diff --git a/docs/my-website/docs/providers/google_code_assist.md b/docs/my-website/docs/providers/google_code_assist.md
new file mode 100644
index 00000000000..6dd3491445f
--- /dev/null
+++ b/docs/my-website/docs/providers/google_code_assist.md
@@ -0,0 +1,84 @@
+# Google Code Assist
+
+Use Google Code Assist models through LiteLLM using Gemini OAuth credentials.
+
+| Property | Details |
+|-------|-------|
+| Description | Google Code Assist API via Google Cloud Code Assist backend |
+| Provider Route on LiteLLM | `google_code_assist/` |
+| Supported Endpoints | `/chat/completions` |
+| Base Endpoint | `https://cloudcode-pa.googleapis.com` |
+
+## Model Format
+
+Use:
+
+`google_code_assist/<gemini-model>`
+
+Example:
+
+`google_code_assist/gemini-2.5-pro`
+
+## Authentication
+
+Google Code Assist requires OAuth credentials (not API key auth).
+
+LiteLLM checks credentials in this order:
+
+1. `GEMINI_OAUTH_TOKEN`
+2. `GEMINI_CREDENTIALS_PATH`
+3. `~/.config/litellm/gemini_oauth/oauth_creds.json`
+4. `~/.gemini/oauth_creds.json`
+5. `~/.config/gcloud/application_default_credentials.json`
+
+### Login via CLI
+
+```bash
+export GEMINI_OAUTH_CLIENT_ID="<your-google-oauth-client-id>"
+export GEMINI_OAUTH_CLIENT_SECRET="<your-google-oauth-client-secret>"
+litellm-proxy gemini login
+```
+
+This opens a browser loopback OAuth flow and stores credentials locally.
+
+## Usage - LiteLLM Python SDK
+
+```python
+from litellm import completion
+
+response = completion(
+    model="google_code_assist/gemini-2.5-pro",
+    messages=[{"role": "user", "content": "Write a Python function to parse CSV safely."}],
+)
+
+print(response.choices[0].message.content)
+```
+
+## Usage - LiteLLM Proxy
+
+```yaml
+model_list:
+  - model_name: google-code-assist
+    litellm_params:
+      model: google_code_assist/gemini-2.5-pro
+```
+
+```bash
+litellm --config /path/to/config.yaml
+```
+
+```bash
+curl http://localhost:4000/v1/chat/completions \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer <YOUR_LITELLM_KEY>" \
+  -d '{
+    "model": "google-code-assist",
+    "messages": [{"role": "user", "content": "Refactor this code for readability."}]
+  }'
+```
+
+## Optional Params
+
+- `google_code_assist_project`: Optional project override sent to the Code Assist backend request.
+
+LiteLLM also performs the required `loadCodeAssist` handshake before `generateContent` automatically.
diff --git a/litellm/__init__.py b/litellm/__init__.py
index 77fa48625d9..522183758fd 100644
--- a/litellm/__init__.py
+++ b/litellm/__init__.py
@@ -456,6 +456,10 @@ default_fallbacks: Optional[List] = None
 fallbacks: Optional[List] = None
 context_window_fallbacks: Optional[List] = None
 content_policy_fallbacks: Optional[List] = None
+# Backward-compatible default: do not silently reroute gemini/* calls unless explicitly enabled.
+auto_fallback_to_google_code_assist: bool = os.getenv(
+    "LITELLM_AUTO_FALLBACK_TO_GOOGLE_CODE_ASSIST", "false"
+).lower() in ("1", "true", "yes", "on")
 allowed_fails: int = 3
 allow_dynamic_callback_disabling: bool = True
 num_retries_per_request: Optional[int] = (
diff --git a/litellm/llms/gemini/authenticator.py b/litellm/llms/gemini/authenticator.py
new file mode 100644
index 00000000000..89b44a09601
--- /dev/null
+++ b/litellm/llms/gemini/authenticator.py
@@ -0,0 +1,291 @@
+import json
+import os
+import tempfile
+import time
+import webbrowser
+import http.server
+import html
+import urllib.parse
+import secrets
+import hashlib
+import base64
+from typing import Any, Dict
+
+import httpx
+
+from litellm._logging import verbose_logger
+from litellm.secret_managers.main import get_secret_str
+
+GEMINI_SCOPES = [
+    "https://www.googleapis.com/auth/cloud-platform",
+    "https://www.googleapis.com/auth/userinfo.email",
+    "https://www.googleapis.com/auth/userinfo.profile",
+    "https://www.googleapis.com/auth/generative-language",
+]
+
+# Google OAuth URLs
+GOOGLE_AUTH_URL = "https://accounts.google.com/o/oauth2/v2/auth"
+GOOGLE_TOKEN_URL = "https://oauth2.googleapis.com/token"
+
+
+class GeminiAuthenticator:
+    def __init__(self) -> None:
+        """Initialize the Gemini authenticator with configurable token paths."""
+        # Token storage paths
+        self.token_dir = os.getenv(
+            "GEMINI_OAUTH_TOKEN_DIR",
+            os.path.expanduser("~/.config/litellm/gemini_oauth"),
+        )
+        self.oauth_creds_file = os.path.join(
+            self.token_dir,
+            os.getenv("GEMINI_OAUTH_CREDS_FILE", "oauth_creds.json"),
+        )
+        self._ensure_token_dir()
+
+    @staticmethod
+    def _get_oauth_client_credentials() -> tuple[str, str]:
+        client_id = get_secret_str("GEMINI_OAUTH_CLIENT_ID")
+        client_secret = get_secret_str("GEMINI_OAUTH_CLIENT_SECRET")
+
+        if not client_id or not client_secret:
+            raise ValueError(
+                "Missing Gemini OAuth client credentials. "
+                "Set GEMINI_OAUTH_CLIENT_ID and GEMINI_OAUTH_CLIENT_SECRET."
+            )
+        return client_id, client_secret
+
+    @staticmethod
+    def _get_access_token_or_raise(creds: Dict[str, Any], source: str) -> str:
+        token = creds.get("access_token")
+        if not token or not isinstance(token, str):
+            raise Exception(
+                f"OAuth login failed: missing access_token in {source} response."
+            )
+        return token
+
+    def get_token(self) -> str:
+        """
+        Get the OAuth token, refreshing if necessary.
+
+        Returns:
+            str: The Gemini access token.
+
+        Raises:
+            Exception: If unable to obtain or refresh an access token.
+        """
+        try:
+            if os.path.exists(self.oauth_creds_file):
+                with open(self.oauth_creds_file, "r") as f:
+                    creds = json.load(f)
+
+                    # Check if access_token exists and is valid (rough check)
+                    if (
+                        creds.get("access_token")
+                        and creds.get("expires_at", 0) > time.time() + 60
+                    ):
+                        return creds.get("access_token")
+
+                    # If expired but has refresh_token, try to refresh
+                    if creds.get("refresh_token"):
+                        verbose_logger.debug(
+                            "Gemini access token expired, refreshing..."
+                        )
+                        return self._refresh_token(creds.get("refresh_token"))
+        except Exception as e:
+            verbose_logger.warning(f"Error reading Gemini OAuth credentials: {e}")
+
+        # If we get here, we need to log in
+        verbose_logger.info("Starting Gemini OAuth login flow...")
+        creds = self._login()
+        self._write_oauth_creds(creds)
+        return self._get_access_token_or_raise(creds, "authorization_code")
+
+    def _refresh_token(self, refresh_token: str) -> str:
+        """Refresh the access token using the refresh token."""
+        client_id, client_secret = self._get_oauth_client_credentials()
+        data = {
+            "client_id": client_id,
+            "client_secret": client_secret,
+            "refresh_token": refresh_token,
+            "grant_type": "refresh_token",
+        }
+        resp = httpx.post(GOOGLE_TOKEN_URL, data=data)
+        resp.raise_for_status()
+        new_creds = resp.json()
+
+        # Load existing creds to merge if possible
+        creds = {}
+        if os.path.exists(self.oauth_creds_file):
+            try:
+                with open(self.oauth_creds_file, "r") as f:
+                    creds = json.load(f)
+            except Exception:
+                pass
+
+        creds.update(new_creds)
+        if "expires_in" in new_creds:
+            creds["expires_at"] = time.time() + new_creds["expires_in"]
+
+        self._write_oauth_creds(creds)
+
+        return self._get_access_token_or_raise(creds, "refresh_token")
+
+    def _ensure_token_dir(self) -> None:
+        """Ensure the token directory exists."""
+        if not os.path.exists(self.token_dir):
+            os.makedirs(self.token_dir, mode=0o700, exist_ok=True)
+        else:
+            try:
+                os.chmod(self.token_dir, 0o700)
+            except OSError:
+                pass
+
+    def _write_oauth_creds(self, creds: Dict[str, Any]) -> None:
+        """
+        Write oauth credentials with user-only permissions.
+        """
+        fd, tmp_path = tempfile.mkstemp(dir=self.token_dir, prefix=".tmp_creds_")
+        try:
+            os.chmod(tmp_path, 0o600)
+            with os.fdopen(fd, "w", encoding="utf-8") as f:
+                json.dump(creds, f)
+            os.replace(tmp_path, self.oauth_creds_file)
+            try:
+                os.chmod(self.oauth_creds_file, 0o600)
+            except OSError:
+                pass
+        except Exception:
+            try:
+                os.unlink(tmp_path)
+            except OSError:
+                pass
+            raise
+
+    def _login(self) -> Dict[str, Any]:
+        """Perform loopback flow login."""
+        client_id, client_secret = self._get_oauth_client_credentials()
+        # PKCE
+        code_verifier = secrets.token_urlsafe(64)
+        code_challenge = (
+            base64.urlsafe_b64encode(hashlib.sha256(code_verifier.encode()).digest())
+            .decode()
+            .replace("=", "")
+        )
+
+        state = secrets.token_urlsafe(32)
+
+        # Local web server for callback
+        auth_code = None
+        error = None
+
+        class CallbackHandler(http.server.BaseHTTPRequestHandler):
+            def do_GET(self):
+                nonlocal auth_code, error
+                parsed_url = urllib.parse.urlparse(self.path)
+                if parsed_url.path != "/oauth2callback":
+                    self.send_response(404)
+                    self.end_headers()
+                    return
+
+                query = parsed_url.query
+                params = urllib.parse.parse_qs(query)
+
+                if params.get("state", [None])[0] != state:
+                    error = "state_mismatch"
+                    self.send_response(400)
+                    self.send_header("Content-type", "text/html")
+                    self.end_headers()
+                    self.wfile.write(
+                        b"<html><body><h1>Authentication failed</h1><p>State mismatch. Possible CSRF attack.</p></body></html>"
+                    )
+                elif "code" in params:
+                    auth_code = params["code"][0]
+                    self.send_response(200)
+                    self.send_header("Content-type", "text/html")
+                    self.end_headers()
+                    self.wfile.write(
+                        b"<html><body><h1>Authentication successful!</h1><p>You can close this tab and return to the terminal.</p></body></html>"
+                    )
+                elif "error" in params:
+                    error = params["error"][0]
+                    self.send_response(200)
+                    self.send_header("Content-type", "text/html")
+                    self.end_headers()
+                    self.wfile.write(
+                        (
+                            "<html><body><h1>Authentication failed</h1><p>"
+                            f"{html.escape(error)}"
+                            "</p></body></html>"
+                        ).encode()
+                    )
+                else:
+                    self.send_response(404)
+                    self.end_headers()
+
+            def log_message(self, format, *args):
+                # Suppress logging to avoid noise in the terminal
+                pass
+
+        server = http.server.HTTPServer(("127.0.0.1", 0), CallbackHandler)
+        port = server.server_port
+        redirect_uri = f"http://127.0.0.1:{port}/oauth2callback"
+
+        params = {
+            "client_id": client_id,
+            "redirect_uri": redirect_uri,
+            "response_type": "code",
+            "scope": " ".join(GEMINI_SCOPES),
+            "state": state,
+            "code_challenge": code_challenge,
+            "code_challenge_method": "S256",
+            "access_type": "offline",
+            "prompt": "consent",
+        }
+        auth_url = f"{GOOGLE_AUTH_URL}?{urllib.parse.urlencode(params)}"
+
+        print(  # noqa: T201
+            f"Please visit the following URL to authenticate:\n\n{auth_url}\n"
+        )
+        webbrowser.open(auth_url)
+
+        # Wait for callback; browsers may hit non-callback paths first (e.g. /favicon.ico).
+        # Use a bounded loop so headless/CI environments fail fast instead of hanging forever.
+        loopback_timeout_s = float(
+            os.getenv("GEMINI_OAUTH_LOOPBACK_TIMEOUT_SECONDS", "120")
+        )
+        loopback_timeout_s = max(loopback_timeout_s, 1.0)
+        deadline = time.monotonic() + loopback_timeout_s
+        server.timeout = 1.0
+        try:
+            # Note: deadline is checked after handle_request() returns, so the loop can overshoot by up to server.timeout (1s) — acceptable for a one-shot CLI login.
+            while auth_code is None and error is None:
+                server.handle_request()
+                if time.monotonic() >= deadline:
+                    raise Exception(
+                        "OAuth login timed out. Re-run `litellm-proxy gemini login` "
+                        f"and complete the browser flow within {int(loopback_timeout_s)} seconds."
+                    )
+        finally:
+            server.server_close()
+
+        if error:
+            raise Exception(f"OAuth login failed: {error}")
+        if not auth_code:
+            raise Exception("OAuth login failed: No code received")
+
+        # Exchange code for token
+        data = {
+            "client_id": client_id,
+            "client_secret": client_secret,
+            "code": auth_code,
+            "code_verifier": code_verifier,
+            "grant_type": "authorization_code",
+            "redirect_uri": redirect_uri,
+        }
+        resp = httpx.post(GOOGLE_TOKEN_URL, data=data)
+        resp.raise_for_status()
+        creds = resp.json()
+        if "expires_in" in creds:
+            creds["expires_at"] = time.time() + creds["expires_in"]
+
+        return creds
diff --git a/litellm/llms/gemini/common_utils.py b/litellm/llms/gemini/common_utils.py
index bc963d62b5f..4b389977f81 100644
--- a/litellm/llms/gemini/common_utils.py
+++ b/litellm/llms/gemini/common_utils.py
@@ -1,10 +1,12 @@
 import base64
 import datetime
+import json
 from typing import Any, Dict, List, Optional, Union
 
