diff --git a/backend/crates/gateway-core/src/event.rs b/backend/crates/gateway-core/src/event.rs
index bcc5d5ea7..aa6cb4159 100644
--- a/backend/crates/gateway-core/src/event.rs
+++ b/backend/crates/gateway-core/src/event.rs
@@ -521,7 +521,7 @@ impl fmt::Debug for ProviderResponseHeader {
     }
 }
 
-/// Core 消费的实际上游响应事实。
+/// Core 消费的 Provider 执行观测，不会原样进入客户端响应。
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ProviderResponseObservation {
     transport: UpstreamTransport,
@@ -575,7 +575,7 @@ impl ProviderResponseObservation {
         self
     }
 
-    /// 附加 Provider 在响应中确认的服务档位。
+    /// 附加 Provider 确定的统计档位，Core 不重新解释其来源。
     ///
     /// # Errors
     ///
@@ -590,7 +590,7 @@ impl ProviderResponseObservation {
         Ok(self)
     }
 
-    /// 附加合法服务档位；不适合持久化的上游观测值会被忽略。
+    /// 附加 Provider 确定的统计档位；不适合持久化的值会被忽略。
     #[must_use]
     pub fn with_service_tier_if_valid(mut self, service_tier: impl Into<String>) -> Self {
         let service_tier = service_tier.into();
diff --git a/backend/crates/providers/openai/src/provider/observation.rs b/backend/crates/providers/openai/src/provider/observation.rs
index 1a399fe34..80a6e32ff 100644
--- a/backend/crates/providers/openai/src/provider/observation.rs
+++ b/backend/crates/providers/openai/src/provider/observation.rs
@@ -117,8 +117,9 @@ impl OpenAiResponseObservationState {
         if let Some(metadata) = self.provider_metadata() {
             observation = observation.with_provider_metadata(metadata);
         }
-        if let Some(service_tier) = self.effective_service_tier() {
-            observation = observation.with_service_tier_if_valid(service_tier.to_owned());
+        // 统计与计费采用最终发送档位；响应回显只作为独立诊断事实保留。
+        if let Some(service_tier) = &self.requested_service_tier {
+            observation = observation.with_service_tier_if_valid(service_tier.clone());
         }
         Some(observation)
     }
@@ -161,12 +162,6 @@ impl OpenAiResponseObservationState {
         true
     }
 
-    pub(super) fn effective_service_tier(&self) -> Option<&str> {
-        self.upstream_service_tier
-            .as_deref()
-            .or(self.requested_service_tier.as_deref())
-    }
-
     pub(super) fn merge_rate_limit_headers(&mut self, updates: &[(String, String)]) -> bool {
         let mut changed = false;
         for (name, value) in selected_observation_headers(updates) {
diff --git a/backend/crates/providers/openai/src/transport/canonical.rs b/backend/crates/providers/openai/src/transport/canonical.rs
index 7e542305f..77be5b8f1 100644
--- a/backend/crates/providers/openai/src/transport/canonical.rs
+++ b/backend/crates/providers/openai/src/transport/canonical.rs
@@ -158,7 +158,7 @@ impl CodexCanonicalDecoder {
         self
     }
 
-    /// 响应未报告实际档位时，才使用请求档位估算费用。
+    /// 使用最终发送给上游的请求档位估算费用，不由响应回显覆盖。
     #[must_use]
     pub fn with_requested_service_tier(mut self, service_tier: Option<&str>) -> Self {
         self.requested_service_tier = normalize_service_tier(service_tier);
@@ -217,7 +217,7 @@ impl CodexCanonicalDecoder {
         std::mem::take(&mut self.timing_signals)
     }
 
-    /// 返回本 attempt 已从上游响应生命周期帧观察到的实际服务档位。
+    /// 返回本 attempt 的上游响应回显档位，仅供诊断，不作为本地计费依据。
     #[must_use]
     pub fn response_service_tier(&self) -> Option<&str> {
         self.response_service_tier.as_deref()
@@ -861,10 +861,8 @@ impl CodexCanonicalDecoder {
             .filter(|model| !model.is_empty())
             .unwrap_or(&self.fallback_model)
             .to_owned();
-        let service_tier = self
-            .response_service_tier
-            .as_deref()
-            .or(self.requested_service_tier.as_deref());
+        // 与用量统计统一按最终发送档位估算，响应回显不改变本地计价口径。
+        let service_tier = self.requested_service_tier.as_deref();
         let tool_calls = billable_tool_calls(response);
         if let Some(breakdown) = usage
             .filter(|usage| billable_usage_is_complete(response, *usage))
diff --git a/backend/crates/providers/openai/tests/provider/contract.rs b/backend/crates/providers/openai/tests/provider/contract.rs
index f314b8508..62a0afc9a 100644
--- a/backend/crates/providers/openai/tests/provider/contract.rs
+++ b/backend/crates/providers/openai/tests/provider/contract.rs
@@ -4843,10 +4843,157 @@ async fn completed_response_persists_session_affinity_before_stream_consumer_sto
     drop(stream);
 
     assert_eq!(affinity.binding_count(), 1);
-    assert_eq!(observed_service_tier.as_deref(), Some("default"));
+    assert_eq!(observed_service_tier.as_deref(), Some("priority"));
     assert_eq!(upstream_service_tier.as_deref(), Some("default"));
 }
 
