgroundContext = toContext(c)
-
-		// TODO(dsymonds): Wire up the shutdown handler to do a final flush.
-		go c.logFlusher(make(chan int))
-	})
-
-	return backgroundContext
-}
-
 // RegisterTestRequest registers the HTTP request req for testing, such that
-// any API calls are sent to the provided URL. It returns a closure to delete
-// the registration.
+// any API calls are sent to the provided URL.
 // It should only be used by aetest package.
-func RegisterTestRequest(req *http.Request, apiURL *url.URL, decorate func(netcontext.Context) netcontext.Context) (*http.Request, func()) {
-	c := &context{
-		req:    req,
-		apiURL: apiURL,
-	}
-	ctx := withContext(decorate(req.Context()), c)
-	req = req.WithContext(ctx)
-	c.req = req
-	return req, func() {}
+func RegisterTestRequest(req *http.Request, apiURL *url.URL, appID string) *http.Request {
+	ctx := req.Context()
+	ctx = withAPIHostOverride(ctx, apiURL.Hostname())
+	ctx = withAPIPortOverride(ctx, apiURL.Port())
+	ctx = WithAppIDOverride(ctx, appID)
+
+	// use the unregistered request as a placeholder so that withContext can read the headers
+	c := &context{req: req}
+	c.req = req.WithContext(withContext(ctx, c))
+	return c.req
 }
 
 var errTimeout = &CallError{
@@ -401,10 +359,11 @@ func (c *context) WriteHeader(code int) {
 	c.outCode = code
 }
 
-func (c *context) post(body []byte, timeout time.Duration) (b []byte, err error) {
+func post(ctx netcontext.Context, body []byte, timeout time.Duration) (b []byte, err error) {
+	apiURL := apiURL(ctx)
 	hreq := &http.Request{
 		Method: "POST",
-		URL:    c.apiURL,
+		URL:    apiURL,
 		Header: http.Header{
 			apiEndpointHeader: apiEndpointHeaderValue,
 			apiMethodHeader:   apiMethodHeaderValue,
@@ -413,13 +372,16 @@ func (c *context) post(body []byte, timeout time.Duration) (b []byte, err error)
 		},
 		Body:          ioutil.NopCloser(bytes.NewReader(body)),
 		ContentLength: int64(len(body)),
-		Host:          c.apiURL.Host,
-	}
-	if info := c.req.Header.Get(dapperHeader); info != "" {
-		hreq.Header.Set(dapperHeader, info)
+		Host:          apiURL.Host,
 	}
-	if info := c.req.Header.Get(traceHeader); info != "" {
-		hreq.Header.Set(traceHeader, info)
+	c := fromContext(ctx)
+	if c != nil {
+		if info := c.req.Header.Get(dapperHeader); info != "" {
+			hreq.Header.Set(dapperHeader, info)
+		}
+		if info := c.req.Header.Get(traceHeader); info != "" {
+			hreq.Header.Set(traceHeader, info)
+		}
 	}
 
 	tr := apiHTTPClient.Transport.(*http.Transport)
@@ -480,10 +442,6 @@ func Call(ctx netcontext.Context, service, method string, in, out proto.Message)
 	}
 
 	c := fromContext(ctx)
-	if c == nil {
-		// Give a good error message rather than a panic lower down.
-		return errNotAppEngineContext
-	}
 
 	// Apply transaction modifications if we're in a transaction.
 	if t := transactionFromContext(ctx); t != nil {
@@ -504,20 +462,13 @@ func Call(ctx netcontext.Context, service, method string, in, out proto.Message)
 		return err
 	}
 
