diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2639a810d56..88bdd1e8522 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## master / unreleased
 * [ENHANCEMENT] Update Go version to 1.19.3. #4988
 * [ENHANCEMENT] Querier: limit series query to only ingesters if `start` param is not specified. #4976
+* [ENHANCEMENT] Query-frontend/scheduler: add a new limit `frontend.max-outstanding-requests-per-tenant` for configuring queue size per tenant. Started deprecating two flags `-query-scheduler.max-outstanding-requests-per-tenant` and `-querier.max-outstanding-requests-per-tenant`, and change their value default to 0. Now if both the old flag and new flag are specified, the old flag's queue size will be picked. #5005
 * [FEATURE] Querier/Query Frontend: support Prometheus /api/v1/status/buildinfo API. #4978
 * [FEATURE] Ingester: Add active series to all_user_stats page. #4972
 * [FEATURE] Query Frontend: Log query params in query frontend even if error happens. #5005
diff --git a/docs/configuration/config-file-reference.md b/docs/configuration/config-file-reference.md
index e717e6ec7a7..0f7c425cc39 100644
--- a/docs/configuration/config-file-reference.md
+++ b/docs/configuration/config-file-reference.md
@@ -172,11 +172,12 @@ runtime_config:
 [memberlist: <memberlist_config>]
 
 query_scheduler:
-  # Maximum number of outstanding requests per tenant per query-scheduler.
-  # In-flight requests above this limit will fail with HTTP response status code
-  # 429.
+  # Deprecated (use frontend.max-outstanding-requests-per-tenant instead) and
+  # will be removed in v1.17.0: Maximum number of outstanding requests per
+  # tenant per query-scheduler. In-flight requests above this limit will fail
+  # with HTTP response status code 429.
   # CLI flag: -query-scheduler.max-outstanding-requests-per-tenant
-  [max_outstanding_requests_per_tenant: <int> | default = 100]
+  [max_outstanding_requests_per_tenant: <int> | default = 0]
 
   # If a querier disconnects without sending notification about graceful
   # shutdown, the query-scheduler will keep the querier in the tenant's shard
@@ -916,10 +917,11 @@ The `query_frontend_config` configures the Cortex query-frontend.
 # CLI flag: -frontend.query-stats-enabled
 [query_stats_enabled: <boolean> | default = false]
 
-# Maximum number of outstanding requests per tenant per frontend; requests
-# beyond this error with HTTP 429.
+# Deprecated (use frontend.max-outstanding-requests-per-tenant instead) and will
+# be removed in v1.17.0: Maximum number of outstanding requests per tenant per
+# frontend; requests beyond this error with HTTP 429.
 # CLI flag: -querier.max-outstanding-requests-per-tenant
-[max_outstanding_per_tenant: <int> | default = 100]
+[max_outstanding_per_tenant: <int> | default = 0]
 
 # If a querier disconnects without sending notification about graceful shutdown,
 # the query-frontend will keep the querier in the tenant's shard until the
@@ -2724,6 +2726,11 @@ The `limits_config` configures default and per-tenant limits imposed by Cortex s
 # CLI flag: -frontend.max-queriers-per-tenant
 [max_queriers_per_tenant: <int> | default = 0]
 
+# Maximum number of outstanding requests per tenant per request queue (either
+# query frontend or query scheduler); requests beyond this error with HTTP 429.
+# CLI flag: -frontend.max-outstanding-requests-per-tenant
+[max_outstanding_requests_per_tenant: <int> | default = 100]
+
 # Duration to delay the evaluation of rules to ensure the underlying metrics
 # have been pushed to Cortex.
 # CLI flag: -ruler.evaluation-delay-duration
diff --git a/pkg/frontend/frontend_test.go b/pkg/frontend/frontend_test.go
index b17606042a2..2ca1d628905 100644
--- a/pkg/frontend/frontend_test.go
+++ b/pkg/frontend/frontend_test.go
@@ -25,6 +25,7 @@ import (
 	"google.golang.org/grpc"
 
