From abae9cbbc5df515e72d07b435e84db79c98047fd Mon Sep 17 00:00:00 2001
From: Kit Langton <kit.langton@gmail.com>
Date: Tue, 11 Aug 2026 12:14:03 -0400
Subject: [PATCH] fix(core): resolve Bedrock region templates

---
 packages/core/src/model-resolver.ts       |  7 +++++++
 packages/core/test/model-resolver.test.ts | 22 ++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/packages/core/src/model-resolver.ts b/packages/core/src/model-resolver.ts
index 346c2402cfd9..734f4ed3c3d5 100644
--- a/packages/core/src/model-resolver.ts
+++ b/packages/core/src/model-resolver.ts
@@ -254,7 +254,14 @@ function prepareRuntimeModel(model: Info, credential: Credential.Value | undefin
     if (credential?.type === "key" && credential.metadata !== undefined)
       draft.body = Provider.mergeOverlay(draft.body, credential.metadata)
     if (typeof draft.settings?.baseURL !== "string") return
+    const bedrockRegion =
+      Provider.isAISDK(draft.package) &&
+      Provider.packageName(draft.package) === "@ai-sdk/amazon-bedrock/mantle" &&
+      typeof draft.settings.region === "string"
+        ? draft.settings.region
+        : undefined
     draft.settings.baseURL = draft.settings.baseURL.replace(/\$\{([^}]+)\}/g, (placeholder, name: string) => {
+      if (name === "AWS_REGION" && bedrockRegion) return bedrockRegion
       return process.env[name] ?? placeholder
     })
   })
diff --git a/packages/core/test/model-resolver.test.ts b/packages/core/test/model-resolver.test.ts
index 7d04516f8cc2..cf5584fc6269 100644
--- a/packages/core/test/model-resolver.test.ts
+++ b/packages/core/test/model-resolver.test.ts
@@ -152,6 +152,28 @@ describe("ModelResolver", () => {
     }),
   )
 
+  it.effect("resolves the Bedrock Mantle catalog endpoint from the configured region", () =>
+    withEnv({ AWS_REGION: undefined }, () =>
+      Effect.gen(function* () {
+        const resolved = yield* ModelResolver.fromCatalogModel(
+          model(Provider.aisdk("@ai-sdk/amazon-bedrock/mantle"), {
+            providerID: Provider.ID.amazonBedrock,
+            modelID: "openai.gpt-oss-120b",
+            settings: {
+              region: "us-west-2",
+              baseURL: "https://bedrock-mantle.${AWS_REGION}.api.aws/openai/v1",
+            },
+          }),
+        )
+
+        expect(resolved.route).toMatchObject({
+          id: "bedrock-mantle-responses",
+          endpoint: { baseURL: "https://bedrock-mantle.us-west-2.api.aws/openai/v1" },
+        })
+      }),
+    ),
+  )
+
   it.effect("uses the API modelID instead of the catalog ID for native OpenAI routes", () =>
     Effect.gen(function* () {
       const catalog = model(Provider.aisdk("@ai-sdk/openai"), {