feat: show ETA on prefill progress bar

Track when prefill starts via performance.now() and extrapolate
remaining time from observed tokens/sec. Displays "~Xs remaining"
(or "~Xm Ys remaining" for longer prompts) next to the percentage.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dashboard/src/lib/components/ChatMessages.svelte

@@ -12,6 +12,7 @@
   } from "$lib/stores/app.svelte";
   import type { MessageAttachment } from "$lib/stores/app.svelte";
   import MarkdownContent from "./MarkdownContent.svelte";
+  import PrefillProgressBar from "./PrefillProgressBar.svelte";
   import TokenHeatmap from "./TokenHeatmap.svelte";
   import PrefillProgressBar from "./PrefillProgressBar.svelte";
   import ImageLightbox from "./ImageLightbox.svelte";
@@ -625,7 +626,9 @@
                       <MarkdownContent
                         content={message.content || (loading ? response : "")}
                       />
-                      {#if loading && !message.content}
+                      {#if loading && !message.content && prefill}
+                        <PrefillProgressBar progress={prefill} class="mt-2" />
+                      {:else if loading && !message.content}
                         <span
                           class="inline-block w-2 h-4 bg-exo-yellow/70 ml-1 cursor-blink"
                         ></span>

dashboard/src/lib/components/PrefillProgressBar.svelte

@@ -14,6 +14,21 @@
       : 0,
   );
 
+  const etaText = $derived.by(() => {
+    if (progress.processed <= 0 || progress.total <= 0) return null;
+    const elapsedMs = performance.now() - progress.startedAt;
+    if (elapsedMs < 200) return null; // need a minimum sample window
+    const tokensPerMs = progress.processed / elapsedMs;
+    const remainingTokens = progress.total - progress.processed;
+    const remainingMs = remainingTokens / tokensPerMs;
+    const remainingSec = Math.ceil(remainingMs / 1000);
+    if (remainingSec <= 0) return null;
+    if (remainingSec < 60) return `~${remainingSec}s remaining`;
+    const mins = Math.floor(remainingSec / 60);
+    const secs = remainingSec % 60;
+    return `~${mins}m ${secs}s remaining`;
+  });
+
   function formatTokenCount(count: number | undefined): string {
     if (count == null) return "0";
     if (count >= 1000) {
@@ -40,8 +55,11 @@
       style="width: {percentage}%"
     ></div>
   </div>
-  <div class="text-right text-xs text-exo-light-gray/70 mt-0.5 font-mono">
-    {percentage}%
+  <div
+    class="flex items-center justify-between text-xs text-exo-light-gray/70 mt-0.5 font-mono"
+  >
+    <span>{etaText ?? ""}</span>
+    <span>{percentage}%</span>
   </div>
 </div>
 

dashboard/src/lib/stores/app.svelte.ts

@@ -276,6 +276,8 @@ export interface TokenData {
 export interface PrefillProgress {
   processed: number;
   total: number;
+  /** Timestamp (performance.now()) when prefill started. */
+  startedAt: number;
 }
 
 export interface Message {
@@ -520,12 +522,12 @@ class AppStore {
   messages = $state<Message[]>([]);
   currentResponse = $state("");
   isLoading = $state(false);
+  prefillProgress = $state<PrefillProgress | null>(null);
 
   // Performance metrics
   ttftMs = $state<number | null>(null); // Time to first token in ms
   tps = $state<number | null>(null); // Tokens per second
   totalTokens = $state<number>(0); // Total tokens in current response
-  prefillProgress = $state<PrefillProgress | null>(null);
 
   // Abort controller for stopping generation
   private currentAbortController: AbortController | null = null;
@@ -2018,6 +2020,7 @@ class AppStore {
   ): Promise<void> {
     const decoder = new TextDecoder();
     let buffer = "";
+    let currentEventType = "";
 
     while (true) {
       const { done, value } = await reader.read();
@@ -2033,7 +2036,15 @@ class AppStore {
 
       for (const line of lines) {
         const trimmed = line.trim();
-        if (!trimmed) continue;
+        if (!trimmed) {
+          currentEventType = "";
+          continue;
+        }
+
+        if (trimmed.startsWith("event: ")) {
+          currentEventType = trimmed.slice(7);
+          continue;
+        }
 
         // Handle SSE comments (": key json") for prefill progress etc.
         if (trimmed.startsWith(": ") && onEvent) {
@@ -2055,14 +2066,22 @@ class AppStore {
 
         if (trimmed.startsWith("data: ")) {
           const data = trimmed.slice(6);
-          if (data === "[DONE]") continue;
+          if (data === "[DONE]") {
+            currentEventType = "";
+            continue;
+          }
 
           try {
-            const parsed = JSON.parse(data) as T;
-            onChunk(parsed);
+            const parsed = JSON.parse(data);
+            if (currentEventType && onEvent?.[currentEventType]) {
+              onEvent[currentEventType](parsed);
+            } else {
+              onChunk(parsed as T);
+            }
           } catch {
             // Skip malformed JSON
           }
+          currentEventType = "";
         }
       }
     }
@@ -2163,6 +2182,7 @@ class AppStore {
 