-	ticket := c.req.Header.Get(ticketHeader)
-	// Use a test ticket under test environment.
-	if ticket == "" {
-		if appid := ctx.Value(&appIDOverrideKey); appid != nil {
-			ticket = appid.(string) + defaultTicketSuffix
+	ticket := ""
+	if c != nil {
+		ticket = c.req.Header.Get(ticketHeader)
+		if dri := c.req.Header.Get(devRequestIdHeader); IsDevAppServer() && dri != "" {
+			ticket = dri
 		}
 	}
-	// Fall back to use background ticket when the request ticket is not available in Flex or dev_appserver.
-	if ticket == "" {
-		ticket = DefaultTicket()
-	}
-	if dri := c.req.Header.Get(devRequestIdHeader); IsDevAppServer() && dri != "" {
-		ticket = dri
-	}
 	req := &remotepb.Request{
 		ServiceName: &service,
 		Method:      &method,
@@ -529,7 +480,7 @@ func Call(ctx netcontext.Context, service, method string, in, out proto.Message)
 		return err
 	}
 
-	hrespBody, err := c.post(hreqBody, timeout)
+	hrespBody, err := post(ctx, hreqBody, timeout)
 	if err != nil {
 		return err
 	}
diff --git a/internal/api_common.go b/internal/api_common.go
index e0c0b214..f6101d3b 100644
--- a/internal/api_common.go
+++ b/internal/api_common.go
@@ -5,13 +5,19 @@
 package internal
 
 import (
+	netcontext "context"
 	"errors"
 	"os"
 
 	"github.com/golang/protobuf/proto"
-	netcontext "golang.org/x/net/context"
 )
 
+type ctxKey string
+
+func (c ctxKey) String() string {
+	return "appengine context key: " + string(c)
+}
+
 var errNotAppEngineContext = errors.New("not an App Engine context")
 
 type CallOverrideFunc func(ctx netcontext.Context, service, method string, in, out proto.Message) error
@@ -55,6 +61,18 @@ func WithAppIDOverride(ctx netcontext.Context, appID string) netcontext.Context
 	return netcontext.WithValue(ctx, &appIDOverrideKey, appID)
 }
 
+var apiHostOverrideKey = ctxKey("holds a string, being the alternate API_HOST")
+
+func withAPIHostOverride(ctx netcontext.Context, apiHost string) netcontext.Context {
+	return netcontext.WithValue(ctx, apiHostOverrideKey, apiHost)
+}
+
+var apiPortOverrideKey = ctxKey("holds a string, being the alternate API_PORT")
+
+func withAPIPortOverride(ctx netcontext.Context, apiPort string) netcontext.Context {
+	return netcontext.WithValue(ctx, apiPortOverrideKey, apiPort)
+}
+
 var namespaceKey = "holds the namespace string"
 
 func withNamespace(ctx netcontext.Context, ns string) netcontext.Context {
diff --git a/internal/api_test.go b/internal/api_test.go
index c20f52f9..c1be17db 100644
--- a/internal/api_test.go
+++ b/internal/api_test.go
@@ -10,6 +10,7 @@ package internal
 import (
 	"bufio"
 	"bytes"
+	netcontext "context"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -18,13 +19,13 @@ import (
 	"net/url"
 	"os"
 	"os/exec"
+	"runtime"
 	"strings"
 	"sync/atomic"
 	"testing"
 	"time"
 
 	"github.com/golang/protobuf/proto"
-	netcontext "golang.org/x/net/context"
 
 	basepb "google.golang.org/appengine/internal/base"
 	remotepb "google.golang.org/appengine/internal/remote_api"
@@ -41,6 +42,8 @@ type fakeAPIHandler struct {
 	hang chan int // used for RunSlowly RPC
 
