diff --git a/examples/audience/Assets/SampleApp/Resources/AudienceSample.uxml b/examples/audience/Assets/SampleApp/Resources/AudienceSample.uxml
index a8b8bd303..ffe03aa5f 100644
--- a/examples/audience/Assets/SampleApp/Resources/AudienceSample.uxml
+++ b/examples/audience/Assets/SampleApp/Resources/AudienceSample.uxml
@@ -3,9 +3,6 @@
 
     <ui:VisualElement name="root" class="root">
 
-        <ui:Label name="prod-warning" class="prod-warning hidden"
-                  text="⚠ USING PROD ENDPOINT — ACTIONS HERE AFFECT PROD DATA ⚠" />
-
         <ui:VisualElement name="sticky-outer" class="sticky-outer">
             <ui:VisualElement class="sticky-top-main">
 
@@ -78,7 +75,7 @@
                         <ui:VisualElement class="field placeholder-host">
                             <ui:Label class="field-label" text="PUBLISHABLE KEY" />
                             <ui:TextField name="publishable-key" />
-                            <ui:Label class="field-placeholder" text="pk_imapik-test-yourkey" />
+                            <ui:Label class="field-placeholder" text="pk_imapik-yourkey" />
                         </ui:VisualElement>
 
                         <ui:VisualElement class="field">
@@ -99,6 +96,12 @@
                                      text="Mirror SDK internal log output into the in-page event log below." />
                         </ui:VisualElement>
 
+                        <ui:VisualElement class="field">
+                            <ui:Toggle name="test-mode" label="TEST MODE" value="true" />
+                            <ui:Label class="helper-text below-field"
+                                     text="Tags all outbound events with test: true so the backend can filter them from production analytics." />
+                        </ui:VisualElement>
+
                         <ui:VisualElement name="mobile-attribution-field" class="field">
                             <ui:Toggle name="enable-mobile-attribution" label="MOBILE ATTRIBUTION" />
                             <ui:Label class="helper-text below-field"
@@ -120,7 +123,7 @@
                             <ui:TextField name="base-url" />
                             <ui:Label class="field-placeholder" text="(derived from key)" />
                             <ui:Label class="helper-text below-field"
-                                     text="Bypass the SDK's prefix-based routing and target a specific backend. Leave empty to derive from the publishable key." />
+                                     text="Target a specific backend. Leave empty to use the production endpoint." />
                         </ui:VisualElement>
 
                         <ui:VisualElement class="advanced-grid">
diff --git a/examples/audience/Assets/SampleApp/Scripts/AudienceSample.UI.cs b/examples/audience/Assets/SampleApp/Scripts/AudienceSample.UI.cs
index 903f37ca8..059bf91fb 100644
--- a/examples/audience/Assets/SampleApp/Scripts/AudienceSample.UI.cs
+++ b/examples/audience/Assets/SampleApp/Scripts/AudienceSample.UI.cs
@@ -51,6 +51,7 @@ private static readonly (string TabId, string PanelId)[] Tabs =
         // ---- UXML element fields (Setup tab) ----
 
         private TextField _publishableKey, _baseUrl, _flushInterval, _flushSize;
+        private Toggle _testMode;
         private DropdownField _initialConsent;
         private Toggle _debug, _enableMobileAttribution;
         private Button _btnInit, _btnFlush, _btnReset, _btnShutdown, _btnDeleteData, _btnRequestAtt;
@@ -75,7 +76,7 @@ private static readonly (string TabId, string PanelId)[] Tabs =
         // ---- UXML element fields (Tabs + status bar + header) ----
 
         private readonly List<Button> _tabButtons = new List<Button>();
-        private Label _prodWarning, _sdkVersionLabel, _titleLabel;
+        private Label _sdkVersionLabel, _titleLabel;
         private Label _statusEndpoint, _statusConsent, _statusAnon, _statusUser, _statusSession, _statusQueue;
 
         // ---- UXML element fields (Log pane) ----
@@ -164,7 +165,7 @@ private T Require<T>(string name) where T : VisualElement =>
 
         private void BindElements()
         {
-            _prodWarning      = Require<Label>("prod-warning");
+
             _sdkVersionLabel  = Require<Label>("sdk-version");
             _titleLabel       = _root.Q<Label>(className: "title");
 
@@ -181,17 +182,19 @@ private void BindElements()
             _baseUrl        = Require<TextField>("base-url");
             _initialConsent = Require<DropdownField>("initial-consent");
             _debug                    = Require<Toggle>("debug");
+            _testMode                 = Require<Toggle>("test-mode");
             _enableMobileAttribution  = Require<Toggle>("enable-mobile-attribution");
             // Inject a tick Label — Unity 2021.3 runtime panels render the
             // checked state as a plain coloured square otherwise. USS hides
             // the tick when unchecked.
-            var debugCheckmark = _debug.Q<VisualElement>(className: "unity-toggle__checkmark");
-            if (debugCheckmark != null)
+            foreach (var toggle in new[] { _debug, _testMode, _enableMobileAttribution })
             {
+                var checkmark = toggle.Q<VisualElement>(className: "unity-toggle__checkmark");
+                if (checkmark == null) continue;
                 var tick = new Label("✓");
                 tick.AddToClassList("debug-tick");
                 tick.pickingMode = PickingMode.Ignore;
-                debugCheckmark.Add(tick);
+                checkmark.Add(tick);
             }
             _flushInterval = Require<TextField>("flush-interval");
             _flushSize     = Require<TextField>("flush-size");
@@ -610,15 +613,9 @@ private void RefreshStatusBar()
             var key = (_publishableKey.value ?? "").Trim();
             var overrideUrl = (_baseUrl?.value ?? "").Trim();
             bool keyEmpty = string.IsNullOrEmpty(key);
-            bool isTest = !keyEmpty && IsTestKey(key);
             bool hasOverride = !string.IsNullOrEmpty(overrideUrl);
-            // BaseUrl override skips prefix-based routing, so the prod-warning
-            // rule no longer applies (studio is in explicit-target mode).
-            string? derivedFromKey = keyEmpty ? null : (isTest ? Constants.SandboxBaseUrl : Constants.ProductionBaseUrl);
-            string? endpoint = hasOverride ? overrideUrl : derivedFromKey;
-            bool warnState = hasOverride || (!keyEmpty && !isTest);
-            SetStatusCell(_statusEndpoint, endpoint, warnState ? "state-warn" : "state-ok");
-            _prodWarning.EnableInClassList("hidden", hasOverride || keyEmpty || isTest);
+            string? endpoint = hasOverride ? overrideUrl : (keyEmpty ? null : Constants.ProductionBaseUrl);
+            SetStatusCell(_statusEndpoint, endpoint, hasOverride ? "state-warn" : "state-ok");
 
