diff --git a/aibridge/config/config.go b/aibridge/config/config.go
index b01282b0cc7..acc1192319f 100644
--- a/aibridge/config/config.go
+++ b/aibridge/config/config.go
@@ -3,6 +3,8 @@ package config
 import (
 	"time"
 
+	"golang.org/x/xerrors"
+
 	"github.com/coder/coder/v2/aibridge/keypool"
 )
 
@@ -25,13 +27,34 @@ type Anthropic struct {
 	SendActorHeaders bool
 }
 
+// BedrockProtocol selects which AWS Bedrock wire protocol a provider targets.
+type BedrockProtocol string
+
+const (
+	// BedrockProtocolInvokeModel is the legacy InvokeModel protocol
+	// (bedrock-runtime.{region}.amazonaws.com), which translates the native
+	// Messages request into Bedrock's InvokeModel format. It is the default
+	// for the zero value.
+	BedrockProtocolInvokeModel BedrockProtocol = "invoke-model"
+	// BedrockProtocolMantle is the mantle protocol
+	// (bedrock-mantle.{region}.api.aws/anthropic/v1/messages). It is a
+	// passthrough: the gateway forwards the native Messages request body
+	// unchanged and only applies AWS SigV4 signing (service bedrock-mantle).
+	BedrockProtocolMantle BedrockProtocol = "mantle"
+)
+
 type AWSBedrock struct {
 	Region                     string
 	AccessKey, AccessKeySecret string
 	Model, SmallFastModel      string
-	// If set, requests will be sent to this URL instead of the default AWS Bedrock endpoint
-	// (https://bedrock-runtime.{region}.amazonaws.com).
-	// This is useful for routing requests through a proxy or for testing.
+	// BaseURL configures the upstream Bedrock endpoint.
+	//
+	// For InvokeModel, it is optional. When empty, requests use the default
+	// https://bedrock-runtime.{region}.amazonaws.com endpoint. Set it to route
+	// InvokeModel requests through a proxy or test server.
+	//
+	// For mantle, it is required and must be the Messages API prefix without
+	// /v1/messages, e.g. https://bedrock-mantle.{region}.api.aws/anthropic.
 	BaseURL string
 	// RoleARN, when set, is assumed via STS before calling Bedrock. The base
 	// identity (static keys or the AWS SDK default credential chain, e.g.
@@ -42,6 +65,35 @@ type AWSBedrock struct {
 	// It is meaningful only alongside RoleARN and must match the
 	// sts:ExternalId condition on the target role's trust policy.
 	ExternalID string
+	// Protocol selects the Bedrock wire protocol. The zero value behaves as
+	// BedrockProtocolInvokeModel.
+	Protocol BedrockProtocol
+}
+
+// Validate verifies protocol-specific Bedrock configuration.
+func (c AWSBedrock) Validate() error {
+	switch c.Protocol {
+	case "", BedrockProtocolInvokeModel:
+		if c.Region == "" && c.BaseURL == "" {
+			return xerrors.New("region or base url required")
+		}
+		if c.Model == "" {
+			return xerrors.New("model required")
+		}
+		if c.SmallFastModel == "" {
+			return xerrors.New("small fast model required")
+		}
+	case BedrockProtocolMantle:
+		if c.Region == "" {
+			return xerrors.New("region required")
+		}
+		if c.BaseURL == "" {
+			return xerrors.New("base_url required")
+		}
+	default:
+		return xerrors.Errorf("unknown bedrock protocol: %q", c.Protocol)
+	}
+	return nil
 }
 