     this.isLoading = true;
     this.currentResponse = "";
+    this.prefillProgress = null;
     this.ttftMs = null;
     this.tps = null;
     this.totalTokens = 0;
@@ -2367,6 +2387,11 @@ class AppStore {
           }
 
           if (tokenContent) {
+            // Clear prefill progress once tokens start arriving
+            if (this.prefillProgress !== null) {
+              this.prefillProgress = null;
+            }
+
             // Track first token for TTFT
             if (firstTokenTime === null) {
               firstTokenTime = performance.now();
@@ -2420,6 +2445,7 @@ class AppStore {
             this.prefillProgress = {
               processed: inner.processed_tokens,
               total: inner.total_tokens,
+              startedAt: this.prefillProgress?.startedAt ?? performance.now(),
             };
           },
         },
@@ -2474,6 +2500,7 @@ class AppStore {
       this.prefillProgress = null;
       this.isLoading = false;
       this.currentResponse = "";
+      this.prefillProgress = null;
       this.saveConversationsToStorage();
     }
   }
@@ -3106,10 +3133,10 @@ export const hasStartedChat = () => appStore.hasStartedChat;
 export const messages = () => appStore.messages;
 export const currentResponse = () => appStore.currentResponse;
 export const isLoading = () => appStore.isLoading;
+export const prefillProgress = () => appStore.prefillProgress;
 export const ttftMs = () => appStore.ttftMs;
 export const tps = () => appStore.tps;
 export const totalTokens = () => appStore.totalTokens;
-export const prefillProgress = () => appStore.prefillProgress;
 export const topologyData = () => appStore.topologyData;
 export const instances = () => appStore.instances;
 export const runners = () => appStore.runners;

src/exo/download/coordinator.py

@@ -338,17 +338,7 @@ class DownloadCoordinator:
                             ),
                         )
                     elif progress.status in ["in_progress", "not_started"]:
-                        if (
-                            progress.downloaded_bytes.in_bytes
-                            >= progress.total_bytes.in_bytes
-                            > 0
-                        ):
-                            status = DownloadCompleted(
-                                node_id=self.node_id,
-                                shard_metadata=progress.shard,
-                                total_bytes=progress.total_bytes,
-                            )
-                        elif progress.downloaded_bytes_this_session.in_bytes == 0:
+                        if progress.downloaded_bytes_this_session.in_bytes == 0:
                             status = DownloadPending(
                                 node_id=self.node_id,
                                 shard_metadata=progress.shard,

src/exo/main.py

@@ -258,7 +258,7 @@ def main():
     target = min(max(soft, 65535), hard)
     resource.setrlimit(resource.RLIMIT_NOFILE, (target, hard))
 
-    mp.set_start_method("spawn", force=True)
+    mp.set_start_method("spawn")
     # TODO: Refactor the current verbosity system
     logger_setup(EXO_LOG, args.verbosity)
     logger.info("Starting EXO")

src/exo/master/adapters/responses.py

@@ -31,6 +31,7 @@ from exo.shared.types.openai_responses import (
     ResponseOutputText,
     ResponsesRequest,
     ResponsesResponse,
+    ResponsesStreamEvent,
     ResponseTextDeltaEvent,
     ResponseTextDoneEvent,
     ResponseUsage,
@@ -38,6 +39,11 @@ from exo.shared.types.openai_responses import (
 from exo.shared.types.text_generation import InputMessage, TextGenerationTaskParams
 
 
+def _format_sse(event: ResponsesStreamEvent) -> str:
+    """Format a streaming event as an SSE message."""
+    return f"event: {event.type}\ndata: {event.model_dump_json()}\n\n"
+
+
 def _extract_content(content: str | list[ResponseContentPart]) -> str:
     """Extract plain text from a content field that may be a string or list of parts."""
     if isinstance(content, str):
@@ -219,13 +225,13 @@ async def generate_responses_stream(
     created_event = ResponseCreatedEvent(
         sequence_number=next(seq), response=initial_response
     )
-    yield f"event: response.created\ndata: {created_event.model_dump_json()}\n\n"
+    yield _format_sse(created_event)
 
     # response.in_progress
     in_progress_event = ResponseInProgressEvent(
         sequence_number=next(seq), response=initial_response
     )
-    yield f"event: response.in_progress\ndata: {in_progress_event.model_dump_json()}\n\n"
+    yield _format_sse(in_progress_event)
 
     # response.output_item.added
     initial_item = ResponseMessageItem(
@@ -236,7 +242,7 @@ async def generate_responses_stream(
     item_added = ResponseOutputItemAddedEvent(
         sequence_number=next(seq), output_index=0, item=initial_item
     )
-    yield f"event: response.output_item.added\ndata: {item_added.model_dump_json()}\n\n"
+    yield _format_sse(item_added)
 
