Export turn cost as an OTEL metric (#40488)

## What changed

- Emit `codex.turn.cost_microusd` as a counter with turn, conversation,
  interruption, speed, and reasoning-effort attributes. Convert the estimated
  USD string to microdollars, rounding to the nearest microdollar and skipping
  values that cannot be represented safely.
- Start turn-cost collection when an OTLP metrics exporter is configured, even
  when the OTEL log exporter is disabled.

## Testing

- Verify cost conversion, rounding, and metric attributes with an in-memory
  metrics snapshot.
- Verify that a metrics-only OTLP configuration starts the turn-cost worker.

GitOrigin-RevId: e60587079f097f10cc1b6d1bf889d3f7a0dc3d5f

codex-rs/app-server/src/turn_cost_worker.rs

@@ -95,10 +95,16 @@ enum BackendAvailability {
 
 impl TurnCostWorker {
     pub(crate) fn spawn(config: Arc<Config>, auth_manager: Arc<AuthManager>) -> Option<Self> {
-        if !matches!(
+        let has_otel_log_exporter = matches!(
             config.otel.exporter,
             OtelExporterKind::OtlpHttp { .. } | OtelExporterKind::OtlpGrpc { .. }
-        ) || config.model_provider.is_amazon_bedrock()
+        );
+        let has_otel_metrics_exporter = matches!(
+            config.otel.metrics_exporter,
+            OtelExporterKind::OtlpHttp { .. } | OtelExporterKind::OtlpGrpc { .. }
+        );
+        if !(has_otel_log_exporter || has_otel_metrics_exporter)
+            || config.model_provider.is_amazon_bedrock()
         {
             return None;
         }

codex-rs/app-server/src/turn_cost_worker_tests.rs

@@ -21,6 +21,39 @@ use wiremock::matchers::path;
 
 const TURN_COST_PATH: &str = "/v1/analytics/codex/turn-costs";
 
+#[tokio::test]
+async fn worker_starts_with_otlp_metrics_exporter_without_log_exporter() {
+    let server = MockServer::start().await;
+    Mock::given(method("POST"))
+        .and(path(TURN_COST_PATH))
+        .respond_with(ResponseTemplate::new(200).set_body_json(serde_json::json!({
+            "turns": []
+        })))
+        .expect(1)
+        .mount(&server)
+        .await;
+    let codex_home = TempDir::new().expect("temporary Codex home");
+    let mut config = ConfigBuilder::default()
+        .codex_home(codex_home.path().to_path_buf())
+        .build()
+        .await
+        .expect("test config");
+    config.chatgpt_base_url = server.uri();
+    config.otel.exporter = OtelExporterKind::None;
+    config.otel.metrics_exporter = OtelExporterKind::OtlpGrpc {
+        endpoint: server.uri(),
+        headers: HashMap::new(),
+        tls: None,
+    };
+    let auth_manager = AuthManager::from_auth_for_testing(CodexAuth::from_api_key("sk-test"));
+
+    let worker = TurnCostWorker::spawn(Arc::new(config), auth_manager)
+        .expect("OTLP metrics exporter should enable turn-cost collection");
+    wait_for_request_count(&server, /*expected*/ 1).await;
+    worker.shutdown();
+    server.verify().await;
+}
+
 #[tokio::test]
 async fn handle_observes_only_matching_model_provider() {
     let codex_home = TempDir::new().expect("temporary Codex home");

