diff --git a/x402.go b/x402.go
index 92b6e80..a85b565 100644
--- a/x402.go
+++ b/x402.go
@@ -33,40 +33,6 @@ func createNonce() (string, error) {
 	return "0x" + common.Bytes2Hex(nonce), nil
 }
 
-// BlockRunServiceCode is BlockRun's x402 builder code — the ERC-8021 Schema 2
-// service code (s) that tags every payment this SDK signs as BlockRun-originated
-// for on-chain attribution.
-// See https://docs.cdp.coinbase.com/x402/core-concepts/builder-codes
-const BlockRunServiceCode = "blockrun"
-
-// withBuilderCodeServiceCode merges BlockRun's service code (s) into the
-// payload's builder-code extension, preserving any app code (a) the server
-// echoed back in its 402. The CDP facilitator reads builder-code.info.s and
-// encodes it into the settlement calldata suffix — no CBOR happens client-side.
-func withBuilderCodeServiceCode(extensions map[string]any) map[string]any {
-	merged := map[string]any{}
-	for k, v := range extensions {
-		merged[k] = v
-	}
-
-	builderCode := map[string]any{}
-	info := map[string]any{}
-	if bc, ok := merged["builder-code"].(map[string]any); ok {
-		for k, v := range bc {
-			builderCode[k] = v
-		}
-		if existingInfo, ok := bc["info"].(map[string]any); ok {
-			for k, v := range existingInfo {
-				info[k] = v
-			}
-		}
-	}
-	info["s"] = []string{BlockRunServiceCode}
-	builderCode["info"] = info
-	merged["builder-code"] = builderCode
-	return merged
-}
-
 // CreatePaymentPayload creates a signed x402 v2 payment payload.
 //
 // This uses EIP-712 typed data signing to create a payment authorization
@@ -213,7 +179,7 @@ func CreatePaymentPayload(
 				Nonce:       nonce,
 			},
 		},
-		Extensions: withBuilderCodeServiceCode(extensions),
+		Extensions: extensions,
 	}
 
 	// Encode as JSON then base64
diff --git a/x402_test.go b/x402_test.go
deleted file mode 100644
index cb3c38c..0000000
--- a/x402_test.go
+++ /dev/null
@@ -1,94 +0,0 @@
-package blockrun
-
-import (
-	"encoding/base64"
-	"encoding/json"
-	"testing"
-)
-
-func decodeServiceCodeInfo(t *testing.T, payload string) map[string]any {
-	t.Helper()
-	decoded, err := base64.StdEncoding.DecodeString(payload)
-	if err != nil {
-		t.Fatalf("failed to decode payload: %v", err)
-	}
-	var pp PaymentPayload
-	if err := json.Unmarshal(decoded, &pp); err != nil {
-		t.Fatalf("failed to unmarshal payload: %v", err)
-	}
-	bc, ok := pp.Extensions["builder-code"].(map[string]any)
-	if !ok {
-		t.Fatalf("missing builder-code extension: %v", pp.Extensions)
-	}
-	info, ok := bc["info"].(map[string]any)
-	if !ok {
-		t.Fatalf("missing builder-code.info: %v", bc)
-	}
-	return info
-}
-
-func assertServiceCode(t *testing.T, info map[string]any) {
-	t.Helper()
-	s, ok := info["s"].([]any)
-	if !ok || len(s) != 1 || s[0] != "blockrun" {
-		t.Errorf("expected service code [blockrun], got %v", info["s"])
-	}
-}
-
-func TestCreatePaymentPayloadAttachesServiceCode(t *testing.T) {
-	client, err := NewLLMClient(testPrivateKey)
-	if err != nil {
-		t.Fatalf("failed to create client: %v", err)
-	}
-
-	payload, err := CreatePaymentPayload(
-		client.privateKey,
-		"0x1234567890123456789012345678901234567890",
-		"1000",
-		"eip155:8453",
-		"https://blockrun.ai/api/v1/chat/completions",
-		"Test payment",
-		300,
-		nil,
-		nil,
-	)
-	if err != nil {
-		t.Fatalf("failed to create payment payload: %v", err)
-	}
-
-	assertServiceCode(t, decodeServiceCodeInfo(t, payload))
-}
-
-func TestCreatePaymentPayloadPreservesEchoedAppCode(t *testing.T) {
-	client, err := NewLLMClient(testPrivateKey)
-	if err != nil {
-		t.Fatalf("failed to create client: %v", err)
-	}
-
-	extensions := map[string]any{
-		"builder-code": map[string]any{
-			"info": map[string]any{"a": "blockrun"},
-		},
-	}
-
-	payload, err := CreatePaymentPayload(
-		client.privateKey,
-		"0x1234567890123456789012345678901234567890",
-		"1000",
-		"eip155:8453",
-		"https://blockrun.ai/api/v1/chat/completions",
-		"Test payment",
-		300,
-		nil,
-		extensions,
-	)
-	if err != nil {
-		t.Fatalf("failed to create payment payload: %v", err)
-	}
-
-	info := decodeServiceCodeInfo(t, payload)
-	assertServiceCode(t, info)
-	if info["a"] != "blockrun" {
-		t.Errorf("expected echoed app code blockrun, got %v", info["a"])
-	}
-}