diff --git a/chatlas/_provider_bedrock.py b/chatlas/_provider_bedrock.py
index 12fdd603..5436df5b 100644
--- a/chatlas/_provider_bedrock.py
+++ b/chatlas/_provider_bedrock.py
@@ -109,7 +109,8 @@ def ChatBedrock(
     base_url
         Override the endpoint URL. The default is the standard endpoint for
         the selected `api` and your region, honoring the official AWS SDKs'
-        endpoint override environment variables:
+        endpoint override environment variables (a service-specific variable
+        outranks the generic `AWS_ENDPOINT_URL`):
         `AWS_ENDPOINT_URL_BEDROCK_RUNTIME` for `"converse"`, and
         `AWS_ENDPOINT_URL_BEDROCK_MANTLE` for `"messages"` and `"responses"`
         (which append their API-specific path to the override). For the
@@ -464,17 +465,23 @@ def aws_endpoint_url(var: str, default: str) -> str:
 
 
 def bedrock_base_url(api: BedrockAPI, region: str) -> str:
-    # Match the official AWS SDKs, which read service-specific endpoint
-    # overrides: AWS_ENDPOINT_URL_BEDROCK_RUNTIME for the runtime (converse)
-    # service and AWS_ENDPOINT_URL_BEDROCK_MANTLE for mantle.
+    # Match the official AWS SDKs' endpoint resolution precedence: the
+    # service-specific override (AWS_ENDPOINT_URL_BEDROCK_RUNTIME for the
+    # runtime (converse) service, AWS_ENDPOINT_URL_BEDROCK_MANTLE for mantle)
+    # outranks the generic AWS_ENDPOINT_URL, which outranks the regional
+    # endpoint computed from `region`.
     if api == "converse":
         return aws_endpoint_url(
             "AWS_ENDPOINT_URL_BEDROCK_RUNTIME",
-            f"https://bedrock-runtime.{region}.amazonaws.com",
+            aws_endpoint_url(
+                "AWS_ENDPOINT_URL",
+                f"https://bedrock-runtime.{region}.amazonaws.com",
+            ),
         )
 
     host = aws_endpoint_url(
-        "AWS_ENDPOINT_URL_BEDROCK_MANTLE", MANTLE_HOST.format(region=region)
+        "AWS_ENDPOINT_URL_BEDROCK_MANTLE",
+        aws_endpoint_url("AWS_ENDPOINT_URL", MANTLE_HOST.format(region=region)),
     )
     if api == "messages":
         # The Anthropic SDK appends "/v1/messages" itself, so the "/v1" is
diff --git a/tests/test_provider_bedrock_mantle.py b/tests/test_provider_bedrock_mantle.py
index 63545ded..b006f462 100644
--- a/tests/test_provider_bedrock_mantle.py
+++ b/tests/test_provider_bedrock_mantle.py
@@ -103,6 +103,25 @@ def test_converse_uses_the_runtime_endpoint(self):
             "https://bedrock-runtime.us-west-2.amazonaws.com"
         )
 
+    def test_generic_endpoint_url_applies_to_converse(self, monkeypatch):
+        monkeypatch.delenv("AWS_ENDPOINT_URL_BEDROCK_RUNTIME", raising=False)
+        monkeypatch.setenv("AWS_ENDPOINT_URL", "https://proxy.example")
+        assert bedrock_base_url("converse", "us-west-2") == "https://proxy.example"
+
+    def test_generic_endpoint_url_applies_to_mantle(self, monkeypatch):
+        monkeypatch.delenv("AWS_ENDPOINT_URL_BEDROCK_MANTLE", raising=False)
+        monkeypatch.setenv("AWS_ENDPOINT_URL", "https://proxy.example")
+        assert bedrock_base_url("messages", "us-west-2") == (
+            "https://proxy.example/anthropic"
+        )
+
+    def test_service_specific_var_outranks_generic(self, monkeypatch):
+        monkeypatch.setenv("AWS_ENDPOINT_URL", "https://generic.example")
+        monkeypatch.setenv(
+            "AWS_ENDPOINT_URL_BEDROCK_RUNTIME", "https://specific.example"
+        )
+        assert bedrock_base_url("converse", "us-west-2") == "https://specific.example"
+
 
 class TestChatBedrockDispatch:
     def test_responses_model_builds_an_openai_backed_provider(self):