 // OpenAI carries configuration for an OpenAI provider.
diff --git a/aibridge/config/config_test.go b/aibridge/config/config_test.go
new file mode 100644
index 00000000000..f2d80fbc7b2
--- /dev/null
+++ b/aibridge/config/config_test.go
@@ -0,0 +1,113 @@
+package config_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/aibridge/config"
+)
+
+func TestAWSBedrockValidate(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name     string
+		cfg      config.AWSBedrock
+		errorMsg string
+	}{
+		{
+			name: "invoke model valid",
+			cfg: config.AWSBedrock{
+				Region:         "us-east-1",
+				Model:          "anthropic.claude-sonnet",
+				SmallFastModel: "anthropic.claude-haiku",
+			},
+		},
+		{
+			name: "invoke model valid with base url instead of region",
+			cfg: config.AWSBedrock{
+				BaseURL:        "https://bedrock-runtime.example.com",
+				Model:          "anthropic.claude-sonnet",
+				SmallFastModel: "anthropic.claude-haiku",
+			},
+		},
+		{
+			name: "invoke model missing region and base url",
+			cfg: config.AWSBedrock{
+				Model:          "anthropic.claude-sonnet",
+				SmallFastModel: "anthropic.claude-haiku",
+			},
+			errorMsg: "region or base url required",
+		},
+		{
+			name: "invoke model missing model",
+			cfg: config.AWSBedrock{
+				Region:         "us-east-1",
+				SmallFastModel: "anthropic.claude-haiku",
+			},
+			errorMsg: "model required",
+		},
+		{
+			name: "invoke model missing small fast model",
+			cfg: config.AWSBedrock{
+				Region: "us-east-1",
+				Model:  "anthropic.claude-sonnet",
+			},
+			errorMsg: "small fast model required",
+		},
+		{
+			name: "unknown protocol rejected",
+			cfg: config.AWSBedrock{
+				Protocol: config.BedrockProtocol("unknown"),
+			},
+			errorMsg: "unknown bedrock protocol",
+		},
+		{
+			name: "mantle valid official api prefix",
+			cfg: config.AWSBedrock{
+				Region:   "us-east-1",
+				BaseURL:  "https://bedrock-mantle.us-east-1.api.aws/anthropic",
+				Protocol: config.BedrockProtocolMantle,
+			},
+		},
+		{
+			name: "mantle valid proxy api prefix",
+			cfg: config.AWSBedrock{
+				Region:   "us-east-1",
+				BaseURL:  "https://proxy.internal/proxy",
+				Protocol: config.BedrockProtocolMantle,
+			},
+		},
+		{
+			name: "mantle missing region",
+			cfg: config.AWSBedrock{
+				BaseURL:  "https://bedrock-mantle.us-east-1.api.aws",
+				Protocol: config.BedrockProtocolMantle,
+			},
+			errorMsg: "region required",
+		},
+		{
+			name: "mantle missing base url",
+			cfg: config.AWSBedrock{
+				Region:   "us-east-1",
+				Protocol: config.BedrockProtocolMantle,
+			},
+			errorMsg: "base_url required",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			err := tt.cfg.Validate()
+			if tt.errorMsg != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), tt.errorMsg)
+				return
+			}
+			require.NoError(t, err)
+		})
+	}
+}
diff --git a/aibridge/intercept/messages/base.go b/aibridge/intercept/messages/base.go
index 4eb8ef3a50e..0d6ed533b54 100644
--- a/aibridge/intercept/messages/base.go
+++ b/aibridge/intercept/messages/base.go
@@ -1,10 +1,14 @@
 package messages
 
 import (
+	"bytes"
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"math"
 	"net/http"
 	"strconv"
@@ -17,6 +21,7 @@ import (
 	"github.com/anthropics/anthropic-sdk-go/shared"
 	"github.com/anthropics/anthropic-sdk-go/shared/constant"
 	"github.com/aws/aws-sdk-go-v2/aws"
+	v4 "github.com/aws/aws-sdk-go-v2/aws/signer/v4"
 	"github.com/google/uuid"
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/trace"
@@ -64,6 +69,22 @@ var bedrockSupportedBetaFlags = map[string]bool{
 	"tool-examples-2025-10-29": true,
 }
 
+// BedrockPRMUserAgent is Coder's AWS attribution marker for outbound
+// Bedrock requests.
+//
+// It is appended to Bedrock User-Agent headers so AWS can recognize the
+// traffic as Coder-associated Bedrock usage.
+const BedrockPRMUserAgent = "sdk-ua-app-id/APN_1.1%2Fpc_cdfmjwn8i6u8l9fwz8h82e4w3%24"
+
+// bedrockMantleSigningService is the AWS SigV4 service name for mantle.
+const bedrockMantleSigningService = "bedrock-mantle"
+
+func appendBedrockPRMUserAgent(req *http.Request) {
+	if ua := req.Header.Get("User-Agent"); ua != "" {
+		req.Header.Set("User-Agent", ua+" "+BedrockPRMUserAgent)
+	}
+}
+
 // BedrockRuntime carries everything a Bedrock-backed interception needs: the
 // static Bedrock config plus the AWS credentials provider.
 type BedrockRuntime struct {
@@ -109,12 +130,29 @@ func (i *interceptionBase) CorrelatingToolCallID() *string {
 	return i.reqPayload.correlatingToolCallID()
 }
 
+// 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
+}
+
+// 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)
+}
+
 func (i *interceptionBase) Model() string {
 	if len(i.reqPayload) == 0 {
 		return "coder-aibridge-unknown"
 	}
 
