AWS Bedrock Mantle

AWS Bedrock Mantle provider - a single endpoint serving Claude (native Anthropic Messages) and OpenAI-family / Gemma models (OpenAI-compatible), with AWS SigV4 or API-key auth

Overview

Bedrock Mantle is a single AWS endpoint, served on the bedrock-mantle.{region}.api.aws host, that exposes a broad model catalog through two surfaces:

• Native Anthropic Messages API (/anthropic/v1/messages) for Claude models.
• OpenAI-compatible API (/v1/... or /openai/v1/...) for OpenAI-family (gpt-*), Gemma, and other open models.

Bifrost dispatches each request to the correct surface automatically based on the model family — you address the provider the same way regardless: bedrock_mantle/<model>.

Bedrock Mantle is distinct from the Bedrock provider, which uses the Converse / InvokeModel APIs on bedrock-runtime. Mantle is its own provider with its own credentials block (bedrock_mantle_key_config).

Model IDs

Mantle model IDs are sent verbatim to the endpoint and differ from the Converse IDs used by the Bedrock provider — there is no cross-region prefix (global./us.) and no version suffix (-v1:0):

Surface	Format	Examples
Native Anthropic (Claude)	anthropic.{model}	anthropic.claude-opus-4-8, anthropic.claude-haiku-4-5
OpenAI-compatible	openai.{model} / google.{model} / …	openai.gpt-oss-120b, openai.gpt-5.5, google.gemma-4-31b

You can discover the exact IDs your account serves with a list-models request (the /v1/models catalog). An optional leading region/ prefix may be used to address a specific region per request (e.g. bedrock_mantle/us-west-2/anthropic.claude-opus-4-8).

Supported Operations

Operation	Supported
Chat Completions (+ streaming)	✅
Responses API (+ streaming)	✅
Tool calling (+ streaming)	✅
Vision (image input, Claude)	✅
Reasoning / extended thinking (Claude)	✅
Structured outputs	✅
Prompt caching (Claude)	✅
List models	✅
Text completion, embeddings, batch, files, images, audio, count tokens, rerank	❌

For Claude models, request/response handling (beta headers, cache control, reasoning, message conversion) follows the same rules as the Bedrock provider’s Anthropic behavior — refer to that page for the deep parameter mapping.

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Setup & Configuration

Bedrock Mantle authenticates with AWS SigV4 (the bedrock-mantle signing service) or an optional Bearer API key. A region is required on the key config (there is no default).

1. SigV4 — Explicit Credentials

config.json

{
  "providers": {
    "bedrock_mantle": {
      "keys": [
        {
          "name": "mantle-static",
          "value": "",
          "models": ["*"],
          "weight": 1.0,
          "bedrock_mantle_key_config": {
            "region": "us-east-1",
            "access_key": "env.AWS_ACCESS_KEY_ID",
            "secret_key": "env.AWS_SECRET_ACCESS_KEY",
            "session_token": "env.AWS_SESSION_TOKEN"
          }
        }
      ]
    }
  }
}

session_token is optional (only needed for temporary credentials).

2. SigV4 — Inherited AWS Credentials / IAM Role

Leave access_key and secret_key empty and Bifrost inherits credentials from the AWS SDK default chain — IRSA (IAM Roles for Service Accounts), EC2 instance profile, or AWS_* environment variables. Only region is required.

config.json

{
  "providers": {
    "bedrock_mantle": {
      "keys": [
        {
          "name": "mantle-iam",
          "value": "",
          "models": ["*"],
          "weight": 1.0,
          "bedrock_mantle_key_config": {
            "region": "us-east-1"
          }
        }
      ]
    }
  }
}

To assume an IAM role before requests (works with both explicit and inherited credentials), add role_arn (and optionally external_id / session_name):

config.json

{
  "bedrock_mantle_key_config": {
    "region": "us-west-2",
    "role_arn": "env.AWS_ROLE_ARN",
    "external_id": "env.AWS_EXTERNAL_ID",
    "session_name": "bifrost-session"
  }
}

3. API Key (Bearer)

Alternatively, authenticate with a Bedrock Mantle API key sent as a Bearer token. Set the top-level key value and leave the SigV4 credentials empty (region is still required):

config.json

{
  "providers": {
    "bedrock_mantle": {
      "keys": [
        {
          "name": "mantle-api-key",
          "value": "env.BEDROCK_MANTLE_API_KEY",
          "models": ["*"],
          "weight": 1.0,
          "bedrock_mantle_key_config": {
            "region": "us-east-1"
          }
        }
      ]
    }
  }
}

---

Usage

Address models with the bedrock_mantle/ prefix:

cURL

curl -X POST http://localhost:8080/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "bedrock_mantle/anthropic.claude-opus-4-8",
    "messages": [{ "role": "user", "content": "Hello!" }]
  }'

Both surfaces are addressed identically — bedrock_mantle/anthropic.claude-opus-4-8 (native Anthropic) and bedrock_mantle/openai.gpt-oss-120b (OpenAI-compatible) — Bifrost routes each to the right API.