diff --git a/go/adk/pkg/models/anthropic_adk.go b/go/adk/pkg/models/anthropic_adk.go
index 85234d3359..92353a496b 100644
--- a/go/adk/pkg/models/anthropic_adk.go
+++ b/go/adk/pkg/models/anthropic_adk.go
@@ -259,7 +259,6 @@ func genaiContentsToAnthropicMessages(contents []*genai.Content, config *genai.G
 				Content: toolResultBlocks,
 			})
 		} else {
-			// Regular user message
 			var contentBlocks []anthropic.ContentBlockParamUnion
 
 			// Add images first
@@ -272,9 +271,13 @@ func genaiContentsToAnthropicMessages(contents []*genai.Content, config *genai.G
 				contentBlocks = append(contentBlocks, anthropic.NewTextBlock(strings.Join(textParts, "\n")))
 			}
 
+			msgRole := anthropic.MessageParamRoleUser
+			if role == "model" || role == "assistant" {
+				msgRole = anthropic.MessageParamRoleAssistant
+			}
 			if len(contentBlocks) > 0 {
 				messages = append(messages, anthropic.MessageParam{
-					Role:    anthropic.MessageParamRoleUser,
+					Role:    msgRole,
 					Content: contentBlocks,
 				})
 			}
diff --git a/go/adk/pkg/models/anthropic_adk_test.go b/go/adk/pkg/models/anthropic_adk_test.go
index 7c8de5b21d..7f786e5833 100644
--- a/go/adk/pkg/models/anthropic_adk_test.go
+++ b/go/adk/pkg/models/anthropic_adk_test.go
@@ -171,6 +171,23 @@ func TestAnthropicUsageToGenai(t *testing.T) {
 	}
 }
 
+func TestGenaiContentsToAnthropicMessagesKeepsAssistantTextRole(t *testing.T) {
+	contents := []*genai.Content{
+		{Role: "user", Parts: []*genai.Part{{Text: "hi"}}},
+		{Role: "model", Parts: []*genai.Part{{Text: "hello, how can I help?"}}},
+		{Role: "user", Parts: []*genai.Part{{Text: "list the pods"}}},
+		{Role: "assistant", Parts: []*genai.Part{{Text: "there are no pods"}}},
+	}
+
+	messages, _ := genaiContentsToAnthropicMessages(contents, nil)
+
+	require.Len(t, messages, 4)
+	assert.Equal(t, anthropic.MessageParamRoleUser, messages[0].Role)
+	assert.Equal(t, anthropic.MessageParamRoleAssistant, messages[1].Role)
+	assert.Equal(t, anthropic.MessageParamRoleUser, messages[2].Role)
+	assert.Equal(t, anthropic.MessageParamRoleAssistant, messages[3].Role)
+}
+
 // anthropicTestServer serves canned Messages API responses and records the
 // request body the SDK sent.
 func anthropicTestServer(t *testing.T, handler func(w http.ResponseWriter)) (*AnthropicModel, *[]byte) {