From d8f7217b71a050e16daccc2590cea335d5930fb0 Mon Sep 17 00:00:00 2001
From: Yujong Lee <yujong@berri.ai>
Date: Sun, 11 Oct 2026 22:28:19 +0000
Subject: [PATCH] fix(bedrock): prefer regional endpoint host regions

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
---
 .../messages/transformation.rs                | 40 ++++++++++++++++++-
 .../bedrock_mantle/messages/transformation.rs | 39 +++++++++++++++++-
 2 files changed, 76 insertions(+), 3 deletions(-)

diff --git a/litellm-rust/crates/llms/src/bedrock/claude_platform/messages/transformation.rs b/litellm-rust/crates/llms/src/bedrock/claude_platform/messages/transformation.rs
index 07c8b11edba..f9f5e4f7b22 100644
--- a/litellm-rust/crates/llms/src/bedrock/claude_platform/messages/transformation.rs
+++ b/litellm-rust/crates/llms/src/bedrock/claude_platform/messages/transformation.rs
@@ -194,7 +194,8 @@ fn platform_region(
             .strip_suffix(".api.aws")
             .map(str::to_string)
     });
-    let region = resolve_aws_region(host_region.as_deref(), &params.aws, env)
+    let region = host_region
+        .or_else(|| resolve_aws_region(None, &params.aws, env))
         .or_else(|| resolve_non_empty(None, env, &["AWS_DEFAULT_REGION"]))
         .ok_or_else(|| Error::Auth(AwsParams::REGION.missing("Claude Platform on AWS")))?;
     validated_region(region)
@@ -320,6 +321,43 @@ mod tests {
         }
     }
 
+    #[rstest]
+    #[case::explicit_regional_endpoint(
+        "https://aws-external-anthropic.us-west-2.api.aws",
+        "us-east-1",
+        "us-west-2"
+    )]
+    fn public_regional_host_precedes_configured_region(
+        #[case] api_base: &str,
+        #[case] configured_region: &str,
+        #[case] expected_region: &str,
+    ) {
+        let params = LitellmParams {
+            api_base: Some(api_base.into()),
+            aws: AwsParams {
+                aws_region_name: Some(configured_region.into()),
+                ..Default::default()
+            },
+            ..Default::default()
+        };
+        let env = |name: &str| {
+            (name == "ANTHROPIC_AWS_WORKSPACE_ID").then(|| "workspace".into())
+        };
+        let url = BEDROCK_CLAUDE_PLATFORM_MESSAGES_CONFIG
+            .get_complete_url(None, "claude-test", &params, false, &env)
+            .unwrap();
+        let environment = BEDROCK_CLAUDE_PLATFORM_MESSAGES_CONFIG
+            .validate_environment(vec![], None, "claude-test", &params, &env)
+            .unwrap();
+        assert_eq!(
+            url,
+            "https://aws-external-anthropic.us-west-2.api.aws/v1/messages"
+        );
+        assert!(
+            matches!(environment.auth, AuthScheme::AwsSigV4 { region, service: SERVICE, .. } if region == expected_region)
+        );
+    }
+
     #[rstest]
     #[case::default(json!({}), false)]
     #[case::override_empty(json!({"claude_platform_unsupported_params": []}), true)]
diff --git a/litellm-rust/crates/llms/src/bedrock_mantle/messages/transformation.rs b/litellm-rust/crates/llms/src/bedrock_mantle/messages/transformation.rs
index 1e7327d7811..215866fd1f9 100644
--- a/litellm-rust/crates/llms/src/bedrock_mantle/messages/transformation.rs
+++ b/litellm-rust/crates/llms/src/bedrock_mantle/messages/transformation.rs
@@ -250,9 +250,10 @@ fn mantle_region(
     params: &LitellmParams,
     env: &dyn Fn(&str) -> Option<String>,
 ) -> Result<String, Error> {
-    let region = resolve_non_empty(params.aws.aws_region_name.as_deref(), &|_| None, &[])
+    let region = mantle_base(base, params, env)
+        .and_then(|base| mantle_host_region(&base))
+        .or_else(|| resolve_non_empty(params.aws.aws_region_name.as_deref(), &|_| None, &[]))
         .or_else(|| mantle_model(model).1)
-        .or_else(|| mantle_base(base, params, env).and_then(|base| mantle_host_region(&base)))
         .or_else(|| resolve_non_empty(None, env, REGION_ENVS))
         .unwrap_or_else(|| "us-east-1".into());
     validated_region(region)
@@ -323,6 +324,40 @@ mod tests {
         );
     }
 
+    #[rstest]
+    #[case::explicit_regional_endpoint(
+        "https://bedrock-mantle.us-west-2.api.aws",
+        "us-east-1",
+        "us-west-2"
+    )]
+    fn public_regional_host_precedes_configured_region(
+        #[case] api_base: &str,
+        #[case] configured_region: &str,
+        #[case] expected_region: &str,
+    ) {
+        let params = LitellmParams {
+            api_base: Some(api_base.into()),
+            aws: AwsParams {
+                aws_region_name: Some(configured_region.into()),
+                ..Default::default()
+            },
+            ..Default::default()
+        };
+        let url = BEDROCK_MANTLE_MESSAGES_CONFIG
+            .get_complete_url(None, "claude-test", &params, false, &|_| None)
+            .unwrap();
+        let environment = BEDROCK_MANTLE_MESSAGES_CONFIG
+            .validate_environment(vec![], None, "claude-test", &params, &|_| None)
+            .unwrap();
+        assert_eq!(
+            url,
+            "https://bedrock-mantle.us-west-2.api.aws/anthropic/v1/messages"
+        );
+        assert!(
+            matches!(environment.auth, AuthScheme::AwsSigV4 { region, service: "bedrock", .. } if region == expected_region)
+        );
+    }
+
     #[rstest]
     #[case::aws_default_region("AWS_DEFAULT_REGION", "eu-west-1")]
     fn aws_default_region_selects_mantle_endpoint(