 import httpx
 
 import litellm
+from litellm._logging import verbose_logger
 from litellm.constants import DEFAULT_MAX_RECURSE_DEPTH
 from litellm.llms.base_llm.base_utils import BaseLLMModelInfo, BaseTokenCounter
 from litellm.llms.base_llm.chat.transformation import BaseLLMException
@@ -155,6 +157,196 @@ def get_api_key_from_env() -> Optional[str]:
     return get_secret_str("GOOGLE_API_KEY") or get_secret_str("GEMINI_API_KEY")
 
 
+def should_fallback_to_google_code_assist(error: Exception) -> bool:
+    """
+    Returns True if the error indicates missing OAuth scope for Gemini calls.
+    """
+
+    def _iter_exception_chain(exc: BaseException):
+        seen = set()
+        current: Optional[BaseException] = exc
+        while current is not None and id(current) not in seen:
+            seen.add(id(current))
+            yield current
+            current = current.__cause__ or current.__context__
+
+    def _contains_scope_code(value: Any) -> bool:
+        if isinstance(value, str):
+            return "ACCESS_TOKEN_SCOPE_INSUFFICIENT" in value
+        if isinstance(value, dict):
+            for v in value.values():
+                if _contains_scope_code(v):
+                    return True
+            return False
+        if isinstance(value, list):
+            for item in value:
+                if _contains_scope_code(item):
+                    return True
+            return False
+        return False
+
+    def _extract_json_payload_from_response(response: Any) -> Optional[dict]:
+        if response is None:
+            return None
+        try:
+            payload = response.json()
+            if isinstance(payload, dict):
+                return payload
+        except Exception:
+            pass
+        try:
+            text = getattr(response, "text", None)
+            if isinstance(text, str):
+                payload = json.loads(text)
+                if isinstance(payload, dict):
+                    return payload
+        except Exception:
+            pass
+        return None
+
+    for exc in _iter_exception_chain(error):
+        if isinstance(exc, httpx.HTTPStatusError):
+            response = getattr(exc, "response", None)
+            if response is None or getattr(response, "status_code", None) != 403:
+                continue
+
+            payload = _extract_json_payload_from_response(response)
+            if payload and _contains_scope_code(payload):
+                return True
+            continue
+
+        status_code = getattr(exc, "status_code", None)
+        if status_code != 403:
+            continue
+
+        body = getattr(exc, "body", None)
+        if body and _contains_scope_code(body):
+            return True
+
+        response = getattr(exc, "response", None)
+        payload = _extract_json_payload_from_response(response)
+        if payload and _contains_scope_code(payload):
+            return True
+
+        message = getattr(exc, "message", None)
+        if message and _contains_scope_code(message):
+            return True
+
+    return False
+
+
+def get_gemini_oauth_token() -> Optional[dict]:  # noqa: PLR0915
+    """
+    Returns the Gemini OAuth token and metadata.
+    Check:
+    1. GEMINI_OAUTH_TOKEN env var
+    2. GEMINI_CREDENTIALS_PATH env var
+    3. ~/.config/litellm/gemini_oauth/oauth_creds.json
+    4. ~/.gemini/oauth_creds.json (gemini-cli default)
+    5. ~/.config/gcloud/application_default_credentials.json (Standard ADC)
+    """
+    import json
+    import time
+    from pathlib import Path
+
+    def _is_expired(creds_data: dict) -> bool:
+        expires_at = creds_data.get("expires_at")
+        if isinstance(expires_at, (int, float)):
+            return expires_at <= (time.time() + 60)
+
+        expiry = creds_data.get("expiry") or creds_data.get("expires_on")
+        if isinstance(expiry, str):
+            try:
+                expires_dt = datetime.datetime.fromisoformat(
+                    expiry.replace("Z", "+00:00")
+                )
+                return expires_dt.timestamp() <= (time.time() + 60)
+            except Exception:
+                return False
+
+        return False
+
+    # 1. Check GEMINI_OAUTH_TOKEN
+    token = get_secret_str("GEMINI_OAUTH_TOKEN")
+    if token:
+        return {"token": token}
+
+    # 2. Check GEMINI_CREDENTIALS_PATH or default paths
+    paths_to_check = []
+    env_path = get_secret_str("GEMINI_CREDENTIALS_PATH")
+    if env_path:
+        paths_to_check.append(Path(env_path).expanduser())
+
+    paths_to_check.extend(
+        [
+            Path("~/.config/litellm/gemini_oauth/oauth_creds.json").expanduser(),
+            Path("~/.gemini/oauth_creds.json").expanduser(),
+            Path("~/.config/gcloud/application_default_credentials.json").expanduser(),
+        ]
+    )
+
+    for creds_path in paths_to_check:
+        if creds_path.exists():
+            try:
+                # Try to use google-auth if available
+                try:
+                    from google.oauth2 import credentials
+                    from google.auth.transport.requests import Request
+
+                    creds = credentials.Credentials.from_authorized_user_file(
+                        str(creds_path)
+                    )
+                    if not creds.valid:
+                        verbose_logger.debug(
+                            f"Refreshing Gemini token for {creds_path}"
+                        )
+                        creds.refresh(Request())
+                    if creds.token:
+                        result = {"token": creds.token}
+                        # Extract project ID if present
+                        with open(creds_path, "r") as f:
+                            creds_data = json.load(f)
+                            project_id = creds_data.get(
+                                "quota_project_id"
+                            ) or creds_data.get("project_id")
+                            if project_id:
+                                result["project_id"] = project_id
+                        return result
+                except Exception:
+                    # Fallback to manual reading
+                    with open(creds_path, "r") as f:
+                        creds_data = json.load(f)
+                        if _is_expired(creds_data):
+                            verbose_logger.warning(
+                                "Gemini OAuth token appears expired in %s. "
+                                "Run `litellm-proxy gemini login` to refresh credentials.",
+                                creds_path,
+                            )
+                            continue
+                        token = creds_data.get("access_token")
+                        if not token and "token" in creds_data:
+                            token_field = creds_data["token"]
+                            if isinstance(token_field, dict):
+                                token = token_field.get("accessToken")
+                            elif isinstance(token_field, str):
+                                token = token_field
+
+                        if token:
+                            result = {"token": token}
+                            project_id = creds_data.get(
+                                "quota_project_id"
+                            ) or creds_data.get("project_id")
+                            if project_id:
+                                result["project_id"] = project_id
+                            return result
+            except Exception as e:
+                verbose_logger.error(
+                    f"Error reading Gemini credentials from {creds_path}: {e}"
+                )
+
+    return None
+
+
 class GoogleAIStudioTokenCounter(BaseTokenCounter):
     """Token counter implementation for Google AI Studio provider."""
 
diff --git a/litellm/llms/gemini/fallback_handler.py b/litellm/llms/gemini/fallback_handler.py
new file mode 100644
index 00000000000..cd1cf75d5bc
--- /dev/null
+++ b/litellm/llms/gemini/fallback_handler.py
@@ -0,0 +1,57 @@
+from typing import Any, Awaitable, Callable, Dict
+
+from litellm._logging import verbose_logger
+from litellm.llms.gemini.common_utils import should_fallback_to_google_code_assist
+from litellm.llms.google_code_assist.chat import get_google_code_assist_chat
+
+_google_code_assist_chat = get_google_code_assist_chat()
+
+
+async def run_gemini_acompletion_with_code_assist_fallback(
+    primary_call: Callable[[], Awaitable[Any]],
+    fallback_kwargs: Dict[str, Any],
+    auto_fallback_to_google_code_assist: bool = False,
+) -> Any:
+    """
+    Execute Gemini async completion and fallback to Google Code Assist when
+    OAuth scope is insufficient.
+    """
+    try:
+        return await primary_call()
+    except Exception as e:
+        if not auto_fallback_to_google_code_assist:
+            raise e
+
+        if not should_fallback_to_google_code_assist(e):
+            raise e
+
+        verbose_logger.warning(
+            "Gemini request failed with ACCESS_TOKEN_SCOPE_INSUFFICIENT. "
+            "Falling back to google_code_assist."
+        )
+        return await _google_code_assist_chat.acompletion(**fallback_kwargs)
+
+
+def run_gemini_completion_with_code_assist_fallback(
+    primary_call: Callable[[], Any],
+    fallback_kwargs: Dict[str, Any],
+    auto_fallback_to_google_code_assist: bool = False,
+) -> Any:
+    """
+    Execute Gemini sync completion and fallback to Google Code Assist when
+    OAuth scope is insufficient.
+    """
+    try:
+        return primary_call()
+    except Exception as e:
+        if not auto_fallback_to_google_code_assist:
+            raise e
+
+        if not should_fallback_to_google_code_assist(e):
+            raise e
+
+        verbose_logger.warning(
+            "Gemini request failed with ACCESS_TOKEN_SCOPE_INSUFFICIENT. "
+            "Falling back to google_code_assist."
+        )
+        return _google_code_assist_chat.completion(**fallback_kwargs)
diff --git a/litellm/llms/gemini/google_genai/transformation.py b/litellm/llms/gemini/google_genai/transformation.py
index 7c4c7dba626..7b5dafea8b6 100644
--- a/litellm/llms/gemini/google_genai/transformation.py
+++ b/litellm/llms/gemini/google_genai/transformation.py
@@ -2,6 +2,7 @@
 Transformation for Calling Google models in their native format.
 """
 
+import asyncio
 from typing import TYPE_CHECKING, Any, Dict, List, Literal, Optional, Tuple, Union, cast
 
 import httpx
@@ -11,6 +12,7 @@ from litellm.litellm_core_utils.litellm_logging import Logging as LiteLLMLogging
 from litellm.llms.base_llm.google_genai.transformation import (
     BaseGoogleGenAIGenerateContentConfig,
 )
+from litellm.llms.gemini.common_utils import get_gemini_oauth_token
 from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import VertexLLM
 from litellm.types.router import GenericLiteLLMParams
 