 	LogFlushes int32 // atomic
+
+	allowMissingTicket bool
 }
 
 func (f *fakeAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
@@ -67,7 +70,7 @@ func (f *fakeAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, fmt.Sprintf("Bad encoded API request: %v", err), 500)
 		return
 	}
-	if *apiReq.RequestId != "s3cr3t" && *apiReq.RequestId != DefaultTicket() {
+	if *apiReq.RequestId != "s3cr3t" && !f.allowMissingTicket {
 		writeResponse(&remotepb.Response{
 			RpcError: &remotepb.RpcError{
 				Code:   proto.Int32(int32(remotepb.RpcError_SECURITY_VIOLATION)),
@@ -147,18 +150,25 @@ func setup() (f *fakeAPIHandler, c *context, cleanup func()) {
 	f = &fakeAPIHandler{}
 	srv := httptest.NewServer(f)
 	u, err := url.Parse(srv.URL + apiPath)
+	restoreAPIHost := restoreEnvVar("API_HOST")
+	restoreAPIPort := restoreEnvVar("API_HOST")
+	os.Setenv("API_HOST", u.Hostname())
+	os.Setenv("API_PORT", u.Port())
 	if err != nil {
 		panic(fmt.Sprintf("url.Parse(%q): %v", srv.URL+apiPath, err))
 	}
 	return f, &context{
-		req: &http.Request{
-			Header: http.Header{
-				ticketHeader: []string{"s3cr3t"},
-				dapperHeader: []string{"trace-001"},
+			req: &http.Request{
+				Header: http.Header{
+					ticketHeader: []string{"s3cr3t"},
+					dapperHeader: []string{"trace-001"},
+				},
 			},
-		},
-		apiURL: u,
-	}, srv.Close
+		}, func() {
+			restoreAPIHost()
+			restoreAPIPort()
+			srv.Close()
+		}
 }
 
 func restoreEnvVar(key string) (cleanup func()) {
@@ -192,8 +202,9 @@ func TestAPICall(t *testing.T) {
 func TestAPICallTicketUnavailable(t *testing.T) {
 	resetEnv := SetTestEnv()
 	defer resetEnv()
-	_, c, cleanup := setup()
+	f, c, cleanup := setup()
 	defer cleanup()
+	f.allowMissingTicket = true
 
 	c.req.Header.Set(ticketHeader, "")
 	req := &basepb.StringProto{
@@ -243,13 +254,9 @@ func TestAPICallRPCFailure(t *testing.T) {
 func TestAPICallDialFailure(t *testing.T) {
 	// See what happens if the API host is unresponsive.
 	// This should time out quickly, not hang forever.
-	_, c, cleanup := setup()
-	defer cleanup()
-	// Reset the URL to the production address so that dialing fails.
-	c.apiURL = apiURL()
-
+	// We intentially don't set up the fakeAPIHandler for this test to cause the dail failure.
 	start := time.Now()
-	err := Call(toContext(c), "foo", "bar", &basepb.VoidProto{}, &basepb.VoidProto{})
+	err := Call(netcontext.Background(), "foo", "bar", &basepb.VoidProto{}, &basepb.VoidProto{})
 	const max = 1 * time.Second
 	if taken := time.Since(start); taken > max {
 		t.Errorf("Dial hang took too long: %v > %v", taken, max)
@@ -282,7 +289,6 @@ func TestDelayedLogFlushing(t *testing.T) {
 
 			http.HandleFunc(path, func(w http.ResponseWriter, r *http.Request) {
 				logC := WithContext(netcontext.Background(), r)
-				fromContext(logC).apiURL = c.apiURL // Otherwise it will try to use the default URL.
 				Logf(logC, 1, "It's a lovely day.")
 				w.WriteHeader(200)
 				time.Sleep(1200 * time.Millisecond)
@@ -344,7 +350,6 @@ func TestLogFlushing(t *testing.T) {
 			path := "/quick_log_" + tc.logToLogservice
 			http.HandleFunc(path, func(w http.ResponseWriter, r *http.Request) {
 				logC := WithContext(netcontext.Background(), r)
-				fromContext(logC).apiURL = c.apiURL // Otherwise it will try to use the default URL.
 				Logf(logC, 1, "It's a lovely day.")
 				w.WriteHeader(200)
 				w.Write(make([]byte, 100<<10)) // write 100 KB to force HTTP flush
@@ -435,7 +440,8 @@ func TestAPICallAllocations(t *testing.T) {
 	}
 
 	// Run the test API server in a subprocess so we aren't counting its allocations.
-	u, cleanup := launchHelperProcess(t)
+	cleanup := launchHelperProcess(t)
+
 	defer cleanup()
 	c := &context{
 		req: &http.Request{
@@ -444,7 +450,6 @@ func TestAPICallAllocations(t *testing.T) {
 				dapperHeader: []string{"trace-001"},
 			},
 		},
-		apiURL: u,
 	}
 
 	req := &basepb.StringProto{
@@ -463,13 +468,18 @@ func TestAPICallAllocations(t *testing.T) {
 	}
 
