diff --git a/agent/anthropic_adapter.py b/agent/anthropic_adapter.py
index a2a052d0a8..5dee1209f5 100644
--- a/agent/anthropic_adapter.py
+++ b/agent/anthropic_adapter.py
@@ -162,6 +162,64 @@ def _is_oauth_token(key: str) -> bool:
     return True
 
 
+def build_vertex_client(project: str, region: str = "us-east5"):
+    """Build an AnthropicVertex client using GCP Application Default Credentials.
+
+    Uses the same Messages API as Anthropic direct, but authenticated via
+    GCP IAM (attached service account, ADC, or explicit key file).
+
+    Args:
+        project: GCP project ID (required)
+        region: GCP region where Claude on Vertex AI is generally available
+            (default: us-east5)
+
+    Returns:
+        AnthropicVertex client instance (same interface as Anthropic)
+    """
+    try:
+        from anthropic import AnthropicVertex
+    except ImportError:
+        raise ImportError(
+            "anthropic[vertex] is required for Vertex AI provider. "
+            "Install with: pip install 'anthropic[vertex]'"
+        )
+    from httpx import Timeout
+
+    kwargs = {
+        "project_id": project,
+        "region": region,
+        "timeout": Timeout(timeout=900.0, connect=10.0),
+    }
+
+    # If GOOGLE_APPLICATION_CREDENTIALS is set, the SDK uses it automatically.
+    # Otherwise, ADC picks up the attached service account on GCP VMs.
+
+    # Note: Beta headers are not forwarded to Vertex AI — feature availability
+    # may differ from the direct Anthropic API. The AnthropicVertex SDK handles
+    # feature negotiation with the Vertex endpoint.
+
+    return AnthropicVertex(**kwargs)
+
+
+def resolve_vertex_credentials():
+    """Resolve Vertex AI credentials from environment.
+
+    Returns:
+        Tuple of (project_id, region) or (None, None) if not configured.
+    """
+    project = (
+        os.environ.get("VERTEX_PROJECT")
+        or os.environ.get("GOOGLE_CLOUD_PROJECT")
+        or os.environ.get("GCP_PROJECT_ID")
+    )
+    region = os.environ.get("VERTEX_REGION", "us-east5")
+
+    if not project:
+        return None, None
+
+    return project, region
+
+
 def build_anthropic_client(api_key: str, base_url: str = None):
     """Create an Anthropic client, auto-detecting setup-tokens vs API keys.
 
diff --git a/agent/auxiliary_client.py b/agent/auxiliary_client.py
index 0de263c415..c0bc1c4bce 100644
--- a/agent/auxiliary_client.py
+++ b/agent/auxiliary_client.py
@@ -59,6 +59,7 @@
     "minimax": "MiniMax-M2.7-highspeed",
     "minimax-cn": "MiniMax-M2.7-highspeed",
     "anthropic": "claude-haiku-4-5-20251001",
+    "vertex-ai": "claude-haiku-4-5-20251001",
     "ai-gateway": "google/gemini-3-flash",
     "opencode-zen": "gemini-3-flash",
     "opencode-go": "glm-5",
@@ -512,6 +513,8 @@ def _resolve_api_key_provider() -> Tuple[Optional[OpenAI], Optional[str]]:
             continue
         if provider_id == "anthropic":
             return _try_anthropic()
+        if provider_id == "vertex-ai":
+            return _try_vertex()
 
         creds = resolve_api_key_provider_credentials(provider_id)
         api_key = str(creds.get("api_key", "")).strip()
@@ -667,6 +670,23 @@ def _try_codex() -> Tuple[Optional[Any], Optional[str]]:
     return CodexAuxiliaryClient(real_client, _CODEX_AUX_MODEL), _CODEX_AUX_MODEL
 
 
+def _try_vertex() -> Tuple[Optional[Any], Optional[str]]:
+    """Try to build a Vertex AI auxiliary client (Claude via GCP)."""
+    try:
+        from agent.anthropic_adapter import build_vertex_client, resolve_vertex_credentials
+    except ImportError:
+        return None, None
+
+    project, region = resolve_vertex_credentials()
+    if not project:
+        return None, None
+
+    model = _API_KEY_PROVIDER_AUX_MODELS.get("vertex-ai", "claude-haiku-4-5-20251001")
+    logger.debug("Auxiliary client: Vertex AI (%s) project=%s region=%s", model, project, region)
+    real_client = build_vertex_client(project, region)
+    return AnthropicAuxiliaryClient(real_client, model, "", ""), model
+
+
 def _try_anthropic() -> Tuple[Optional[Any], Optional[str]]:
     try:
         from agent.anthropic_adapter import build_anthropic_client, resolve_anthropic_token
@@ -968,6 +988,14 @@ def resolve_provider_client(
             final_model = model or default_model
             return (_to_async_client(client, final_model) if async_mode else (client, final_model))
 