@@ -200,6 +202,7 @@ class GoogleGenAIConfig(BaseGoogleGenAIGenerateContentConfig, VertexLLM):
         stream: bool,
         api_base: Optional[str],
         litellm_params: dict,
+        gemini_auth_data: Optional[dict] = None,
     ) -> Tuple[dict, str]:
         """
         Build final headers and API URL from auth components.
@@ -217,6 +220,7 @@ class GoogleGenAIConfig(BaseGoogleGenAIGenerateContentConfig, VertexLLM):
             custom_llm_provider=self.custom_llm_provider,
             api_base=api_base,
             should_use_v1beta1_features=True,
+            gemini_auth_data=gemini_auth_data,
         )
 
         headers = self.validate_environment(
@@ -291,6 +295,12 @@ class GoogleGenAIConfig(BaseGoogleGenAIGenerateContentConfig, VertexLLM):
             custom_llm_provider=self.custom_llm_provider,
         )
 
+        gemini_auth_data: Optional[dict] = None
+        if self.custom_llm_provider == "gemini":
+            gemini_api_key = self._get_google_ai_studio_api_key(dict(litellm_params))
+            if gemini_api_key is None:
+                gemini_auth_data = await asyncio.to_thread(get_gemini_oauth_token)
+
         return self._build_final_headers_and_url(
             model=model,
             auth_header=_auth_header,
@@ -300,6 +310,7 @@ class GoogleGenAIConfig(BaseGoogleGenAIGenerateContentConfig, VertexLLM):
             stream=stream,
             api_base=api_base,
             litellm_params=litellm_params,
+            gemini_auth_data=gemini_auth_data,
         )
 
     def transform_generate_content_request(
diff --git a/litellm/llms/google_code_assist/chat.py b/litellm/llms/google_code_assist/chat.py
new file mode 100644
index 00000000000..26c30e2b3d1
--- /dev/null
+++ b/litellm/llms/google_code_assist/chat.py
@@ -0,0 +1,258 @@
+import asyncio
+import httpx
+from typing import Any, Dict, Optional
+
+import litellm
+from litellm._logging import verbose_logger
+from litellm.llms.custom_httpx.http_handler import _get_httpx_client, AsyncHTTPHandler
+from .transformation import GoogleCodeAssistConfig, GoogleCodeAssistError
+
+_CODE_ASSIST_BASE_URL = "https://cloudcode-pa.googleapis.com"
+_CODE_ASSIST_GENERATE_URL = f"{_CODE_ASSIST_BASE_URL}/v1internal:generateContent"
+_CODE_ASSIST_LOAD_URL = f"{_CODE_ASSIST_BASE_URL}/v1internal:loadCodeAssist"
+
+
+class GoogleCodeAssistChat:
+    """
+    Handler for Google Code Assist API.
+    Provides both synchronous and asynchronous completion methods.
+    """
+
+    def __init__(self) -> None:
+        self.config = GoogleCodeAssistConfig()
+
+    def completion(
+        self,
+        model: str,
+        messages: list,
+        model_response: litellm.utils.ModelResponse,
+        print_verbose: Any,
+        logging_obj: Any,
+        optional_params: dict,
+        litellm_params: dict,
+        logger_fn=None,
+    ) -> litellm.utils.ModelResponse:
+        """
+        Synchronous completion for Google Code Assist.
+        """
+        try:
+            from litellm.llms.gemini.common_utils import get_gemini_oauth_token
+
+            # 1. Get OAuth data
+            gemini_auth_data = get_gemini_oauth_token()
+            if not gemini_auth_data:
+                raise GoogleCodeAssistError(
+                    status_code=401,
+                    message="Missing Gemini OAuth token. Run 'litellm-proxy gemini login' or set GEMINI_OAUTH_TOKEN.",
+                )
+
+            token = gemini_auth_data.get("token")
+            initial_project_id = gemini_auth_data.get("project_id")
+            if not token:
+                raise GoogleCodeAssistError(
+                    status_code=401,
+                    message="Missing Gemini OAuth token value. Re-run 'litellm-proxy gemini login'.",
+                )
+
+            client = _get_httpx_client()
+
+            # 2. MANDATORY HANDSHAKE: loadCodeAssist
+            final_project_id = self._handle_handshake(client, token, initial_project_id)
+            litellm_params["google_code_assist_project"] = final_project_id
+
+            # 3. Transform request
+            data = self.config.transform_request(
+                model=model,
+                messages=messages,
+                optional_params=optional_params,
+                litellm_params=litellm_params,
+            )
+
+            # 4. Call Completion API
+            url = _CODE_ASSIST_GENERATE_URL
+            headers = self._get_headers(token)
+
+            response = client.post(
+                url=url,
+                headers=headers,
+                json=data,
+            )
+            response.raise_for_status()
+
+            # 5. Transform response
+            return self.config.transform_response(
+                model=model,
+                raw_response=response,
+                model_response=model_response,
+                logging_obj=logging_obj,
+                request_data=data,
+                messages=messages,
+                optional_params=optional_params,
+                litellm_params=litellm_params,
+                encoding=None,
+            )
+
+        except Exception as e:
+            raise self._handle_error(e)
+
+    async def acompletion(
+        self,
+        model: str,
+        messages: list,
+        model_response: litellm.utils.ModelResponse,
+        print_verbose: Any,
+        logging_obj: Any,
+        optional_params: dict,
+        litellm_params: dict,
+        logger_fn=None,
+    ) -> litellm.utils.ModelResponse:
+        """
+        Asynchronous completion for Google Code Assist.
+        """
+        try:
+            from litellm.llms.gemini.common_utils import get_gemini_oauth_token
+
+            gemini_auth_data = await asyncio.to_thread(get_gemini_oauth_token)
+            if not gemini_auth_data:
+                raise GoogleCodeAssistError(
+                    status_code=401,
+                    message="Missing Gemini OAuth token. Run 'litellm-proxy gemini login' or set GEMINI_OAUTH_TOKEN.",
+                )
+
+            token = gemini_auth_data.get("token")
+            initial_project_id = gemini_auth_data.get("project_id")
+            if not token:
+                raise GoogleCodeAssistError(
+                    status_code=401,
+                    message="Missing Gemini OAuth token value. Re-run 'litellm-proxy gemini login'.",
+                )
+
+            async_handler = AsyncHTTPHandler()
+            try:
+                final_project_id = await self._ahandle_handshake(
+                    async_handler, token, initial_project_id
+                )
+                litellm_params["google_code_assist_project"] = final_project_id
+
+                data = self.config.transform_request(
+                    model, messages, optional_params, litellm_params
+                )
+                url = _CODE_ASSIST_GENERATE_URL
+                headers = self._get_headers(token)
+
+                response = await async_handler.post(url=url, headers=headers, json=data)
+                response.raise_for_status()
+
+                return self.config.transform_response(
+                    model=model,
+                    raw_response=response,
+                    model_response=model_response,
+                    logging_obj=logging_obj,
+                    request_data=data,
+                    messages=messages,
+                    optional_params=optional_params,
+                    litellm_params=litellm_params,
+                    encoding=None,
+                )
+            finally:
+                try:
+                    await async_handler.close()
+                except Exception as close_error:
+                    verbose_logger.debug(
+                        f"Failed to close Google Code Assist async HTTP handler: {close_error}"
+                    )
+
+        except Exception as e:
+            raise self._handle_error(e)
+
+    def _handle_handshake(
+        self, client, token: str, initial_project_id: Optional[str]
+    ) -> Optional[str]:
+        """Performs the loadCodeAssist handshake to establish session context."""
+        load_url = _CODE_ASSIST_LOAD_URL
+        load_headers = {
+            "Authorization": f"Bearer {token}",
+            "Content-Type": "application/json",
+            "User-Agent": "GeminiCLI/litellm",
+        }
+        load_payload: Dict[str, Any] = {
+            "metadata": {
+                "ideType": "IDE_UNSPECIFIED",
+                "platform": "PLATFORM_UNSPECIFIED",
+                "pluginType": "GEMINI",
+            }
+        }
+        if initial_project_id:
+            load_payload["cloudaicompanionProject"] = initial_project_id
+            load_payload["metadata"]["duetProject"] = initial_project_id
+
+        try:
+            load_resp = client.post(load_url, headers=load_headers, json=load_payload)
+            load_resp.raise_for_status()
+            return load_resp.json().get("cloudaicompanionProject") or initial_project_id
+        except Exception as e:
+            verbose_logger.debug(f"Gemini Code Assist handshake failed: {e}")
+            return initial_project_id
+
+    async def _ahandle_handshake(
+        self,
+        async_handler: AsyncHTTPHandler,
+        token: str,
+        initial_project_id: Optional[str],
+    ) -> Optional[str]:
+        """Async version of loadCodeAssist handshake for non-blocking async calls."""
+        load_url = _CODE_ASSIST_LOAD_URL
+        load_headers = {
+            "Authorization": f"Bearer {token}",
+            "Content-Type": "application/json",
+            "User-Agent": "GeminiCLI/litellm",
+        }
+        load_payload: Dict[str, Any] = {
+            "metadata": {
+                "ideType": "IDE_UNSPECIFIED",
+                "platform": "PLATFORM_UNSPECIFIED",
+                "pluginType": "GEMINI",
+            }
+        }
+        if initial_project_id:
+            load_payload["cloudaicompanionProject"] = initial_project_id
+            load_payload["metadata"]["duetProject"] = initial_project_id
+
+        try:
+            load_resp = await async_handler.post(
+                url=load_url, headers=load_headers, json=load_payload
+            )
+            load_resp.raise_for_status()
+            return load_resp.json().get("cloudaicompanionProject") or initial_project_id
+        except Exception as e:
+            verbose_logger.debug(f"Gemini Code Assist async handshake failed: {e}")
+            return initial_project_id
+
+    def _get_headers(self, token: str) -> dict:
+        """Returns standard headers for Code Assist API calls."""
+        return {
+            "Authorization": f"Bearer {token}",
+            "Content-Type": "application/json",
+            "User-Agent": "GeminiCLI/litellm",
+            "X-Goog-Api-Client": "litellm-google-code-assist",
+        }
+
+    def _handle_error(self, e: Exception) -> Exception:
+        """Centralized error mapping for Code Assist."""
+        if isinstance(e, httpx.HTTPStatusError):
+            return GoogleCodeAssistError(
+                status_code=e.response.status_code, message=e.response.text
+            )
+        if isinstance(e, GoogleCodeAssistError):
+            return e
+        return GoogleCodeAssistError(status_code=500, message=str(e))
+
+
+_shared_google_code_assist_chat: Optional[GoogleCodeAssistChat] = None
+
+
+def get_google_code_assist_chat() -> GoogleCodeAssistChat:
+    global _shared_google_code_assist_chat
+    if _shared_google_code_assist_chat is None:
+        _shared_google_code_assist_chat = GoogleCodeAssistChat()
+    return _shared_google_code_assist_chat
diff --git a/litellm/llms/google_code_assist/transformation.py b/litellm/llms/google_code_assist/transformation.py
new file mode 100644
index 00000000000..49c87c10b04
--- /dev/null
+++ b/litellm/llms/google_code_assist/transformation.py
@@ -0,0 +1,182 @@
+import json
+import uuid
+import copy
+import httpx
+from typing import Any
+
+from litellm._logging import verbose_logger
+from litellm.llms.base_llm.chat.transformation import BaseLLMException
+from litellm.types.utils import ModelResponse
+from ..vertex_ai.gemini.vertex_and_google_ai_studio_gemini import VertexGeminiConfig
+
+
+class GoogleCodeAssistError(BaseLLMException):
+    """
+    Exception raised for errors in the Google Code Assist API.
+    """
+
+    def __init__(self, status_code, message):
+        super().__init__(status_code=status_code, message=message)
+
+
+class ParsedJSONResponseAdapter:
+    """
+    Adapter that provides the subset of httpx.Response surface used by
+    VertexGeminiConfig.transform_response.
+    """
+
+    def __init__(self, json_data: dict):
+        self._json = json_data
+        self.status_code = 200
+        self.text = json.dumps(json_data)
+        self.headers = httpx.Headers({"content-type": "application/json"})
+
+    def json(self):
+        return self._json
+
+
+class GoogleCodeAssistConfig(VertexGeminiConfig):
+    """
+    Reference: https://cloud.google.com/gemini/docs/api/reference/rest/v1internal/projects.locations.codeAssist/generateContent
+
+    The class `GoogleCodeAssistConfig` provides configuration for the Google Code Assist API.
+    It inherits from `VertexGeminiConfig` to provide consistent parameter mapping.
+
+    - `temperature` (float): This controls the degree of randomness in token selection.
+    - `max_output_tokens` (integer): This sets the limitation for the maximum amount of token in the text output.
+    - `top_p` (float): The tokens are selected from the most probable to the least probable until the sum of their probabilities equals the `top_p` value.
+    - `top_k` (integer): The value of `top_k` determines how many of the most probable tokens are considered in the selection.
+    - `stop_sequences` (List[str]): The set of character sequences that will stop output generation.
+    """
+
+    def transform_request(
+        self,
+        model: str,
+        messages: list,
+        optional_params: dict,
+        litellm_params: dict,
+        headers: dict = {},
+    ) -> dict:
+        """
+        Transforms standard LiteLLM request to Code Assist API format.
+        Matches gemini-cli 'toGenerateContentRequest'.
+        """
+        # 1. Map messages to Gemini format
+        from ..vertex_ai.gemini.transformation import (
+            _gemini_convert_messages_with_history,
+            _transform_system_message,
+        )
+
+        # Create a copy to avoid mutating the original list
+        messages_copy = copy.deepcopy(messages)
+        model_name = model.split("/")[-1]
+
+        # Separate system instruction
+        system_instruction, filtered_messages = _transform_system_message(
+            supports_system_message=True, messages=messages_copy
+        )
+
+        # Convert the rest of messages
+        contents = _gemini_convert_messages_with_history(
+            messages=filtered_messages, model=model_name
+        )
+
+        # 2. Build vertex-style nested request
+        generation_config = {}
+        # Handle parameter mapping
+        base_params = self.map_openai_params(
+            {}, optional_params.copy(), model_name, False
+        )
+
+        for key in ["temperature", "topP", "topK", "maxOutputTokens", "stopSequences"]:
+            if key in base_params:
+                generation_config[key] = base_params.pop(key)
+
+        # Support thinkingConfig
+        if "thinkingConfig" in base_params:
+            generation_config["thinkingConfig"] = base_params.pop("thinkingConfig")
+        elif "include_thoughts" in base_params:
+            generation_config["thinkingConfig"] = {
+                "includeThoughts": base_params.pop("include_thoughts")
+            }
+
+        # Forward any remaining mapped params into generation_config so they are not silently dropped.
+        for key, value in base_params.items():
+            if key not in generation_config:
+                verbose_logger.debug(
+                    "google_code_assist: forwarding mapped param '%s' into generationConfig",
+                    key,
+                )
+                generation_config[key] = value
+
+        # Log unmapped/unrecognized caller keys so users have visibility (do not auto-forward —
+        # they may not be valid Gemini fields).
+        for key in optional_params:
+            if key not in base_params and key not in generation_config:
+                verbose_logger.debug(
+                    "google_code_assist: dropping unrecognized optional_param '%s' "
+                    "(not produced by VertexGeminiConfig.map_openai_params)",
+                    key,
+                )
+
+        vertex_request = {
+            "contents": contents,
+            "session_id": litellm_params.get("session_id", str(uuid.uuid4())),
+        }
+
+        if system_instruction:
+            vertex_request["systemInstruction"] = {
+                "role": "system",
+                "parts": system_instruction["parts"],
+            }
+
+        if generation_config:
+            vertex_request["generationConfig"] = generation_config
+
+        # 3. Wrap in Code Assist envelope (matches verified gemini-cli structure)
+        user_prompt_id = f"litellm-{uuid.uuid4()}"
+
+        ca_request = {
+            "model": model_name,
+            "user_prompt_id": user_prompt_id,
+            "request": vertex_request,
+        }
+
+        # Add project ID if available
+        if litellm_params.get("google_code_assist_project"):
+            ca_request["project"] = litellm_params["google_code_assist_project"]
+
+        return ca_request
+
+    def transform_response(
+        self,
+        model: str,
+        raw_response: Any,
+        model_response: ModelResponse,
+        logging_obj: Any,
+        request_data: dict,
+        messages: list,
+        optional_params: dict,
+        litellm_params: dict,
+        encoding: Any,
+        api_key: Any = None,
+        json_mode: Any = None,
+    ) -> ModelResponse:
+        """
+        Transforms Code Assist API response to standard LiteLLM format.
+        """
+        data = raw_response.json()
+        # Code Assist wraps the response in a "response" key
+        gemini_response = data.get("response", data)
+
+        return super().transform_response(
+            model=model,
+            raw_response=ParsedJSONResponseAdapter(gemini_response),  # type: ignore[arg-type]
+            model_response=model_response,
+            logging_obj=logging_obj,
+            request_data=request_data,
+            messages=messages,
+            optional_params=optional_params,
+            litellm_params=litellm_params,
+            encoding=encoding,
+        )
diff --git a/litellm/llms/vertex_ai/common_utils.py b/litellm/llms/vertex_ai/common_utils.py
index fae175612b1..f779c03f43a 100644
--- a/litellm/llms/vertex_ai/common_utils.py
+++ b/litellm/llms/vertex_ai/common_utils.py
@@ -413,28 +413,12 @@ def _get_gemini_url(
         endpoint = "generateContent"
         if stream is True:
             endpoint = "streamGenerateContent"
-            url = "https://generativelanguage.googleapis.com/{}/{}:{}?alt=sse".format(
-                api_version, _gemini_model_name, endpoint
-            )
-        else:
-            url = "https://generativelanguage.googleapis.com/{}/{}:{}".format(
-                api_version, _gemini_model_name, endpoint
-            )
     elif mode == "embedding":
         endpoint = "embedContent"
-        url = "https://generativelanguage.googleapis.com/v1beta/{}:{}".format(
-            _gemini_model_name, endpoint
-        )
     elif mode == "batch_embedding":
         endpoint = "batchEmbedContents"
-        url = "https://generativelanguage.googleapis.com/v1beta/{}:{}".format(
-            _gemini_model_name, endpoint
-        )
     elif mode == "count_tokens":
         endpoint = "countTokens"
-        url = "https://generativelanguage.googleapis.com/v1beta/{}:{}".format(
-            _gemini_model_name, endpoint
-        )
     elif mode == "image_generation":
         raise ValueError(
             "LiteLLM's `gemini/` route does not support image generation yet. Let us know if you need this feature by opening an issue at https://github.com/BerriAI/litellm/issues"
@@ -442,6 +426,19 @@ def _get_gemini_url(
     else:
         raise ValueError(f"Unsupported mode: {mode}")
 