-	if i.bedrock != nil {
+	// InvokeModel is the only protocol that remaps the model: it replaces the
+	// client's model with the operator-configured one. Every other case (mantle
+	// passthrough, non-Bedrock providers) returns the model the client sent in
+	// the body.
+	if i.isBedrockInvokeModel() {
 		model := i.bedrock.Cfg.Model
 		if i.isSmallFastModel() {
 			model = i.bedrock.Cfg.SmallFastModel
@@ -245,15 +283,25 @@ func (i *interceptionBase) newMessagesService(ctx context.Context, opts ...optio
 		opts = append(opts, option.WithMiddleware(mw))
 	}
 
-	if i.bedrock != nil {
+	if i.isBedrockInvokeModel() {
 		ctx, cancel := context.WithTimeout(ctx, time.Second*30)
 		defer cancel()
-		bedrockOpts, err := i.withAWSBedrockOptions(ctx)
+		bedrockOpts, err := i.withBedrockInvokeModelOptions(ctx)
+		if err != nil {
+			return anthropic.MessageService{}, err
+		}
+		opts = append(opts, bedrockOpts...)
+		i.augmentRequestForBedrockInvokeModel()
+	}
+
+	if i.isBedrockMantle() {
+		ctx, cancel := context.WithTimeout(ctx, time.Second*30)
+		defer cancel()
+		bedrockOpts, err := i.withBedrockMantleOptions(ctx)
 		if err != nil {
 			return anthropic.MessageService{}, err
 		}
 		opts = append(opts, bedrockOpts...)
-		i.augmentRequestForBedrock()
 	}
 
 	return anthropic.NewMessageService(opts...), nil
@@ -267,23 +315,18 @@ func (i *interceptionBase) withBody() option.RequestOption {
 	return option.WithRequestBody("application/json", []byte(i.reqPayload))
 }
 
-// withAWSBedrockOptions returns request options for authenticating with AWS Bedrock.
+// withBedrockInvokeModelOptions returns request options for the AWS Bedrock
+// InvokeModel protocol.
 //
 // Credentials come from i.bedrock.Creds. It is a shared credentials cache, so the per-request Retrieve()
 // below is served from that cache and does not re-resolve or re-assume on every request.
-func (i *interceptionBase) withAWSBedrockOptions(ctx context.Context) ([]option.RequestOption, error) {
+func (i *interceptionBase) withBedrockInvokeModelOptions(ctx context.Context) ([]option.RequestOption, error) {
 	if i.bedrock == nil {
 		return nil, xerrors.New("nil bedrock runtime")
 	}
 	cfg := i.bedrock.Cfg
-	if cfg.Region == "" && cfg.BaseURL == "" {
-		return nil, xerrors.New("region or base url required")
-	}
-	if cfg.Model == "" {
-		return nil, xerrors.New("model required")
-	}
-	if cfg.SmallFastModel == "" {
-		return nil, xerrors.New("small fast model required")
+	if err := cfg.Validate(); err != nil {
+		return nil, err
 	}
 
 	// Fail fast: ensure credentials can be resolved before signing. Served from
@@ -300,9 +343,7 @@ func (i *interceptionBase) withAWSBedrockOptions(ctx context.Context) ([]option.
 
 	var out []option.RequestOption
 	out = append(out, option.WithMiddleware(func(req *http.Request, next option.MiddlewareNext) (*http.Response, error) {
-		if ua := req.Header.Get("User-Agent"); ua != "" {
-			req.Header.Set("User-Agent", ua+" sdk-ua-app-id/APN_1.1%2Fpc_cdfmjwn8i6u8l9fwz8h82e4w3%24")
-		}
+		appendBedrockPRMUserAgent(req)
 		return next(req)
 	}))
 	out = append(out, bedrock.WithConfig(awsCfg))
@@ -315,11 +356,66 @@ func (i *interceptionBase) withAWSBedrockOptions(ctx context.Context) ([]option.
 	return out, nil
 }
 