+        if provider == "vertex-ai":
+            client, default_model = _try_vertex()
+            if client is None:
+                logger.warning("resolve_provider_client: vertex-ai requested but no GCP credentials found (set VERTEX_PROJECT)")
+                return None, None
+            final_model = model or default_model
+            return (_to_async_client(client, final_model) if async_mode else (client, final_model))
+
         creds = resolve_api_key_provider_credentials(provider)
         api_key = str(creds.get("api_key", "")).strip()
         if not api_key:
diff --git a/hermes_cli/auth.py b/hermes_cli/auth.py
index 940a155645..cf67e8ef02 100644
--- a/hermes_cli/auth.py
+++ b/hermes_cli/auth.py
@@ -156,6 +156,13 @@ class ProviderConfig:
         inference_base_url="https://api.anthropic.com",
         api_key_env_vars=("ANTHROPIC_API_KEY", "ANTHROPIC_TOKEN", "CLAUDE_CODE_OAUTH_TOKEN"),
     ),
+    "vertex-ai": ProviderConfig(
+        id="vertex-ai",
+        name="Google Vertex AI (Claude)",
+        auth_type="api_key",
+        inference_base_url="",  # Region-dependent, resolved at runtime
+        api_key_env_vars=("VERTEX_PROJECT",),  # Uses ADC, not API key
+    ),
     "alibaba": ProviderConfig(
         id="alibaba",
         name="Alibaba Cloud (DashScope)",
diff --git a/pyproject.toml b/pyproject.toml
index 38974e3287..f93442c074 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -57,6 +57,7 @@ mcp = ["mcp>=1.2.0,<2"]
 homeassistant = ["aiohttp>=3.9.0,<4"]
 sms = ["aiohttp>=3.9.0,<4"]
 acp = ["agent-client-protocol>=0.8.1,<0.9"]
+vertex = ["anthropic[vertex]>=0.39.0,<1"]
 dingtalk = ["dingtalk-stream>=0.1.0,<1"]
 feishu = ["lark-oapi>=1.5.3,<2"]
 rl = [
@@ -85,6 +86,7 @@ all = [
   "hermes-agent[acp]",
   "hermes-agent[voice]",
   "hermes-agent[dingtalk]",
+  "hermes-agent[vertex]",
   "hermes-agent[feishu]",
 ]
 
diff --git a/run_agent.py b/run_agent.py
index 30453c01ce..9489e7eb76 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -589,6 +589,8 @@ def __init__(
         elif (provider_name is None) and "chatgpt.com/backend-api/codex" in self._base_url_lower:
             self.api_mode = "codex_responses"
             self.provider = "openai-codex"
+        elif self.provider == "vertex-ai":
+            self.api_mode = "anthropic_messages"
         elif self.provider == "anthropic" or (provider_name is None and "api.anthropic.com" in self._base_url_lower):
             self.api_mode = "anthropic_messages"
             self.provider = "anthropic"
@@ -782,7 +784,21 @@ def __init__(
         self._anthropic_client = None
         self._is_anthropic_oauth = False
 
-        if self.api_mode == "anthropic_messages":
+        if self.api_mode == "anthropic_messages" and self.provider == "vertex-ai":
+            from agent.anthropic_adapter import build_vertex_client, resolve_vertex_credentials
+            project, region = resolve_vertex_credentials()
+            if not project:
+                raise ValueError("VERTEX_PROJECT environment variable is required for vertex-ai provider")
+            self._anthropic_client = build_vertex_client(project, region)
+            self._anthropic_api_key = ""
+            self._anthropic_base_url = ""
+            self._is_anthropic_oauth = False
+            self.api_key = ""
+            self.client = None
+            self._client_kwargs = {}
+            if not self.quiet_mode:
+                print(f"🤖 AI Agent initialized with model: {self.model} (Vertex AI, project={project}, region={region})")
+        elif self.api_mode == "anthropic_messages":
             from agent.anthropic_adapter import build_anthropic_client, resolve_anthropic_token
             # Only fall back to ANTHROPIC_TOKEN when the provider is actually Anthropic.
             # Other anthropic_messages providers (MiniMax, Alibaba, etc.) must use their own API key.