             var consent = _initialised ? ImmutableAudience.CurrentConsent : ConsentOrder[Mathf.Clamp(_initialConsent?.index ?? 0, 0, ConsentOrder.Length - 1)];
             int cIdx = Array.IndexOf(ConsentOrder, consent);
@@ -676,16 +673,18 @@ internal readonly struct InitForm
             public readonly string BaseUrl;
             public readonly ConsentLevel Consent;
             public readonly bool Debug;
+            public readonly bool TestMode;
             public readonly bool EnableMobileAttribution;
             public readonly int? FlushIntervalMs;
             public readonly int? FlushSize;
 
-            public InitForm(string publishableKey, string baseUrl, ConsentLevel consent, bool debug, bool enableMobileAttribution, int? flushIntervalMs, int? flushSize)
+            public InitForm(string publishableKey, string baseUrl, ConsentLevel consent, bool debug, bool testMode, bool enableMobileAttribution, int? flushIntervalMs, int? flushSize)
             {
                 PublishableKey = publishableKey;
                 BaseUrl = baseUrl;
                 Consent = consent;
                 Debug = debug;
+                TestMode = testMode;
                 EnableMobileAttribution = enableMobileAttribution;
                 FlushIntervalMs = flushIntervalMs;
                 FlushSize = flushSize;
@@ -702,6 +701,7 @@ internal InitForm CaptureInitForm()
                 baseUrl:                 (_baseUrl.value ?? "").Trim(),
                 consent:                 ConsentOrder[consentIdx],
                 debug:                   _debug.value,
+                testMode:                _testMode.value,
                 enableMobileAttribution: _enableMobileAttribution.value,
                 flushIntervalMs:         flushIntervalMs,
                 flushSize:               flushSize);
@@ -780,9 +780,6 @@ private bool IsAliasReady()
                 && (fromId != toId || (_aliasFromType.value ?? "") != (_aliasToType.value ?? ""));
         }
 
-        private static bool IsTestKey(string? key) =>
-            !string.IsNullOrEmpty(key) && key!.StartsWith(Constants.TestKeyPrefix, StringComparison.Ordinal);
-
         private static void FlashCopied(VisualElement ve)
         {
             ve.AddToClassList("copied");
diff --git a/examples/audience/Assets/SampleApp/Scripts/AudienceSample.cs b/examples/audience/Assets/SampleApp/Scripts/AudienceSample.cs
index 153192fa1..91ceed56e 100644
--- a/examples/audience/Assets/SampleApp/Scripts/AudienceSample.cs
+++ b/examples/audience/Assets/SampleApp/Scripts/AudienceSample.cs
@@ -331,9 +331,8 @@ private void OnSdkStateChanged()
         // ---- Config builders ----
 
         // Maps the captured Setup form to AudienceConfig. BaseUrl null → SDK
-        // derives the endpoint from the publishable key prefix (test → sandbox,
-        // else production). The flushInterval clamp emits a warn row when
-        // the user requests <1s.
+        // targets the production endpoint. The flushInterval clamp emits a warn
+        // row when the user requests <1s.
         private AudienceConfig BuildAudienceConfig(InitForm form, Action<AudienceError> onError)
         {
             var config = new AudienceConfig
@@ -342,6 +341,7 @@ private AudienceConfig BuildAudienceConfig(InitForm form, Action<AudienceError>
                 BaseUrl                 = string.IsNullOrEmpty(form.BaseUrl) ? null : form.BaseUrl,
                 Consent                 = form.Consent,
                 Debug                   = form.Debug,
+                TestMode                = form.TestMode,
                 EnableMobileAttribution = form.EnableMobileAttribution,
                 OnError                 = onError,
             };
@@ -364,6 +364,7 @@ private static Dictionary<string, object> BuildConfigEcho(AudienceConfig config)
             {
                 ["consent"]                  = config.Consent.ToString(),
                 ["debug"]                    = config.Debug,
+                ["testMode"]                 = config.TestMode,
                 ["enableMobileAttribution"]  = config.EnableMobileAttribution,
                 ["flushIntervalSeconds"]     = config.FlushIntervalSeconds,
                 ["flushSize"]                = config.FlushSize,
@@ -377,7 +378,7 @@ private static Dictionary<string, object> BuildConfigEcho(AudienceConfig config)
             return echo;
         }
 
-        // Keeps the pk_imapik-test- / pk_imapik- prefix visible; masks the rest.
+        // Keeps the pk_imapik- prefix visible; masks the rest.
         // Caller must guard against null/empty; signature non-nullable so the
         // dictionary insertion in BuildInitConfigEcho doesn't trip CS8601.
         private static string RedactPublishableKey(string key)
diff --git a/examples/audience/Assets/SampleApp/Tests/Runtime/SampleAppLiveFireTests.cs b/examples/audience/Assets/SampleApp/Tests/Runtime/SampleAppLiveFireTests.cs
index f68a89233..534bcf29c 100644
--- a/examples/audience/Assets/SampleApp/Tests/Runtime/SampleAppLiveFireTests.cs
+++ b/examples/audience/Assets/SampleApp/Tests/Runtime/SampleAppLiveFireTests.cs
@@ -45,15 +45,13 @@ public void SetUp()
                 System.IO.Directory.Delete(sdkDir, recursive: true);
 
