diff --git a/sdk/cosmos/azure-cosmos-tests/src/test/java/com/azure/cosmos/implementation/ConfigsTests.java b/sdk/cosmos/azure-cosmos-tests/src/test/java/com/azure/cosmos/implementation/ConfigsTests.java
index 89885ae320f6..54b0a0c2ef30 100644
--- a/sdk/cosmos/azure-cosmos-tests/src/test/java/com/azure/cosmos/implementation/ConfigsTests.java
+++ b/sdk/cosmos/azure-cosmos-tests/src/test/java/com/azure/cosmos/implementation/ConfigsTests.java
@@ -170,11 +170,11 @@ public void http2MaxConcurrentStreams() {
 
     @Test(groups = { "emulator" })
     public void thinClientEnabledTest() {
-        assertThat(isThinClientEnabled()).isFalse();
+        assertThat(isThinClientEnabled()).isTrue();
         System.clearProperty("COSMOS.THINCLIENT_ENABLED");
-        System.setProperty("COSMOS.THINCLIENT_ENABLED", "true");
+        System.setProperty("COSMOS.THINCLIENT_ENABLED", "false");
         try {
-            assertThat(isThinClientEnabled()).isTrue();
+            assertThat(isThinClientEnabled()).isFalse();
         } finally {
             System.clearProperty("COSMOS.THINCLIENT_ENABLED");
         }
diff --git a/sdk/cosmos/azure-cosmos/CHANGELOG.md b/sdk/cosmos/azure-cosmos/CHANGELOG.md
index 8475b83dc5ee..3571663c32ee 100644
--- a/sdk/cosmos/azure-cosmos/CHANGELOG.md
+++ b/sdk/cosmos/azure-cosmos/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 #### Features Added
 * Added support for N-Region synchronous commit feature - See [PR 47757](https://github.com/Azure/azure-sdk-for-java/pull/47757)
+* Auto-enable thin client mode under gateway mode when the account's gateway metadata response indicates a thin client endpoint is available. Use system property `COSMOS.THINCLIENT_ENABLED=false` (or env var `COSMOS_THINCLIENT_ENABLED=false`) to opt out. No new public API is introduced.
 
 #### Breaking Changes
 
diff --git a/sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/Configs.java b/sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/Configs.java
index beadb0af6cf4..74ececaf92a1 100644
--- a/sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/Configs.java
+++ b/sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/Configs.java
@@ -50,7 +50,7 @@ public class Configs {
     private static final String DEFAULT_THINCLIENT_ENDPOINT = "";
     private static final String THINCLIENT_ENDPOINT = "COSMOS.THINCLIENT_ENDPOINT";
     private static final String THINCLIENT_ENDPOINT_VARIABLE = "COSMOS_THINCLIENT_ENDPOINT";
-    private static final boolean DEFAULT_THINCLIENT_ENABLED = false;
+    private static final boolean DEFAULT_THINCLIENT_ENABLED = true;
     private static final String THINCLIENT_ENABLED = "COSMOS.THINCLIENT_ENABLED";
     private static final String THINCLIENT_ENABLED_VARIABLE = "COSMOS_THINCLIENT_ENABLED";
 
diff --git a/sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/RxDocumentClientImpl.java b/sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/RxDocumentClientImpl.java
index 192f8175978f..ccac248899d0 100644
--- a/sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/RxDocumentClientImpl.java
+++ b/sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/RxDocumentClientImpl.java
@@ -272,6 +272,7 @@ public class RxDocumentClientImpl implements AsyncDocumentClient, IAuthorization
     private final GlobalPartitionEndpointManagerForPerPartitionAutomaticFailover globalPartitionEndpointManagerForPerPartitionAutomaticFailover;
     private final RetryPolicy retryPolicy;
     private HttpClient reactorHttpClient;
+    private HttpClient thinClientReactorHttpClient;
     private Function<HttpClient, HttpClient> httpClientInterceptor;
     private volatile boolean useMultipleWriteLocations;
 
