diff --git a/src/api/providers/anthropic.ts b/src/api/providers/anthropic.ts
index e8b90c7481..aa080c87a8 100644
--- a/src/api/providers/anthropic.ts
+++ b/src/api/providers/anthropic.ts
@@ -1,5 +1,5 @@
 import { createAnthropic } from "@ai-sdk/anthropic"
-import { streamText, generateText, ToolSet, ModelMessage } from "ai"
+import { streamText, generateText, ToolSet } from "ai"
 
 import {
 	type ModelInfo,
@@ -24,6 +24,7 @@ import {
 	yieldResponseMessage,
 } from "../transform/ai-sdk"
 import { applyToolCacheOptions, applySystemPromptCaching } from "../transform/cache-breakpoints"
+import { sanitizeMessagesForProvider } from "../transform/sanitize-messages"
 import { calculateApiCostAnthropic } from "../../shared/cost"
 
 import { DEFAULT_HEADERS } from "./constants"
@@ -76,8 +77,8 @@ export class AnthropicHandler extends BaseProvider implements SingleCompletionHa
 	): ApiStream {
 		const modelConfig = this.getModel()
 
-		// Convert messages to AI SDK format
-		const aiSdkMessages = messages as ModelMessage[]
+		// Sanitize messages for the provider API (allowlist: role, content, providerOptions).
+		const aiSdkMessages = sanitizeMessagesForProvider(messages)
 
 		// Convert tools to AI SDK format
 		const openAiTools = this.convertToolsForOpenAI(metadata?.tools)