diff --git a/aibridge/config/config.go b/aibridge/config/config.go
index acc1192319fb4..ee0c5fec8a672 100644
--- a/aibridge/config/config.go
+++ b/aibridge/config/config.go
@@ -70,10 +70,20 @@ type AWSBedrock struct {
 	Protocol BedrockProtocol
 }
 
+// ResolvedProtocol returns the configured protocol, mapping the empty value to
+// the legacy InvokeModel protocol so existing providers keep the legacy
+// behavior.
+func (c AWSBedrock) ResolvedProtocol() BedrockProtocol {
+	if c.Protocol == "" {
+		return BedrockProtocolInvokeModel
+	}
+	return c.Protocol
+}
+
 // Validate verifies protocol-specific Bedrock configuration.
 func (c AWSBedrock) Validate() error {
-	switch c.Protocol {
-	case "", BedrockProtocolInvokeModel:
+	switch c.ResolvedProtocol() {
+	case BedrockProtocolInvokeModel:
 		if c.Region == "" && c.BaseURL == "" {
 			return xerrors.New("region or base url required")
 		}
diff --git a/aibridge/intercept/messages/base.go b/aibridge/intercept/messages/base.go
index a0025d6881b99..1a9ea0dfb858a 100644
--- a/aibridge/intercept/messages/base.go
+++ b/aibridge/intercept/messages/base.go
@@ -133,14 +133,13 @@ func (i *interceptionBase) CorrelatingToolCallID() *string {
 // isBedrockMantle reports whether the interception targets the Bedrock mantle
 // protocol.
 func (i *interceptionBase) isBedrockMantle() bool {
-	return i.bedrock != nil && i.bedrock.Cfg.Protocol == aibconfig.BedrockProtocolMantle
+	return i.bedrock != nil && i.bedrock.Cfg.ResolvedProtocol() == aibconfig.BedrockProtocolMantle
 }
 
 // isBedrockInvokeModel reports whether the interception targets the Bedrock
 // InvokeModel protocol.
 func (i *interceptionBase) isBedrockInvokeModel() bool {
-	return i.bedrock != nil &&
-		(i.bedrock.Cfg.Protocol == "" || i.bedrock.Cfg.Protocol == aibconfig.BedrockProtocolInvokeModel)
+	return i.bedrock != nil && i.bedrock.Cfg.ResolvedProtocol() == aibconfig.BedrockProtocolInvokeModel
 }
 
 func (i *interceptionBase) Model() string {
@@ -164,7 +163,7 @@ func (i *interceptionBase) Model() string {
 }
 
 func (i *interceptionBase) baseTraceAttributes(r *http.Request, streaming bool) []attribute.KeyValue {
-	return []attribute.KeyValue{
+	attrs := []attribute.KeyValue{
 		attribute.String(tracing.RequestPath, r.URL.Path),
 		attribute.String(tracing.InterceptionID, i.id.String()),
 		attribute.String(tracing.InitiatorID, aibcontext.ActorIDFromContext(r.Context())),
@@ -173,6 +172,10 @@ func (i *interceptionBase) baseTraceAttributes(r *http.Request, streaming bool)
 		attribute.Bool(tracing.Streaming, streaming),
 		attribute.Bool(tracing.IsBedrock, i.bedrock != nil),
 	}
+	if i.bedrock != nil {
+		attrs = append(attrs, attribute.String(tracing.BedrockProtocol, string(i.bedrock.Cfg.ResolvedProtocol())))
+	}
+	return attrs
 }
 
 func (i *interceptionBase) injectTools() {
diff --git a/aibridge/internal/integrationtest/trace_internal_test.go b/aibridge/internal/integrationtest/trace_internal_test.go
index 23fcbdeae8b75..43719c3f177ff 100644
--- a/aibridge/internal/integrationtest/trace_internal_test.go
+++ b/aibridge/internal/integrationtest/trace_internal_test.go
@@ -187,6 +187,9 @@ func TestTraceAnthropic(t *testing.T) {
 				attribute.Bool(tracing.Streaming, tc.streaming),
 				attribute.Bool(tracing.IsBedrock, tc.bedrock),
 			}
+			if tc.bedrock {
+				attrs = append(attrs, attribute.String(tracing.BedrockProtocol, string(config.BedrockProtocolInvokeModel)))
+			}
 
