diff --git a/README.md b/README.md
index b5747e371..913d1663b 100644
--- a/README.md
+++ b/README.md
@@ -90,6 +90,23 @@ LlmAgent rootAgent = LlmAgent.builder()
     .build();
 ```
 
+Models are resolved through the `LlmRegistry` by name. In addition to Gemini,
+Vertex AI, Apigee, and Claude, you can use the [OrcaRouter](https://www.orcarouter.ai)
+model gateway as an OpenAI-compatible endpoint — set the `ORCAROUTER_API_KEY`
+environment variable and pass a model like `orcarouter/auto`:
+
+```java
+LlmAgent agent = LlmAgent.builder()
+    .name("assistant")
+    .model("orcarouter/auto") // Routed through the OrcaRouter gateway
+    .instruction("You are a helpful assistant.")
+    .build();
+```
+
+The gateway also runs gateway-level, zero-trust security for AI agents on the
+same endpoint — screening every prompt/response and governing every tool call
+on a default-deny basis, with no application code changes.
+
 ### Development UI
 
 Same as the beloved Python Development UI.
diff --git a/core/src/main/java/com/google/adk/models/LlmRegistry.java b/core/src/main/java/com/google/adk/models/LlmRegistry.java
index acc038695..224983562 100644
--- a/core/src/main/java/com/google/adk/models/LlmRegistry.java
+++ b/core/src/main/java/com/google/adk/models/LlmRegistry.java
@@ -40,6 +40,7 @@ public interface LlmFactory {
     registerLlm("gemini-.*", modelName -> Gemini.builder().modelName(modelName).build());
     registerLlm("apigee/.*", modelName -> ApigeeLlm.builder().modelName(modelName).build());
     registerLlm("gemma-.*", modelName -> Gemini.builder().modelName(modelName).build());
+    registerLlm("orcarouter/.*", modelName -> new OrcaRouterLlm(modelName));
   }
 
   /**
diff --git a/core/src/main/java/com/google/adk/models/OrcaRouterLlm.java b/core/src/main/java/com/google/adk/models/OrcaRouterLlm.java
new file mode 100644
index 000000000..5870b91c4
--- /dev/null
+++ b/core/src/main/java/com/google/adk/models/OrcaRouterLlm.java
@@ -0,0 +1,128 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.adk.models;
+
+import static com.google.common.base.Strings.isNullOrEmpty;
+
+import com.google.adk.models.chat.ChatCompletionsClient;
+import com.google.adk.models.chat.ChatCompletionsHttpClient;
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.ImmutableMap;
+import com.google.genai.types.HttpOptions;
+import io.reactivex.rxjava3.core.Flowable;
+import java.util.Objects;
+import org.jspecify.annotations.Nullable;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A {@link BaseLlm} implementation for calling the <a
+ * href="https://www.orcarouter.ai">OrcaRouter</a> model gateway.
+ *
+ * <p>OrcaRouter is an OpenAI-compatible model gateway that routes each request to a model hosted by
+ * one of its upstream providers. This implementation talks to the gateway's {@code
+ * /v1/chat/completions} endpoint using {@link ChatCompletionsHttpClient}, supporting both
+ * non-streaming and streaming responses.
+ *
+ * <p>The API key is read from the {@code ORCAROUTER_API_KEY} environment variable. The base URL
+ * defaults to {@code https://api.orcarouter.ai/v1} and can be overridden with the {@code
+ * ORCAROUTER_BASE_URL} environment variable.
+ *
+ * <p>Model names must use the {@code orcarouter/<model>} format, e.g. {@code orcarouter/auto}
+ * (smart routing) or {@code orcarouter/fusion}. The gateway accepts the model identifier as-is,
+ * including the {@code orcarouter/} namespace prefix.
+ */
+public class OrcaRouterLlm extends BaseLlm {
+  private static final Logger logger = LoggerFactory.getLogger(OrcaRouterLlm.class);
+
+  static final String API_KEY_ENV_VAR = "ORCAROUTER_API_KEY";
+  static final String BASE_URL_ENV_VAR = "ORCAROUTER_BASE_URL";
+  static final String DEFAULT_BASE_URL = "https://api.orcarouter.ai/v1";
+  static final String MODEL_PREFIX = "orcarouter/";
+
+  private final ChatCompletionsClient chatCompletionsClient;
+
+  /**
+   * Constructs a new {@code OrcaRouterLlm} instance.
+   *
+   * <p>The chat completions client is built from the {@code ORCAROUTER_API_KEY} and {@code
+   * ORCAROUTER_BASE_URL} environment variables.