 	// Lots of room for improvement...
-	const min, max float64 = 60, 86
+	var min, max float64 = 60, 86
+	if strings.HasPrefix(runtime.Version(), "go1.11.") || strings.HasPrefix(runtime.Version(), "go1.12.") {
+		// add a bit more overhead for versions before go1.13
+		// see https://go.dev/doc/go1.13#compilers
+		max = 90
+	}
 	if avg < min || max < avg {
 		t.Errorf("Allocations per API call = %g, want in [%g,%g]", avg, min, max)
 	}
 }
 
-func launchHelperProcess(t *testing.T) (apiURL *url.URL, cleanup func()) {
+func launchHelperProcess(t *testing.T) (cleanup func()) {
 	cmd := exec.Command(os.Args[0], "-test.run=TestHelperProcess")
 	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
 	stdin, err := cmd.StdinPipe()
@@ -504,7 +514,13 @@ func launchHelperProcess(t *testing.T) (apiURL *url.URL, cleanup func()) {
 		t.Fatal("Helper process never reported")
 	}
 
-	return u, func() {
+	restoreAPIHost := restoreEnvVar("API_HOST")
+	restoreAPIPort := restoreEnvVar("API_HOST")
+	os.Setenv("API_HOST", u.Hostname())
+	os.Setenv("API_PORT", u.Port())
+	return func() {
+		restoreAPIHost()
+		restoreAPIPort()
 		stdin.Close()
 		if err := cmd.Wait(); err != nil {
 			t.Errorf("Helper process did not exit cleanly: %v", err)
@@ -529,20 +545,3 @@ func TestHelperProcess(*testing.T) {
 	// Wait for stdin to be closed.
 	io.Copy(ioutil.Discard, os.Stdin)
 }
-
-func TestBackgroundContext(t *testing.T) {
-	resetEnv := SetTestEnv()
-	defer resetEnv()
-
-	ctx, key := fromContext(BackgroundContext()), "X-Magic-Ticket-Header"
-	if g, w := ctx.req.Header.Get(key), "my-app-id/default.20150612t184001.0"; g != w {
-		t.Errorf("%v = %q, want %q", key, g, w)
-	}
-
-	// Check that using the background context doesn't panic.
-	req := &basepb.StringProto{
-		Value: proto.String("Doctor Who"),
-	}
-	res := &basepb.StringProto{}
-	Call(BackgroundContext(), "actordb", "LookupActor", req, res) // expected to fail
-}
diff --git a/v2/aetest/instance.go b/v2/aetest/instance.go
index 3143a89c..985a52cc 100644
--- a/v2/aetest/instance.go
+++ b/v2/aetest/instance.go
@@ -110,7 +110,6 @@ type instance struct {
 	appDir         string
 	appID          string
 	startupTimeout time.Duration
-	relFuncs       []func() // funcs to release any associated contexts
 }
 
 // NewRequest returns an *http.Request associated with this instance.
@@ -121,21 +120,11 @@ func (i *instance) NewRequest(method, urlStr string, body io.Reader) (*http.Requ
 	}
 
 	// Associate this request.
-	req, release := internal.RegisterTestRequest(req, i.apiURL, func(ctx context.Context) context.Context {
-		ctx = internal.WithAppIDOverride(ctx, "dev~"+i.appID)
-		return ctx
-	})
-	i.relFuncs = append(i.relFuncs, release)
-
-	return req, nil
+	return internal.RegisterTestRequest(req, i.apiURL, "dev~"+i.appID), nil
 }
 
 // Close kills the child api_server.py process, releasing its resources.
 func (i *instance) Close() (err error) {
-	for _, rel := range i.relFuncs {
-		rel()
-	}
-	i.relFuncs = nil
 	child := i.child
 	if child == nil {
 		return nil
diff --git a/v2/appengine.go b/v2/appengine.go
index cabc4ac0..02e1f24e 100644
--- a/v2/appengine.go
+++ b/v2/appengine.go
@@ -135,6 +135,9 @@ func APICall(ctx context.Context, service, method string, in, out proto.Message)
 }
 