codex-rs/otel/src/events/session_telemetry.rs

@@ -23,6 +23,7 @@ use crate::metrics::STARTUP_PHASE_DURATION_METRIC;
 use crate::metrics::SessionMetricTagValues;
 use crate::metrics::TOOL_CALL_COUNT_METRIC;
 use crate::metrics::TOOL_CALL_DURATION_METRIC;
+use crate::metrics::TURN_COST_MICROUSD_METRIC;
 use crate::metrics::TURN_TTFT_DURATION_METRIC;
 use crate::metrics::WEBSOCKET_EVENT_COUNT_METRIC;
 use crate::metrics::WEBSOCKET_EVENT_DURATION_METRIC;
@@ -281,6 +282,45 @@ impl SessionTelemetry {
         speed: Option<&str>,
         reasoning_effort: Option<&str>,
     ) {
+        let (dollars, fractional) = estimated_usd.split_once('.').unwrap_or((estimated_usd, ""));
+        let fractional = fractional.as_bytes();
+        let fractional_precision = 6_usize;
+        let estimated_microusd = dollars.parse::<u64>().ok().and_then(|dollars| {
+            if !fractional.iter().all(u8::is_ascii_digit) {
+                return None;
+            }
+            let fractional_microusd = fractional
+                .iter()
+                .take(fractional_precision)
+                .fold(0_u64, |value, digit| value * 10 + u64::from(digit - b'0'))
+                * 10_u64.pow(fractional_precision.saturating_sub(fractional.len()) as u32);
+            let round_up = fractional
+                .get(fractional_precision)
+                .is_some_and(|digit| *digit >= b'5');
+            let estimated_microusd = dollars
+                .checked_mul(1_000_000)?
+                .checked_add(fractional_microusd)?
+                .checked_add(u64::from(round_up))?;
+            i64::try_from(estimated_microusd).ok()
+        });
+        if let Some(estimated_microusd) = estimated_microusd {
+            let conversation_id = self.metadata.conversation_id.to_string();
+            let mut tags = vec![
+                ("turn.id", turn_id),
+                ("conversation.id", conversation_id.as_str()),
+                (
+                    "turn.interrupted",
+                    if interrupted { "true" } else { "false" },
+                ),
+            ];
+            if let Some(speed) = speed {
+                tags.push(("speed", speed));
+            }
+            if let Some(reasoning_effort) = reasoning_effort {
+                tags.push(("reasoning_effort", reasoning_effort));
+            }
+            self.counter(TURN_COST_MICROUSD_METRIC, estimated_microusd, &tags);
+        }
         log_event!(
             self,
             event.name = "codex.turn_cost",

codex-rs/otel/src/metrics/config.rs

@@ -7,6 +7,7 @@ use crate::metrics::names::RESPONSES_API_ENGINE_SERVICE_TBT_DURATION_METRIC;
 use crate::metrics::names::RESPONSES_API_ENGINE_SERVICE_TTFT_DURATION_METRIC;
 use crate::metrics::names::TOOL_CALL_COUNT_METRIC;
 use crate::metrics::names::TOOL_CALL_DURATION_METRIC;
+use crate::metrics::names::TURN_COST_MICROUSD_METRIC;
 use crate::metrics::names::TURN_TOKEN_USAGE_METRIC;
 use crate::metrics::validation::validate_tag_key;
 use crate::metrics::validation::validate_tag_value;
@@ -27,6 +28,7 @@ const STATSIG_DISABLED_METRICS: &[&str] = &[
     RESPONSES_API_ENGINE_SERVICE_TTFT_DURATION_METRIC,
     TOOL_CALL_COUNT_METRIC,
     TOOL_CALL_DURATION_METRIC,
+    TURN_COST_MICROUSD_METRIC,
     TURN_TOKEN_USAGE_METRIC,
 ];
 

codex-rs/otel/src/metrics/names.rs

@@ -31,6 +31,7 @@ pub const TURN_NETWORK_PROXY_METRIC: &str = "codex.turn.network_proxy";
 pub const TURN_MEMORY_METRIC: &str = "codex.turn.memory";
 pub const TURN_TOOL_CALL_METRIC: &str = "codex.turn.tool.call";
 pub const TURN_TOKEN_USAGE_METRIC: &str = "codex.turn.token_usage";
+pub const TURN_COST_MICROUSD_METRIC: &str = "codex.turn.cost_microusd";
 pub const TURN_UNIFIED_EXEC_RUNNING_PROCESSES_METRIC: &str =
     "codex.turn.unified_exec.running_processes";
 pub const GUARDIAN_REVIEW_COUNT_METRIC: &str = "codex.guardian.review";