 	"github.com/cortexproject/cortex/pkg/frontend/transport"
+	frontendv1 "github.com/cortexproject/cortex/pkg/frontend/v1"
 	"github.com/cortexproject/cortex/pkg/frontend/v1/frontendv1pb"
 	querier_worker "github.com/cortexproject/cortex/pkg/querier/worker"
 	"github.com/cortexproject/cortex/pkg/util/concurrency"
@@ -253,7 +254,7 @@ func testFrontend(t *testing.T, config CombinedFrontendConfig, handler http.Hand
 	httpListen, err := net.Listen("tcp", "localhost:0")
 	require.NoError(t, err)
 
-	rt, v1, v2, err := InitFrontend(config, limits{}, 0, logger, nil)
+	rt, v1, v2, err := InitFrontend(config, frontendv1.MockLimits{}, 0, logger, nil)
 	require.NoError(t, err)
 	require.NotNil(t, rt)
 	// v1 will be nil if DownstreamURL is defined.
@@ -306,11 +307,3 @@ func defaultFrontendConfig() CombinedFrontendConfig {
 	flagext.DefaultValues(&config.FrontendV2)
 	return config
 }
-
-type limits struct {
-	queriers int
-}
-
-func (l limits) MaxQueriersPerUser(_ string) int {
-	return l.queriers
-}
diff --git a/pkg/frontend/v1/frontend.go b/pkg/frontend/v1/frontend.go
index 93eaf4b73d1..541e17dc4b4 100644
--- a/pkg/frontend/v1/frontend.go
+++ b/pkg/frontend/v1/frontend.go
@@ -37,13 +37,25 @@ type Config struct {
 
 // RegisterFlags adds the flags required to config this to the given FlagSet.
 func (cfg *Config) RegisterFlags(f *flag.FlagSet) {
-	f.IntVar(&cfg.MaxOutstandingPerTenant, "querier.max-outstanding-requests-per-tenant", 100, "Maximum number of outstanding requests per tenant per frontend; requests beyond this error with HTTP 429.")
+	f.IntVar(&cfg.MaxOutstandingPerTenant, "querier.max-outstanding-requests-per-tenant", 0, "Deprecated (use frontend.max-outstanding-requests-per-tenant instead) and will be removed in v1.17.0: Maximum number of outstanding requests per tenant per frontend; requests beyond this error with HTTP 429.")
 	f.DurationVar(&cfg.QuerierForgetDelay, "query-frontend.querier-forget-delay", 0, "If a querier disconnects without sending notification about graceful shutdown, the query-frontend will keep the querier in the tenant's shard until the forget delay has passed. This feature is useful to reduce the blast radius when shuffle-sharding is enabled.")
 }
 
 type Limits interface {
 	// Returns max queriers to use per tenant, or 0 if shuffle sharding is disabled.
 	MaxQueriersPerUser(user string) int
+
+	queue.Limits
+}
+
+// MockLimits implements the Limits interface. Used in tests only.
+type MockLimits struct {
+	Queriers int
+	queue.MockLimits
+}
+
+func (l MockLimits) MaxQueriersPerUser(_ string) int {
+	return l.Queriers
 }
 
 // Frontend queues HTTP requests, dispatches them to backends, and handles retries
@@ -100,7 +112,7 @@ func New(cfg Config, limits Limits, log log.Logger, registerer prometheus.Regist
 		}),
 	}
 