 // BackgroundContext returns a context not associated with a request.
+//
+// Deprecated: App Engine no longer has a special background context.
+// Just use context.Background().
 func BackgroundContext() context.Context {
-	return internal.BackgroundContext()
+	return context.Background()
 }
diff --git a/v2/internal/api.go b/v2/internal/api.go
index 96df8204..9bf67ad6 100644
--- a/v2/internal/api.go
+++ b/v2/internal/api.go
@@ -17,8 +17,6 @@ import (
 	"os"
 	"runtime"
 	"strconv"
-	"strings"
-	"sync"
 	"sync/atomic"
 	"time"
 
@@ -28,8 +26,7 @@ import (
 )
 
 const (
-	apiPath             = "/rpc_http"
-	defaultTicketSuffix = "/default.20150612t184001.0"
+	apiPath = "/rpc_http"
 )
 
 var (
@@ -62,23 +59,24 @@ var (
 		},
 	}
 
-	defaultTicketOnce     sync.Once
-	defaultTicket         string
-	backgroundContextOnce sync.Once
-	backgroundContext     netcontext.Context
-
 	logStream io.Writer        = os.Stderr // For test hooks.
 	timeNow   func() time.Time = time.Now  // For test hooks.
 )
 
-func apiURL() *url.URL {
+func apiURL(ctx netcontext.Context) *url.URL {
 	host, port := "appengine.googleapis.internal", "10001"
 	if h := os.Getenv("API_HOST"); h != "" {
 		host = h
 	}
+	if hostOverride := ctx.Value(apiHostOverrideKey); hostOverride != nil {
+		host = hostOverride.(string)
+	}
 	if p := os.Getenv("API_PORT"); p != "" {
 		port = p
 	}
+	if portOverride := ctx.Value(apiPortOverrideKey); portOverride != nil {
+		port = portOverride.(string)
+	}
 	return &url.URL{
 		Scheme: "http",
 		Host:   host + ":" + port,
@@ -90,7 +88,6 @@ func handleHTTP(w http.ResponseWriter, r *http.Request) {
 	c := &context{
 		req:       r,
 		outHeader: w.Header(),
-		apiURL:    apiURL(),
 	}
 	r = r.WithContext(withContext(r.Context(), c))
 	c.req = r
@@ -183,8 +180,6 @@ type context struct {
 	outCode   int
 	outHeader http.Header
 	outBody   []byte
-
-	apiURL *url.URL
 }
 
 var contextKey = "holds a *context"
@@ -252,56 +247,20 @@ func WithContext(parent netcontext.Context, req *http.Request) netcontext.Contex
 	}
 }
 
-// DefaultTicket returns a ticket used for background context or dev_appserver.
-func DefaultTicket() string {
-	defaultTicketOnce.Do(func() {
-		if IsDevAppServer() {
-			defaultTicket = "testapp" + defaultTicketSuffix
-			return
-		}
-		appID := partitionlessAppID()
-		escAppID := strings.Replace(strings.Replace(appID, ":", "_", -1), ".", "_", -1)
-		majVersion := VersionID(nil)
-		if i := strings.Index(majVersion, "."); i > 0 {
-			majVersion = majVersion[:i]
-		}
-		defaultTicket = fmt.Sprintf("%s/%s.%s.%s", escAppID, ModuleName(nil), majVersion, InstanceID())
-	})
-	return defaultTicket
-}
-
-func BackgroundContext() netcontext.Context {
-	backgroundContextOnce.Do(func() {
-		// Compute background security ticket.
-		ticket := DefaultTicket()
-
-		c := &context{
-			req: &http.Request{
-				Header: http.Header{
-					ticketHeader: []string{ticket},
-				},
-			},
-			apiURL: apiURL(),
-		}
-		backgroundContext = toContext(c)
-	})
-
-	return backgroundContext
-}
-
 // RegisterTestRequest registers the HTTP request req for testing, such that
 // any API calls are sent to the provided URL. It returns a closure to delete
 // the registration.
 // It should only be used by aetest package.
-func RegisterTestRequest(req *http.Request, apiURL *url.URL, decorate func(netcontext.Context) netcontext.Context) (*http.Request, func()) {
-	c := &context{
-		req:    req,
-		apiURL: apiURL,
-	}
-	ctx := withContext(decorate(req.Context()), c)
-	req = req.WithContext(ctx)
-	c.req = req
-	return req, func() {}
+func RegisterTestRequest(req *http.Request, apiURL *url.URL, appID string) *http.Request {
+	ctx := req.Context()
+	ctx = withAPIHostOverride(ctx, apiURL.Hostname())
+	ctx = withAPIPortOverride(ctx, apiURL.Port())
+	ctx = WithAppIDOverride(ctx, appID)
+
+	// use the unregistered request as a placeholder so that withContext can read the headers
+	c := &context{req: req}
+	c.req = req.WithContext(withContext(ctx, c))
+	return c.req
 }
 