-// augmentRequestForBedrock will change the model used for the request since AWS Bedrock doesn't support
+// withBedrockMantleOptions returns request options for the AWS Bedrock mantle
+// endpoint (bedrock-mantle.{region}.api.aws/anthropic/v1/messages). It speaks
+// the native Messages wire format, so this middleware only SigV4-signs the
+// request (service "bedrock-mantle") and forwards it; the response is plain
+// SSE.
+func (i *interceptionBase) withBedrockMantleOptions(ctx context.Context) ([]option.RequestOption, error) {
+	cfg := i.bedrock.Cfg
+	if err := cfg.Validate(); err != nil {
+		return nil, err
+	}
+
+	// Fail fast: ensure credentials can be resolved before signing. Served from
+	// the shared cache on most requests (no network); on the cold or refresh
+	// path this performs the actual STS/IMDS call.
+	if _, err := i.bedrock.Creds.Retrieve(ctx); err != nil {
+		return nil, xerrors.Errorf("resolve AWS credentials: %w", err)
+	}
+
+	signer := v4.NewSigner()
+	var out []option.RequestOption
+	out = append(out, option.WithBaseURL(cfg.BaseURL))
+	// Appended last so it runs innermost (right before the HTTP send) and signs
+	// the request after all other headers are set.
+	out = append(out, option.WithMiddleware(func(req *http.Request, next option.MiddlewareNext) (*http.Response, error) {
+		appendBedrockPRMUserAgent(req)
+
+		creds, err := i.bedrock.Creds.Retrieve(req.Context())
+		if err != nil {
+			return nil, err
+		}
+
+		// SigV4 requires a payload hash, so read the body to hash it and then
+		// restore it for the downstream HTTP client to send.
+		var body []byte
+		if req.Body != nil {
+			var err error
+			body, err = io.ReadAll(req.Body)
+			if err != nil {
+				return nil, err
+			}
+			_ = req.Body.Close()
+			req.Body = io.NopCloser(bytes.NewReader(body))
+			req.ContentLength = int64(len(body))
+		}
+
+		hash := sha256.Sum256(body)
+		if err := signer.SignHTTP(req.Context(), creds, req, hex.EncodeToString(hash[:]), bedrockMantleSigningService, cfg.Region, time.Now()); err != nil {
+			return nil, err
+		}
+		return next(req)
+	}))
+
+	return out, nil
+}
+
+// augmentRequestForBedrockInvokeModel will change the model used for the request since AWS Bedrock doesn't support
 // Anthropics' model names. It also converts adaptive thinking to enabled with a budget for models that
 // don't support adaptive thinking natively, or enabled thinking to adaptive for models that only support
 // adaptive (Opus 4.7+).
-func (i *interceptionBase) augmentRequestForBedrock() {
+func (i *interceptionBase) augmentRequestForBedrockInvokeModel() {
 	if i.bedrock == nil {
 		return
 	}
diff --git a/aibridge/intercept/messages/base_internal_test.go b/aibridge/intercept/messages/base_internal_test.go
index 714f32b2c0f..eef99ea86e1 100644
--- a/aibridge/intercept/messages/base_internal_test.go
+++ b/aibridge/intercept/messages/base_internal_test.go
@@ -183,7 +183,7 @@ func TestAWSBedrockValidation(t *testing.T) {
 					Creds: credentials.NewStaticCredentialsProvider("test-key", "test-secret", ""),
 				},
 			}
-			opts, err := base.withAWSBedrockOptions(context.Background())
+			opts, err := base.withBedrockInvokeModelOptions(context.Background())
 
 			if tt.expectError {
 				require.Error(t, err)
@@ -198,12 +198,12 @@ func TestAWSBedrockValidation(t *testing.T) {
 
 // TestAWSBedrockOptionsRequireRuntime verifies that option assembly fails when
 // the Bedrock runtime was not set. This should never happen in practice, since
-// withAWSBedrockOptions is only called when i.bedrock != nil.
+// withBedrockInvokeModelOptions is only called when i.bedrock != nil.
 func TestAWSBedrockOptionsRequireRuntime(t *testing.T) {
 	t.Parallel()
 
 	base := &interceptionBase{}
-	_, err := base.withAWSBedrockOptions(context.Background())
+	_, err := base.withBedrockInvokeModelOptions(context.Background())
 	require.Error(t, err)
 	require.Contains(t, err.Error(), "nil bedrock runtime")
 }
@@ -800,7 +800,7 @@ func TestAugmentRequestForBedrock_AdaptiveThinking(t *testing.T) {
 				logger:        slog.Make(),
 			}
 