-	f.requestQueue = queue.NewRequestQueue(cfg.MaxOutstandingPerTenant, cfg.QuerierForgetDelay, f.queueLength, f.discardedRequests)
+	f.requestQueue = queue.NewRequestQueue(cfg.MaxOutstandingPerTenant, cfg.QuerierForgetDelay, f.queueLength, f.discardedRequests, f.limits)
 	f.activeUsers = util.NewActiveUsersCleanupWithDefaultValues(f.cleanupInactiveUserMetrics)
 
 	var err error
diff --git a/pkg/frontend/v1/frontend_test.go b/pkg/frontend/v1/frontend_test.go
index 7f89d3a1b90..3c512aef800 100644
--- a/pkg/frontend/v1/frontend_test.go
+++ b/pkg/frontend/v1/frontend_test.go
@@ -116,6 +116,7 @@ func TestFrontendPropagateTrace(t *testing.T) {
 }
 
 func TestFrontendCheckReady(t *testing.T) {
+	limits := MockLimits{MockLimits: queue.MockLimits{MaxOutstanding: 100}}
 	for _, tt := range []struct {
 		name             string
 		connectedClients int
@@ -131,6 +132,7 @@ func TestFrontendCheckReady(t *testing.T) {
 				requestQueue: queue.NewRequestQueue(5, 0,
 					prometheus.NewGaugeVec(prometheus.GaugeOpts{}, []string{"user"}),
 					prometheus.NewCounterVec(prometheus.CounterOpts{}, []string{"user"}),
+					limits,
 				),
 			}
 			for i := 0; i < tt.connectedClients; i++ {
@@ -243,7 +245,8 @@ func testFrontend(t *testing.T, config Config, handler http.Handler, test func(a
 	httpListen, err := net.Listen("tcp", "localhost:0")
 	require.NoError(t, err)
 
-	v1, err := New(config, limits{}, logger, reg)
+	limits := MockLimits{MockLimits: queue.MockLimits{MaxOutstanding: 100}}
+	v1, err := New(config, limits, logger, reg)
 	require.NoError(t, err)
 	require.NotNil(t, v1)
 	require.NoError(t, services.StartAndAwaitRunning(context.Background(), v1))
@@ -292,11 +295,3 @@ func defaultFrontendConfig() Config {
 	flagext.DefaultValues(&config)
 	return config
 }
-
-type limits struct {
-	queriers int
-}
-
-func (l limits) MaxQueriersPerUser(_ string) int {
-	return l.queriers
-}
diff --git a/pkg/frontend/v1/queue_test.go b/pkg/frontend/v1/queue_test.go
index 7b72cf02b3a..e58f73176d5 100644
--- a/pkg/frontend/v1/queue_test.go
+++ b/pkg/frontend/v1/queue_test.go
@@ -16,6 +16,7 @@ import (
 	"google.golang.org/grpc/metadata"
 
 	"github.com/cortexproject/cortex/pkg/frontend/v1/frontendv1pb"
+	"github.com/cortexproject/cortex/pkg/scheduler/queue"
 	"github.com/cortexproject/cortex/pkg/util/flagext"
 	"github.com/cortexproject/cortex/pkg/util/services"
 )
@@ -23,7 +24,8 @@ import (
 func setupFrontend(t *testing.T, config Config) (*Frontend, error) {
 	logger := log.NewNopLogger()
 
-	frontend, err := New(config, limits{queriers: 3}, logger, nil)
+	limits := MockLimits{Queriers: 3, MockLimits: queue.MockLimits{MaxOutstanding: 100}}
+	frontend, err := New(config, limits, logger, nil)
 	require.NoError(t, err)
 
 	t.Cleanup(func() {
diff --git a/pkg/scheduler/queue/queue.go b/pkg/scheduler/queue/queue.go
index 37de027368a..bdaad09ee6d 100644
--- a/pkg/scheduler/queue/queue.go
+++ b/pkg/scheduler/queue/queue.go
@@ -61,9 +61,9 @@ type RequestQueue struct {
 	discardedRequests *prometheus.CounterVec // Per user.
 }
 