 var errTimeout = &CallError{
@@ -346,10 +305,11 @@ func (c *context) WriteHeader(code int) {
 	c.outCode = code
 }
 
-func (c *context) post(body []byte, timeout time.Duration) (b []byte, err error) {
+func post(ctx netcontext.Context, body []byte, timeout time.Duration) (b []byte, err error) {
+	apiURL := apiURL(ctx)
 	hreq := &http.Request{
 		Method: "POST",
-		URL:    c.apiURL,
+		URL:    apiURL,
 		Header: http.Header{
 			apiEndpointHeader: apiEndpointHeaderValue,
 			apiMethodHeader:   apiMethodHeaderValue,
@@ -358,13 +318,16 @@ func (c *context) post(body []byte, timeout time.Duration) (b []byte, err error)
 		},
 		Body:          ioutil.NopCloser(bytes.NewReader(body)),
 		ContentLength: int64(len(body)),
-		Host:          c.apiURL.Host,
-	}
-	if info := c.req.Header.Get(dapperHeader); info != "" {
-		hreq.Header.Set(dapperHeader, info)
+		Host:          apiURL.Host,
 	}
-	if info := c.req.Header.Get(traceHeader); info != "" {
-		hreq.Header.Set(traceHeader, info)
+	c := fromContext(ctx)
+	if c != nil {
+		if info := c.req.Header.Get(dapperHeader); info != "" {
+			hreq.Header.Set(dapperHeader, info)
+		}
+		if info := c.req.Header.Get(traceHeader); info != "" {
+			hreq.Header.Set(traceHeader, info)
+		}
 	}
 
 	tr := apiHTTPClient.Transport.(*http.Transport)
@@ -425,10 +388,6 @@ func Call(ctx netcontext.Context, service, method string, in, out proto.Message)
 	}
 
 	c := fromContext(ctx)
-	if c == nil {
-		// Give a good error message rather than a panic lower down.
-		return errNotAppEngineContext
-	}
 
 	// Apply transaction modifications if we're in a transaction.
 	if t := transactionFromContext(ctx); t != nil {
@@ -449,20 +408,13 @@ func Call(ctx netcontext.Context, service, method string, in, out proto.Message)
 		return err
 	}
 
-	ticket := c.req.Header.Get(ticketHeader)
-	// Use a test ticket under test environment.
-	if ticket == "" {
-		if appid := ctx.Value(&appIDOverrideKey); appid != nil {
-			ticket = appid.(string) + defaultTicketSuffix
+	ticket := ""
+	if c != nil {
+		ticket = c.req.Header.Get(ticketHeader)
+		if dri := c.req.Header.Get(devRequestIdHeader); IsDevAppServer() && dri != "" {
+			ticket = dri
 		}
 	}
-	// Fall back to use background ticket when the request ticket is not available in Flex or dev_appserver.
-	if ticket == "" {
-		ticket = DefaultTicket()
-	}
-	if dri := c.req.Header.Get(devRequestIdHeader); IsDevAppServer() && dri != "" {
-		ticket = dri
-	}
 	req := &remotepb.Request{
 		ServiceName: &service,
 		Method:      &method,
@@ -474,7 +426,7 @@ func Call(ctx netcontext.Context, service, method string, in, out proto.Message)
 		return err
 	}
 