             // Unity's bundled Mono runtime ships a curated root-CA set that
-            // does not include the chain api.sandbox.immutable.com presents,
-            // so HttpClient under Mono2x raises "SSL connection could not be
-            // established" on every Flush. The cert is valid; only Mono's
-            // verification fails. IL2CPP uses the OS CA store and is fine.
+            // may not include the full chain the backend presents, so
+            // HttpClient under Mono2x can raise "SSL connection could not be
+            // established". The cert is valid; only Mono's verification fails.
+            // IL2CPP uses the OS CA store and is fine.
             //
-            // Bypass cert validation IN THE TEST PROCESS ONLY so the same
-            // suite exercises both backends. Production SDK code is
-            // untouched. Acceptable risk: this test process talks only to
-            // sandbox; live-fire payloads carry no real user data.
+            // Bypass cert validation IN THE TEST PROCESS ONLY. Production SDK
+            // code is untouched.
             System.Net.ServicePointManager.ServerCertificateValidationCallback =
                 (_, _, _, _) => true;
 
@@ -89,8 +87,7 @@ private IEnumerator LoadAndInit(string? initialConsent = null, Action<VisualElem
         }
 
         // Scene load + AudienceSample lookup + root capture, without clicking
-        // btn-init. Useful for tests that need to inspect pre-init UI state
-        // (e.g. prod-warning visibility for non-test keys).
+        // btn-init. Useful for tests that need to inspect pre-init UI state.
         private IEnumerator LoadSceneOnly()
         {
             _key = Environment.GetEnvironmentVariable(SampleAppUi.EnvKey) ?? "";
@@ -331,7 +328,7 @@ public IEnumerator Reset_RegeneratesAnonymousIdAndAcceptsTrack()
         {
             // Reset clears identity + queue and rolls a new anonymousId. A
             // following Track must serialise with the new anonymousId and
-            // round-trip to sandbox without errors.
+            // round-trip to the backend without errors.
             yield return LoadAndInit();
 
             _root!.Q<Button>(SampleAppUi.Buttons.TypedEvent("progression")).Click();
@@ -495,12 +492,11 @@ public IEnumerator TypedEvent_LinkClicked_FlushReportsOk()
         [UnityTest]
         public IEnumerator Init_WithBaseUrlOverride_FlushReportsOk()
         {
-            // Explicit BaseUrl skips the publishable-key prefix routing in
-            // Constants. Same target endpoint here, but the override branch is
-            // a different config setup path that IL2CPP could strip independently.
+            // Explicit BaseUrl exercises the override code path independently
+            // of the default-production path — IL2CPP could strip either branch.
             yield return LoadAndInit(configure: root =>
             {
-                root.Q<TextField>(SampleAppUi.Setup.BaseUrl).value = SampleAppUi.SandboxBaseUrl;
+                root.Q<TextField>(SampleAppUi.Setup.BaseUrl).value = SampleAppUi.ExplicitBaseUrl;
             });
 
             _root!.Q<Button>(SampleAppUi.Buttons.TypedEvent("progression")).Click();
@@ -738,30 +734,5 @@ public IEnumerator IdentityPanel_PopulatesUserIdAfterIdentify()
                 "identity-user-id label should reflect ImmutableAudience.UserId after Identify");
         }
 
-        [UnityTest]
-        public IEnumerator ProdWarning_HiddenForTestKey()
-        {
-            // The default env-var key is a test key (pk_imapik-test-…). The
-            // prod-warning banner should stay hidden after RefreshStatusBar.
-            yield return LoadSceneOnly();
-            _root!.Q<TextField>(SampleAppUi.Setup.PublishableKey).value = _key;
-            yield return null;
-
-            Assert.IsTrue(_root.Q<Label>(SampleAppUi.ProdWarning).ClassListContains(SampleAppUi.HiddenClass),
-                "prod-warning should be hidden when the publishable-key is a test key");
-        }
-
-        [UnityTest]
-        public IEnumerator ProdWarning_VisibleForNonTestKey()
-        {
-            // A key without the "test-" segment looks production. Don't actually
-            // Init so we don't live-fire to prod; just verify the warning UI.
-            yield return LoadSceneOnly();
-            _root!.Q<TextField>(SampleAppUi.Setup.PublishableKey).value = "pk_imapik-fakeprod-zzzz";
-            yield return null;
-
-            Assert.IsFalse(_root.Q<Label>(SampleAppUi.ProdWarning).ClassListContains(SampleAppUi.HiddenClass),
-                "prod-warning should be visible when the publishable-key looks like a prod key");
-        }
     }
 }
diff --git a/examples/audience/Assets/SampleApp/Tests/Runtime/SampleAppUi.cs b/examples/audience/Assets/SampleApp/Tests/Runtime/SampleAppUi.cs
index 3746e0792..52dc9f8e4 100644
--- a/examples/audience/Assets/SampleApp/Tests/Runtime/SampleAppUi.cs
+++ b/examples/audience/Assets/SampleApp/Tests/Runtime/SampleAppUi.cs
@@ -19,9 +19,9 @@ internal static class SampleAppUi
         // Scene asset name registered in EditorBuildSettings.
         internal const string SceneName = "SampleApp";
 
-        // The env var that carries the sandbox publishable key into the
-        // built player at test time. Test runs inject it on the Unity CLI;
-        // CI wires it from the AUDIENCE_TEST_PUBLISHABLE_KEY repo secret.
+        // The env var that carries the publishable key into the built player at
+        // test time. Test runs inject it on the Unity CLI; CI wires it from
+        // the AUDIENCE_TEST_PUBLISHABLE_KEY repo secret.
         internal const string EnvKey = "AUDIENCE_TEST_PUBLISHABLE_KEY";
 
         // Mirrors AudiencePaths.RootDirName — the SDK persists consent /
@@ -29,8 +29,8 @@ internal static class SampleAppUi
         // wipes this between tests so on-disk state can't leak.
         internal const string SdkPersistedDirName = "imtbl_audience";
 
-        // Mirrors Constants.SandboxBaseUrl — used by the BaseUrl-override test.
-        internal const string SandboxBaseUrl = "https://api.sandbox.immutable.com";
+        // Used by the BaseUrl-override test to exercise the explicit-target code path.
+        internal const string ExplicitBaseUrl = "https://api.immutable.com";
 
         // ---- UXML element names ----
         // All names verified against examples/audience/Assets/SampleApp/Resources/AudienceSample.uxml.
@@ -41,6 +41,7 @@ internal static class Setup
             internal const string InitialConsent = "initial-consent";
             internal const string BaseUrl = "base-url";
             internal const string Debug = "debug";
+            internal const string TestMode = "test-mode";
             internal const string FlushInterval = "flush-interval";
             internal const string FlushSize = "flush-size";
         }
@@ -126,10 +127,6 @@ internal static class Panels
         // it as `root.Q<ScrollView>(SampleAppUi.LogScrollView)`.
         internal const string LogScrollView = "log";
 