+   *
+   * @param modelName the OrcaRouter model name (e.g., {@code orcarouter/auto})
+   * @throws IllegalArgumentException if the model name is not in the {@code orcarouter/<model>}
+   *     format or the API key is not configured
+   */
+  public OrcaRouterLlm(String modelName) {
+    this(modelName, buildChatCompletionsClient());
+  }
+
+  /**
+   * Constructs a new {@code OrcaRouterLlm} instance with the given chat completions client, for
+   * testing purposes.
+   *
+   * @param modelName the OrcaRouter model name (e.g., {@code orcarouter/auto})
+   * @param chatCompletionsClient the client used to call the gateway
+   */
+  @VisibleForTesting
+  OrcaRouterLlm(String modelName, ChatCompletionsClient chatCompletionsClient) {
+    super(validateModelName(modelName));
+    this.chatCompletionsClient =
+        Objects.requireNonNull(chatCompletionsClient, "chatCompletionsClient cannot be null");
+  }
+
+  /** Builds the production chat completions client from environment variables. */
+  private static ChatCompletionsClient buildChatCompletionsClient() {
+    String apiKey = System.getenv(API_KEY_ENV_VAR);
+    if (isNullOrEmpty(apiKey)) {
+      throw new IllegalArgumentException(
+          "OrcaRouter API key is not set. Set the " + API_KEY_ENV_VAR + " environment variable.");
+    }
+    String baseUrl = System.getenv(BASE_URL_ENV_VAR);
+    if (isNullOrEmpty(baseUrl)) {
+      baseUrl = DEFAULT_BASE_URL;
+    }
+    HttpOptions httpOptions =
+        HttpOptions.builder()
+            .baseUrl(baseUrl)
+            .headers(ImmutableMap.of("Authorization", "Bearer " + apiKey))
+            .build();
+    logger.debug("OrcaRouterLlm constructed with baseUrl={}", baseUrl);
+    return new ChatCompletionsHttpClient(httpOptions);
+  }
+
+  @Override
+  public Flowable<LlmResponse> generateContent(LlmRequest llmRequest, boolean stream) {
+    String modelToUse = llmRequest.model().orElse(model());
+    LlmRequest newLlmRequest = llmRequest.toBuilder().model(validateModelName(modelToUse)).build();
+    return chatCompletionsClient.complete(newLlmRequest, stream);
+  }
+
+  @Override
+  public BaseLlmConnection connect(LlmRequest llmRequest) {
+    throw new UnsupportedOperationException(
+        "Streaming connections are not supported for OrcaRouter models.");
+  }
+
+  private static String validateModelName(@Nullable String modelName) {
+    if (isNullOrEmpty(modelName)
+        || !modelName.startsWith(MODEL_PREFIX)
+        || modelName.length() == MODEL_PREFIX.length()) {
+      throw new IllegalArgumentException(
+          "Invalid OrcaRouter model name, expected orcarouter/<model>: " + modelName);
+    }
+    return modelName;
+  }
+}
diff --git a/core/src/test/java/com/google/adk/models/OrcaRouterLlmTest.java b/core/src/test/java/com/google/adk/models/OrcaRouterLlmTest.java
new file mode 100644
index 000000000..8572b77ba
--- /dev/null
+++ b/core/src/test/java/com/google/adk/models/OrcaRouterLlmTest.java
@@ -0,0 +1,162 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.adk.models;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertThrows;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import com.google.adk.models.chat.ChatCompletionsClient;
+import com.google.common.collect.ImmutableList;
+import com.google.genai.types.Content;
+import com.google.genai.types.Part;
+import io.reactivex.rxjava3.core.Flowable;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnit;
+import org.mockito.junit.MockitoRule;
+
+@RunWith(JUnit4.class)
+public class OrcaRouterLlmTest {
+
+  @Rule public final MockitoRule mocks = MockitoJUnit.rule();
+  @Mock private ChatCompletionsClient mockCcClient;
+
+  @Test
+  public void build_withValidModelStrings_succeeds() {
+    String[] validModelStrings = {
+      "orcarouter/auto",
+      "orcarouter/fusion",
+      "orcarouter/fusion-flash",
+      "orcarouter/fusion-mini",
+      "orcarouter/deepseek/deepseek-v4-pro"
+    };
+
+    for (String modelName : validModelStrings) {
+      OrcaRouterLlm llm = new OrcaRouterLlm(modelName, mockCcClient);
+      assertThat(llm).isNotNull();
+      assertThat(llm.model()).isEqualTo(modelName);
+    }
+  }
+
+  @Test
+  public void build_withInvalidModelStrings_throwsException() {
+    String[] invalidModelStrings = {