+    base_url = "https://generativelanguage.googleapis.com/{}/{}:{}".format(
+        api_version if mode == "chat" else "v1beta", _gemini_model_name, endpoint
+    )
+
+    params = []
+    if mode == "chat" and stream is True:
+        params.append("alt=sse")
+
+    if params:
+        url = f"{base_url}?{'&'.join(params)}"
+    else:
+        url = base_url
+
     return url, endpoint
 
 
diff --git a/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py b/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
index 474ddb402a1..a655d4864d7 100644
--- a/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
+++ b/litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py
@@ -2,6 +2,7 @@
 ## httpx client for vertex ai calls
 ## Initial implementation - covers gemini + image gen calls
 import json
+import asyncio
 import time
 from copy import deepcopy
 from functools import partial
@@ -2721,6 +2722,11 @@ class VertexLLM(VertexBase):
             project_id=vertex_project,
             custom_llm_provider=custom_llm_provider,
         )
+        gemini_auth_data = None
+        if custom_llm_provider == "gemini" and gemini_api_key is None:
+            from litellm.llms.gemini.common_utils import get_gemini_oauth_token
+
+            gemini_auth_data = await asyncio.to_thread(get_gemini_oauth_token)
 
         # Extract use_psc_endpoint_format from optional_params
         use_psc_endpoint_format = optional_params.get("use_psc_endpoint_format", False)
@@ -2728,6 +2734,7 @@ class VertexLLM(VertexBase):
         auth_header, api_base = self._get_token_and_url(
             model=model,
             gemini_api_key=gemini_api_key,
+            gemini_auth_data=gemini_auth_data,
             auth_header=_auth_header,
             vertex_project=vertex_project,
             vertex_location=vertex_location,
@@ -2823,6 +2830,11 @@ class VertexLLM(VertexBase):
             project_id=vertex_project,
             custom_llm_provider=custom_llm_provider,
         )
+        gemini_auth_data = None
+        if custom_llm_provider == "gemini" and gemini_api_key is None:
+            from litellm.llms.gemini.common_utils import get_gemini_oauth_token
+
+            gemini_auth_data = await asyncio.to_thread(get_gemini_oauth_token)
 
         # Extract use_psc_endpoint_format from optional_params
         use_psc_endpoint_format = optional_params.get("use_psc_endpoint_format", False)
@@ -2830,6 +2842,7 @@ class VertexLLM(VertexBase):
         auth_header, api_base = self._get_token_and_url(
             model=model,
             gemini_api_key=gemini_api_key,
+            gemini_auth_data=gemini_auth_data,
             auth_header=_auth_header,
             vertex_project=vertex_project,
             vertex_location=vertex_location,
diff --git a/litellm/llms/vertex_ai/gemini_embeddings/batch_embed_content_handler.py b/litellm/llms/vertex_ai/gemini_embeddings/batch_embed_content_handler.py
index 2371bc4865a..df77f7654b0 100644
--- a/litellm/llms/vertex_ai/gemini_embeddings/batch_embed_content_handler.py
+++ b/litellm/llms/vertex_ai/gemini_embeddings/batch_embed_content_handler.py
@@ -2,6 +2,7 @@
 Google AI Studio /batchEmbedContents Embeddings Endpoint
 """
 
+import asyncio
 import json
 from typing import Any, Dict, Literal, Optional, Union
 
@@ -130,6 +131,36 @@ class GoogleBatchEmbeddings(VertexLLM):
         client=None,
         extra_headers: Optional[dict] = None,
     ) -> EmbeddingResponse:
+        optional_params = optional_params or {}
+
+        is_multimodal = _is_multimodal_input(input)
+        use_embed_content = is_multimodal or (custom_llm_provider == "vertex_ai")
+        mode: Literal["embedding", "batch_embedding"]
+        if use_embed_content:
+            mode = "embedding"
+        else:
+            mode = "batch_embedding"
+
+        if aembedding is True:
+            return self._async_batch_embeddings_with_auth_resolution(  # type: ignore
+                model=model,
+                input=input,
+                model_response=model_response,
+                custom_llm_provider=custom_llm_provider,
+                optional_params=optional_params,
+                logging_obj=logging_obj,
+                api_key=api_key,
+                api_base=api_base,
+                use_embed_content=use_embed_content,
+                mode=mode,
+                timeout=timeout,
+                client=client,
+                vertex_project=vertex_project,
+                vertex_location=vertex_location,
+                vertex_credentials=vertex_credentials,
+                extra_headers=extra_headers,
+            )
+
         _auth_header, vertex_project = self._ensure_access_token(
             credentials=vertex_credentials,
             project_id=vertex_project,
@@ -149,16 +180,6 @@ class GoogleBatchEmbeddings(VertexLLM):
         else:
             sync_handler = client  # type: ignore
 
-        optional_params = optional_params or {}
-
-        is_multimodal = _is_multimodal_input(input)
-        use_embed_content = is_multimodal or (custom_llm_provider == "vertex_ai")
-        mode: Literal["embedding", "batch_embedding"]
-        if use_embed_content:
-            mode = "embedding"
-        else:
-            mode = "batch_embedding"
-
         auth_header, url = self._get_token_and_url(
             model=model,
             auth_header=_auth_header,
@@ -184,22 +205,6 @@ class GoogleBatchEmbeddings(VertexLLM):
         if extra_headers is not None:
             headers.update(extra_headers)
 
-        if aembedding is True:
-            return self.async_batch_embeddings(  # type: ignore
-                model=model,
-                api_base=api_base,
-                url=url,
-                data=None,
-                model_response=model_response,
-                timeout=timeout,
-                headers=headers,
-                input=input,
-                use_embed_content=use_embed_content,
-                api_key=api_key,
-                optional_params=optional_params,
-                logging_obj=logging_obj,
-            )
-
         ### TRANSFORMATION (sync path) ###
         request_data: Any
         if use_embed_content:
@@ -257,6 +262,78 @@ class GoogleBatchEmbeddings(VertexLLM):
                 input=input,
             )
 