-        // The banner that warns when the publishable key looks like a prod
-        // key. Toggled via the "hidden" CSS class.
-        internal const string ProdWarning = "prod-warning";
-
         // Mirrors AudienceSample.UI.cs PopulateTypedEventAccordions naming:
         //   input.name = $"typed-{spec.Name.Replace('_', '-')}-{field.Key.ToLowerInvariant().Replace('_', '-')}";
         internal static string TypedEventField(string specName, string fieldKey) =>
@@ -141,9 +138,6 @@ internal static string TypedEventField(string specName, string fieldKey) =>
         // on consent buttons, etc.
         internal const string ActiveClass = "active";
 
-        // Toggled by RefreshStatusBar on the prod-warning banner.
-        internal const string HiddenClass = "hidden";
-
         // ---- Log labels ----
         // Mirrors AudienceSample.cs: every RunAndLog(label, ...) and
         // AppendLog(label, ...) call. Tests await these via WaitForLogEntry.
diff --git a/src/Packages/Audience/Runtime/AudienceConfig.cs b/src/Packages/Audience/Runtime/AudienceConfig.cs
index cd7c7148f..8d7e38d52 100644
--- a/src/Packages/Audience/Runtime/AudienceConfig.cs
+++ b/src/Packages/Audience/Runtime/AudienceConfig.cs
@@ -21,12 +21,19 @@ public class AudienceConfig
         /// Override the default API base URL.
         /// </summary>
         /// <remarks>
-        /// When null, publishable keys starting with <c>pk_imapik-test-</c>
-        /// resolve to Sandbox. All other keys resolve to Production. Set
-        /// explicitly to target a different backend.
+        /// When null, all events are sent to the production backend. Set
+        /// explicitly to target a different backend (e.g. an internal dev
+        /// environment).
         /// </remarks>
         public string? BaseUrl { get; set; }
 
+        /// <summary>
+        /// Enables test mode. When <c>true</c>, all events are tagged with
+        /// <c>test: true</c> so the backend can filter them from production
+        /// analytics. Default <c>false</c>.
+        /// </summary>
+        public bool TestMode { get; set; } = false;
+
         /// <summary>
         /// Initial consent level.
         /// </summary>
diff --git a/src/Packages/Audience/Runtime/Core/Constants.cs b/src/Packages/Audience/Runtime/Core/Constants.cs
index f217812d5..4ac8220b4 100644
--- a/src/Packages/Audience/Runtime/Core/Constants.cs
+++ b/src/Packages/Audience/Runtime/Core/Constants.cs
@@ -4,8 +4,6 @@ namespace Immutable.Audience
 {
     internal static class Constants
     {
-        internal const string TestKeyPrefix = "pk_imapik-test-";
-        internal const string SandboxBaseUrl = "https://api.sandbox.immutable.com";
         internal const string ProductionBaseUrl = "https://api.immutable.com";
 
         internal const string MessagesPath = "/v1/audience/messages";
@@ -26,21 +24,17 @@ internal static class Constants
 
         internal const string PublishableKeyHeader = "x-immutable-publishable-key";
 
-        internal static string MessagesUrl(string? publishableKey, string? baseUrlOverride = null) =>
-            BaseUrl(publishableKey, baseUrlOverride) + MessagesPath;
-        internal static string ConsentUrl(string? publishableKey, string? baseUrlOverride = null) =>
-            BaseUrl(publishableKey, baseUrlOverride) + ConsentPath;
-        internal static string DataUrl(string? publishableKey, string? baseUrlOverride = null) =>
-            BaseUrl(publishableKey, baseUrlOverride) + DataPath;
+        internal static string MessagesUrl(string? baseUrlOverride = null) =>
+            BaseUrl(baseUrlOverride) + MessagesPath;
+        internal static string ConsentUrl(string? baseUrlOverride = null) =>
+            BaseUrl(baseUrlOverride) + ConsentPath;
+        internal static string DataUrl(string? baseUrlOverride = null) =>
+            BaseUrl(baseUrlOverride) + DataPath;
 
-        // Override wins when non-empty; otherwise test keys map to Sandbox
-        // and every other key maps to Production. Matches @imtbl/audience.
-        internal static string BaseUrl(string? publishableKey, string? baseUrlOverride = null)
+        internal static string BaseUrl(string? baseUrlOverride = null)
         {
             if (!string.IsNullOrEmpty(baseUrlOverride)) return baseUrlOverride!;
-            return publishableKey != null && publishableKey.StartsWith(TestKeyPrefix)
-                ? SandboxBaseUrl
-                : ProductionBaseUrl;
+            return ProductionBaseUrl;
         }
     }
 
diff --git a/src/Packages/Audience/Runtime/Events/MessageBuilder.cs b/src/Packages/Audience/Runtime/Events/MessageBuilder.cs
index 43f815248..4a1de52ba 100644
--- a/src/Packages/Audience/Runtime/Events/MessageBuilder.cs
+++ b/src/Packages/Audience/Runtime/Events/MessageBuilder.cs
@@ -12,9 +12,10 @@ internal static Dictionary<string, object> Track(
             string? anonymousId,
             string? userId,
             string packageVersion,
-            Dictionary<string, object>? properties = null)
+            Dictionary<string, object>? properties = null,
+            bool testMode = false)
         {
-            var msg = BuildBase(MessageTypes.Track, packageVersion);
+            var msg = BuildBase(MessageTypes.Track, packageVersion, testMode);
             msg["eventName"] = Truncate(eventName, Constants.MaxFieldLength);
 
             if (!string.IsNullOrEmpty(anonymousId))
@@ -37,9 +38,10 @@ internal static Dictionary<string, object> Identify(
             string? userId,
             string identityType,
             string packageVersion,
-            Dictionary<string, object>? traits = null)
+            Dictionary<string, object>? traits = null,
+            bool testMode = false)
         {
-            var msg = BuildBase(MessageTypes.Identify, packageVersion);
+            var msg = BuildBase(MessageTypes.Identify, packageVersion, testMode);
 
             if (!string.IsNullOrEmpty(anonymousId))
                 msg["anonymousId"] = Truncate(anonymousId, Constants.MaxFieldLength);
@@ -63,9 +65,10 @@ internal static Dictionary<string, object> Alias(
             string fromType,
             string toId,
             string toType,
-            string packageVersion)
+            string packageVersion,
+            bool testMode = false)
         {
-            var msg = BuildBase(MessageTypes.Alias, packageVersion);
+            var msg = BuildBase(MessageTypes.Alias, packageVersion, testMode);
             msg["fromId"] = Truncate(fromId, Constants.MaxFieldLength);
             msg["fromType"] = Truncate(fromType, Constants.MaxFieldLength);
             msg["toId"] = Truncate(toId, Constants.MaxFieldLength);
@@ -73,9 +76,9 @@ internal static Dictionary<string, object> Alias(
             return msg;
         }
 
