litellm - 💡(How to fix) Fix Add native provider for Claude Platform on AWS (AnthropicAWS)

Background

Anthropic GA'd Claude Platform on AWS on 2026-05-11:

• Announcement: https://claude.com/blog/claude-platform-on-aws
• Docs: https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws

It exposes the full Anthropic Messages API on an AWS-hosted endpoint with:

• AWS IAM auth (SigV4 signing) or API key via ANTHROPIC_AWS_API_KEY
• Required x-anthropic-aws-workspace-id header per request (workspace pins to a single AWS region)
• Default base URL pattern: https://gateway.{region}.api.aws
• Day-one feature parity with the public Anthropic API (prompt caching, batch, Files, Skills, MCP connector, Advisor)

Anthropic's official SDKs ship first-class support across Python, TypeScript, Go, Java, C#, PHP, Ruby — e.g. from anthropic import AnthropicAWS in Python — and Claude Code reads ANTHROPIC_AWS_WORKSPACE_ID / ANTHROPIC_AWS_BASE_URL env vars natively.

Current LiteLLM state

LiteLLM today supports Anthropic models via three transports:

• anthropic/ — direct Anthropic public API
• bedrock/ — AWS Bedrock
• vertex_ai/ — GCP Vertex partner-model

There is no provider for Claude Platform on AWS. The provider list and the Claude Code compatibility matrix (https://docs.litellm.ai/docs/claude_code_compatibility) make no mention of it.

A naive workaround (custom auth hook that SigV4-signs after the body is mutated) is brittle because LiteLLM's drop_params / additional_drop_params hooks rewrite the request body, invalidating the signature unless signing happens last.

Proposed

Add a first-class provider:

• Prefix: anthropic_aws/ (or claude_platform_aws/)
• Auth precedence: workspaceId arg > ANTHROPIC_AWS_WORKSPACE_ID env > error
• Credential resolution: boto3 default credential chain (SSO, IAM role, ~/.aws/credentials) for SigV4 signing, falling back to ANTHROPIC_AWS_API_KEY env var if set
• Base URL: explicit override > ANTHROPIC_AWS_BASE_URL env > https://gateway.{region}.api.aws
• Body mutation (drop_params etc.) must complete before SigV4 signing
• Pass-through for anthropic-beta headers
• Listed in https://docs.litellm.ai/docs/claude_code_compatibility once shipped

Concrete use case

Mid-size org running ~$1k+/month dev-tooling spend on LiteLLM-routed CI reviewer + code-audit bots, currently split between direct Anthropic and Bedrock. The split exists today because drop_params is not honored on Bedrock's /v1/messages passthrough route (a separate known bug) — Platform-on-AWS would resolve both: single transport, AWS-commit consolidation, day-one feature parity.

Happy to test a PR end-to-end against our production gateway once available.