+    async def _async_batch_embeddings_with_auth_resolution(
+        self,
+        model: str,
+        input: EmbeddingInput,
+        model_response: EmbeddingResponse,
+        custom_llm_provider: Literal["gemini", "vertex_ai"],
+        optional_params: dict,
+        logging_obj: Any,
+        api_key: Optional[str],
+        api_base: Optional[str],
+        use_embed_content: bool,
+        mode: Literal["embedding", "batch_embedding"],
+        timeout: Optional[Union[float, httpx.Timeout]],
+        client: Optional[AsyncHTTPHandler],
+        vertex_project: Optional[str],
+        vertex_location: Optional[str],
+        vertex_credentials: Optional[Any],
+        extra_headers: Optional[dict],
+    ) -> EmbeddingResponse:
+        _auth_header, vertex_project = await self._ensure_access_token_async(
+            credentials=vertex_credentials,
+            project_id=vertex_project,
+            custom_llm_provider=custom_llm_provider,
+        )
+        gemini_auth_data = None
+        if custom_llm_provider == "gemini" and api_key is None:
+            from litellm.llms.gemini.common_utils import get_gemini_oauth_token
+
+            gemini_auth_data = await asyncio.to_thread(get_gemini_oauth_token)
+
+        auth_header, url = self._get_token_and_url(
+            model=model,
+            auth_header=_auth_header,
+            gemini_api_key=api_key,
+            gemini_auth_data=gemini_auth_data,
+            vertex_project=vertex_project,
+            vertex_location=vertex_location,
+            vertex_credentials=vertex_credentials,
+            stream=None,
+            custom_llm_provider=custom_llm_provider,
+            api_base=api_base,
+            should_use_v1beta1_features=False,
+            mode=mode,
+        )
+
+        headers = {
+            "Content-Type": "application/json; charset=utf-8",
+        }
+        if auth_header is not None:
+            if isinstance(auth_header, dict):
+                headers.update(auth_header)
+            else:
+                headers["Authorization"] = f"Bearer {auth_header}"
+        if extra_headers is not None:
+            headers.update(extra_headers)
+
+        return await self.async_batch_embeddings(
+            model=model,
+            api_base=api_base,
+            url=url,
+            data=None,
+            model_response=model_response,
+            timeout=timeout,
+            headers=headers,
+            client=client,
+            input=input,
+            use_embed_content=use_embed_content,
+            api_key=api_key,
+            optional_params=optional_params,
+            logging_obj=logging_obj,
+        )
+
     async def async_batch_embeddings(
         self,
         model: str,
diff --git a/litellm/llms/vertex_ai/multimodal_embeddings/embedding_handler.py b/litellm/llms/vertex_ai/multimodal_embeddings/embedding_handler.py
index d0ffc7be0a6..08245029abb 100644
--- a/litellm/llms/vertex_ai/multimodal_embeddings/embedding_handler.py
+++ b/litellm/llms/vertex_ai/multimodal_embeddings/embedding_handler.py
@@ -1,3 +1,4 @@
+import asyncio
 import json
 from typing import Literal, Optional, Union
 
@@ -14,6 +15,7 @@ from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import (
     VertexAIError,
     VertexLLM,
 )
+from litellm.types.llms.vertex_ai import VERTEX_CREDENTIALS_TYPES
 from litellm.types.utils import EmbeddingResponse
 
 from .transformation import VertexAIMultimodalEmbeddingConfig
@@ -50,6 +52,25 @@ class VertexMultimodalEmbedding(VertexLLM):
         timeout=300,
         client=None,
     ) -> EmbeddingResponse:
+        if aembedding is True:
+            return self._async_multimodal_embedding_with_auth_resolution(  # type: ignore
+                model=model,
+                input=input,
+                model_response=model_response,
+                custom_llm_provider=custom_llm_provider,
+                optional_params=optional_params,
+                litellm_params=litellm_params,
+                logging_obj=logging_obj,
+                api_key=api_key,
+                api_base=api_base,
+                headers=headers,
+                timeout=timeout,
+                client=client,
+                vertex_project=vertex_project,
+                vertex_location=vertex_location,
+                vertex_credentials=vertex_credentials,
+            )
+
         _auth_header, vertex_project = self._ensure_access_token(
             credentials=vertex_credentials,
             project_id=vertex_project,
@@ -108,21 +129,6 @@ class VertexMultimodalEmbedding(VertexLLM):
             },
         )
 
-        if aembedding is True:
-            return self.async_multimodal_embedding(  # type: ignore
-                model=model,
-                api_base=url,
-                data=request_data,
-                timeout=timeout,
-                headers=headers,
-                client=client,
-                model_response=model_response,
-                optional_params=optional_params,
-                litellm_params=litellm_params,
-                logging_obj=logging_obj,
-                api_key=api_key,
-            )
-
         response = sync_handler.post(
             url=url,
             headers=headers,
@@ -140,6 +146,87 @@ class VertexMultimodalEmbedding(VertexLLM):
             litellm_params=litellm_params,
         )
 
+    async def _async_multimodal_embedding_with_auth_resolution(
+        self,
+        model: str,
+        input: Union[list, str],
+        model_response: EmbeddingResponse,
+        custom_llm_provider: Literal["gemini", "vertex_ai"],
+        optional_params: dict,
+        litellm_params: dict,
+        logging_obj: LiteLLMLoggingObj,
+        api_key: Optional[str],
+        api_base: Optional[str],
+        headers: dict,
+        timeout: Optional[Union[float, httpx.Timeout]],
+        client: Optional[AsyncHTTPHandler],
+        vertex_project: Optional[str],
+        vertex_location: Optional[str],
+        vertex_credentials: Optional[VERTEX_CREDENTIALS_TYPES],
+    ) -> EmbeddingResponse:
+        _auth_header, vertex_project = await self._ensure_access_token_async(
+            credentials=vertex_credentials,
+            project_id=vertex_project,
+            custom_llm_provider=custom_llm_provider,
+        )
+        gemini_auth_data = None
+        if custom_llm_provider == "gemini" and api_key is None:
+            from litellm.llms.gemini.common_utils import get_gemini_oauth_token
+
+            gemini_auth_data = await asyncio.to_thread(get_gemini_oauth_token)
+
+        auth_header, url = self._get_token_and_url(
+            model=model,
+            auth_header=_auth_header,
+            gemini_api_key=api_key,
+            gemini_auth_data=gemini_auth_data,
+            vertex_project=vertex_project,
+            vertex_location=vertex_location,
+            vertex_credentials=vertex_credentials,
+            stream=None,
+            custom_llm_provider=custom_llm_provider,
+            api_base=api_base,
+            should_use_v1beta1_features=False,
+            mode="embedding",
+        )
+
+        request_data = vertex_multimodal_embedding_handler.transform_embedding_request(
+            model, input, optional_params, headers
+        )
+        request_headers = vertex_multimodal_embedding_handler.validate_environment(
+            headers=headers,
+            model=model,
+            messages=[],
+            optional_params=optional_params,
+            api_key=auth_header,
+            api_base=api_base,
+            litellm_params=litellm_params,
+        )
+
+        logging_obj.pre_call(
+            input=input,
+            api_key="",
+            additional_args={
+                "complete_input_dict": request_data,
+                "api_base": url,
+                "headers": request_headers,
+            },
+        )
+
+        return await self.async_multimodal_embedding(
+            model=model,
+            api_base=url,
+            data=request_data,
+            timeout=timeout,
+            headers=request_headers,
+            client=client,
+            model_response=model_response,
+            optional_params=optional_params,
+            litellm_params=litellm_params,
+            logging_obj=logging_obj,
+            api_key=api_key,
+        )
+
     async def async_multimodal_embedding(
         self,
         model: str,
diff --git a/litellm/llms/vertex_ai/vertex_embeddings/embedding_handler.py b/litellm/llms/vertex_ai/vertex_embeddings/embedding_handler.py
index 696341598e5..072a9521b6e 100644
--- a/litellm/llms/vertex_ai/vertex_embeddings/embedding_handler.py
+++ b/litellm/llms/vertex_ai/vertex_embeddings/embedding_handler.py
@@ -1,3 +1,4 @@
+import asyncio
 from typing import Dict, Literal, Optional, Union
 
 import httpx
@@ -174,12 +175,18 @@ class VertexEmbedding(VertexBase):
             project_id=vertex_project,
             custom_llm_provider=custom_llm_provider,
         )
+        gemini_auth_data = None
+        if custom_llm_provider == "gemini" and gemini_api_key is None:
+            from litellm.llms.gemini.common_utils import get_gemini_oauth_token
+
+            gemini_auth_data = await asyncio.to_thread(get_gemini_oauth_token)
         # Extract use_psc_endpoint_format from optional_params
         use_psc_endpoint_format = optional_params.get("use_psc_endpoint_format", False)
 
         auth_header, api_base = self._get_token_and_url(
             model=model,
             gemini_api_key=gemini_api_key,
+            gemini_auth_data=gemini_auth_data,
             auth_header=_auth_header,
             vertex_project=vertex_project,
             vertex_location=vertex_location,
diff --git a/litellm/llms/vertex_ai/vertex_llm_base.py b/litellm/llms/vertex_ai/vertex_llm_base.py
index 6f687dae7e8..a3c6637408b 100644
--- a/litellm/llms/vertex_ai/vertex_llm_base.py
+++ b/litellm/llms/vertex_ai/vertex_llm_base.py
@@ -387,6 +387,7 @@ class VertexBase:
         vertex_location: Optional[str] = None,
         vertex_api_version: Optional[Literal["v1", "v1beta1"]] = None,
         use_psc_endpoint_format: bool = False,
+        gemini_auth_data: Optional[dict] = None,
     ) -> Tuple[Optional[str], str]:
         """
         for cloudflare ai gateway - https://github.com/BerriAI/litellm/issues/4317
@@ -413,12 +414,29 @@ class VertexBase:
                         "Model parameter is required for Gemini custom API base URLs"
                     )
                 url = "{}/models/{}:{}".format(api_base, model, endpoint)
-                if gemini_api_key is None:
-                    raise ValueError(
-                        "Missing Gemini API key. Set the GEMINI_API_KEY or GOOGLE_API_KEY environment variable."
+
+                if gemini_auth_data is None and gemini_api_key is None:
+                    from litellm.llms.gemini.common_utils import (
+                        get_gemini_oauth_token,
                     )
-                if gemini_api_key is not None:
+
+                    gemini_auth_data = get_gemini_oauth_token()
+                gemini_oauth_token = (
+                    gemini_auth_data.get("token") if gemini_auth_data else None
+                )
+
+                if gemini_oauth_token:
+                    auth_header = {"Authorization": f"Bearer {gemini_oauth_token}"}  # type: ignore[assignment]
+                    if gemini_auth_data and gemini_auth_data.get("project_id"):
+                        auth_header["x-goog-user-project"] = gemini_auth_data[  # type: ignore[index]
+                            "project_id"
+                        ]
+                elif gemini_api_key is not None:
                     auth_header = {"x-goog-api-key": gemini_api_key}  # type: ignore[assignment]
+                else:
+                    raise ValueError(
+                        "Missing gemini_api_key. Please set `GEMINI_API_KEY` or `GEMINI_OAUTH_TOKEN`."
+                    )
             else:
                 # For Vertex AI
                 if use_psc_endpoint_format:
@@ -461,6 +479,7 @@ class VertexBase:
         should_use_v1beta1_features: Optional[bool] = False,
         mode: all_gemini_url_modes = "chat",
         use_psc_endpoint_format: bool = False,
+        gemini_auth_data: Optional[dict] = None,
     ) -> Tuple[Optional[str], str]:
         """
         Internal function. Returns the token and url for the call.
@@ -472,16 +491,29 @@ class VertexBase:
         """
         version: Optional[Literal["v1beta1", "v1"]] = None
         if custom_llm_provider == "gemini":
-            if not gemini_api_key:
-                raise ValueError(
-                    "Missing Gemini API key. Set the GEMINI_API_KEY or GOOGLE_API_KEY environment variable."
-                )
+            if gemini_auth_data is None and gemini_api_key is None:
+                from litellm.llms.gemini.common_utils import get_gemini_oauth_token
+
+                gemini_auth_data = get_gemini_oauth_token()
+            gemini_oauth_token = (
+                gemini_auth_data.get("token") if gemini_auth_data else None
+            )
+
             url, endpoint = _get_gemini_url(
                 mode=mode,
                 model=model,
                 stream=stream,
             )
-            auth_header = {"x-goog-api-key": gemini_api_key}  # type: ignore[assignment]
+            if gemini_oauth_token:
+                auth_header = {"Authorization": f"Bearer {gemini_oauth_token}"}  # type: ignore[assignment]
+                if gemini_auth_data and gemini_auth_data.get("project_id"):
+                    auth_header["x-goog-user-project"] = gemini_auth_data["project_id"]  # type: ignore[index]
+            elif gemini_api_key is None:
+                raise ValueError(
+                    "Missing gemini_api_key. Please set `GEMINI_API_KEY` or `GEMINI_OAUTH_TOKEN`."
+                )
+            else:
+                auth_header = {"x-goog-api-key": gemini_api_key}  # type: ignore[assignment]
         else:
             vertex_location = self.get_vertex_region(
                 vertex_region=vertex_location,
@@ -504,6 +536,7 @@ class VertexBase:
             auth_header=auth_header,
             custom_llm_provider=custom_llm_provider,
             gemini_api_key=gemini_api_key,
+            gemini_auth_data=gemini_auth_data,
             endpoint=endpoint,
             stream=stream,
             url=url,
diff --git a/litellm/main.py b/litellm/main.py
index 0079bd750cf..31920d11ad6 100644
--- a/litellm/main.py
+++ b/litellm/main.py
@@ -103,6 +103,11 @@ from litellm.llms.cohere.common_utils import CohereModelInfo
 from litellm.llms.custom_httpx.http_handler import AsyncHTTPHandler, HTTPHandler
 from litellm.llms.openai.chat.gpt_5_transformation import OpenAIGPT5Config
 from litellm.llms.openai_like.json_loader import JSONProviderRegistry
+from litellm.llms.google_code_assist.chat import get_google_code_assist_chat
+from litellm.llms.gemini.fallback_handler import (
+    run_gemini_acompletion_with_code_assist_fallback,
+    run_gemini_completion_with_code_assist_fallback,
+)
 from litellm.llms.vertex_ai.common_utils import (
     VertexAIModelRoute,
     get_vertex_ai_model_route,
@@ -158,6 +163,8 @@ from litellm.utils import (
     validate_openai_optional_params,
 )
 