-        private static Dictionary<string, object> BuildBase(string type, string packageVersion)
+        private static Dictionary<string, object> BuildBase(string type, string packageVersion, bool testMode)
         {
-            return new Dictionary<string, object>
+            var msg = new Dictionary<string, object>
             {
                 [MessageFields.Type] = type,
                 ["messageId"] = Guid.NewGuid().ToString(),
@@ -87,6 +90,9 @@ private static Dictionary<string, object> BuildBase(string type, string packageV
                 },
                 ["surface"] = Constants.Surface
             };
+            if (testMode)
+                msg["test"] = true;
+            return msg;
         }
 
         private static string Truncate(string s, int maxLen)
diff --git a/src/Packages/Audience/Runtime/ImmutableAudience.cs b/src/Packages/Audience/Runtime/ImmutableAudience.cs
index d2a58765c..7a63925bb 100644
--- a/src/Packages/Audience/Runtime/ImmutableAudience.cs
+++ b/src/Packages/Audience/Runtime/ImmutableAudience.cs
@@ -195,8 +195,6 @@ public static void Init(AudienceConfig config)
                     return;
                 }
 
-                WarnIfKeyEnvironmentMismatch(config.PublishableKey, config.BaseUrl);
-
                 _config = config;
                 Log.Enabled = config.Debug;
                 // Persisted consent overrides the config default (prior downgrade survives restart).
@@ -332,7 +330,7 @@ public static void Track(IEvent evt)
             var anonymousId = Identity.GetOrCreate(config.PersistentDataPath!, state.Level);
             // ToProperties returns a fresh dict per call, so no snapshot needed.
             var userId = state.Level == ConsentLevel.Full ? state.UserId : null;
-            var msg = MessageBuilder.Track(eventName, anonymousId, userId, config.PackageVersion, properties);
+            var msg = MessageBuilder.Track(eventName, anonymousId, userId, config.PackageVersion, properties, config.TestMode);
             EnqueueTrack(msg);
         }
 
@@ -359,7 +357,7 @@ public static void Track(string eventName, Dictionary<string, object>? propertie
             var anonymousId = Identity.GetOrCreate(config.PersistentDataPath!, state.Level);
             var userId = state.Level == ConsentLevel.Full ? state.UserId : null;
             var msg = MessageBuilder.Track(eventName, anonymousId, userId, config.PackageVersion,
-                SnapshotCallerDict(properties));
+                SnapshotCallerDict(properties), config.TestMode);
             EnqueueTrack(msg);
         }
 
@@ -405,7 +403,7 @@ public static void Identify(string userId, IdentityType identityType, Dictionary
 
             var anonymousId = Identity.GetOrCreate(config.PersistentDataPath!, level);
             var msg = MessageBuilder.Identify(anonymousId, userId, identityType.ToLowercaseString(),
-                config.PackageVersion, SnapshotCallerDict(traits));
+                config.PackageVersion, SnapshotCallerDict(traits), config.TestMode);
             EnqueueIdentity(msg);
         }
 
@@ -436,7 +434,7 @@ public static void Alias(string fromId, IdentityType fromType, string toId, Iden
             if (config == null) return;
 
             var msg = MessageBuilder.Alias(fromId, fromType.ToLowercaseString(), toId, toType.ToLowercaseString(),
-                config.PackageVersion);
+                config.PackageVersion, config.TestMode);
             EnqueueIdentity(msg);
         }
 
@@ -511,7 +509,7 @@ public static Task DeleteData(string? userId = null)
                 query = "anonymousId=" + Uri.EscapeDataString(anonymousId);
             }
 
-            var url = Constants.DataUrl(config.PublishableKey, config.BaseUrl) + "?" + query;
+            var url = Constants.DataUrl(config.BaseUrl) + "?" + query;
             var onError = config.OnError;
             var publishableKey = config.PublishableKey;
             var cancellationToken = _shutdownCancellationSource?.Token ?? CancellationToken.None;
@@ -675,7 +673,7 @@ private static void SyncConsentToBackend(AudienceConfig config, ConsentLevel lev
             var client = _controlClient;
             if (client == null) return;
 
-            var url = Constants.ConsentUrl(config.PublishableKey, config.BaseUrl);
+            var url = Constants.ConsentUrl(config.BaseUrl);
             var publishableKey = config.PublishableKey;
             var onError = config.OnError;
             var cancellationToken = _shutdownCancellationSource?.Token ?? CancellationToken.None;
@@ -985,25 +983,6 @@ internal static void ResetState()
         private static Dictionary<string, object>? SnapshotCallerDict(Dictionary<string, object>? src) =>
             src != null ? new Dictionary<string, object>(src) : null;
 