-			i.augmentRequestForBedrock()
+			i.augmentRequestForBedrockInvokeModel()
 
 			thinkingType := gjson.GetBytes(i.reqPayload, "thinking.type")
 			if tc.expectThinkingType == "" {
@@ -1126,3 +1126,75 @@ func TestWriteUpstreamError(t *testing.T) {
 		})
 	}
 }
+
+// TestBedrockMantleIsPassthrough verifies a mantle provider reports the mantle
+// protocol and that Model() returns the client's model.
+func TestBedrockMantleIsPassthrough(t *testing.T) {
+	t.Parallel()
+
+	i := &interceptionBase{
+		reqPayload: mustMessagesPayload(t,
+			`{"model":"anthropic.claude-opus-4-8","max_tokens":10000,"thinking":{"type":"adaptive"},"metadata":{"user_id":"u123"},"context_management":{"type":"auto"}}`),
+		bedrock: &BedrockRuntime{
+			Cfg: config.AWSBedrock{
+				Region:   "us-east-1",
+				Protocol: config.BedrockProtocolMantle,
+			},
+		},
+		logger: slog.Make(),
+	}
+
+	require.True(t, i.isBedrockMantle())
+	require.False(t, i.isBedrockInvokeModel())
+	require.Equal(t, "anthropic.claude-opus-4-8", i.Model())
+}
+
+// TestAWSMantleOptionsValidation verifies the mantle protocol requires a
+// region (it scopes the SigV4 signature) but NOT model fields.
+func TestAWSMantleOptionsValidation(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name     string
+		cfg      config.AWSBedrock
+		errorMsg string
+	}{
+		{
+			name: "valid without model fields",
+			cfg: config.AWSBedrock{
+				Region:   "us-east-1",
+				BaseURL:  "https://bedrock-mantle.us-east-1.api.aws/anthropic",
+				Protocol: config.BedrockProtocolMantle,
+			},
+		},
+		{
+			name: "missing region even with base url",
+			cfg: config.AWSBedrock{
+				BaseURL:  "https://proxy.internal",
+				Protocol: config.BedrockProtocolMantle,
+			},
+			errorMsg: "region required",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			base := &interceptionBase{
+				bedrock: &BedrockRuntime{
+					Cfg:   tt.cfg,
+					Creds: credentials.NewStaticCredentialsProvider("test-key", "test-secret", ""),
+				},
+			}
+			opts, err := base.withBedrockMantleOptions(context.Background())
+			if tt.errorMsg != "" {
+				require.Error(t, err)
+				require.Contains(t, err.Error(), tt.errorMsg)
+			} else {
+				require.NoError(t, err)
+				require.NotEmpty(t, opts)
+			}
+		})
+	}
+}
diff --git a/aibridge/internal/integrationtest/bridge_internal_test.go b/aibridge/internal/integrationtest/bridge_internal_test.go
index 024652928e7..1b515735da4 100644
--- a/aibridge/internal/integrationtest/bridge_internal_test.go
+++ b/aibridge/internal/integrationtest/bridge_internal_test.go
@@ -36,6 +36,7 @@ import (
 	"github.com/coder/coder/v2/aibridge/config"
 	"github.com/coder/coder/v2/aibridge/fixtures"
 	"github.com/coder/coder/v2/aibridge/intercept"
+	"github.com/coder/coder/v2/aibridge/intercept/messages"
 	"github.com/coder/coder/v2/aibridge/internal/testutil"
 	"github.com/coder/coder/v2/aibridge/mcp"
 	"github.com/coder/coder/v2/aibridge/provider"
@@ -377,7 +378,7 @@ func TestAWSBedrockIntegration(t *testing.T) {
 
 				// Verify PRM attribution is appended to the User-Agent header.
 				ua := received[0].Header.Get("User-Agent")
-				require.Contains(t, ua, "sdk-ua-app-id/APN_1.1%2Fpc_cdfmjwn8i6u8l9fwz8h82e4w3%24",
+				require.Contains(t, ua, messages.BedrockPRMUserAgent,
 					"expected AWS PRM attribution in User-Agent header")
 
 				interceptions := bridgeServer.Recorder.RecordedInterceptions()
@@ -388,6 +389,62 @@ func TestAWSBedrockIntegration(t *testing.T) {
 		}
 	})
 