-	hrespBody, err := c.post(hreqBody, timeout)
+	hrespBody, err := post(ctx, hreqBody, timeout)
 	if err != nil {
 		return err
 	}
diff --git a/v2/internal/api_common.go b/v2/internal/api_common.go
index a952aaa2..f6101d3b 100644
--- a/v2/internal/api_common.go
+++ b/v2/internal/api_common.go
@@ -12,6 +12,12 @@ import (
 	"github.com/golang/protobuf/proto"
 )
 
+type ctxKey string
+
+func (c ctxKey) String() string {
+	return "appengine context key: " + string(c)
+}
+
 var errNotAppEngineContext = errors.New("not an App Engine context")
 
 type CallOverrideFunc func(ctx netcontext.Context, service, method string, in, out proto.Message) error
@@ -55,6 +61,18 @@ func WithAppIDOverride(ctx netcontext.Context, appID string) netcontext.Context
 	return netcontext.WithValue(ctx, &appIDOverrideKey, appID)
 }
 
+var apiHostOverrideKey = ctxKey("holds a string, being the alternate API_HOST")
+
+func withAPIHostOverride(ctx netcontext.Context, apiHost string) netcontext.Context {
+	return netcontext.WithValue(ctx, apiHostOverrideKey, apiHost)
+}
+
+var apiPortOverrideKey = ctxKey("holds a string, being the alternate API_PORT")
+
+func withAPIPortOverride(ctx netcontext.Context, apiPort string) netcontext.Context {
+	return netcontext.WithValue(ctx, apiPortOverrideKey, apiPort)
+}
+
 var namespaceKey = "holds the namespace string"
 
 func withNamespace(ctx netcontext.Context, ns string) netcontext.Context {
diff --git a/v2/internal/api_test.go b/v2/internal/api_test.go
index c851f5a6..67785b35 100644
--- a/v2/internal/api_test.go
+++ b/v2/internal/api_test.go
@@ -37,6 +37,8 @@ type fakeAPIHandler struct {
 	hang chan int // used for RunSlowly RPC
 
 	LogFlushes int32 // atomic
+
+	allowMissingTicket bool
 }
 
 func (f *fakeAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
@@ -63,7 +65,7 @@ func (f *fakeAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, fmt.Sprintf("Bad encoded API request: %v", err), 500)
 		return
 	}
-	if *apiReq.RequestId != "s3cr3t" && *apiReq.RequestId != DefaultTicket() {
+	if *apiReq.RequestId != "s3cr3t" && !f.allowMissingTicket {
 		writeResponse(&remotepb.Response{
 			RpcError: &remotepb.RpcError{
 				Code:   proto.Int32(int32(remotepb.RpcError_SECURITY_VIOLATION)),
@@ -143,18 +145,25 @@ func setup() (f *fakeAPIHandler, c *context, cleanup func()) {
 	f = &fakeAPIHandler{}
 	srv := httptest.NewServer(f)
 	u, err := url.Parse(srv.URL + apiPath)
+	restoreAPIHost := restoreEnvVar("API_HOST")
+	restoreAPIPort := restoreEnvVar("API_HOST")
+	os.Setenv("API_HOST", u.Hostname())
+	os.Setenv("API_PORT", u.Port())
 	if err != nil {
 		panic(fmt.Sprintf("url.Parse(%q): %v", srv.URL+apiPath, err))
 	}
 	return f, &context{
-		req: &http.Request{
-			Header: http.Header{
-				ticketHeader: []string{"s3cr3t"},
-				dapperHeader: []string{"trace-001"},
+			req: &http.Request{
+				Header: http.Header{
+					ticketHeader: []string{"s3cr3t"},
+					dapperHeader: []string{"trace-001"},
+				},
 			},
-		},
-		apiURL: u,
-	}, srv.Close
+		}, func() {
+			restoreAPIHost()
+			restoreAPIPort()
+			srv.Close()
+		}
 }
 