-        // Only the exact production/sandbox swap is flagged; custom dev/staging
-        // URLs are intentional and left alone.
-        private static void WarnIfKeyEnvironmentMismatch(string publishableKey, string? baseUrlOverride)
-        {
-            if (string.IsNullOrEmpty(baseUrlOverride)) return;
-
-            var trimmed = baseUrlOverride!.TrimEnd('/');
-            var isTestKey = publishableKey.StartsWith(Constants.TestKeyPrefix);
-
-            if (isTestKey && trimmed == Constants.ProductionBaseUrl)
-            {
-                Log.Warn(AudienceLogs.TestKeyAgainstProduction);
-            }
-            else if (!isTestKey && trimmed == Constants.SandboxBaseUrl)
-            {
-                Log.Warn(AudienceLogs.NonTestKeyAgainstSandbox);
-            }
-        }
-
         // Checks the current consent inside the drain lock. If consent has
         // since dropped to None the message is discarded. If it dropped to
         // Anonymous the userId is stripped.
diff --git a/src/Packages/Audience/Runtime/Transport/HttpTransport.cs b/src/Packages/Audience/Runtime/Transport/HttpTransport.cs
index 6ac6e5357..4eefbbb55 100644
--- a/src/Packages/Audience/Runtime/Transport/HttpTransport.cs
+++ b/src/Packages/Audience/Runtime/Transport/HttpTransport.cs
@@ -41,7 +41,7 @@ internal HttpTransport(
         {
             _store = store ?? throw new ArgumentNullException(nameof(store));
             _publishableKey = publishableKey ?? throw new ArgumentNullException(nameof(publishableKey));
-            _url = Constants.MessagesUrl(publishableKey, baseUrlOverride);
+            _url = Constants.MessagesUrl(baseUrlOverride);
             _onError = onError;
             // disposeHandler: false so the consumer can reuse their handler
             // across Init/Shutdown cycles (matches _controlClient's policy).
diff --git a/src/Packages/Audience/Runtime/Utility/Log.cs b/src/Packages/Audience/Runtime/Utility/Log.cs
index a9d77a7d8..772f3aeeb 100644
--- a/src/Packages/Audience/Runtime/Utility/Log.cs
+++ b/src/Packages/Audience/Runtime/Utility/Log.cs
@@ -51,16 +51,6 @@ internal static class AudienceLogs
             "Init called more than once. Ignoring; original config retained. " +
             "Call Shutdown() first if reconfiguring is intended.";
 
-        internal static readonly string TestKeyAgainstProduction =
-            $"Publishable key has the test prefix ({Constants.TestKeyPrefix}) but BaseUrl points to production. " +
-            "The backend will reject events with 401. Either remove the BaseUrl override (test keys " +
-            "default to sandbox) or use a non-test publishable key.";
-
-        internal static readonly string NonTestKeyAgainstSandbox =
-            "Publishable key is not a test key but BaseUrl points to sandbox. " +
-            "The backend will reject events with 401. Either remove the BaseUrl override (non-test " +
-            $"keys default to production) or use a test publishable key ({Constants.TestKeyPrefix}).";
-
         // ---- Track ----
 
         internal const string TrackIEventNull =
diff --git a/src/Packages/Audience/Tests/Runtime/AudienceConfigTests.cs b/src/Packages/Audience/Tests/Runtime/AudienceConfigTests.cs
index 84a198a19..4d7a0e839 100644
--- a/src/Packages/Audience/Tests/Runtime/AudienceConfigTests.cs
+++ b/src/Packages/Audience/Tests/Runtime/AudienceConfigTests.cs
@@ -37,5 +37,19 @@ public void SKAdNetworkIds_RoundTrips()
             var config = new AudienceConfig { SKAdNetworkIds = ids };
             Assert.AreSame(ids, config.SKAdNetworkIds);
         }
+
+        [Test]
+        public void TestMode_DefaultsToFalse()
+        {
+            var config = new AudienceConfig();
+            Assert.IsFalse(config.TestMode);
+        }
+
+        [Test]
+        public void TestMode_RoundTrips()
+        {
+            var config = new AudienceConfig { TestMode = true };
+            Assert.IsTrue(config.TestMode);
+        }
     }
 }
diff --git a/src/Packages/Audience/Tests/Runtime/ConsentSyncTests.cs b/src/Packages/Audience/Tests/Runtime/ConsentSyncTests.cs
index f9d31de2c..102612eeb 100644
--- a/src/Packages/Audience/Tests/Runtime/ConsentSyncTests.cs
+++ b/src/Packages/Audience/Tests/Runtime/ConsentSyncTests.cs
@@ -42,7 +42,7 @@ public void SetConsent_FiresPut_WithExpectedBodyShape()
             var put = WaitForPut(handler);
             var body = JsonReader.DeserializeObject(put.Body);
 
-            Assert.AreEqual(Constants.ConsentUrl("pk_imapik-test-key1"), put.Url);
+            Assert.AreEqual(Constants.ConsentUrl(), put.Url);
             Assert.AreEqual("full", body["status"]);
             Assert.AreEqual(Constants.ConsentSource, body["source"]);
             Assert.IsTrue(body.ContainsKey("anonymousId"));
diff --git a/src/Packages/Audience/Tests/Runtime/ConstantsTests.cs b/src/Packages/Audience/Tests/Runtime/ConstantsTests.cs
index fd7258eae..ec8a8da45 100644
--- a/src/Packages/Audience/Tests/Runtime/ConstantsTests.cs
+++ b/src/Packages/Audience/Tests/Runtime/ConstantsTests.cs
@@ -11,43 +11,22 @@ internal class ConstantsTests
         // -----------------------------------------------------------------
 
         [Test]
-        public void BaseUrl_TestKey_ResolvesToSandbox()
+        public void BaseUrl_NoOverride_ResolvesToProduction()
         {
-            Assert.AreEqual(Constants.SandboxBaseUrl,
-                Constants.BaseUrl("pk_imapik-test-abc"));
+            Assert.AreEqual(Constants.ProductionBaseUrl, Constants.BaseUrl());
         }
 
         [Test]
-        public void BaseUrl_NonTestKey_ResolvesToProduction()
+        public void BaseUrl_Override_WinsOverDefault()
         {
-            Assert.AreEqual(Constants.ProductionBaseUrl,
-                Constants.BaseUrl("pk_imapik-prod-abc"));
-        }
-
-        [Test]
-        public void BaseUrl_NullKey_ResolvesToProduction()
-        {
-            Assert.AreEqual(Constants.ProductionBaseUrl,
-                Constants.BaseUrl(null));
-        }
-
-        [Test]
-        public void BaseUrl_Override_WinsOverKeyPrefix()
-        {
-            // Override wins even for a test-prefixed key that would
-            // otherwise derive to Sandbox.
             const string custom = "https://api.dev.immutable.com";
-            Assert.AreEqual(custom,
-                Constants.BaseUrl("pk_imapik-test-abc", custom));
+            Assert.AreEqual(custom, Constants.BaseUrl(custom));
         }
 