+	// The mantle protocol is a passthrough: the client's model is forwarded in the body
+	// without remapping, only SigV4 signing (service "bedrock-mantle") is applied.
+	t.Run("mantle/v1/messages", func(t *testing.T) {
+		t.Parallel()
+
+		ctx, cancel := context.WithTimeout(t.Context(), testutil.WaitLong)
+		t.Cleanup(cancel)
+
+		fix := fixtures.Parse(t, fixtures.AntSingleBuiltinTool)
+		upstream := testutil.NewMockUpstream(ctx, t, testutil.NewFixtureResponse(fix))
+
+		// Mantle needs only region + credentials for signing (no Model fields:
+		// the client supplies the model).
+		bedrockCfg := &config.AWSBedrock{
+			Region:          "us-west-2",
+			AccessKey:       "test-access-key",
+			AccessKeySecret: "test-secret-key",
+			BaseURL:         upstream.URL + "/anthropic", // Use the mock server.
+			Protocol:        config.BedrockProtocolMantle,
+		}
+		// The client's model must be forwarded unchanged.
+		wantModel := gjson.GetBytes(fix.Request(), "model").String()
+		require.NotEmpty(t, wantModel)
+
+		bridgeServer := newBridgeTestServer(ctx, t, upstream.URL,
+			withCustomProvider(aibridgetest.NewAnthropicProvider(t, anthropicCfg(upstream.URL, apiKey), bedrockCfg)),
+		)
+
+		resp, err := bridgeServer.makeRequest(t, http.MethodPost, pathAnthropicMessages, fix.Request())
+		require.NoError(t, err)
+		defer resp.Body.Close()
+
+		received := upstream.ReceivedRequests()
+		require.Len(t, received, 1)
+
+		// Native passthrough: /anthropic Messages path, model kept in the body
+		// unchanged.
+		require.Equal(t, "/anthropic/v1/messages", received[0].Path)
+		require.Equal(t, wantModel, gjson.GetBytes(received[0].Body, "model").String(),
+			"model should be forwarded unchanged")
+
+		// SigV4-signed for the bedrock-mantle service.
+		authHeader := received[0].Header.Get("Authorization")
+		require.True(t, strings.HasPrefix(authHeader, "AWS4-HMAC-SHA256"), "missing SigV4 auth: %q", authHeader)
+		require.Contains(t, authHeader, "/bedrock-mantle/aws4_request",
+			"signature must be scoped to the bedrock-mantle service")
+
+		require.Contains(t, received[0].Header.Get("User-Agent"),
+			messages.BedrockPRMUserAgent)
+
+		interceptions := bridgeServer.Recorder.RecordedInterceptions()
+		require.Len(t, interceptions, 1)
+		require.Equal(t, wantModel, interceptions[0].Model)
+		bridgeServer.Recorder.VerifyAllInterceptionsEnded(t)
+	})
+
 	// Tests that Bedrock-incompatible fields are stripped and adaptive thinking
 	// is handled correctly per model. Different Bedrock model names trigger
 	// different behavior for beta flag filtering and field stripping.
diff --git a/cli/aibridged.go b/cli/aibridged.go
index 0fd2ae598dc..75ded313c97 100644
--- a/cli/aibridged.go
+++ b/cli/aibridged.go
@@ -214,6 +214,7 @@ func protoToProviderSpec(pp *proto.AIProvider) aiProviderSpec {
 		)
 		bedrock.RoleARN = b.GetRoleArn()
 		bedrock.ExternalID = b.GetExternalId()
+		bedrock.Protocol = codersdk.AIProviderBedrockProtocol(b.GetProtocol())
 		spec.Bedrock = ptr.Ref(bedrock)
 	}
 	return spec
@@ -356,6 +357,7 @@ func bedrockConfig(baseURL string, bedrock *codersdk.AIProviderBedrockSettings)
 		SmallFastModel:  bedrockSettings.SmallFastModel,
 		RoleARN:         bedrockSettings.RoleARN,
 		ExternalID:      bedrockSettings.ExternalID,
+		Protocol:        config.BedrockProtocol(bedrockSettings.ResolvedProtocol()),
 	}
 }
 
diff --git a/coderd/aibridged/proto/aibridged.pb.go b/coderd/aibridged/proto/aibridged.pb.go
index fe68d6ee205..5964870f426 100644
--- a/coderd/aibridged/proto/aibridged.pb.go
+++ b/coderd/aibridged/proto/aibridged.pb.go
@@ -1680,6 +1680,9 @@ type AIProviderKindBedrock struct {
 	SmallFastModel  string `protobuf:"bytes,5,opt,name=small_fast_model,json=smallFastModel,proto3" json:"small_fast_model,omitempty"`
 	RoleArn         string `protobuf:"bytes,6,opt,name=role_arn,json=roleArn,proto3" json:"role_arn,omitempty"`
 	ExternalId      string `protobuf:"bytes,7,opt,name=external_id,json=externalId,proto3" json:"external_id,omitempty"`
+	// protocol selects the Bedrock wire protocol ("invoke-model" or "mantle").
+	// Empty fallbacks to invoke-model.
+	Protocol string `protobuf:"bytes,8,opt,name=protocol,proto3" json:"protocol,omitempty"`
 }
 
 func (x *AIProviderKindBedrock) Reset() {
@@ -1763,6 +1766,13 @@ func (x *AIProviderKindBedrock) GetExternalId() string {
 	return ""
 }
 
