Implements
https://linear.app/codercom/issue/AIGOV-213/add-bedrock-provider
# AWS Bedrock mantle support in AI Gateway
## Summary
Add support for the AWS Bedrock **mantle** endpoint
(`bedrock-mantle.{region}.api.aws/anthropic/v1/messages`) to AI Gateway.
Mantle serves Claude through the native Anthropic Messages API. We model
it as a `protocol` field on the existing Bedrock provider settings
(`invoke-model` default, or `mantle`) rather than as a new provider
type, and we treat mantle as a pure passthrough: SigV4-sign and forward,
no body translation.
## Background
Claude on AWS Bedrock is reachable through two endpoints, each speaking
exactly one wire protocol:
1. **InvokeModel** (existing): `bedrock-runtime.{region}.amazonaws.com`.
Model id in the URL path, request translated into Bedrock's InvokeModel
format, responses returned as a binary AWS eventstream. This is what AI
Gateway already supported for Bedrock.
2. **Mantle** (this doc):
`bedrock-mantle.{region}.api.aws/anthropic/v1/messages`. Native
Anthropic Messages API: model in the body, plain SSE streaming.
## Why a `protocol` field, not a new provider type
The alternative is to model mantle as its own `ai_provider_type`
(`bedrock-mantle`) alongside `bedrock`. I chose the `protocol` field
instead for two reasons:
1. Mantle reads more like a protocol of Bedrock than a separate
provider. It is the same AWS account, credentials, region, and IAM,
reached over a different wire protocol and host. One Bedrock provider
with two protocols (`invoke-model` default and `mantle`) models that
more organically than two provider types.
2. It avoids a database migration. The `protocol` field lives in the
settings JSON blob (empty resolves to `invoke-model`, so existing
providers are unaffected), whereas a new type means an enum value and
the `ALTER TYPE ... ADD VALUE` migration that goes with it.
## Why passthrough, not translation
The client already emits Bedrock-legal requests in mantle mode:
```sh
export CLAUDE_CODE_USE_MANTLE=1
export CLAUDE_CODE_SKIP_MANTLE_AUTH=1
export ANTHROPIC_BEDROCK_MANTLE_BASE_URL=https://<coder>/api/v2/aibridge/<provider-name>
```
So the gateway just forwards the body and SigV4-signs it (service
`bedrock-mantle`), and skips all the InvokeModel body-translation (model
remap, thinking conversion, beta-flag allowlist, field stripping). This
keeps the mantle path thin and avoids a second copy of translation logic
to maintain.
## Consequences
- Protocol-dependent fields: `model` / `small_fast_model` are used by
InvokeModel but ignored by mantle (the client sends the model), and
`base_url` is required for mantle but optional for InvokeModel.
Validation is protocol-aware.
- No central model control on mantle: because it is a passthrough, the
operator cannot pin the model.
- `region` and the `base_url` host must name the same region (the SigV4
scope must match the endpoint); a mismatch surfaces as `Credential
should be scoped to a valid region`.
## Draft UI
<img width="1100" height="579" alt="image"
src="https://github.com/user-attachments/assets/37bab46d-8958-4a96-9f47-1fef3493e1b6"
/>
## Follow-up PRs:
- https://github.com/coder/coder/pull/27156
Yevhenii Shcherbina
63ec93a7ce