+_google_code_assist_chat = get_google_code_assist_chat()
+
 from ._logging import verbose_logger
 from .caching.caching import disable_cache, enable_cache, update_cache
 from .litellm_core_utils.core_helpers import safe_deep_copy
@@ -199,7 +206,9 @@ from .llms.custom_httpx.llm_http_handler import BaseLLMHTTPHandler
 from .llms.custom_llm import CustomLLM, custom_chat_llm_router
 from .llms.databricks.embed.handler import DatabricksEmbeddingHandler
 from .llms.deprecated_providers import aleph_alpha, palm
-from .llms.gemini.common_utils import get_api_key_from_env
+from .llms.gemini.common_utils import (
+    get_api_key_from_env,
+)
 from .llms.groq.chat.handler import GroqChatCompletion
 from .llms.heroku.chat.transformation import HerokuChatConfig
 from .llms.huggingface.embedding.handler import HuggingFaceEmbedding
@@ -3448,27 +3457,76 @@ def completion(  # type: ignore # noqa: PLR0915
 
             api_base = api_base or litellm.api_base or get_secret("GEMINI_API_BASE")
             new_params = safe_deep_copy(optional_params or {})
-            response = vertex_chat_completion.completion(  # type: ignore
-                model=model,
-                messages=messages,
-                model_response=model_response,
-                print_verbose=print_verbose,
-                optional_params=new_params,
-                litellm_params=litellm_params,  # type: ignore
-                logger_fn=logger_fn,
-                encoding=_get_encoding(),
-                vertex_location=vertex_ai_location,
-                vertex_project=vertex_ai_project,
-                vertex_credentials=vertex_credentials,
-                gemini_api_key=gemini_api_key,
-                logging_obj=logging,
-                acompletion=acompletion,
-                timeout=timeout,
-                custom_llm_provider=custom_llm_provider,  # type: ignore
-                client=client,
-                api_base=api_base,
-                extra_headers=headers,
-            )
+            if acompletion is True:
+                response = run_gemini_acompletion_with_code_assist_fallback(
+                    primary_call=lambda: vertex_chat_completion.completion(  # type: ignore
+                        model=model,
+                        messages=messages,
+                        model_response=model_response,
+                        print_verbose=print_verbose,
+                        optional_params=new_params,
+                        litellm_params=litellm_params,  # type: ignore
+                        logger_fn=logger_fn,
+                        encoding=_get_encoding(),
+                        vertex_location=vertex_ai_location,
+                        vertex_project=vertex_ai_project,
+                        vertex_credentials=vertex_credentials,
+                        gemini_api_key=gemini_api_key,
+                        logging_obj=logging,
+                        acompletion=True,
+                        timeout=timeout,
+                        custom_llm_provider=custom_llm_provider,  # type: ignore
+                        client=client,
+                        api_base=api_base,
+                        extra_headers=headers,
+                    ),
+                    fallback_kwargs={
+                        "model": model,
+                        "messages": messages,
+                        "model_response": model_response,
+                        "print_verbose": print_verbose,
+                        "optional_params": optional_params or {},
+                        "litellm_params": litellm_params,  # type: ignore
+                        "logging_obj": logging,
+                        "logger_fn": logger_fn,
+                    },
+                    auto_fallback_to_google_code_assist=litellm.auto_fallback_to_google_code_assist,
+                )
+            else:
+                response = run_gemini_completion_with_code_assist_fallback(
+                    primary_call=lambda: vertex_chat_completion.completion(  # type: ignore
+                        model=model,
+                        messages=messages,
+                        model_response=model_response,
+                        print_verbose=print_verbose,
+                        optional_params=new_params,
+                        litellm_params=litellm_params,  # type: ignore
+                        logger_fn=logger_fn,
+                        encoding=_get_encoding(),
+                        vertex_location=vertex_ai_location,
+                        vertex_project=vertex_ai_project,
+                        vertex_credentials=vertex_credentials,
+                        gemini_api_key=gemini_api_key,
+                        logging_obj=logging,
+                        acompletion=False,
+                        timeout=timeout,
+                        custom_llm_provider=custom_llm_provider,  # type: ignore
+                        client=client,
+                        api_base=api_base,
+                        extra_headers=headers,
+                    ),
+                    fallback_kwargs={
+                        "model": model,
+                        "messages": messages,
+                        "model_response": model_response,
+                        "print_verbose": print_verbose,
+                        "optional_params": optional_params or {},
+                        "litellm_params": litellm_params,  # type: ignore
+                        "logging_obj": logging,
+                        "logger_fn": logger_fn,
+                    },
+                    auto_fallback_to_google_code_assist=litellm.auto_fallback_to_google_code_assist,
+                )
 
