diff --git a/docs/my-website/docs/proxy/customer_usage.md b/docs/my-website/docs/proxy/customer_usage.md
index 8e366586b15..5a6c06fdc81 100644
--- a/docs/my-website/docs/proxy/customer_usage.md
+++ b/docs/my-website/docs/proxy/customer_usage.md
@@ -22,19 +22,49 @@ Customer Usage enables you to track spend and usage for individual customers (en
 
 ## How to Track Spend
 
-Track customer spend by including a `user` field in your API requests. The customer ID will be automatically tracked and associated with all spend from that request.
+Track customer spend by including a `user` field in your API requests or by passing a customer ID header. The customer ID will be automatically tracked and associated with all spend from that request.
 
-### Example using cURL
+<Tabs>
+<TabItem value="body" label="Request Body" default>
+
+### Using Request Body
 
 Make a `/chat/completions` call with the `user` field containing your customer ID:
 
-```bash showLineNumbers title="Track spend with customer ID"
+```bash showLineNumbers title="Track spend with customer ID in body"
+curl -X POST 'http://0.0.0.0:4000/chat/completions' \
+  --header 'Content-Type: application/json' \
+  --header 'Authorization: Bearer sk-1234' \
+  --data '{
+    "model": "gpt-3.5-turbo",
+    "user": "customer-123",
+    "messages": [
+      {
+        "role": "user",
+        "content": "What is the capital of France?"
+      }
+    ]
+  }'
+```
+
+</TabItem>
+<TabItem value="header" label="Request Header">
+
+### Using Request Headers
+
+You can also pass the customer ID via HTTP headers. This is useful for tools that support custom headers but don't allow modifying the request body (like Claude Code with `ANTHROPIC_CUSTOM_HEADERS`).
+
+LiteLLM automatically recognizes these standard headers (no configuration required):
+- `x-litellm-customer-id`
+- `x-litellm-end-user-id`
+
+```bash showLineNumbers title="Track spend with customer ID in header"
 curl -X POST 'http://0.0.0.0:4000/chat/completions' \
   --header 'Content-Type: application/json' \
-  --header 'Authorization: Bearer sk-1234' \ # 👈 YOUR PROXY KEY
+  --header 'Authorization: Bearer sk-1234' \
+  --header 'x-litellm-customer-id: customer-123' \
   --data '{
     "model": "gpt-3.5-turbo",
-    "user": "customer-123", # 👈 CUSTOMER ID
     "messages": [
       {
         "role": "user",
@@ -44,7 +74,22 @@ curl -X POST 'http://0.0.0.0:4000/chat/completions' \
   }'
 ```
 
-The customer ID (`customer-123`) will be automatically upserted into the database with the new spend. If the customer ID already exists, spend will be incremented.
+#### Using with Claude Code
+
+Claude Code supports custom headers via the `ANTHROPIC_CUSTOM_HEADERS` environment variable. Set it to pass your customer ID:
+
+```bash title="Configure Claude Code with customer tracking"
+export ANTHROPIC_BASE_URL="http://0.0.0.0:4000/v1/messages"
+export ANTHROPIC_API_KEY="sk-1234"
+export ANTHROPIC_CUSTOM_HEADERS="x-litellm-customer-id: my-customer-id"
+```
+
+Now all requests from Claude Code will automatically track spend under `my-customer-id`.
+
+</TabItem>
+</Tabs>
+
+The customer ID will be automatically upserted into the database with the new spend. If the customer ID already exists, spend will be incremented.
 
 ### Example using OpenWebUI
 
diff --git a/litellm/constants.py b/litellm/constants.py
index 4ea0be247b3..423cfb51d3f 100644
--- a/litellm/constants.py
+++ b/litellm/constants.py
@@ -1073,6 +1073,13 @@
 
 ########################### LiteLLM Proxy Specific Constants ###########################
 ########################################################################################
+
+# Standard headers that are always checked for customer/end-user ID (no configuration required)
+# These headers work out-of-the-box for tools like Claude Code that support custom headers
+STANDARD_CUSTOMER_ID_HEADERS = [
+    "x-litellm-customer-id",
+    "x-litellm-end-user-id",
+]
 MAX_SPENDLOG_ROWS_TO_QUERY = int(
     os.getenv("MAX_SPENDLOG_ROWS_TO_QUERY", 1_000_000)
 )  # if spendLogs has more than 1M rows, do not query the DB
diff --git a/litellm/proxy/auth/auth_utils.py b/litellm/proxy/auth/auth_utils.py
index 797540deaa4..1a7f05716b3 100644
--- a/litellm/proxy/auth/auth_utils.py
+++ b/litellm/proxy/auth/auth_utils.py
@@ -7,6 +7,7 @@
 
 from litellm import Router, provider_list
 from litellm._logging import verbose_proxy_logger
+from litellm.constants import STANDARD_CUSTOMER_ID_HEADERS
 from litellm.proxy._types import *
 from litellm.types.router import CONFIGURABLE_CLIENTSIDE_AUTH_PARAMS
 
@@ -561,6 +562,32 @@ def get_customer_user_header_from_mapping(user_id_mapping) -> Optional[str]:
             return header_name
     return None
 
+def _get_customer_id_from_standard_headers(
+    request_headers: Optional[dict],
+) -> Optional[str]:
+    """
+    Check standard customer ID headers for a customer/end-user ID.
+
+    This enables tools like Claude Code to pass customer IDs via ANTHROPIC_CUSTOM_HEADERS.
+    No configuration required - these headers are always checked.
+
+    Args:
+        request_headers: The request headers dict
+
+    Returns:
+        The customer ID if found in standard headers, None otherwise
+    """
+    if request_headers is None:
+        return None
+
+    for standard_header in STANDARD_CUSTOMER_ID_HEADERS:
+        for header_name, header_value in request_headers.items():
+            if header_name.lower() == standard_header.lower():
+                user_id_str = str(header_value) if header_value is not None else ""
+                if user_id_str.strip():
+                    return user_id_str
+    return None
+
 