     # response.content_part.added
     initial_part = ResponseOutputText(text="")
@@ -247,7 +253,7 @@ async def generate_responses_stream(
         content_index=0,
         part=initial_part,
     )
-    yield f"event: response.content_part.added\ndata: {part_added.model_dump_json()}\n\n"
+    yield _format_sse(part_added)
 
     accumulated_text = ""
     function_call_items: list[ResponseFunctionCallItem] = []
@@ -281,7 +287,7 @@ async def generate_responses_stream(
                     output_index=next_output_index,
                     item=fc_item,
                 )
-                yield f"event: response.output_item.added\ndata: {fc_added.model_dump_json()}\n\n"
+                yield _format_sse(fc_added)
 
                 # response.function_call_arguments.delta
                 args_delta = ResponseFunctionCallArgumentsDeltaEvent(
@@ -290,7 +296,7 @@ async def generate_responses_stream(
                     output_index=next_output_index,
                     delta=tool.arguments,
                 )
-                yield f"event: response.function_call_arguments.delta\ndata: {args_delta.model_dump_json()}\n\n"
+                yield _format_sse(args_delta)
 
                 # response.function_call_arguments.done
                 args_done = ResponseFunctionCallArgumentsDoneEvent(
@@ -300,7 +306,7 @@ async def generate_responses_stream(
                     name=tool.name,
                     arguments=tool.arguments,
                 )
-                yield f"event: response.function_call_arguments.done\ndata: {args_done.model_dump_json()}\n\n"
+                yield _format_sse(args_done)
 
                 # response.output_item.done
                 fc_done_item = ResponseFunctionCallItem(
@@ -315,7 +321,7 @@ async def generate_responses_stream(
                     output_index=next_output_index,
                     item=fc_done_item,
                 )
-                yield f"event: response.output_item.done\ndata: {fc_item_done.model_dump_json()}\n\n"
+                yield _format_sse(fc_item_done)
 
                 function_call_items.append(fc_done_item)
                 next_output_index += 1
@@ -331,7 +337,7 @@ async def generate_responses_stream(
             content_index=0,
             delta=chunk.text,
         )
-        yield f"event: response.output_text.delta\ndata: {delta_event.model_dump_json()}\n\n"
+        yield _format_sse(delta_event)
 
     # response.output_text.done
     text_done = ResponseTextDoneEvent(
@@ -341,7 +347,7 @@ async def generate_responses_stream(
         content_index=0,
         text=accumulated_text,
     )
-    yield f"event: response.output_text.done\ndata: {text_done.model_dump_json()}\n\n"
+    yield _format_sse(text_done)
 
     # response.content_part.done
     final_part = ResponseOutputText(text=accumulated_text)
@@ -352,7 +358,7 @@ async def generate_responses_stream(
         content_index=0,
         part=final_part,
     )
-    yield f"event: response.content_part.done\ndata: {part_done.model_dump_json()}\n\n"
+    yield _format_sse(part_done)
 
     # response.output_item.done
     final_message_item = ResponseMessageItem(
@@ -363,7 +369,7 @@ async def generate_responses_stream(
     item_done = ResponseOutputItemDoneEvent(
         sequence_number=next(seq), output_index=0, item=final_message_item
     )
-    yield f"event: response.output_item.done\ndata: {item_done.model_dump_json()}\n\n"
+    yield _format_sse(item_done)
 
     # Create usage from usage data if available
     usage = None
@@ -388,4 +394,4 @@ async def generate_responses_stream(
     completed_event = ResponseCompletedEvent(
         sequence_number=next(seq), response=final_response
     )
-    yield f"event: response.completed\ndata: {completed_event.model_dump_json()}\n\n"
+    yield _format_sse(completed_event)

src/exo/master/api.py

@@ -562,6 +562,8 @@ class API:
             if command_id in self._text_generation_queues:
                 del self._text_generation_queues[command_id]
 
+
+
     async def _collect_text_generation_with_stats(
         self, command_id: CommandId
     ) -> BenchChatCompletionResponse:

src/exo/worker/engines/mlx/generator/generate.py

@@ -90,6 +90,8 @@ def prefill(
         )
         if has_ssm:
             snapshots.append(snapshot_ssm_states(cache))
+        if on_prefill_progress is not None:
+            on_prefill_progress(processed, total)
 
         if on_prefill_progress is not None:
             on_prefill_progress(processed, total)

src/exo/worker/runner/runner_supervisor.py

@@ -98,16 +98,11 @@ class RunnerSupervisor:
 
     def shutdown(self):
         logger.info("Runner supervisor shutting down")
-        with contextlib.suppress(ClosedResourceError):
-            self._ev_recv.close()
-        with contextlib.suppress(ClosedResourceError):
-            self._task_sender.close()
-        with contextlib.suppress(ClosedResourceError):
-            self._event_sender.close()
-        with contextlib.suppress(ClosedResourceError):
-            self._cancel_sender.send(TaskId("CANCEL_CURRENT_TASK"))
-        with contextlib.suppress(ClosedResourceError):
-            self._cancel_sender.close()
+        self._ev_recv.close()
+        self._task_sender.close()
+        self._event_sender.close()
+        self._cancel_sender.send(TaskId("CANCEL_CURRENT_TASK"))
+        self._cancel_sender.close()
         self.runner_process.join(5)
         if not self.runner_process.is_alive():
             logger.info("Runner process succesfully terminated")