 func restoreEnvVar(key string) (cleanup func()) {
@@ -188,8 +197,9 @@ func TestAPICall(t *testing.T) {
 func TestAPICallTicketUnavailable(t *testing.T) {
 	resetEnv := SetTestEnv()
 	defer resetEnv()
-	_, c, cleanup := setup()
+	f, c, cleanup := setup()
 	defer cleanup()
+	f.allowMissingTicket = true
 
 	c.req.Header.Set(ticketHeader, "")
 	req := &basepb.StringProto{
@@ -239,13 +249,9 @@ func TestAPICallRPCFailure(t *testing.T) {
 func TestAPICallDialFailure(t *testing.T) {
 	// See what happens if the API host is unresponsive.
 	// This should time out quickly, not hang forever.
-	_, c, cleanup := setup()
-	defer cleanup()
-	// Reset the URL to the production address so that dialing fails.
-	c.apiURL = apiURL()
-
+	// We intentially don't set up the fakeAPIHandler for this test to cause the dail failure.
 	start := time.Now()
-	err := Call(toContext(c), "foo", "bar", &basepb.VoidProto{}, &basepb.VoidProto{})
+	err := Call(netcontext.Background(), "foo", "bar", &basepb.VoidProto{}, &basepb.VoidProto{})
 	const max = 1 * time.Second
 	if taken := time.Since(start); taken > max {
 		t.Errorf("Dial hang took too long: %v > %v", taken, max)
@@ -317,7 +323,7 @@ func TestAPICallAllocations(t *testing.T) {
 	}
 
 	// Run the test API server in a subprocess so we aren't counting its allocations.
-	u, cleanup := launchHelperProcess(t)
+	cleanup := launchHelperProcess(t)
 	defer cleanup()
 	c := &context{
 		req: &http.Request{
@@ -326,7 +332,6 @@ func TestAPICallAllocations(t *testing.T) {
 				dapperHeader: []string{"trace-001"},
 			},
 		},
-		apiURL: u,
 	}
 
 	req := &basepb.StringProto{
@@ -351,7 +356,7 @@ func TestAPICallAllocations(t *testing.T) {
 	}
 }
 
-func launchHelperProcess(t *testing.T) (apiURL *url.URL, cleanup func()) {
+func launchHelperProcess(t *testing.T) (cleanup func()) {
 	cmd := exec.Command(os.Args[0], "-test.run=TestHelperProcess")
 	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
 	stdin, err := cmd.StdinPipe()
@@ -386,7 +391,13 @@ func launchHelperProcess(t *testing.T) (apiURL *url.URL, cleanup func()) {
 		t.Fatal("Helper process never reported")
 	}
 
-	return u, func() {
+	restoreAPIHost := restoreEnvVar("API_HOST")
+	restoreAPIPort := restoreEnvVar("API_HOST")
+	os.Setenv("API_HOST", u.Hostname())
+	os.Setenv("API_PORT", u.Port())
+	return func() {
+		restoreAPIHost()
+		restoreAPIPort()
 		stdin.Close()
 		if err := cmd.Wait(); err != nil {
 			t.Errorf("Helper process did not exit cleanly: %v", err)
@@ -411,20 +422,3 @@ func TestHelperProcess(*testing.T) {
 	// Wait for stdin to be closed.
 	io.Copy(ioutil.Discard, os.Stdin)
 }
-
-func TestBackgroundContext(t *testing.T) {
-	resetEnv := SetTestEnv()
-	defer resetEnv()
-
-	ctx, key := fromContext(BackgroundContext()), "X-Magic-Ticket-Header"
-	if g, w := ctx.req.Header.Get(key), "my-app-id/default.20150612t184001.0"; g != w {
-		t.Errorf("%v = %q, want %q", key, g, w)
-	}
-
-	// Check that using the background context doesn't panic.
-	req := &basepb.StringProto{
-		Value: proto.String("Doctor Who"),
-	}
-	res := &basepb.StringProto{}
-	Call(BackgroundContext(), "actordb", "LookupActor", req, res) // expected to fail
-}