-func NewRequestQueue(maxOutstandingPerTenant int, forgetDelay time.Duration, queueLength *prometheus.GaugeVec, discardedRequests *prometheus.CounterVec) *RequestQueue {
+func NewRequestQueue(maxOutstandingPerTenant int, forgetDelay time.Duration, queueLength *prometheus.GaugeVec, discardedRequests *prometheus.CounterVec, limits Limits) *RequestQueue {
 	q := &RequestQueue{
-		queues:                  newUserQueues(maxOutstandingPerTenant, forgetDelay),
+		queues:                  newUserQueues(maxOutstandingPerTenant, forgetDelay, limits),
 		connectedQuerierWorkers: atomic.NewInt32(0),
 		queueLength:             queueLength,
 		discardedRequests:       discardedRequests,
diff --git a/pkg/scheduler/queue/queue_test.go b/pkg/scheduler/queue/queue_test.go
index b571322224a..ef02a492f3b 100644
--- a/pkg/scheduler/queue/queue_test.go
+++ b/pkg/scheduler/queue/queue_test.go
@@ -26,6 +26,7 @@ func BenchmarkGetNextRequest(b *testing.B) {
 		queue := NewRequestQueue(maxOutstandingPerTenant, 0,
 			prometheus.NewGaugeVec(prometheus.GaugeOpts{}, []string{"user"}),
 			prometheus.NewCounterVec(prometheus.CounterOpts{}, []string{"user"}),
+			MockLimits{MaxOutstanding: 100},
 		)
 		queues = append(queues, queue)
 
@@ -83,6 +84,7 @@ func BenchmarkQueueRequest(b *testing.B) {
 		q := NewRequestQueue(maxOutstandingPerTenant, 0,
 			prometheus.NewGaugeVec(prometheus.GaugeOpts{}, []string{"user"}),
 			prometheus.NewCounterVec(prometheus.CounterOpts{}, []string{"user"}),
+			MockLimits{MaxOutstanding: 100},
 		)
 
 		for ix := 0; ix < queriers; ix++ {
@@ -115,7 +117,9 @@ func TestRequestQueue_GetNextRequestForQuerier_ShouldGetRequestAfterReshardingBe
 
 	queue := NewRequestQueue(1, forgetDelay,
 		prometheus.NewGaugeVec(prometheus.GaugeOpts{}, []string{"user"}),
-		prometheus.NewCounterVec(prometheus.CounterOpts{}, []string{"user"}))
+		prometheus.NewCounterVec(prometheus.CounterOpts{}, []string{"user"}),
+		MockLimits{MaxOutstanding: 100},
+	)
 
 	// Start the queue service.
 	ctx := context.Background()
diff --git a/pkg/scheduler/queue/user_queues.go b/pkg/scheduler/queue/user_queues.go
index cdad43402bd..0f9cd1a0811 100644
--- a/pkg/scheduler/queue/user_queues.go
+++ b/pkg/scheduler/queue/user_queues.go
@@ -8,6 +8,13 @@ import (
 	"github.com/cortexproject/cortex/pkg/util"
 )
 
+// Limits needed for the Query Scheduler - interface used for decoupling.
+type Limits interface {
+	// MaxOutstandingPerTenant returns the limit to the maximum number
+	// of outstanding requests per tenant per request queue.
+	MaxOutstandingPerTenant(user string) int
+}
+
 // querier holds information about a querier registered in the queue.
 type querier struct {
 	// Number of active connections.
@@ -41,6 +48,8 @@ type queues struct {
 
 	// Sorted list of querier names, used when creating per-user shard.
 	sortedQueriers []string
+
+	limits Limits
 }
 
 type userQueue struct {
@@ -59,7 +68,7 @@ type userQueue struct {
 	index int
 }
 
-func newUserQueues(maxUserQueueSize int, forgetDelay time.Duration) *queues {
+func newUserQueues(maxUserQueueSize int, forgetDelay time.Duration, limits Limits) *queues {
 	return &queues{
 		userQueues:       map[string]*userQueue{},
 		users:            nil,
@@ -67,6 +76,7 @@ func newUserQueues(maxUserQueueSize int, forgetDelay time.Duration) *queues {
 		forgetDelay:      forgetDelay,
 		queriers:         map[string]*querier{},
 		sortedQueriers:   nil,
+		limits:           limits,
 	}
 }
 