codex-rs/otel/src/provider.rs

@@ -604,6 +604,7 @@ mod tests {
     use crate::metrics::RESPONSES_API_ENGINE_SERVICE_TTFT_DURATION_METRIC;
     use crate::metrics::TOOL_CALL_COUNT_METRIC;
     use crate::metrics::TOOL_CALL_DURATION_METRIC;
+    use crate::metrics::TURN_COST_MICROUSD_METRIC;
     use crate::metrics::TURN_TOKEN_USAGE_METRIC;
     use opentelemetry_sdk::metrics::InMemoryMetricExporter;
     use pretty_assertions::assert_eq;
@@ -741,6 +742,7 @@ mod tests {
         )?;
         metrics.counter(TOOL_CALL_COUNT_METRIC, /*inc*/ 1, &[])?;
         metrics.record_duration(TOOL_CALL_DURATION_METRIC, Duration::from_millis(25), &[])?;
+        metrics.counter(TURN_COST_MICROUSD_METRIC, /*inc*/ 1, &[])?;
         metrics.histogram(TURN_TOKEN_USAGE_METRIC, /*value*/ 100, &[])?;
         metrics.counter("codex.turns", /*inc*/ 1, &[])?;
         metrics.shutdown()?;

codex-rs/otel/tests/suite/snapshot.rs

@@ -155,3 +155,68 @@ fn manager_snapshot_metrics_collects_without_shutdown() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn manager_turn_cost_records_microusd_metric() -> Result<()> {
+    let exporter = InMemoryMetricExporter::default();
+    let config = MetricsConfig::in_memory("test", "codex-cli", env!("CARGO_PKG_VERSION"), exporter)
+        .with_runtime_reader();
+    let metrics = MetricsClient::new(config)?;
+    let thread_id = ThreadId::new();
+    let conversation_id = thread_id.to_string();
+    let manager = SessionTelemetry::new(
+        thread_id,
+        "gpt-5.6",
+        "gpt-5.6",
+        /*account_id*/ None,
+        /*account_email*/ None,
+        Some(TelemetryAuthMode::ApiKey),
+        "test_originator".to_string(),
+        /*log_user_prompts*/ false,
+        "tty".to_string(),
+        SessionSource::Cli,
+    )
+    .with_metrics(metrics);
+
+    manager.record_turn_cost(
+        "turn-123",
+        "0.0001245",
+        /*interrupted*/ false,
+        Some("fast"),
+        Some("high"),
+    );
+
+    let snapshot = manager.snapshot_metrics()?;
+    let metric = find_metric(&snapshot, "codex.turn.cost_microusd")
+        .expect("turn-cost microdollar metric missing");
+    let point = match metric.data() {
+        AggregatedMetrics::U64(MetricData::Sum(sum)) => {
+            sum.data_points().next().expect("turn-cost data point")
+        }
+        _ => panic!("unexpected turn-cost metric data type"),
+    };
+    assert_eq!(point.value(), 125);
+    assert_eq!(
+        attributes_to_map(point.attributes()),
+        BTreeMap::from([
+            (
+                "app.version".to_string(),
+                env!("CARGO_PKG_VERSION").to_string(),
+            ),
+            (
+                "auth_mode".to_string(),
+                TelemetryAuthMode::ApiKey.to_string(),
+            ),
+            ("conversation.id".to_string(), conversation_id),
+            ("model".to_string(), "gpt-5.6".to_string()),
+            ("originator".to_string(), "test_originator".to_string()),
+            ("reasoning_effort".to_string(), "high".to_string()),
+            ("session_source".to_string(), "cli".to_string()),
+            ("speed".to_string(), "fast".to_string()),
+            ("turn.id".to_string(), "turn-123".to_string()),
+            ("turn.interrupted".to_string(), "false".to_string()),
+        ])
+    );
+
+    Ok(())
+}