         elif custom_llm_provider == "vertex_ai":
             vertex_ai_project = (
@@ -3644,6 +3702,32 @@ def completion(  # type: ignore # noqa: PLR0915
                     )
                     return response
             response = model_response
+
+        elif custom_llm_provider == "google_code_assist":
+            _ca_optional_params = optional_params or {}
+            if acompletion is True:
+                response = _google_code_assist_chat.acompletion(
+                    model=model,
+                    messages=messages,
+                    model_response=model_response,
+                    print_verbose=print_verbose,
+                    optional_params=_ca_optional_params,
+                    litellm_params=litellm_params,  # type: ignore
+                    logging_obj=logging,
+                    logger_fn=logger_fn,
+                )
+            else:
+                response = _google_code_assist_chat.completion(
+                    model=model,
+                    messages=messages,
+                    model_response=model_response,
+                    print_verbose=print_verbose,
+                    optional_params=_ca_optional_params,
+                    litellm_params=litellm_params,  # type: ignore
+                    logging_obj=logging,
+                    logger_fn=logger_fn,
+                )
+
         elif custom_llm_provider == "predibase":
             tenant_id = (
                 optional_params.pop("tenant_id", None)
diff --git a/litellm/proxy/client/cli/README.md b/litellm/proxy/client/cli/README.md
index 6ef837cb521..65e924ce723 100644
--- a/litellm/proxy/client/cli/README.md
+++ b/litellm/proxy/client/cli/README.md
@@ -29,6 +29,18 @@ litellm-proxy --version
 litellm-proxy -v
 ```
 
+## Gemini OAuth Login
+
+Authenticate locally for Gemini OAuth-based providers (for example `google_code_assist/*`):
+
+```bash
+export GEMINI_OAUTH_CLIENT_ID="<your-google-oauth-client-id>"
+export GEMINI_OAUTH_CLIENT_SECRET="<your-google-oauth-client-secret>"
+litellm-proxy gemini login
+```
+
+This starts a browser-based loopback OAuth flow and stores credentials for reuse.
+
 ## Commands
 
 ### Models Management
diff --git a/litellm/proxy/client/cli/commands/gemini.py b/litellm/proxy/client/cli/commands/gemini.py
new file mode 100644
index 00000000000..6c54e735752
--- /dev/null
+++ b/litellm/proxy/client/cli/commands/gemini.py
@@ -0,0 +1,19 @@
+import click
+from litellm.llms.gemini.authenticator import GeminiAuthenticator
+
+
+@click.group(name="gemini")
+def gemini():
+    """Gemini-specific management commands"""
+    pass
+
+
+@gemini.command(name="login")
+def login():
+    """Authenticate with Gemini using the OAuth Authorization Code flow (loopback redirect)"""
+    try:
+        auth = GeminiAuthenticator()
+        auth.get_token()
+        click.echo("✅ Successfully authenticated with Gemini.")
+    except Exception as e:
+        raise click.ClickException(f"Gemini authentication failed: {e}")
diff --git a/litellm/proxy/client/cli/main.py b/litellm/proxy/client/cli/main.py
index 22de5a78614..602af281ced 100644
--- a/litellm/proxy/client/cli/main.py
+++ b/litellm/proxy/client/cli/main.py
@@ -12,6 +12,7 @@ from .commands.chat import chat
 from .commands.credentials import credentials
 from .commands.http import http
 from .commands.keys import keys
+from .commands.gemini import gemini
 
 # local imports
 from .commands.models import models
@@ -107,6 +108,7 @@ cli.add_command(chat)
 cli.add_command(http)
 # Add the keys command group
 cli.add_command(keys)
+cli.add_command(gemini)
 # Add the teams command group
 cli.add_command(teams)
 # Add the users command group
diff --git a/litellm/types/utils.py b/litellm/types/utils.py
index ed29d49fc29..82b7a79eff4 100644
--- a/litellm/types/utils.py
+++ b/litellm/types/utils.py
@@ -3222,6 +3222,7 @@ class LlmProviders(str, Enum):
     VERTEX_AI = "vertex_ai"
     VERTEX_AI_BETA = "vertex_ai_beta"
     GEMINI = "gemini"
+    GOOGLE_CODE_ASSIST = "google_code_assist"
     AI21 = "ai21"
     BASETEN = "baseten"
     BLACK_FOREST_LABS = "black_forest_labs"
diff --git a/litellm/utils.py b/litellm/utils.py
index 027c9fedced..101e1d12698 100644
--- a/litellm/utils.py
+++ b/litellm/utils.py
@@ -8119,6 +8119,10 @@ class ProviderConfigManager:
             LlmProviders.COMETAPI: (lambda: litellm.CometAPIConfig(), False),
             LlmProviders.DATAROBOT: (lambda: litellm.DataRobotConfig(), False),
             LlmProviders.GEMINI: (lambda: litellm.GoogleAIStudioGeminiConfig(), False),
+            LlmProviders.GOOGLE_CODE_ASSIST: (
+                lambda: ProviderConfigManager._get_google_code_assist_config(),
+                False,
+            ),
             LlmProviders.AI21: (lambda: litellm.AI21ChatConfig(), False),
             LlmProviders.AI21_CHAT: (lambda: litellm.AI21ChatConfig(), False),
             LlmProviders.AZURE_TEXT: (lambda: litellm.AzureOpenAITextConfig(), False),
@@ -8238,6 +8242,15 @@ class ProviderConfigManager:
 
         return LangGraphConfig()
 
+    @staticmethod
+    def _get_google_code_assist_config() -> BaseConfig:
+        """Get Google Code Assist config."""
+        from litellm.llms.google_code_assist.transformation import (
+            GoogleCodeAssistConfig,
+        )
+
+        return GoogleCodeAssistConfig()
+
     @staticmethod
     def get_provider_chat_config(  # noqa: PLR0915
         model: str, provider: LlmProviders
diff --git a/provider_endpoints_support.json b/provider_endpoints_support.json
index ed49c146210..cf1a011032e 100644
--- a/provider_endpoints_support.json
+++ b/provider_endpoints_support.json
@@ -1105,6 +1105,29 @@
         "realtime": true
       }
     },
+    "google_code_assist": {
+      "display_name": "Google Code Assist (`google_code_assist`)",
+      "url": "https://docs.litellm.ai/docs/providers/google_code_assist",
+      "endpoints": {
+        "chat_completions": true,
+        "messages": false,
+        "responses": false,
+        "embeddings": false,
+        "image_generations": false,
+        "audio_transcriptions": false,
+        "audio_speech": false,
+        "moderations": false,
+        "batches": false,
+        "rerank": false,
+        "interactions": false,
+        "a2a": false,
+        "vector_stores_search": false,
+        "count_tokens": false,
+        "rag_ingest": false,
+        "realtime": false,
+        "generateContent": false
+      }
+    },
     "gemini": {
       "display_name": "Google AI Studio - Gemini (`gemini`)",
       "url": "https://docs.litellm.ai/docs/providers/gemini",
diff --git a/tests/proxy_unit_tests/test_google_gemini_proxy_request.py b/tests/proxy_unit_tests/test_google_gemini_proxy_request.py
index dbe30037313..8005dd20845 100644
--- a/tests/proxy_unit_tests/test_google_gemini_proxy_request.py
+++ b/tests/proxy_unit_tests/test_google_gemini_proxy_request.py
@@ -419,7 +419,7 @@ async def test_gemini_custom_api_base_proxy_integration():
     print(f"✅ Custom API base streaming URL test passed: {result_url_streaming}")
 
     # Test case 3: Error handling - missing API key
-    with pytest.raises(ValueError, match="Missing Gemini API key"):
+    with pytest.raises(ValueError, match="Missing gemini_api_key"):
         vertex_base._check_custom_proxy(
             api_base=custom_api_base,
             custom_llm_provider="gemini",
diff --git a/tests/test_litellm/llms/gemini/test_fallback_handler.py b/tests/test_litellm/llms/gemini/test_fallback_handler.py
new file mode 100644
index 00000000000..74e2f144627
--- /dev/null
+++ b/tests/test_litellm/llms/gemini/test_fallback_handler.py
@@ -0,0 +1,75 @@
+from unittest.mock import AsyncMock, patch
+
+import pytest
+
+from litellm.llms.gemini.fallback_handler import (
+    run_gemini_acompletion_with_code_assist_fallback,
+    run_gemini_completion_with_code_assist_fallback,
+)
+
+
+def test_run_gemini_completion_with_code_assist_fallback_disabled():
+    def _raise_scope_error():
+        raise Exception("ACCESS_TOKEN_SCOPE_INSUFFICIENT")
+
+    with patch(
+        "litellm.llms.gemini.fallback_handler._google_code_assist_chat.completion"
+    ) as mock_completion:
+        with pytest.raises(Exception, match="ACCESS_TOKEN_SCOPE_INSUFFICIENT"):
+            run_gemini_completion_with_code_assist_fallback(
+                primary_call=_raise_scope_error,
+                fallback_kwargs={},
+                auto_fallback_to_google_code_assist=False,
+            )
+
+        mock_completion.assert_not_called()
+
+
+def test_run_gemini_completion_with_code_assist_fallback_enabled_but_not_match():
+    def _raise_other_error():
+        raise Exception("SOME_OTHER_ERROR")
+
+    with (
+        patch(
+            "litellm.llms.gemini.fallback_handler.should_fallback_to_google_code_assist",
+            return_value=False,
+        ) as mock_should_fallback,
+        patch(
+            "litellm.llms.gemini.fallback_handler._google_code_assist_chat.completion"
+        ) as mock_completion,
+    ):
+        with pytest.raises(Exception, match="SOME_OTHER_ERROR"):
+            run_gemini_completion_with_code_assist_fallback(
+                primary_call=_raise_other_error,
+                fallback_kwargs={},
+                auto_fallback_to_google_code_assist=True,
+            )
+
+        mock_should_fallback.assert_called_once()
+        mock_completion.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_run_gemini_acompletion_with_code_assist_fallback_enabled():
+    async def _raise_scope_error():
+        raise Exception("ACCESS_TOKEN_SCOPE_INSUFFICIENT")
+
+    with (
+        patch(
+            "litellm.llms.gemini.fallback_handler.should_fallback_to_google_code_assist",
+            return_value=True,
+        ),
+        patch(
+            "litellm.llms.gemini.fallback_handler._google_code_assist_chat.acompletion",
+            new_callable=AsyncMock,
+        ) as mock_acompletion,
+    ):
+        mock_acompletion.return_value = "fallback-ok"
+        result = await run_gemini_acompletion_with_code_assist_fallback(
+            primary_call=_raise_scope_error,
+            fallback_kwargs={},
+            auto_fallback_to_google_code_assist=True,
+        )
+
+        assert result == "fallback-ok"
+        mock_acompletion.assert_awaited_once()
diff --git a/tests/test_litellm/llms/gemini/test_gemini_authenticator.py b/tests/test_litellm/llms/gemini/test_gemini_authenticator.py
new file mode 100644
index 00000000000..889ff537c60
--- /dev/null
+++ b/tests/test_litellm/llms/gemini/test_gemini_authenticator.py
@@ -0,0 +1,68 @@
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from litellm.llms.gemini.authenticator import GeminiAuthenticator
+
+
+def test_get_token_raises_if_login_response_missing_access_token(tmp_path):
+    auth = GeminiAuthenticator()
+    auth.oauth_creds_file = str(tmp_path / "oauth_creds.json")
+
+    with (
+        patch.object(auth, "_login", return_value={"refresh_token": "abc"}),
+        patch.object(auth, "_write_oauth_creds"),
+    ):
+        with pytest.raises(Exception, match="missing access_token"):
+            auth.get_token()
+
+
+def test_refresh_token_raises_if_response_missing_access_token(tmp_path):
+    auth = GeminiAuthenticator()
+    auth.oauth_creds_file = str(tmp_path / "oauth_creds.json")
+
+    mock_resp = MagicMock()
+    mock_resp.raise_for_status.return_value = None
+    mock_resp.json.return_value = {"expires_in": 3600}
+
+    with (
+        patch.object(
+            GeminiAuthenticator,
+            "_get_oauth_client_credentials",
+            return_value=("client-id", "client-secret"),
+        ),
+        patch("litellm.llms.gemini.authenticator.httpx.post", return_value=mock_resp),
+        patch.object(auth, "_write_oauth_creds"),
+    ):
+        with pytest.raises(Exception, match="missing access_token"):
+            auth._refresh_token("refresh-token")
+
+
+def test_login_times_out_without_oauth_callback(monkeypatch):
+    auth = GeminiAuthenticator()
+    monkeypatch.setenv("GEMINI_OAUTH_LOOPBACK_TIMEOUT_SECONDS", "1")
+
+    class _NoRequestServer:
+        def __init__(self, *args, **kwargs):
+            self.server_port = 12345
+            self.timeout = None
+
+        def handle_request(self):
+            return None
+
+        def server_close(self):
+            return None
+
+    with (
+        patch.object(
+            GeminiAuthenticator,
+            "_get_oauth_client_credentials",
+            return_value=("client-id", "client-secret"),
+        ),
+        patch(
+            "litellm.llms.gemini.authenticator.http.server.HTTPServer", _NoRequestServer
+        ),
+        patch("litellm.llms.gemini.authenticator.webbrowser.open", return_value=True),
+    ):
+        with pytest.raises(Exception, match="OAuth login timed out"):
+            auth._login()
diff --git a/tests/test_litellm/llms/gemini/test_gemini_common_utils.py b/tests/test_litellm/llms/gemini/test_gemini_common_utils.py
index 70946e10590..92dde78c2f3 100644
--- a/tests/test_litellm/llms/gemini/test_gemini_common_utils.py
+++ b/tests/test_litellm/llms/gemini/test_gemini_common_utils.py
@@ -1,8 +1,13 @@
 from unittest.mock import AsyncMock, patch
 
+import httpx
 import pytest
 
-from litellm.llms.gemini.common_utils import GeminiModelInfo, GoogleAIStudioTokenCounter
+from litellm.llms.gemini.common_utils import (
+    GeminiModelInfo,
+    GoogleAIStudioTokenCounter,
+    should_fallback_to_google_code_assist,
+)
 
 
 class TestGeminiModelInfo:
@@ -221,3 +226,48 @@ class TestGoogleAIStudioTokenCounter:
 
         # Verify the contents are unchanged
         assert cleaned_contents == contents_without_function_response
+
+
+class TestGeminiFallbackDetection:
+    def test_should_fallback_to_google_code_assist_for_structured_403_scope_error(self):
+        request = httpx.Request(
+            "POST", "https://generativelanguage.googleapis.com/test"
+        )
+        response = httpx.Response(
+            status_code=403,
+            json={
+                "error": {
+                    "code": 403,
+                    "message": "Request had insufficient authentication scopes.",
+                    "status": "PERMISSION_DENIED",
+                    "details": [{"reason": "ACCESS_TOKEN_SCOPE_INSUFFICIENT"}],
+                }
+            },
+            request=request,
+        )
+        err = httpx.HTTPStatusError(
+            "403 Client Error: Forbidden for url", request=request, response=response
+        )
+
+        assert should_fallback_to_google_code_assist(err) is True
+
+    def test_should_not_fallback_to_google_code_assist_for_non_403_scope_string(self):
+        request = httpx.Request(
+            "POST", "https://generativelanguage.googleapis.com/test"
+        )
+        response = httpx.Response(
+            status_code=500,
+            json={
+                "error": {
+                    "message": "ACCESS_TOKEN_SCOPE_INSUFFICIENT",
+                }
+            },
+            request=request,
+        )
+        err = httpx.HTTPStatusError(
+            "500 Server Error: Internal Server Error for url",
+            request=request,
+            response=response,
+        )
+
+        assert should_fallback_to_google_code_assist(err) is False