         [Test]
-        public void BaseUrl_EmptyOverride_FallsBackToKeyDerivation()
+        public void BaseUrl_EmptyOverride_FallsBackToProduction()
         {
-            // Empty-string override is treated as "no override" so the
-            // key-prefix fallback still kicks in.
-            Assert.AreEqual(Constants.SandboxBaseUrl,
-                Constants.BaseUrl("pk_imapik-test-abc", ""));
+            Assert.AreEqual(Constants.ProductionBaseUrl, Constants.BaseUrl(""));
         }
 
         // -----------------------------------------------------------------
diff --git a/src/Packages/Audience/Tests/Runtime/Events/MessageBuilderTests.cs b/src/Packages/Audience/Tests/Runtime/Events/MessageBuilderTests.cs
index abe12f166..ef6347067 100644
--- a/src/Packages/Audience/Tests/Runtime/Events/MessageBuilderTests.cs
+++ b/src/Packages/Audience/Tests/Runtime/Events/MessageBuilderTests.cs
@@ -156,6 +156,35 @@ public void AllMessages_Context_LibraryAndLibraryVersionAreNonEmptyStrings()
             }
         }
 
+        [Test]
+        public void Track_TestModeTrue_IncludesTestFlag()
+        {
+            var result = MessageBuilder.Track("evt", null, null, PackageVersion, testMode: true);
+            Assert.IsTrue(result.ContainsKey("test"), "test field must be present when testMode is true");
+            Assert.AreEqual(true, result["test"]);
+        }
+
+        [Test]
+        public void Track_TestModeFalse_ExcludesTestFlag()
+        {
+            var result = MessageBuilder.Track("evt", null, null, PackageVersion, testMode: false);
+            Assert.IsFalse(result.ContainsKey("test"), "test field must not be present when testMode is false");
+        }
+
+        [Test]
+        public void AllMessages_TestModeTrue_AllIncludeTestFlag()
+        {
+            var track = MessageBuilder.Track("evt", null, null, PackageVersion, testMode: true);
+            var identify = MessageBuilder.Identify(null, "u1", "steam", PackageVersion, testMode: true);
+            var alias = MessageBuilder.Alias("f", "t1", "t", "t2", PackageVersion, testMode: true);
+
+            foreach (var msg in new[] { track, identify, alias })
+            {
+                Assert.IsTrue(msg.ContainsKey("test"), $"{msg["type"]} must include test field in test mode");
+                Assert.AreEqual(true, msg["test"]);
+            }
+        }
+
         private static IEnumerable<Dictionary<string, object>> EveryMessageType()
         {
             yield return MessageBuilder.Track("evt", null, null, PackageVersion);
diff --git a/src/Packages/Audience/Tests/Runtime/PublishableKeyPrefixTests.cs b/src/Packages/Audience/Tests/Runtime/PublishableKeyPrefixTests.cs
deleted file mode 100644
index 8c45c879d..000000000
--- a/src/Packages/Audience/Tests/Runtime/PublishableKeyPrefixTests.cs
+++ /dev/null
@@ -1,194 +0,0 @@
-using System.Collections.Concurrent;
-using System.Collections.Generic;
-using System.IO;
-using System.Linq;
-using System.Net;
-using System.Net.Http;
-using System.Threading;
-using System.Threading.Tasks;
-using NUnit.Framework;
-
-namespace Immutable.Audience.Tests
-{
-    [TestFixture]
-    internal class PublishableKeyPrefixTests
-    {
-        private string _testDir;
-
-        [SetUp]
-        public void SetUp()
-        {
-            _testDir = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
-            Directory.CreateDirectory(_testDir);
-        }
-
-        [TearDown]
-        public void TearDown()
-        {
-            ImmutableAudience.ResetState();
-            ImmutableAudience.LaunchContextProvider = null;
-            ImmutableAudience.ContextProvider = null;
-            ImmutableAudience.DefaultPersistentDataPathProvider = null;
-            Identity.Reset(_testDir);
-            if (Directory.Exists(_testDir))
-                Directory.Delete(_testDir, recursive: true);
-        }
-
-        // Fake fixtures on purpose: real keys would be a committed secret.
-        private const string TestPrefixKey = "pk_imapik-test-fixture";
-        private const string NonTestKey = "pk_imapik-fixture";
-        private static readonly string ProductionUrl = Constants.ProductionBaseUrl;
-        private static readonly string SandboxUrl = Constants.SandboxBaseUrl;
-
-        private class UnauthorizedHandler : HttpMessageHandler
-        {
-            protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken ct) =>
-                Task.FromResult(new HttpResponseMessage(HttpStatusCode.Unauthorized)
-                {
-                    Content = new StringContent("{\"error\":\"unknown publishable key\"}")
-                });
-        }
-
-        private AudienceConfig MakeConfig(string publishableKey, string baseUrl = null) =>
-            new AudienceConfig
-            {
-                PublishableKey = publishableKey,
-                BaseUrl = baseUrl,
-                Consent = ConsentLevel.Anonymous,
-                PersistentDataPath = _testDir,
-                FlushIntervalSeconds = TestDefaults.FlushIntervalSeconds,
-                FlushSize = TestDefaults.FlushSize,
-                HttpHandler = new UnauthorizedHandler()
-            };
-
-        // -----------------------------------------------------------------
-        // Init-time mismatch warning
-        // -----------------------------------------------------------------
-
-        [Test]
-        public void Init_TestKeyAgainstProductionUrl_LogsMismatchWarning()
-        {
-            var lines = new List<string>();
-            Log.Writer = lines.Add;
-            try
-            {
-                ImmutableAudience.Init(MakeConfig(TestPrefixKey, ProductionUrl));
-
-                Assert.That(lines, Has.Some.Contains(AudienceLogs.TestKeyAgainstProduction),
-                    "Init must warn when a test-prefix key is paired with the production BaseUrl");
-            }
-            finally { Log.Writer = null; }
-        }
-
-        [Test]
-        public void Init_NonTestKeyAgainstSandboxUrl_LogsMismatchWarning()
-        {
-            var lines = new List<string>();
-            Log.Writer = lines.Add;