 def get_end_user_id_from_request_body(
     request_body: dict, request_headers: Optional[dict] = None
@@ -569,7 +596,12 @@ def get_end_user_id_from_request_body(
     # and to ensure it's fetched at runtime.
     from litellm.proxy.proxy_server import general_settings
 
-    # Check 1 : Follow the user header mappings feature, if not found, then check for deprecated user_header_name (only if request_headers is provided)
+    # Check 1: Standard customer ID headers (always checked, no configuration required)
+    customer_id = _get_customer_id_from_standard_headers(request_headers=request_headers)
+    if customer_id is not None:
+        return customer_id
+
+    # Check 2: Follow the user header mappings feature, if not found, then check for deprecated user_header_name (only if request_headers is provided)
     # User query: "system not respecting user_header_name property"
     # This implies the key in general_settings is 'user_header_name'.
     if request_headers is not None:
@@ -602,19 +634,19 @@ def get_end_user_id_from_request_body(
                     if user_id_str.strip():
                         return user_id_str
 
-    # Check 2: 'user' field in request_body (commonly OpenAI)
+    # Check 3: 'user' field in request_body (commonly OpenAI)
     if "user" in request_body and request_body["user"] is not None:
         user_from_body_user_field = request_body["user"]
         return str(user_from_body_user_field)
 
-    # Check 3: 'litellm_metadata.user' in request_body (commonly Anthropic)
+    # Check 4: 'litellm_metadata.user' in request_body (commonly Anthropic)
     litellm_metadata = request_body.get("litellm_metadata")
     if isinstance(litellm_metadata, dict):
         user_from_litellm_metadata = litellm_metadata.get("user")
         if user_from_litellm_metadata is not None:
             return str(user_from_litellm_metadata)
 
-    # Check 4: 'metadata.user_id' in request_body (another common pattern)
+    # Check 5: 'metadata.user_id' in request_body (another common pattern)
     metadata_dict = request_body.get("metadata")
     if isinstance(metadata_dict, dict):
         user_id_from_metadata_field = metadata_dict.get("user_id")
diff --git a/tests/test_litellm/proxy/auth/test_auth_utils.py b/tests/test_litellm/proxy/auth/test_auth_utils.py
index b1bef63933e..62f9cc33b64 100644
--- a/tests/test_litellm/proxy/auth/test_auth_utils.py
+++ b/tests/test_litellm/proxy/auth/test_auth_utils.py
@@ -1,9 +1,13 @@
 """
-Unit tests for auth_utils functions related to rate limiting.
+Unit tests for auth_utils functions related to rate limiting and customer ID extraction.
 """
 
+from unittest.mock import patch
+
 from litellm.proxy._types import UserAPIKeyAuth
 from litellm.proxy.auth.auth_utils import (
+    _get_customer_id_from_standard_headers,
+    get_end_user_id_from_request_body,
     get_key_model_rpm_limit,
     get_key_model_tpm_limit,
 )
@@ -129,3 +133,56 @@ def test_model_max_budget_priority_over_team(self):
         )
         result = get_key_model_tpm_limit(user_api_key_dict)
         assert result == {"gpt-4": 10000}
+
+
+class TestGetCustomerIdFromStandardHeaders:
+    """Tests for _get_customer_id_from_standard_headers helper function."""
+
+    def test_should_return_customer_id_from_x_litellm_customer_id_header(self):
+        """Should extract customer ID from x-litellm-customer-id header."""
+        headers = {"x-litellm-customer-id": "customer-123"}
+        result = _get_customer_id_from_standard_headers(request_headers=headers)
+        assert result == "customer-123"
+
+    def test_should_return_customer_id_from_x_litellm_end_user_id_header(self):
+        """Should extract customer ID from x-litellm-end-user-id header."""
+        headers = {"x-litellm-end-user-id": "end-user-456"}
+        result = _get_customer_id_from_standard_headers(request_headers=headers)
+        assert result == "end-user-456"
+
+    def test_should_return_none_when_headers_is_none(self):
+        """Should return None when headers is None."""
+        result = _get_customer_id_from_standard_headers(request_headers=None)
+        assert result is None
+
+    def test_should_return_none_when_no_standard_headers_present(self):
+        """Should return None when no standard customer ID headers are present."""
+        headers = {"x-other-header": "some-value"}
+        result = _get_customer_id_from_standard_headers(request_headers=headers)
+        assert result is None
+
+
+class TestGetEndUserIdFromRequestBodyWithStandardHeaders:
+    """Tests for get_end_user_id_from_request_body with standard customer ID headers."""
+
+    def test_should_prioritize_standard_header_over_body_user(self):
+        """Standard customer ID header should take precedence over body user field."""
+        headers = {"x-litellm-customer-id": "header-customer"}
+        request_body = {"user": "body-user"}
+
+        with patch("litellm.proxy.proxy_server.general_settings", {}):
+            result = get_end_user_id_from_request_body(
+                request_body=request_body, request_headers=headers
+            )
+        assert result == "header-customer"
+
+    def test_should_fall_back_to_body_when_no_standard_header(self):
+        """Should fall back to body user when no standard headers are present."""
+        headers = {"x-other-header": "value"}
+        request_body = {"user": "body-user"}
+
+        with patch("litellm.proxy.proxy_server.general_settings", {}):
+            result = get_end_user_id_from_request_body(
+                request_body=request_body, request_headers=headers
+            )
+        assert result == "body-user"