@@ -106,8 +116,14 @@ func (q *queues) getOrAddQueue(userID string, maxQueriers int) chan Request {
 	uq := q.userQueues[userID]
 
 	if uq == nil {
+		queueSize := q.limits.MaxOutstandingPerTenant(userID)
+		// 0 is the default value of the flag. If the old flag is set
+		// then we use its value for compatibility reason.
+		if q.maxUserQueueSize != 0 {
+			queueSize = q.maxUserQueueSize
+		}
 		uq = &userQueue{
-			ch:    make(chan Request, q.maxUserQueueSize),
+			ch:    make(chan Request, queueSize),
 			seed:  util.ShuffleShardSeed(userID, ""),
 			index: -1,
 		}
@@ -303,3 +319,12 @@ func shuffleQueriersForUser(userSeed int64, queriersToSelect int, allSortedQueri
 
 	return result
 }
+
+// MockLimits implements the Limits interface. Used in tests only.
+type MockLimits struct {
+	MaxOutstanding int
+}
+
+func (l MockLimits) MaxOutstandingPerTenant(_ string) int {
+	return l.MaxOutstanding
+}
diff --git a/pkg/scheduler/queue/user_queues_test.go b/pkg/scheduler/queue/user_queues_test.go
index 699dd79dfd9..cc986cac416 100644
--- a/pkg/scheduler/queue/user_queues_test.go
+++ b/pkg/scheduler/queue/user_queues_test.go
@@ -13,7 +13,7 @@ import (
 )
 
 func TestQueues(t *testing.T) {
-	uq := newUserQueues(0, 0)
+	uq := newUserQueues(0, 0, MockLimits{})
 	assert.NotNil(t, uq)
 	assert.NoError(t, isConsistent(uq))
 
@@ -68,7 +68,7 @@ func TestQueues(t *testing.T) {
 }
 
 func TestQueuesWithQueriers(t *testing.T) {
-	uq := newUserQueues(0, 0)
+	uq := newUserQueues(0, 0, MockLimits{})
 	assert.NotNil(t, uq)
 	assert.NoError(t, isConsistent(uq))
 
@@ -145,7 +145,7 @@ func TestQueuesConsistency(t *testing.T) {
 
 	for testName, testData := range tests {
 		t.Run(testName, func(t *testing.T) {
-			uq := newUserQueues(0, testData.forgetDelay)
+			uq := newUserQueues(0, testData.forgetDelay, MockLimits{})
 			assert.NotNil(t, uq)
 			assert.NoError(t, isConsistent(uq))
 
@@ -194,7 +194,7 @@ func TestQueues_ForgetDelay(t *testing.T) {
 	)
 
 	now := time.Now()
-	uq := newUserQueues(0, forgetDelay)
+	uq := newUserQueues(0, forgetDelay, MockLimits{})
 	assert.NotNil(t, uq)
 	assert.NoError(t, isConsistent(uq))
 
@@ -286,7 +286,7 @@ func TestQueues_ForgetDelay_ShouldCorrectlyHandleQuerierReconnectingBeforeForget
 	)
 
 	now := time.Now()
-	uq := newUserQueues(0, forgetDelay)
+	uq := newUserQueues(0, forgetDelay, MockLimits{})
 	assert.NotNil(t, uq)
 	assert.NoError(t, isConsistent(uq))
 
diff --git a/pkg/scheduler/scheduler.go b/pkg/scheduler/scheduler.go
index 772e60c87a1..115de295c31 100644
--- a/pkg/scheduler/scheduler.go
+++ b/pkg/scheduler/scheduler.go
@@ -86,7 +86,7 @@ type Config struct {
 }
 