diff --git a/tests/test_litellm/llms/google_code_assist/__init__.py b/tests/test_litellm/llms/google_code_assist/__init__.py
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/tests/test_litellm/llms/google_code_assist/test_google_code_assist.py b/tests/test_litellm/llms/google_code_assist/test_google_code_assist.py
new file mode 100644
index 00000000000..aaafdd5a5ba
--- /dev/null
+++ b/tests/test_litellm/llms/google_code_assist/test_google_code_assist.py
@@ -0,0 +1,216 @@
+import pytest
+from unittest.mock import AsyncMock, MagicMock, patch
+import httpx
+import json
+from litellm.llms.google_code_assist.chat import (
+    GoogleCodeAssistChat,
+    get_google_code_assist_chat,
+)
+from litellm.types.utils import ModelResponse
+
+
+class TestGoogleCodeAssist:
+    def test_get_google_code_assist_chat_returns_singleton(self):
+        assert get_google_code_assist_chat() is get_google_code_assist_chat()
+
+    @patch("litellm.llms.google_code_assist.chat._get_httpx_client")
+    @patch("litellm.llms.gemini.common_utils.get_gemini_oauth_token")
+    def test_completion_basic(self, mock_get_token, mock_get_client):
+        """
+        Test basic completion with mocked handshake and API call.
+        """
+        mock_get_token.return_value = {
+            "token": "test-token",
+            "project_id": "test-project",
+        }
+
+        mock_client = MagicMock()
+        mock_get_client.return_value = mock_client
+
+        # Mock handshake response
+        handshake_data = {"cloudaicompanionProject": "final-project"}
+        mock_handshake_resp = httpx.Response(
+            status_code=200,
+            content=json.dumps(handshake_data).encode(),
+            request=httpx.Request("POST", "https://handshake"),
+        )
+
+        # Mock completion response
+        completion_data = {
+            "response": {
+                "candidates": [
+                    {
+                        "content": {
+                            "role": "model",
+                            "parts": [{"text": "Hello world"}],
+                        },
+                        "finishReason": "STOP",
+                    }
+                ],
+                "usageMetadata": {
+                    "promptTokenCount": 5,
+                    "candidatesTokenCount": 2,
+                    "totalTokenCount": 7,
+                },
+            }
+        }
+        mock_completion_resp = httpx.Response(
+            status_code=200,
+            content=json.dumps(completion_data).encode(),
+            request=httpx.Request("POST", "https://completion"),
+        )
+
+        mock_client.post.side_effect = [mock_handshake_resp, mock_completion_resp]
+
+        handler = GoogleCodeAssistChat()
+        response = handler.completion(
+            model="google_code_assist/gemini-1.5-flash",
+            messages=[{"role": "user", "content": "hi"}],
+            model_response=ModelResponse(),
+            print_verbose=False,
+            logging_obj=MagicMock(),
+            optional_params={},
+            litellm_params={},
+        )
+
+        assert response.choices[0].message.content == "Hello world"
+        assert response.usage.total_tokens == 7
+
+    @patch("litellm.llms.gemini.common_utils.get_gemini_oauth_token")
+    def test_completion_raises_when_token_missing(self, mock_get_token):
+        mock_get_token.return_value = {"token": None}
+
+        handler = GoogleCodeAssistChat()
+        with pytest.raises(Exception, match="Missing Gemini OAuth token value"):
+            handler.completion(
+                model="google_code_assist/gemini-1.5-flash",
+                messages=[{"role": "user", "content": "hi"}],
+                model_response=ModelResponse(),
+                print_verbose=False,
+                logging_obj=MagicMock(),
+                optional_params={},
+                litellm_params={},
+            )
+
+    @pytest.mark.asyncio
+    @patch("litellm.llms.google_code_assist.chat.AsyncHTTPHandler.post")
+    @patch(
+        "litellm.llms.google_code_assist.chat.AsyncHTTPHandler.close",
+        new_callable=AsyncMock,
+    )
+    @patch("litellm.llms.gemini.common_utils.get_gemini_oauth_token")
+    async def test_acompletion_basic(
+        self, mock_get_token, mock_async_close, mock_async_post
+    ):
+        """
+        Test async completion.
+        """
+        mock_get_token.return_value = {"token": "test-token"}
+
+        # Handshake (async)
+        handshake_data = {"cloudaicompanionProject": "final-project"}
+        mock_handshake_resp = httpx.Response(
+            status_code=200,
+            content=json.dumps(handshake_data).encode(),
+            request=httpx.Request("POST", "https://handshake"),
+        )
+
+        # Completion (async)
+        completion_data = {
+            "response": {
+                "candidates": [
+                    {
+                        "content": {
+                            "role": "model",
+                            "parts": [{"text": "Async success"}],
+                        },
+                        "finishReason": "STOP",
+                    }
+                ],
+                "usageMetadata": {
+                    "promptTokenCount": 5,
+                    "candidatesTokenCount": 2,
+                    "totalTokenCount": 7,
+                },
+            }
+        }
+        mock_completion_resp = httpx.Response(
+            status_code=200,
+            content=json.dumps(completion_data).encode(),
+            request=httpx.Request("POST", "https://completion"),
+        )
+        mock_async_post.side_effect = [mock_handshake_resp, mock_completion_resp]
+
+        handler = GoogleCodeAssistChat()
+        response = await handler.acompletion(
+            model="google_code_assist/gemini-1.5-flash",
+            messages=[{"role": "user", "content": "hi"}],
+            model_response=ModelResponse(),
+            print_verbose=False,
+            logging_obj=MagicMock(),
+            optional_params={},
+            litellm_params={},
+        )
+
+        assert response.choices[0].message.content == "Async success"
+        mock_async_close.assert_awaited_once()
+
+    @pytest.mark.asyncio
+    @patch(
+        "litellm.llms.google_code_assist.chat.asyncio.to_thread", new_callable=AsyncMock
+    )
+    async def test_acompletion_uses_thread_for_oauth_lookup(self, mock_to_thread):
+        mock_to_thread.return_value = {"token": "test-token"}
+
+        with (
+            patch(
+                "litellm.llms.google_code_assist.chat.GoogleCodeAssistChat._ahandle_handshake",
+                new_callable=AsyncMock,
+                return_value="final-project",
+            ),
+            patch(
+                "litellm.llms.google_code_assist.chat.AsyncHTTPHandler.post",
+                new_callable=AsyncMock,
+            ) as mock_async_post,
+            patch(
+                "litellm.llms.google_code_assist.chat.AsyncHTTPHandler.close",
+                new_callable=AsyncMock,
+            ),
+        ):
+            completion_data = {
+                "response": {
+                    "candidates": [
+                        {
+                            "content": {
+                                "role": "model",
+                                "parts": [{"text": "Async success"}],
+                            },
+                            "finishReason": "STOP",
+                        }
+                    ],
+                    "usageMetadata": {
+                        "promptTokenCount": 5,
+                        "candidatesTokenCount": 2,
+                        "totalTokenCount": 7,
+                    },
+                }
+            }
+            mock_completion_resp = httpx.Response(
+                status_code=200,
+                content=json.dumps(completion_data).encode(),
+                request=httpx.Request("POST", "https://completion"),
+            )
+            mock_async_post.return_value = mock_completion_resp
+
+            handler = GoogleCodeAssistChat()
+            await handler.acompletion(
+                model="google_code_assist/gemini-1.5-flash",
+                messages=[{"role": "user", "content": "hi"}],
+                model_response=ModelResponse(),
+                print_verbose=False,
+                logging_obj=MagicMock(),
+                optional_params={},
+                litellm_params={},
+            )
+
+        mock_to_thread.assert_awaited_once()
diff --git a/tests/test_litellm/llms/google_code_assist/test_google_code_assist_transformation.py b/tests/test_litellm/llms/google_code_assist/test_google_code_assist_transformation.py
new file mode 100644
index 00000000000..ccaebc5b2d6
--- /dev/null
+++ b/tests/test_litellm/llms/google_code_assist/test_google_code_assist_transformation.py
@@ -0,0 +1,42 @@
+from unittest.mock import patch
+
+from litellm.llms.google_code_assist.transformation import GoogleCodeAssistConfig
+
+
+def test_transform_request_uses_base_model_name_for_internal_gemini_helpers():
+    class _CaptureConfig(GoogleCodeAssistConfig):
+        def __init__(self):
+            super().__init__()
+            self.model_seen_by_map = None
+
+        def map_openai_params(
+            self,
+            non_default_params: dict,
+            optional_params: dict,
+            model: str,
+            messages: list,
+        ) -> dict:
+            self.model_seen_by_map = model
+            return {"thinkingConfig": {"includeThoughts": True}}
+
+    config = _CaptureConfig()
+    with (
+        patch(
+            "litellm.llms.vertex_ai.gemini.transformation._transform_system_message",
+            return_value=(None, [{"role": "user", "content": "hi"}]),
+        ),
+        patch(
+            "litellm.llms.vertex_ai.gemini.transformation._gemini_convert_messages_with_history",
+            return_value=[{"role": "user", "parts": [{"text": "hi"}]}],
+        ) as mock_convert,
+    ):
+        result = config.transform_request(
+            model="google_code_assist/gemini-2.5-pro",
+            messages=[{"role": "user", "content": "hi"}],
+            optional_params={"thinkingConfig": {"includeThoughts": False}},
+            litellm_params={},
+        )
+
+    assert config.model_seen_by_map == "gemini-2.5-pro"
+    assert mock_convert.call_args.kwargs["model"] == "gemini-2.5-pro"
+    assert result["model"] == "gemini-2.5-pro"
diff --git a/tests/test_litellm/llms/vertex_ai/test_vertex_ai_common_utils.py b/tests/test_litellm/llms/vertex_ai/test_vertex_ai_common_utils.py
index 7cb3faf6177..eb3b5daea68 100644
--- a/tests/test_litellm/llms/vertex_ai/test_vertex_ai_common_utils.py
+++ b/tests/test_litellm/llms/vertex_ai/test_vertex_ai_common_utils.py
@@ -11,6 +11,7 @@ sys.path.insert(
 )  # Adds the parent directory to the system path
 
 from litellm.llms.vertex_ai.common_utils import (
+    _get_gemini_url,
     _get_vertex_url,
     convert_anyof_null_to_nullable,
     get_vertex_location_from_url,
@@ -603,6 +604,33 @@ def test_get_vertex_url_global_region(stream, expected_endpoint_suffix):
     assert url == expected_url
 
 
+def test_get_gemini_url_stream_query_param_only_for_chat_mode():
+    chat_url, _ = _get_gemini_url(
+        mode="chat",
+        model="gemini-1.5-flash",
+        stream=True,
+    )
+    embedding_url, _ = _get_gemini_url(
+        mode="embedding",
+        model="gemini-1.5-flash",
+        stream=True,
+    )
+
+    assert "alt=sse" in chat_url
+    assert "alt=sse" not in embedding_url
+
+
+def test_get_gemini_url_requires_literal_true_for_streaming_endpoint_and_alt_sse():
+    url, endpoint = _get_gemini_url(
+        mode="chat",
+        model="gemini-1.5-flash",
+        stream=1,  # type: ignore[arg-type]  # truthy non-bool should not be treated as streaming=True
+    )
+
+    assert endpoint == "generateContent"
+    assert "alt=sse" not in url
+
+
 @pytest.mark.parametrize(
     "model_cost_entry, vertex_region, expected_region",
     [
@@ -1096,6 +1124,58 @@ def test_get_token_url():
     pass
 
 
+def test_get_token_and_url_gemini_raises_if_no_api_key_and_no_oauth_token():
+    from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import (
+        VertexLLM,
+    )
+
+    vertex_llm = VertexLLM()
+    with patch(
+        "litellm.llms.gemini.common_utils.get_gemini_oauth_token", return_value=None
+    ):
+        with pytest.raises(ValueError, match="Missing gemini_api_key"):
+            vertex_llm._get_token_and_url(
+                auth_header=None,
+                vertex_project="",
+                vertex_location="",
+                vertex_credentials="",
+                gemini_api_key=None,
+                custom_llm_provider="gemini",
+                should_use_v1beta1_features=False,
+                api_base=None,
+                model="gemini-2.5-pro",
+                stream=False,
+            )
+
+
+def test_get_token_and_url_gemini_uses_prefetched_auth_data_without_lookup():
+    from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import (
+        VertexLLM,
+    )
+
+    vertex_llm = VertexLLM()
+    with patch("litellm.llms.gemini.common_utils.get_gemini_oauth_token") as mock_get:
+        auth_header, _ = vertex_llm._get_token_and_url(
+            auth_header=None,
+            vertex_project="",
+            vertex_location="",
+            vertex_credentials="",
+            gemini_api_key=None,
+            gemini_auth_data={"token": "oauth-token", "project_id": "my-project"},
+            custom_llm_provider="gemini",
+            should_use_v1beta1_features=False,
+            api_base=None,
+            model="gemini-2.5-pro",
+            stream=False,
+        )
+
+    assert auth_header == {
+        "Authorization": "Bearer oauth-token",
+        "x-goog-user-project": "my-project",
+    }
+    mock_get.assert_not_called()
+
+
 @pytest.mark.asyncio
 async def test_vertex_ai_token_counter_routes_partner_models():
     """
@@ -1457,11 +1537,7 @@ def test_vertex_request_labels_from_litellm_params_extracts_requester_metadata()
 
 
 def test_vertex_request_labels_from_litellm_params_accepts_litellm_metadata():
-    lp = {
-        "litellm_metadata": {
-            "requester_metadata": {"team": "platform", "count": 3}
-        }
-    }
+    lp = {"litellm_metadata": {"requester_metadata": {"team": "platform", "count": 3}}}
     assert vertex_request_labels_from_litellm_params(lp) == {"team": "platform"}
 
 
diff --git a/tests/test_litellm/llms/vertex_ai/test_vertex_llm_base.py b/tests/test_litellm/llms/vertex_ai/test_vertex_llm_base.py
index 88aac07a0c9..dbd4581cf9a 100644
--- a/tests/test_litellm/llms/vertex_ai/test_vertex_llm_base.py
+++ b/tests/test_litellm/llms/vertex_ai/test_vertex_llm_base.py
@@ -821,7 +821,7 @@ class TestVertexBase:
 
         if custom_llm_provider == "gemini" and api_base and gemini_api_key is None:
             # Test case 5: Should raise ValueError for Gemini without API key
-            with pytest.raises(ValueError, match="Missing Gemini API key"):
+            with pytest.raises(ValueError, match="Missing gemini_api_key"):
                 vertex_base._check_custom_proxy(
                     api_base=api_base,
                     custom_llm_provider=custom_llm_provider,