diff --git a/docs/providers/bedrock.md b/docs/providers/bedrock.md
index 23850a49ab52..d11eb1b125dc 100644
--- a/docs/providers/bedrock.md
+++ b/docs/providers/bedrock.md
@@ -38,6 +38,18 @@ Choose your preferred auth method and follow the setup steps.
         export AWS_BEARER_TOKEN_BEDROCK="..."
         ```
       </Step>
+      <Step title="Opt in to provider data sharing for Claude Fable 5">
+        Claude Fable 5 and Claude Mythos-class Bedrock models require the Bedrock Data Retention API mode `provider_data_share` before invocation. This opt-in allows Bedrock to share prompts and completions with Anthropic and retain them for up to 30 days for trust and safety review.
+
+        ```bash
+        curl -X PUT https://bedrock-mantle.us-east-1.api.aws/v1/data_retention \
+          -H "x-api-key: $BEDROCK_API_KEY" \
+          -H "Content-Type: application/json" \
+          -d '{ "mode": "provider_data_share" }'
+        ```
+
+        Use another Bedrock model in the config if you cannot accept that retention mode.
+      </Step>
       <Step title="Add a Bedrock provider and model to your config">
         No `apiKey` is required. Configure the provider with `auth: "aws-sdk"`:
 
diff --git a/src/llm/providers/anthropic.test.ts b/src/llm/providers/anthropic.test.ts
index 234e551ca5b0..05ec2f27ecec 100644
--- a/src/llm/providers/anthropic.test.ts
+++ b/src/llm/providers/anthropic.test.ts
@@ -87,6 +87,7 @@ describe("Anthropic provider", () => {
     const model = makeAnthropicModel({
       provider: "microsoft-foundry",
       baseUrl: "https://example.services.ai.azure.com/anthropic",
+      authHeader: true,
     });
     const context = {
       messages: [{ role: "user", content: "hello", timestamp: 1 }],
@@ -108,6 +109,30 @@ describe("Anthropic provider", () => {
     expect(config.defaultHeaders?.["x-api-key"]).toBeUndefined();
   });
 
+  it("keeps Microsoft Foundry API-key profiles on Anthropic API key auth", async () => {
+    const model = makeAnthropicModel({
+      provider: "microsoft-foundry",
+      baseUrl: "https://example.services.ai.azure.com/anthropic",
+      authHeader: false,
+    });
+    const context = {
+      messages: [{ role: "user", content: "hello", timestamp: 1 }],
+    } satisfies Context;
+
+    streamAnthropic(model, context, {
+      apiKey: "foundry-resource-key",
+    });
+
+    await vi.waitFor(() => expect(anthropicMockState.configs).toHaveLength(1));
+    const config = anthropicMockState.configs[0] as {
+      apiKey?: string | null;
+      authToken?: string | null;
+    };
+
+    expect(config.apiKey).toBe("foundry-resource-key");
+    expect(config.authToken).toBeNull();
+  });
+
   it("preserves provider-signed Anthropic thinking and drops reasoning_content placeholders", async () => {
     const highSurrogate = String.fromCharCode(0xd83d);
     const signedThinking = `keep${highSurrogate}signed`;
diff --git a/src/llm/providers/anthropic.ts b/src/llm/providers/anthropic.ts
index a03a321a54b6..4f6fb964210b 100644
--- a/src/llm/providers/anthropic.ts
+++ b/src/llm/providers/anthropic.ts
@@ -945,7 +945,7 @@ function createClient(
     return { client, isOAuthToken: false };
   }
 
-  if (model.provider === "microsoft-foundry") {
+  if (model.provider === "microsoft-foundry" && model.authHeader === true) {
     const client = new Anthropic({
       apiKey: null,
       authToken: apiKey,