 func (cfg *Config) RegisterFlags(f *flag.FlagSet) {
-	f.IntVar(&cfg.MaxOutstandingPerTenant, "query-scheduler.max-outstanding-requests-per-tenant", 100, "Maximum number of outstanding requests per tenant per query-scheduler. In-flight requests above this limit will fail with HTTP response status code 429.")
+	f.IntVar(&cfg.MaxOutstandingPerTenant, "query-scheduler.max-outstanding-requests-per-tenant", 0, "Deprecated (use frontend.max-outstanding-requests-per-tenant instead) and will be removed in v1.17.0: Maximum number of outstanding requests per tenant per query-scheduler. In-flight requests above this limit will fail with HTTP response status code 429.")
 	f.DurationVar(&cfg.QuerierForgetDelay, "query-scheduler.querier-forget-delay", 0, "If a querier disconnects without sending notification about graceful shutdown, the query-scheduler will keep the querier in the tenant's shard until the forget delay has passed. This feature is useful to reduce the blast radius when shuffle-sharding is enabled.")
 	cfg.GRPCClientConfig.RegisterFlagsWithPrefix("query-scheduler.grpc-client-config", f)
 }
@@ -111,7 +111,7 @@ func NewScheduler(cfg Config, limits Limits, log log.Logger, registerer promethe
 		Name: "cortex_query_scheduler_discarded_requests_total",
 		Help: "Total number of query requests discarded.",
 	}, []string{"user"})
-	s.requestQueue = queue.NewRequestQueue(cfg.MaxOutstandingPerTenant, cfg.QuerierForgetDelay, s.queueLength, s.discardedRequests)
+	s.requestQueue = queue.NewRequestQueue(cfg.MaxOutstandingPerTenant, cfg.QuerierForgetDelay, s.queueLength, s.discardedRequests, s.limits)
 
 	s.queueDuration = promauto.With(registerer).NewHistogram(prometheus.HistogramOpts{
 		Name:    "cortex_query_scheduler_queue_duration_seconds",
@@ -143,6 +143,8 @@ func NewScheduler(cfg Config, limits Limits, log log.Logger, registerer promethe
 type Limits interface {
 	// MaxQueriersPerUser returns max queriers to use per tenant, or 0 if shuffle sharding is disabled.
 	MaxQueriersPerUser(user string) int
+
+	queue.Limits
 }
 
 type schedulerRequest struct {
diff --git a/pkg/scheduler/scheduler_test.go b/pkg/scheduler/scheduler_test.go
index 14449dc8c45..b2ef66cc651 100644
--- a/pkg/scheduler/scheduler_test.go
+++ b/pkg/scheduler/scheduler_test.go
@@ -20,7 +20,9 @@ import (
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials/insecure"
 
+	frontendv1 "github.com/cortexproject/cortex/pkg/frontend/v1"
 	"github.com/cortexproject/cortex/pkg/frontend/v2/frontendv2pb"
+	"github.com/cortexproject/cortex/pkg/scheduler/queue"
 	"github.com/cortexproject/cortex/pkg/scheduler/schedulerpb"
 	"github.com/cortexproject/cortex/pkg/util/flagext"
 	"github.com/cortexproject/cortex/pkg/util/httpgrpcutil"
@@ -35,7 +37,7 @@ func setupScheduler(t *testing.T, reg prometheus.Registerer) (*Scheduler, schedu
 	flagext.DefaultValues(&cfg)
 	cfg.MaxOutstandingPerTenant = testMaxOutstandingPerTenant
 
-	s, err := NewScheduler(cfg, &limits{queriers: 2}, log.NewNopLogger(), reg)
+	s, err := NewScheduler(cfg, frontendv1.MockLimits{Queriers: 2, MockLimits: queue.MockLimits{MaxOutstanding: 100}}, log.NewNopLogger(), reg)
 	require.NoError(t, err)
 
 	server := grpc.NewServer()
@@ -494,14 +496,6 @@ func verifyNoPendingRequestsLeft(t *testing.T, scheduler *Scheduler) {
 	})
 }
 
