Bitropy patches on v1.82.3-stable: passthrough credential priority + header security

[pkieszcz]

What this is

2 patches on top of upstream v1.82.3-stable that fix the Anthropic passthrough endpoint for Claude Code Max (OAuth) and BYOK scenarios.

This PR shows exactly what we changed — only 2 files, 2 commits.

Full documentation: PASSTHROUGH_PATCHES.md

Patches

1. Strip x-litellm-api-key from forwarded headers (security)

File: litellm/passthrough/utils.py (+1 line)

Without this, the x-litellm-api-key proxy auth header is forwarded to Anthropic, leaking credentials.

Upstream PR: BerriAI#20432 (open, unreviewed since Feb 2026)

2. Credential priority for Anthropic passthrough (critical)

File: litellm/proxy/pass_through_endpoints/llm_passthrough_endpoints.py (+19/-6 lines)

The upstream code always sends x-api-key: "{}".format(anthropic_api_key) as a custom header, which:

• Sends literal x-api-key: None when no server ANTHROPIC_API_KEY is set
• Overwrites client-provided credentials (OAuth tokens, BYOK keys) even when server key IS set

New behavior (credential priority):

Client sends	Server has key	Result
OAuth token (Claude Max)	Any	Client pays (Max subscription)
Own x-api-key (BYOK)	Any	Client pays (own API key)
Nothing	Yes	Company pays (server key)
Nothing	No	No credentials (Anthropic rejects)

Background

• This bug was first fixed in upstream PR Fix: support claude code auth via subscription (anthropic) BerriAI/litellm#14821 (Sep 2025) but reverted 3 days later
• Follow-up PRs [Feat] Add Support for Claude Code Max/OAuth 2 on LiteLLM AI Gateway  BerriAI/litellm#19453 and fix(proxy): preserve and forward OAuth Authorization headers through proxy layer BerriAI/litellm#19912 fixed OAuth for the regular completion path but NOT the passthrough
• Upstream PR fix: stop leaking x-litellm-api-key to Anthropic + support OAuth tokens in passthrough BerriAI/litellm#20432 (our patch Bitropy patches on v1.82.3-stable: passthrough credential priority + header security #1) has been open unreviewed for 6+ weeks
• The built-in /anthropic/ route has auth included — no premium license or custom pass_through_endpoints config needed

Testing

Tested locally on v1.82.4 (main-stable) with header inspection (request catcher) and real Anthropic API:

• ✅ Claude Code Max (OAuth) passthrough
• ✅ BYOK (client x-api-key) passthrough
• ✅ Mixed mode (server key fallback)
• ✅ Auth: wrong/missing litellm key rejected
• ✅ x-litellm-api-key stripped from upstream requests
• ✅ Spend tracking for streaming passthrough (v1.82.x fix)

Deploy

Image: europe-central2-docker.pkg.dev/bitropy-management/images/litellm:v1.82.3-stable-patched

Claude Code config

{
  "env": {
    "ANTHROPIC_BASE_URL": "https://ai.demo.internal.bitropy.io/anthropic",
    "ANTHROPIC_CUSTOM_HEADERS": "x-litellm-api-key: sk-<your-virtual-key>"
  }
}

⚠️ Use ANTHROPIC_CUSTOM_HEADERS, NOT ANTHROPIC_API_KEY. See PASSTHROUGH_PATCHES.md for why.

🤖 Generated with Claude Code