diff --git a/tensorzero-core/src/providers/amux.rs b/tensorzero-core/src/providers/amux.rs
index 4a1cbe094c..ed439b316c 100644
--- a/tensorzero-core/src/providers/amux.rs
+++ b/tensorzero-core/src/providers/amux.rs
@@ -268,6 +268,37 @@ fn parse_urls(body: &Value) -> Vec<String> {
     Vec::new()
 }
 
+/// Terminal classification of a single poll response.
+enum PollOutcome {
+    Done,
+    Failed(String),
+    Pending,
+}
+
+/// Classify an Amux poll response into a terminal/pending state.
+///
+/// The universal poll endpoint wraps the task under `data`:
+/// `{ code, message, data: { status, url, error } }`. We read the status from
+/// there, falling back to the root so a flat shape still works. Amux reports
+/// terminal success as `"succeeded"` (not `"completed"`) and failure as
+/// `"failed"`; both spellings of success/failure are accepted defensively.
+fn classify_poll(body: &Value) -> PollOutcome {
+    let task = body.get("data").unwrap_or(body);
+    match task.get("status").and_then(Value::as_str).unwrap_or("") {
+        "succeeded" | "completed" => PollOutcome::Done,
+        "failed" | "error" => {
+            let reason = task
+                .get("error")
+                .and_then(|err| err.get("message"))
+                .and_then(Value::as_str)
+                .unwrap_or("(no reason given)")
+                .to_string();
+            PollOutcome::Failed(reason)
+        }
+        _ => PollOutcome::Pending,
+    }
+}
+
 async fn poll_async_result(
     http_client: &TensorzeroHttpClient,
     api_key: &str,
@@ -325,17 +356,9 @@ async fn poll_async_result(
             }));
         }
 
-        // Universal status values: queued | in_progress | completed | failed |
-        // unknown.
-        let status_str = body.get("status").and_then(Value::as_str).unwrap_or("");
-        match status_str {
-            "completed" => return Ok(body),
-            "failed" => {
-                let reason = body
-                    .get("error")
-                    .and_then(|err| err.get("message"))
-                    .and_then(Value::as_str)
-                    .unwrap_or("(no reason given)");
+        match classify_poll(&body) {
+            PollOutcome::Done => return Ok(body),
+            PollOutcome::Failed(reason) => {
                 return Err(Error::new(ErrorDetails::InferenceServer {
                     message: format!("Amux generation failed: {reason}"),
                     provider_type: PROVIDER_TYPE.to_string(),
@@ -343,7 +366,7 @@ async fn poll_async_result(
                     raw_response: Some(body.to_string()),
                 }));
             }
-            _ => {}
+            PollOutcome::Pending => {}
         }
 
         tokio::time::sleep(poll_interval).await;
@@ -402,3 +425,75 @@ async fn post_media_callback(
 
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde_json::json;
+
+    #[test]
+    fn classify_poll_detects_nested_succeeded() {
+        // The real Amux universal poll shape nests status under `data` and
+        // reports success as "succeeded" — the bug this fixes: the old code
+        // read root `status` and only matched "completed", so it never
+        // terminated and timed out after the full async budget.
+        let body = json!({
+            "code": "success",
+            "data": { "status": "succeeded", "url": "https://cdn.amux.ai/x.mp4" }
+        });
+        assert!(
+            matches!(classify_poll(&body), PollOutcome::Done),
+            "nested data.status=succeeded must classify as Done"
+        );
+    }
+
+    #[test]
+    fn classify_poll_detects_nested_failed_with_reason() {
+        let body = json!({
+            "code": "success",
+            "data": { "status": "failed", "error": { "message": "render blew up" } }
+        });
+        match classify_poll(&body) {
+            PollOutcome::Failed(reason) => assert_eq!(
+                reason, "render blew up",
+                "failure reason must come from data.error.message"
+            ),
+            _ => panic!("nested data.status=failed must classify as Failed"),
+        }
+    }
+
+    #[test]
+    fn classify_poll_treats_in_progress_as_pending() {
+        for status in ["queued", "in_progress", "unknown", ""] {
+            let body = json!({ "data": { "status": status } });
+            assert!(
+                matches!(classify_poll(&body), PollOutcome::Pending),
+                "status={status:?} must keep polling (Pending)"
+            );
+        }
+    }
+
+    #[test]
+    fn classify_poll_tolerates_flat_shape() {
+        // Defensive fallback: if Amux ever returns a flat (un-nested) body,
+        // the root-level status is still honored.
+        let body = json!({ "status": "completed", "url": "https://cdn.amux.ai/x.mp4" });
+        assert!(
+            matches!(classify_poll(&body), PollOutcome::Done),
+            "flat root status=completed must classify as Done"
+        );
+    }
+
+    #[test]
+    fn parse_urls_reads_nested_data_url() {
+        let body = json!({
+            "code": "success",
+            "data": { "status": "succeeded", "url": "https://cdn.amux.ai/x.mp4" }
+        });
+        assert_eq!(
+            parse_urls(&body),
+            vec!["https://cdn.amux.ai/x.mp4".to_string()],
+            "the completed video URL must be extracted from data.url"
+        );
+    }
+}