-type limits struct {
-	queriers int
-}
-
-func (l limits) MaxQueriersPerUser(_ string) int {
-	return l.queriers
-}
-
 type frontendMock struct {
 	mu   sync.Mutex
 	resp map[uint64]*httpgrpc.HTTPResponse
diff --git a/pkg/util/validation/limits.go b/pkg/util/validation/limits.go
index 24869b15506..3f4e67dc36d 100644
--- a/pkg/util/validation/limits.go
+++ b/pkg/util/validation/limits.go
@@ -81,6 +81,9 @@ type Limits struct {
 	MaxQueriersPerTenant         int            `yaml:"max_queriers_per_tenant" json:"max_queriers_per_tenant"`
 	QueryVerticalShardSize       int            `yaml:"query_vertical_shard_size" json:"query_vertical_shard_size" doc:"hidden"`
 
+	// Query Frontend / Scheduler enforced limits.
+	MaxOutstandingPerTenant int `yaml:"max_outstanding_requests_per_tenant" json:"max_outstanding_requests_per_tenant"`
+
 	// Ruler defaults and limits.
 	RulerEvaluationDelay        model.Duration `yaml:"ruler_evaluation_delay_duration" json:"ruler_evaluation_delay_duration"`
 	RulerTenantShardSize        int            `yaml:"ruler_tenant_shard_size" json:"ruler_tenant_shard_size"`
@@ -161,6 +164,8 @@ func (l *Limits) RegisterFlags(f *flag.FlagSet) {
 	f.IntVar(&l.MaxQueriersPerTenant, "frontend.max-queriers-per-tenant", 0, "Maximum number of queriers that can handle requests for a single tenant. If set to 0 or value higher than number of available queriers, *all* queriers will handle requests for the tenant. Each frontend (or query-scheduler, if used) will select the same set of queriers for the same tenant (given that all queriers are connected to all frontends / query-schedulers). This option only works with queriers connecting to the query-frontend / query-scheduler, not when using downstream URL.")
 	f.IntVar(&l.QueryVerticalShardSize, "frontend.query-vertical-shard-size", 0, "[Experimental] Number of shards to use when distributing shardable PromQL queries.")
 
+	f.IntVar(&l.MaxOutstandingPerTenant, "frontend.max-outstanding-requests-per-tenant", 100, "Maximum number of outstanding requests per tenant per request queue (either query frontend or query scheduler); requests beyond this error with HTTP 429.")
+
 	f.Var(&l.RulerEvaluationDelay, "ruler.evaluation-delay-duration", "Duration to delay the evaluation of rules to ensure the underlying metrics have been pushed to Cortex.")
 	f.IntVar(&l.RulerTenantShardSize, "ruler.tenant-shard-size", 0, "The default tenant's shard size when the shuffle-sharding strategy is used by ruler. When this setting is specified in the per-tenant overrides, a value of 0 disables shuffle sharding for the tenant.")
 	f.IntVar(&l.RulerMaxRulesPerRuleGroup, "ruler.max-rules-per-rule-group", 0, "Maximum number of rules per rule group per-tenant. 0 to disable.")
@@ -446,6 +451,12 @@ func (o *Overrides) MaxQueryParallelism(userID string) int {
 	return o.GetOverridesForUser(userID).MaxQueryParallelism
 }
 
+// MaxOutstandingPerTenant returns the limit to the maximum number
+// of outstanding requests per tenant per request queue.
+func (o *Overrides) MaxOutstandingPerTenant(userID string) int {
+	return o.GetOverridesForUser(userID).MaxOutstandingPerTenant
+}
+
 // EnforceMetricName whether to enforce the presence of a metric name.
 func (o *Overrides) EnforceMetricName(userID string) bool {
 	return o.GetOverridesForUser(userID).EnforceMetricName