+func (x *AIProviderKindBedrock) GetProtocol() string {
+	if x != nil {
+		return x.Protocol
+	}
+	return ""
+}
+
 var File_coderd_aibridged_proto_aibridged_proto protoreflect.FileDescriptor
 
 var file_coderd_aibridged_proto_aibridged_proto_rawDesc = []byte{
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+	0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
diff --git a/coderd/aibridged/proto/aibridged.proto b/coderd/aibridged/proto/aibridged.proto
index 41795abdb9a..49fb453d6ff 100644
--- a/coderd/aibridged/proto/aibridged.proto
+++ b/coderd/aibridged/proto/aibridged.proto
@@ -235,4 +235,7 @@ message AIProviderKindBedrock {
   string small_fast_model = 5;
   string role_arn = 6;
   string external_id = 7;
+  // protocol selects the Bedrock wire protocol ("invoke-model" or "mantle").
+  // Empty fallbacks to invoke-model.
+  string protocol = 8;
 }
diff --git a/coderd/aibridgedserver/aibridgedserver.go b/coderd/aibridgedserver/aibridgedserver.go
index cdfe739d027..e2750907485 100644
--- a/coderd/aibridgedserver/aibridgedserver.go
+++ b/coderd/aibridgedserver/aibridgedserver.go
@@ -1109,6 +1109,7 @@ func aiProviderToProto(row database.AIProvider, keys []database.AIProviderKey) (
 			SmallFastModel:  settings.Bedrock.SmallFastModel,
 			RoleArn:         settings.Bedrock.RoleARN,
 			ExternalId:      settings.Bedrock.ExternalID,
+			Protocol:        string(settings.Bedrock.Protocol),
 		}
 	}
 
diff --git a/codersdk/aiproviders.go b/codersdk/aiproviders.go
index 8956587b0b0..3ceb04589cf 100644
--- a/codersdk/aiproviders.go
+++ b/codersdk/aiproviders.go
@@ -283,6 +283,13 @@ func (req CreateAIProviderRequest) Validate() []ValidationError {
 				Detail: "external_id is server-generated and cannot be set",
 			})
 		}
+		// The Mantle protocol signs requests with SigV4, which requires a region.
+		if req.Settings.Bedrock.ResolvedProtocol() == AIProviderBedrockProtocolMantle && req.Settings.Bedrock.Region == "" {
+			validations = append(validations, ValidationError{
+				Field:  "settings.region",
+				Detail: "region is required for the mantle protocol",
+			})
+		}
 	}
 	if req.Type == AIProviderTypeCopilot && len(req.APIKeys) > 0 {
 		validations = append(validations, ValidationError{
diff --git a/codersdk/aiproviders_bedrock.go b/codersdk/aiproviders_bedrock.go
index be17f6c95d0..688e18b4710 100644
--- a/codersdk/aiproviders_bedrock.go
+++ b/codersdk/aiproviders_bedrock.go
@@ -8,6 +8,23 @@ const AIProviderSettingsTypeBedrock = "bedrock"
 // AIProviderBedrockSettings.
 const AIProviderBedrockSettingsVersion = 1
 
+// AIProviderBedrockProtocol selects which AWS Bedrock wire protocol a provider
+// targets.
+type AIProviderBedrockProtocol string
+
+const (
+	// AIProviderBedrockProtocolInvokeModel is the legacy InvokeModel protocol
+	// (bedrock-runtime.{region}.amazonaws.com), which translates the native
+	// Messages request into Bedrock's InvokeModel format. It is the default
+	// for the zero value.
+	AIProviderBedrockProtocolInvokeModel AIProviderBedrockProtocol = "invoke-model"
+	// AIProviderBedrockProtocolMantle is the mantle protocol
+	// (bedrock-mantle.{region}.api.aws/anthropic/v1/messages). It is a
+	// passthrough: the gateway forwards the native Messages request body
+	// unchanged and only applies AWS SigV4 signing (service bedrock-mantle).
+	AIProviderBedrockProtocolMantle AIProviderBedrockProtocol = "mantle"
+)
+
 // AIProviderBedrockSettings configures providers that authenticate
 // against AWS Bedrock. AccessKey and AccessKeySecret are write-only:
 // servers strip them from GET and list responses. Both secret fields
@@ -40,6 +57,19 @@ type AIProviderBedrockSettings struct {
 	// reject any client-supplied value that differs from the stored one (an
 	// update may echo the stored value back).
 	ExternalID string `json:"external_id,omitempty"`
+	// Protocol selects the Bedrock wire protocol. An empty value resolves to
+	// AIProviderBedrockProtocolInvokeModel, so existing rows keep the legacy
+	// behavior.
+	Protocol AIProviderBedrockProtocol `json:"protocol,omitempty"`
+}
+
+// ResolvedProtocol returns the configured protocol, mapping the empty value to
+// the legacy InvokeModel protocol.
+func (b AIProviderBedrockSettings) ResolvedProtocol() AIProviderBedrockProtocol {
+	if b.Protocol == "" {
+		return AIProviderBedrockProtocolInvokeModel
+	}
+	return b.Protocol
 }
 