 			require.Len(t, sr.Ended(), totalCount)
 			verifyTraces(t, sr, tc.expect, attrs)
@@ -311,6 +314,9 @@ func TestTraceAnthropicErr(t *testing.T) {
 				attribute.Bool(tracing.Streaming, tc.streaming),
 				attribute.Bool(tracing.IsBedrock, tc.bedrock),
 			}
+			if tc.bedrock {
+				attrs = append(attrs, attribute.String(tracing.BedrockProtocol, string(config.BedrockProtocolInvokeModel)))
+			}
 
 			verifyTraces(t, sr, tc.expect, attrs)
 		})
@@ -422,6 +428,9 @@ func TestInjectedToolsTrace(t *testing.T) {
 			}
 			if tc.expectProvider == config.ProviderAnthropic {
 				attrs = append(attrs, attribute.Bool(tracing.IsBedrock, tc.bedrock))
+				if tc.bedrock {
+					attrs = append(attrs, attribute.String(tracing.BedrockProtocol, string(config.BedrockProtocolInvokeModel)))
+				}
 			}
 
 			verifyTraces(t, sr, []expectTrace{{"Intercept.ProcessRequest.ToolCall", 1, codes.Unset}}, attrs)
diff --git a/aibridge/provider/anthropic.go b/aibridge/provider/anthropic.go
index 9424d4c9601a5..460b38102cd8c 100644
--- a/aibridge/provider/anthropic.go
+++ b/aibridge/provider/anthropic.go
@@ -79,6 +79,9 @@ func NewAnthropic(ctx context.Context, cfg config.Anthropic, bedrockCfg *config.
 		if runtimeCfg.Region == "" {
 			runtimeCfg.Region = resolvedRegion
 		}
+		if err := runtimeCfg.Validate(); err != nil {
+			return nil, xerrors.Errorf("bedrock config: %w", err)
+		}
 		bedrock = &messages.BedrockRuntime{Cfg: runtimeCfg, Creds: creds}
 	}
 
diff --git a/aibridge/provider/anthropic_internal_test.go b/aibridge/provider/anthropic_internal_test.go
index 9df6f0371843f..cdc8afe9148aa 100644
--- a/aibridge/provider/anthropic_internal_test.go
+++ b/aibridge/provider/anthropic_internal_test.go
@@ -114,6 +114,42 @@ func TestNewAnthropic_KeyResolution(t *testing.T) {
 	}
 }
 
+// NOTE: no t.Parallel() because the subtests use t.Setenv.
+func TestNewAnthropic_BedrockRegionResolution(t *testing.T) {
+	t.Run("mantle_region_from_env", func(t *testing.T) {
+		t.Setenv("AWS_REGION", "us-west-2")
+
+		p, err := NewAnthropic(context.Background(), config.Anthropic{}, &config.AWSBedrock{
+			BaseURL:         "https://bedrock-mantle.us-west-2.api.aws/anthropic",
+			Protocol:        config.BedrockProtocolMantle,
+			AccessKey:       "test-key",
+			AccessKeySecret: "test-secret",
+		})
+		require.NoError(t, err)
+		require.NotNil(t, p.bedrock)
+		require.Equal(t, "us-west-2", p.bedrock.Cfg.Region)
+	})
+
+	t.Run("mantle_no_region_anywhere", func(t *testing.T) {
+		// Clear every source the AWS SDK consults for a region so none
+		// resolves, then confirm construction rejects the mantle provider.
+		t.Setenv("AWS_REGION", "")
+		t.Setenv("AWS_DEFAULT_REGION", "")
+		t.Setenv("AWS_PROFILE", "")
+		t.Setenv("AWS_CONFIG_FILE", "/dev/null")
+		t.Setenv("AWS_SHARED_CREDENTIALS_FILE", "/dev/null")
+		t.Setenv("AWS_EC2_METADATA_DISABLED", "true")
+
+		_, err := NewAnthropic(context.Background(), config.Anthropic{}, &config.AWSBedrock{
+			BaseURL:         "https://proxy.internal",
+			Protocol:        config.BedrockProtocolMantle,
+			AccessKey:       "test-key",
+			AccessKeySecret: "test-secret",
+		})
+		require.ErrorContains(t, err, "region required")
+	})
+}
+
 func TestAnthropic_CreateInterceptor(t *testing.T) {
 	t.Parallel()
 
