diff --git a/crates/copilot_chat/src/copilot_chat.rs b/crates/copilot_chat/src/copilot_chat.rs
index d1f339f89a01d1ed0d17e03b8712b42232177db8..850190701e526fe3fad896a17cdc704b89253fea 100644
--- a/crates/copilot_chat/src/copilot_chat.rs
+++ b/crates/copilot_chat/src/copilot_chat.rs
@@ -370,7 +370,7 @@ pub enum Tool {
 #[serde(rename_all = "lowercase")]
 pub enum ToolChoice {
     Auto,
-    Any,
+    Required,
     None,
 }
 
@@ -1736,4 +1736,22 @@ mod tests {
         // Only /v1/messages endpoint -> supports_response = false (doesn't have /responses)
         assert!(!model_with_messages.supports_response());
     }
+
+    #[test]
+    fn test_tool_choice_required_serializes_as_required() {
+        // Regression test: ToolChoice::Required must serialize as "required" (not "any")
+        // for OpenAI-compatible APIs. Reverting the rename would break this.
+        assert_eq!(
+            serde_json::to_string(&ToolChoice::Required).unwrap(),
+            "\"required\""
+        );
+        assert_eq!(
+            serde_json::to_string(&ToolChoice::Auto).unwrap(),
+            "\"auto\""
+        );
+        assert_eq!(
+            serde_json::to_string(&ToolChoice::None).unwrap(),
+            "\"none\""
+        );
+    }
 }
diff --git a/crates/copilot_chat/src/responses.rs b/crates/copilot_chat/src/responses.rs
index 4f30ba1eb083c8a70c9a91853c7df37e65783ce3..1241a76fb1410461cef7337e2339180b18da7a3f 100644
--- a/crates/copilot_chat/src/responses.rs
+++ b/crates/copilot_chat/src/responses.rs
@@ -52,7 +52,7 @@ pub enum ToolDefinition {
 #[serde(rename_all = "lowercase")]
 pub enum ToolChoice {
     Auto,
-    Any,
+    Required,
     None,
     #[serde(untagged)]
     Other(ToolDefinition),
@@ -408,3 +408,26 @@ pub async fn stream_response(
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_tool_choice_required_serializes_as_required() {
+        // Regression test: ToolChoice::Required must serialize as "required" (not "any")
+        // for OpenAI Responses API. Reverting the rename would break this.
+        assert_eq!(
+            serde_json::to_string(&ToolChoice::Required).unwrap(),
+            "\"required\""
+        );
+        assert_eq!(
+            serde_json::to_string(&ToolChoice::Auto).unwrap(),
+            "\"auto\""
+        );
+        assert_eq!(
+            serde_json::to_string(&ToolChoice::None).unwrap(),
+            "\"none\""
+        );
+    }
+}
diff --git a/crates/language_models/src/provider/copilot_chat.rs b/crates/language_models/src/provider/copilot_chat.rs
index 7063db83bf65b82a4f314ad97e9463b106400c0b..e90d8208b4f37cfc31487768b94a2b943e2320ce 100644
--- a/crates/language_models/src/provider/copilot_chat.rs
+++ b/crates/language_models/src/provider/copilot_chat.rs
@@ -1046,7 +1046,7 @@ fn into_copilot_chat(
         tools,
         tool_choice: tool_choice.map(|choice| match choice {
             LanguageModelToolChoice::Auto => ToolChoice::Auto,
-            LanguageModelToolChoice::Any => ToolChoice::Any,
+            LanguageModelToolChoice::Any => ToolChoice::Required,
             LanguageModelToolChoice::None => ToolChoice::None,
         }),
         thinking_budget: None,
@@ -1255,7 +1255,7 @@ fn into_copilot_responses(
 
     let mapped_tool_choice = tool_choice.map(|choice| match choice {
         LanguageModelToolChoice::Auto => responses::ToolChoice::Auto,
-        LanguageModelToolChoice::Any => responses::ToolChoice::Any,
+        LanguageModelToolChoice::Any => responses::ToolChoice::Required,
         LanguageModelToolChoice::None => responses::ToolChoice::None,
     });