 // IsConfigured reports whether any load-bearing Bedrock field is set,
diff --git a/codersdk/aiproviders_test.go b/codersdk/aiproviders_test.go
index a0ce28ec4ea..5fd1dd238ca 100644
--- a/codersdk/aiproviders_test.go
+++ b/codersdk/aiproviders_test.go
@@ -212,3 +212,47 @@ func TestAIProviderRequest_ValidateRoleARN(t *testing.T) {
 		})
 	}
 }
+
+func TestAIProviderRequest_ValidateBedrockMantle(t *testing.T) {
+	t.Parallel()
+
+	hasFieldError := func(vs []codersdk.ValidationError, field string) bool {
+		for _, v := range vs {
+			if v.Field == field {
+				return true
+			}
+		}
+		return false
+	}
+
+	t.Run("MantleRequiresRegion", func(t *testing.T) {
+		t.Parallel()
+		create := codersdk.CreateAIProviderRequest{
+			Type:    codersdk.AIProviderTypeBedrock,
+			Name:    "bedrock",
+			BaseURL: "https://bedrock-mantle.us-east-1.api.aws",
+			Settings: codersdk.AIProviderSettings{
+				Bedrock: &codersdk.AIProviderBedrockSettings{
+					Protocol: codersdk.AIProviderBedrockProtocolMantle,
+				},
+			},
+		}
+		require.True(t, hasFieldError(create.Validate(), "settings.region"))
+
+		create.Settings.Bedrock.Region = "us-east-1"
+		require.False(t, hasFieldError(create.Validate(), "settings.region"))
+	})
+
+	t.Run("InvokeModelDoesNotRequireRegionField", func(t *testing.T) {
+		t.Parallel()
+		// The default (invoke-model) protocol keeps its existing rules; the
+		// mantle-specific region check must not fire for it.
+		create := codersdk.CreateAIProviderRequest{
+			Type:     codersdk.AIProviderTypeBedrock,
+			Name:     "bedrock",
+			BaseURL:  "https://bedrock-runtime.us-east-1.amazonaws.com",
+			Settings: codersdk.AIProviderSettings{},
+		}
+		require.False(t, hasFieldError(create.Validate(), "settings.region"))
+	})
+}
diff --git a/site/src/api/typesGenerated.ts b/site/src/api/typesGenerated.ts
index 7095d7de7ab..55a67b560f0 100644
--- a/site/src/api/typesGenerated.ts
+++ b/site/src/api/typesGenerated.ts
@@ -313,6 +313,14 @@ export interface AIProvider {
 	readonly updated_at: string;
 }
 
+// From codersdk/aiproviders_bedrock.go
+export type AIProviderBedrockProtocol = "invoke-model" | "mantle";
+
+export const AIProviderBedrockProtocols: AIProviderBedrockProtocol[] = [
+	"invoke-model",
+	"mantle",
+];
+
 // From codersdk/aiproviders_bedrock.go
 /**
  * AIProviderBedrockSettings configures providers that authenticate
@@ -362,6 +370,12 @@ export interface AIProviderBedrockSettings {
 	 * update may echo the stored value back).
 	 */
 	readonly external_id?: string;
+	/**
+	 * Protocol selects the Bedrock wire protocol. An empty value resolves to
+	 * AIProviderBedrockProtocolInvokeModel, so existing rows keep the legacy
+	 * behavior without a schema version bump.
+	 */
+	readonly protocol?: AIProviderBedrockProtocol;
 }
 
 // From codersdk/aiproviders_bedrock.go