+      "auto", "orcarouter", "orcarouter/", "orcarouter", "gemini-2.5-flash", "", null
+    };
+
+    for (String modelName : invalidModelStrings) {
+      assertThrows(
+          IllegalArgumentException.class, () -> new OrcaRouterLlm(modelName, mockCcClient));
+    }
+  }
+
+  @Test
+  public void generateContent_sendsToCcClient() {
+    when(mockCcClient.complete(any(), anyBoolean())).thenReturn(Flowable.empty());
+
+    OrcaRouterLlm llm = new OrcaRouterLlm("orcarouter/auto", mockCcClient);
+    LlmRequest request =
+        LlmRequest.builder()
+            .model("orcarouter/auto")
+            .contents(ImmutableList.of(Content.builder().parts(Part.fromText("hello")).build()))
+            .build();
+    llm.generateContent(request, false).test().assertNoErrors();
+
+    ArgumentCaptor<LlmRequest> requestCaptor = ArgumentCaptor.forClass(LlmRequest.class);
+    verify(mockCcClient).complete(requestCaptor.capture(), eq(false));
+    assertThat(requestCaptor.getValue().model()).hasValue("orcarouter/auto");
+  }
+
+  @Test
+  public void generateContent_sendsStreamingToCcClient() {
+    when(mockCcClient.complete(any(), anyBoolean())).thenReturn(Flowable.empty());
+
+    OrcaRouterLlm llm = new OrcaRouterLlm("orcarouter/fusion", mockCcClient);
+    LlmRequest request =
+        LlmRequest.builder()
+            .model("orcarouter/fusion")
+            .contents(ImmutableList.of(Content.builder().parts(Part.fromText("hi")).build()))
+            .build();
+    llm.generateContent(request, true).test().assertNoErrors();
+
+    ArgumentCaptor<LlmRequest> requestCaptor = ArgumentCaptor.forClass(LlmRequest.class);
+    verify(mockCcClient).complete(requestCaptor.capture(), eq(true));
+    assertThat(requestCaptor.getValue().model()).hasValue("orcarouter/fusion");
+  }
+
+  @Test
+  public void generateContent_requestLevelModelOverride_preservesPrefix() {
+    when(mockCcClient.complete(any(), anyBoolean())).thenReturn(Flowable.empty());
+
+    OrcaRouterLlm llm = new OrcaRouterLlm("orcarouter/auto", mockCcClient);
+    LlmRequest request =
+        LlmRequest.builder()
+            .model("orcarouter/fusion-flash")
+            .contents(ImmutableList.of(Content.builder().parts(Part.fromText("hello")).build()))
+            .build();
+    llm.generateContent(request, false).test().assertNoErrors();
+
+    ArgumentCaptor<LlmRequest> requestCaptor = ArgumentCaptor.forClass(LlmRequest.class);
+    verify(mockCcClient).complete(requestCaptor.capture(), eq(false));
+    assertThat(requestCaptor.getValue().model()).hasValue("orcarouter/fusion-flash");
+  }
+
+  @Test
+  public void generateContent_invalidRequestLevelOverride_throwsException() {
+    OrcaRouterLlm llm = new OrcaRouterLlm("orcarouter/auto", mockCcClient);
+    LlmRequest request =
+        LlmRequest.builder()
+            .model("gemini-2.5-flash")
+            .contents(ImmutableList.of(Content.builder().parts(Part.fromText("hello")).build()))
+            .build();
+
+    IllegalArgumentException e =
+        assertThrows(IllegalArgumentException.class, () -> llm.generateContent(request, false));
+    assertThat(e)
+        .hasMessageThat()
+        .contains("Invalid OrcaRouter model name, expected orcarouter/<model>: gemini-2.5-flash");
+  }
+
+  @Test
+  public void connect_throwsUnsupportedOperationException() {
+    OrcaRouterLlm llm = new OrcaRouterLlm("orcarouter/auto", mockCcClient);
+    LlmRequest request = LlmRequest.builder().model("orcarouter/auto").build();
+    UnsupportedOperationException e =
+        assertThrows(UnsupportedOperationException.class, () -> llm.connect(request));
+    assertThat(e)
+        .hasMessageThat()
+        .contains("Streaming connections are not supported for OrcaRouter models.");
+  }
+
+  @Test
+  public void llmRegistry_resolvesOrcaRouterModels() {
+    // ORCAROUTER_API_KEY must be set for the production path; clear it to assert the error path
+    // first, then check the registry wiring with a registered pattern.
+    assertThat(LlmRegistry.matchesAnyPattern("orcarouter/auto")).isTrue();
+    assertThat(LlmRegistry.matchesAnyPattern("orcarouter/fusion")).isTrue();
+    assertThat(LlmRegistry.matchesAnyPattern("gemini-2.5-flash")).isTrue();
+    assertThat(LlmRegistry.matchesAnyPattern("claude-sonnet-5")).isFalse();
+  }
+}