-            try
-            {
-                ImmutableAudience.Init(MakeConfig(NonTestKey, SandboxUrl));
-
-                Assert.That(lines, Has.Some.Contains(AudienceLogs.NonTestKeyAgainstSandbox),
-                    "Init must warn when a non-test key is paired with the sandbox BaseUrl");
-            }
-            finally { Log.Writer = null; }
-        }
-
-        [Test]
-        public void Init_TestKeyAgainstSandboxUrl_DoesNotWarn()
-        {
-            var lines = new List<string>();
-            Log.Writer = lines.Add;
-            try
-            {
-                ImmutableAudience.Init(MakeConfig(TestPrefixKey, SandboxUrl));
-
-                Assert.That(
-                    lines.Where(l =>
-                        l.Contains(AudienceLogs.TestKeyAgainstProduction) ||
-                        l.Contains(AudienceLogs.NonTestKeyAgainstSandbox)),
-                    Is.Empty,
-                    "test-key + sandbox-URL is the canonical pairing; no warning expected");
-            }
-            finally { Log.Writer = null; }
-        }
-
-        [Test]
-        public void Init_TestKeyAgainstCustomDevUrl_DoesNotWarn()
-        {
-            var lines = new List<string>();
-            Log.Writer = lines.Add;
-            try
-            {
-                // Fake fixture URL on purpose.
-                ImmutableAudience.Init(MakeConfig(TestPrefixKey, "https://api.dev.example.com"));
-
-                Assert.That(
-                    lines.Where(l =>
-                        l.Contains(AudienceLogs.TestKeyAgainstProduction) ||
-                        l.Contains(AudienceLogs.NonTestKeyAgainstSandbox)),
-                    Is.Empty,
-                    "custom BaseUrl must not be flagged as a mismatch");
-            }
-            finally { Log.Writer = null; }
-        }
-
-        [Test]
-        public void Init_NoBaseUrlOverride_DoesNotWarn()
-        {
-            var lines = new List<string>();
-            Log.Writer = lines.Add;
-            try
-            {
-                ImmutableAudience.Init(MakeConfig(TestPrefixKey, baseUrl: null));
-
-                Assert.That(
-                    lines.Where(l =>
-                        l.Contains(AudienceLogs.TestKeyAgainstProduction) ||
-                        l.Contains(AudienceLogs.NonTestKeyAgainstSandbox)),
-                    Is.Empty,
-                    "no override means no mismatch; no warning expected");
-            }
-            finally { Log.Writer = null; }
-        }
-
-        [Test]
-        public void Init_TrailingSlashOnProductionUrl_StillDetectsMismatch()
-        {
-            var lines = new List<string>();
-            Log.Writer = lines.Add;
-            try
-            {
-                ImmutableAudience.Init(MakeConfig(TestPrefixKey, ProductionUrl + "/"));
-
-                Assert.That(lines, Has.Some.Contains(AudienceLogs.TestKeyAgainstProduction),
-                    "trailing slash on the production URL must not bypass the mismatch check");
-            }
-            finally { Log.Writer = null; }
-        }
-
-        // -----------------------------------------------------------------
-        // Runtime: backend 401 surfaces via OnError
-        // -----------------------------------------------------------------
-
-        [Test]
-        public async Task Track_BackendReturns401_SurfacesValidationRejected()
-        {
-            var errors = new ConcurrentBag<AudienceError>();
-            var config = MakeConfig(TestPrefixKey, ProductionUrl);
-            config.OnError = errors.Add;
-
-            ImmutableAudience.Init(config);
-            ImmutableAudience.Track("event_against_prod_with_test_key");
-            await ImmutableAudience.FlushAsync();
-
-            Assert.IsTrue(errors.Any(e => e.Code == AudienceErrorCode.ValidationRejected),
-                $"401 from backend must surface as ValidationRejected via OnError; observed {errors.Count} error(s)");
-            Assert.IsTrue(errors.Any(e => e.Message.Contains("401")),
-                "OnError message should include the 401 status code so the studio can correlate with backend logs");
-            Assert.IsTrue(errors.Any(e => e.Message.Contains("unknown publishable key")),
-                "OnError should propagate the backend's error body so studios can see why");
-        }
-    }
-}
diff --git a/src/Packages/Audience/Tests/Runtime/PublishableKeyPrefixTests.cs.meta b/src/Packages/Audience/Tests/Runtime/PublishableKeyPrefixTests.cs.meta
deleted file mode 100644
index cc693ecfd..000000000
--- a/src/Packages/Audience/Tests/Runtime/PublishableKeyPrefixTests.cs.meta
+++ /dev/null
@@ -1,11 +0,0 @@
-fileFormatVersion: 2
-guid: 3c9d8e1a4b7f2c5d6a8e9f0b1d2c3e4f
-MonoImporter:
-  externalObjects: {}
-  serializedVersion: 2
-  defaultReferences: []
-  executionOrder: 0
-  icon: {instanceID: 0}
-  userData:
-  assetBundleName:
-  assetBundleVariant:
diff --git a/src/Packages/Audience/Tests/Runtime/Transport/HttpTransportTests.cs b/src/Packages/Audience/Tests/Runtime/Transport/HttpTransportTests.cs
index d049705eb..4f3365977 100644
--- a/src/Packages/Audience/Tests/Runtime/Transport/HttpTransportTests.cs
+++ b/src/Packages/Audience/Tests/Runtime/Transport/HttpTransportTests.cs
@@ -124,21 +124,6 @@ public async Task SendBatchAsync_200_SendsPlainJsonPayloadWithoutContentEncoding
         }
 #endif
 
-        [Test]
-        public async Task SendBatchAsync_200_UsesCorrectUrlForTestKey()
-        {
-            _store.Write("{\"type\":\"track\"}");
-
-            HttpRequestMessage? captured = null;
-            var handler = new MockHandler(HttpStatusCode.OK, "{\"accepted\":1,\"rejected\":0}",
-                onRequest: req => captured = req);
-            using var transport = new HttpTransport(_store, "pk_imapik-test-key1", handler: handler);
-
-            await transport.SendBatchAsync();
-
-            StringAssert.StartsWith(Constants.SandboxBaseUrl, captured!.RequestUri!.ToString());
-        }
-
         [Test]
         public async Task SendBatchAsync_200_UsesCorrectUrlForProdKey()
         {