From 4bafb26c12f090e2190c9246e4f18a108caa277a Mon Sep 17 00:00:00 2001
From: Ishaan Jaffer <ishaanjaffer0324@gmail.com>
Date: Wed, 21 Jan 2026 19:03:26 -0800
Subject: [PATCH] fix utils

---
 litellm/constants.py         |  5 +++++
 litellm/passthrough/utils.py | 16 +++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/litellm/constants.py b/litellm/constants.py
index 13a26c6d0ea..5da0cf1489f 100644
--- a/litellm/constants.py
+++ b/litellm/constants.py
@@ -1131,6 +1131,11 @@ ALLOWED_VERTEX_AI_PASSTHROUGH_HEADERS = {
     "content-type",  # Required for request body parsing
 }
 
+# Prefix for headers that should be forwarded to the provider with the prefix stripped
+# e.g., 'x-pass-anthropic-beta: value' becomes 'anthropic-beta: value'
+# Works for all LLM pass-through endpoints (Vertex AI, Anthropic, Bedrock, etc.)
+PASS_THROUGH_HEADER_PREFIX = "x-pass-"
+
 BASE_MCP_ROUTE = "/mcp"
 
 BATCH_STATUS_POLL_INTERVAL_SECONDS = int(
diff --git a/litellm/passthrough/utils.py b/litellm/passthrough/utils.py
index 4bf66d49881..fbbf9cd2581 100644
--- a/litellm/passthrough/utils.py
+++ b/litellm/passthrough/utils.py
@@ -3,6 +3,8 @@ from urllib.parse import parse_qs
 
 import httpx
 
+from litellm.constants import PASS_THROUGH_HEADER_PREFIX
+
 
 class BasePassthroughUtils:
     @staticmethod
@@ -27,7 +29,11 @@ class BasePassthroughUtils:
         forward_headers: Optional[bool] = False,
     ):
         """
-        Helper to forward headers from original request
+        Helper to forward headers from original request.
+
+        Also handles 'x-pass-' prefixed headers which are always forwarded
+        with the prefix stripped, regardless of forward_headers setting.
+        e.g., 'x-pass-anthropic-beta: value' becomes 'anthropic-beta: value'
         """
         if forward_headers is True:
             # Header We Should NOT forward
@@ -36,6 +42,14 @@ class BasePassthroughUtils:
 
             # Combine request headers with custom headers
             headers = {**request_headers, **headers}
+
+        # Always process x-pass- prefixed headers (strip prefix and forward)
+        for header_name, header_value in request_headers.items():
+            if header_name.lower().startswith(PASS_THROUGH_HEADER_PREFIX):
+                # Strip the 'x-pass-' prefix to get the actual header name
+                actual_header_name = header_name[len(PASS_THROUGH_HEADER_PREFIX) :]
+                headers[actual_header_name] = header_value
+
         return headers
 
 class CommonUtils: