diff --git a/apps/sdk-contract-tests/include/definitions.hpp b/apps/sdk-contract-tests/include/definitions.hpp
index deb67d1d9..7c08d367c 100644
--- a/apps/sdk-contract-tests/include/definitions.hpp
+++ b/apps/sdk-contract-tests/include/definitions.hpp
@@ -80,6 +80,14 @@ NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(ConfigClientSideParams,
                                                 evaluationReasons,
                                                 useReport);
 
+struct ConfigTags {
+    std::optional<std::string> applicationId;
+    std::optional<std::string> applicationVersion;
+};
+NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(ConfigTags,
+                                                applicationId,
+                                                applicationVersion);
+
 struct ConfigParams {
     std::string credential;
     std::optional<uint32_t> startWaitTimeMs;
@@ -89,6 +97,7 @@ struct ConfigParams {
     std::optional<ConfigEventParams> events;
     std::optional<ConfigServiceEndpointsParams> serviceEndpoints;
     std::optional<ConfigClientSideParams> clientSide;
+    std::optional<ConfigTags> tags;
 };
 NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(ConfigParams,
                                                 credential,
@@ -98,7 +107,8 @@ NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT(ConfigParams,
                                                 polling,
                                                 events,
                                                 serviceEndpoints,
-                                                clientSide);
+                                                clientSide,
+                                                tags);
 
 struct ContextSingleParams {
     std::optional<std::string> kind;
diff --git a/apps/sdk-contract-tests/src/entity_manager.cpp b/apps/sdk-contract-tests/src/entity_manager.cpp
index b9055f349..cf81109b3 100644
--- a/apps/sdk-contract-tests/src/entity_manager.cpp
+++ b/apps/sdk-contract-tests/src/entity_manager.cpp
@@ -114,6 +114,15 @@ std::optional<std::string> EntityManager::create(ConfigParams const& in) {
         datasource.UseReport(*in.clientSide->useReport);
     }
 
+    if (in.tags) {
+        if (in.tags->applicationId) {
+            config_builder.AppInfo().Identifier(*in.tags->applicationId);
+        }
+        if (in.tags->applicationVersion) {
+            config_builder.AppInfo().Version(*in.tags->applicationVersion);
+        }
+    }
+
     auto config = config_builder.Build();
     if (!config) {
         LD_LOG(logger_, LogLevel::kWarn)
diff --git a/apps/sdk-contract-tests/test-suppressions.txt b/apps/sdk-contract-tests/test-suppressions.txt
index cfdacd3ff..882dab53b 100644
--- a/apps/sdk-contract-tests/test-suppressions.txt
+++ b/apps/sdk-contract-tests/test-suppressions.txt
@@ -1,6 +1,5 @@
 events/summary events/basic counter behavior
 events/summary events/reset after each flush
-tags/disallowed characters
 
 # The Client doesn't need to know how to deserialize users.
 context type/convert/old user to context/{"key": ""}
diff --git a/libs/client-sdk/src/data_sources/polling_data_source.cpp b/libs/client-sdk/src/data_sources/polling_data_source.cpp
index 5d098f7bb..b07567a41 100644
--- a/libs/client-sdk/src/data_sources/polling_data_source.cpp
+++ b/libs/client-sdk/src/data_sources/polling_data_source.cpp
@@ -57,6 +57,10 @@ static network::HttpRequest MakeRequest(Config const& config,
 
     builder.Header("authorization", config.SdkKey());
 
+    if (auto app_tag = config.ApplicationTag()) {
+        builder.Header("x-launchdarkly-tags", *app_tag);
+    }
+
     // If no URL is set, then we will fail the request.
     return {url.value_or(""), method, builder.Build(), body};
 }
diff --git a/libs/client-sdk/src/data_sources/streaming_data_source.cpp b/libs/client-sdk/src/data_sources/streaming_data_source.cpp
index 3e3980bc9..1dc681082 100644
--- a/libs/client-sdk/src/data_sources/streaming_data_source.cpp
+++ b/libs/client-sdk/src/data_sources/streaming_data_source.cpp
@@ -33,6 +33,7 @@ StreamingDataSource::StreamingDataSource(
       context_(std::move(context)),
       http_config_(config.HttpProperties()),
       data_source_config_(config.DataSourceConfig()),
+      app_tags_(config.ApplicationTag()),
       sdk_key_(config.SdkKey()),
       streaming_endpoint_(config.ServiceEndpoints().StreamingBaseUrl()) {}
 
@@ -108,6 +109,10 @@ void StreamingDataSource::Start() {
     }
     client_builder.header("user-agent", http_config_.UserAgent());
 
+    if (app_tags_) {
+        client_builder.header("x-launchdarkly-tags", *app_tags_);
+    }
+
     // TODO: Handle proxy support.
 
     auto weak_self = weak_from_this();
diff --git a/libs/client-sdk/src/data_sources/streaming_data_source.hpp b/libs/client-sdk/src/data_sources/streaming_data_source.hpp
index 61ad2817c..218a86975 100644
--- a/libs/client-sdk/src/data_sources/streaming_data_source.hpp
+++ b/libs/client-sdk/src/data_sources/streaming_data_source.hpp
@@ -48,6 +48,8 @@ class StreamingDataSource final
 
     config::shared::built::HttpProperties http_config_;
 
+    std::optional<std::string> app_tags_;
+
     std::string sdk_key_;
 
     Logger const& logger_;