diff --git a/packages/ai/src/providers/openai-completions.ts b/packages/ai/src/providers/openai-completions.ts
index 1637b289..cd81bc93 100644
--- a/packages/ai/src/providers/openai-completions.ts
+++ b/packages/ai/src/providers/openai-completions.ts
@@ -26,6 +26,26 @@ import { parseStreamingJson } from "../utils/json-parse.js";
 import { sanitizeSurrogates } from "../utils/sanitize-unicode.js";
 
 import { transformMessages } from "./transorm-messages.js";
+import type { Message } from "../types.js";
+
+/**
+ * Check if conversation messages contain tool calls or tool results.
+ * This is needed because Anthropic (via proxy) requires the tools param
+ * to be present when messages include tool_calls or tool role messages.
+ */
+function hasToolHistory(messages: Message[]): boolean {
+	for (const msg of messages) {
+		if (msg.role === "toolResult") {
+			return true;
+		}
+		if (msg.role === "assistant") {
+			if (msg.content.some((block) => block.type === "toolCall")) {
+				return true;
+			}
+		}
+	}
+	return false;
+}
 
 export interface OpenAICompletionsOptions extends StreamOptions {
 	toolChoice?: "auto" | "none" | "required" | { type: "function"; function: { name: string } };
@@ -296,6 +316,9 @@ function buildParams(model: Model<"openai-completions">, context: Context, optio
 
 	if (context.tools) {
 		params.tools = convertTools(context.tools);
+	} else if (hasToolHistory(context.messages)) {
+		// Anthropic (via LiteLLM/proxy) requires tools param when conversation has tool_calls/tool_results
+		params.tools = [];
 	}
 
 	if (options?.toolChoice) {