diff --git a/aibridge/tracing/tracing.go b/aibridge/tracing/tracing.go
index 7adaf3f65e355..f01e3f1f33026 100644
--- a/aibridge/tracing/tracing.go
+++ b/aibridge/tracing/tracing.go
@@ -17,12 +17,13 @@ const (
 	// trace attribute key constants
 	RequestPath = "request_path"
 
-	InterceptionID = "interception_id"
-	InitiatorID    = "user_id"
-	Provider       = "provider"
-	Model          = "model"
-	Streaming      = "streaming"
-	IsBedrock      = "aws_bedrock"
+	InterceptionID  = "interception_id"
+	InitiatorID     = "user_id"
+	Provider        = "provider"
+	Model           = "model"
+	Streaming       = "streaming"
+	IsBedrock       = "aws_bedrock"
+	BedrockProtocol = "aws_bedrock_protocol"
 
 	PassthroughURL         = "passthrough_url"
 	PassthroughUpstreamURL = "passthrough_upstream_url"
diff --git a/cli/aibridged_internal_test.go b/cli/aibridged_internal_test.go
index d8d02c131461b..59b2153c6f591 100644
--- a/cli/aibridged_internal_test.go
+++ b/cli/aibridged_internal_test.go
@@ -175,6 +175,8 @@ func TestBuildProviders(t *testing.T) {
 		cfg.LegacyBedrock.Region = serpent.String("us-west-2")
 		cfg.LegacyBedrock.AccessKey = serpent.String("AKID")
 		cfg.LegacyBedrock.AccessKeySecret = serpent.String("secret")
+		cfg.LegacyBedrock.Model = serpent.String("anthropic.claude-3-5-sonnet-20241022-v2:0")
+		cfg.LegacyBedrock.SmallFastModel = serpent.String("anthropic.claude-3-5-haiku-20241022-v1:0")
 
 		providers, err := buildFromEnv(t, cfg)
 		require.NoError(t, err)
@@ -191,6 +193,8 @@ func TestBuildProviders(t *testing.T) {
 		cfg.LegacyBedrock.Region = serpent.String("us-west-2")
 		cfg.LegacyBedrock.AccessKey = serpent.String("AKID")
 		cfg.LegacyBedrock.AccessKeySecret = serpent.String("secret")
+		cfg.LegacyBedrock.Model = serpent.String("anthropic.claude-3-5-sonnet-20241022-v2:0")
+		cfg.LegacyBedrock.SmallFastModel = serpent.String("anthropic.claude-3-5-haiku-20241022-v1:0")
 
 		providers, err := buildFromEnv(t, cfg)
 		require.NoError(t, err)
diff --git a/cli/server_aibridge_internal_test.go b/cli/server_aibridge_internal_test.go
index 7a3732cef7784..781b642f938cd 100644
--- a/cli/server_aibridge_internal_test.go
+++ b/cli/server_aibridge_internal_test.go
@@ -727,6 +727,8 @@ func TestBuildProviderFromProtoSetsAPIDumpDir(t *testing.T) {
 					Region:          "us-east-1",
 					AccessKey:       "AKID",
 					AccessKeySecret: "secret",
+					Model:           "anthropic.claude-3-5-sonnet-20241022-v2:0",
+					SmallFastModel:  "anthropic.claude-3-5-haiku-20241022-v1:0",
 				},
 			},
 			expectedType: aibridge.ProviderAnthropic,