@@ -683,14 +684,7 @@ private RxDocumentClientImpl(URI serviceEndpoint,
             this.apiType = apiType;
             this.clientTelemetryConfig = clientTelemetryConfig;
             this.useThinClient = Configs.isThinClientEnabled()
-                && this.connectionPolicy.getConnectionMode() == ConnectionMode.GATEWAY
-                && this.connectionPolicy.getHttp2ConnectionConfig() != null
-                && ImplementationBridgeHelpers
-                    .Http2ConnectionConfigHelper
-                    .getHttp2ConnectionConfigAccessor()
-                    .isEffectivelyEnabled(
-                        this.connectionPolicy.getHttp2ConnectionConfig()
-                    );
+                && this.connectionPolicy.getConnectionMode() == ConnectionMode.GATEWAY;
         } catch (RuntimeException e) {
             logger.error("unexpected failure in initializing client.", e);
             close();
@@ -809,11 +803,19 @@ public void init(CosmosClientMetadataCachesSnapshot metadataCachesSnapshot, Func
                 this.reactorHttpClient,
                 this.apiType);
 
+            if (this.useThinClient) {
+                HttpClient thinClientHttp = thinClientHttpClient();
+                if (httpClientInterceptor != null) {
+                    thinClientHttp = httpClientInterceptor.apply(thinClientHttp);
+                }
+                this.thinClientReactorHttpClient = thinClientHttp;
+            }
+
             this.thinProxy = createThinProxy(this.sessionContainer,
                 this.consistencyLevel,
                 this.userAgentContainer,
                 this.globalEndpointManager,
-                this.reactorHttpClient);
+                this.useThinClient ? this.thinClientReactorHttpClient : this.reactorHttpClient);
 
             this.perPartitionFailoverConfigModifier
                 = (databaseAccount -> {
@@ -1000,6 +1002,36 @@ private HttpClient httpClient() {
         }
     }
 
+    private HttpClient thinClientHttpClient() {
+        // The thin client proxy communicates over HTTP/2; create a dedicated HTTP client with HTTP/2 enabled.
+        // If the user has already supplied an Http2ConnectionConfig with enabled=true, use it directly.
+        // Otherwise create a new Http2ConnectionConfig with HTTP/2 forced on, preserving any pool-size
+        // and stream-concurrency settings the user may have configured.
+        Http2ConnectionConfig userHttp2Config = this.connectionPolicy.getHttp2ConnectionConfig();
+        Http2ConnectionConfig http2Config;
+        if (userHttp2Config != null && Boolean.TRUE.equals(userHttp2Config.isEnabled())) {
+            http2Config = userHttp2Config;
+        } else {
+            http2Config = new Http2ConnectionConfig().setEnabled(true);
+            if (userHttp2Config != null) {
+                http2Config
+                    .setMaxConnectionPoolSize(userHttp2Config.getMaxConnectionPoolSize())
+                    .setMinConnectionPoolSize(userHttp2Config.getMinConnectionPoolSize())
+                    .setMaxConcurrentStreams(userHttp2Config.getMaxConcurrentStreams());
+            }
+        }
+
+        HttpClientConfig httpClientConfig = new HttpClientConfig(this.configs)
+            .withMaxIdleConnectionTimeout(this.connectionPolicy.getIdleHttpConnectionTimeout())
+            .withPoolSize(this.connectionPolicy.getMaxConnectionPoolSize())
+            .withProxy(this.connectionPolicy.getProxy())
+            .withNetworkRequestTimeout(this.connectionPolicy.getHttpNetworkRequestTimeout())
+            .withServerCertValidationDisabled(this.connectionPolicy.isServerCertValidationDisabled())
+            .withHttp2ConnectionConfig(http2Config);
+
+        return HttpClient.createFixed(httpClientConfig);
+    }
+
     private void createStoreModel(boolean subscribeRntbdStatus) {
         // EnableReadRequestsFallback, if not explicitly set on the connection policy,
         // is false if the account's consistency is bounded staleness,
@@ -1530,7 +1562,7 @@ private void addUserAgentSuffix(UserAgentContainer userAgentContainer, Set<UserA
             userAgentFeatureFlags.remove(UserAgentFeatureFlags.PerPartitionCircuitBreaker);
         }
 
-        if (!Configs.isThinClientEnabled()) {
+        if (!this.useThinClient) {
             userAgentFeatureFlags.remove(UserAgentFeatureFlags.ThinClient);
         }
 
@@ -6587,6 +6619,10 @@ public void close() {
             LifeCycleUtils.closeQuietly(this.storeClientFactory);
             logger.info("Shutting down reactorHttpClient ...");
             LifeCycleUtils.closeQuietly(this.reactorHttpClient);
+            if (this.thinClientReactorHttpClient != null) {
+                logger.info("Shutting down thinClientReactorHttpClient ...");
+                LifeCycleUtils.closeQuietly(this.thinClientReactorHttpClient);
+            }
             logger.info("Shutting down CpuMonitor ...");
             CpuMemoryMonitor.unregister(this);