+#[tokio::test]
+async fn responses_should_observe_and_bill_the_outbound_service_tier_on_both_transports() {
+    for use_websocket in [false, true] {
+        for (requested, reported, expected_cost) in [
+            (Some("priority"), Some("default"), 6_875_000),
+            (Some("priority"), None, 6_875_000),
+            (Some("default"), Some("priority"), 3_437_500),
+            (None, Some("priority"), 3_437_500),
+        ] {
+            let store = Arc::new(MemoryAccountStore::default());
+            create_account(&store, "acct_provider_contract").await;
+            let mut created =
+                json!({"type":"response.created","response":{"id":"resp_tier","model":"gpt-5.4"}});
+            let mut completed = json!({
+                "type":"response.completed",
+                "response":{
+                    "id":"resp_tier","model":"gpt-5.4","status":"completed","output":[],
+                    "usage":{"input_tokens":100,"output_tokens":10,"input_tokens_details":{"cached_tokens":25,"cache_write_tokens":0},"total_tokens":110}
+                }
+            });
+            if let Some(reported) = reported {
+                created["response"]["service_tier"] = json!("auto");
+                completed["response"]["service_tier"] = json!(reported);
+            }
+            let response_frames = format!(
+                "event: response.created\ndata: {created}\n\nevent: response.completed\ndata: {completed}\n\n"
+            );
+            let (base_url, http_server, websocket_server) = if use_websocket {
+                let listener = TcpListener::bind("127.0.0.1:0").await.expect("listener");
+                let base_url = format!("http://{}", listener.local_addr().expect("address"));
+                let server = tokio::spawn(async move {
+                    let (socket, _) = listener.accept().await.expect("accept WebSocket");
+                    let mut websocket = accept_codex_test_websocket(socket).await;
+                    let request = websocket.next().await.expect("request").expect("frame");
+                    let request: Value = serde_json::from_str(request.to_text().expect("text"))
+                        .expect("request JSON");
+                    for event in [created, completed] {
+                        websocket
+                            .send(Message::Text(event.to_string().into()))
+                            .await
+                            .expect("response");
+                    }
+                    request
+                });
+                (base_url, None, Some(server))
+            } else {
+                let server = MockServer::start().await;
+                Mock::given(method("POST"))
+                    .and(path("/codex/responses"))
+                    .respond_with(
+                        ResponseTemplate::new(200)
+                            .set_body_raw(response_frames.clone(), "text/event-stream"),
+                    )
+                    .expect(1)
+                    .mount(&server)
+                    .await;
+                (server.uri(), Some(server), None)
+            };
+            let mut body = Map::from_iter([
+                ("model".to_owned(), json!("gpt-5.4")),
+                ("input".to_owned(), json!("hello")),
+            ]);
+            if let Some(requested) = requested {
+                body.insert("service_tier".to_owned(), json!(requested));
+            }
+            let payload = ProtocolPayload::json_object("openai", body)
+                .expect("payload")
+                .with_context(Map::from_iter([(
+                    "use_websocket".to_owned(),
+                    json!(use_websocket),
+                )]));
+            let mut stream = provider_with_base_url(&store, base_url)
+                .execute(
+                    planned_request(
+                        "openai",
+                        Operation::Generate(GenerateRequest::from_protocol_payload(payload)),
+                    ),
+                    context("req_service_tier", CancellationToken::new()),
+                )
+                .await
+                .expect("provider stream");
+            let mut observations = Vec::new();
+            let mut costs = Vec::new();
+            let mut raw_response = Vec::new();
+            while let Some(event) = stream.next().await {
+                let event = event.expect("provider event");
+                if let Some(observation) = event.response_observation() {
+                    observations.push(observation.clone());
+                }
+                for fact in event.canonical_facts() {
+                    if let GatewayEvent::CalculatedCost(cost) = fact {
+                        costs.push(cost.total().amount().scaled());
+                    }
+                }
+                if let Some(frame) = event.wire_event().and_then(|wire| wire.raw_sse_frame()) {
+                    raw_response.extend_from_slice(frame);
+                }
+            }
+            let outbound = if let Some(server) = http_server {
+                server.verify().await;
+                let requests = server.received_requests().await.expect("upstream requests");
+                captured_request_body(&requests[0])
+            } else {
+                websocket_server
+                    .expect("WebSocket server")
+                    .await
+                    .expect("server task")
+            };
+            assert_eq!(
+                outbound.get("service_tier").and_then(Value::as_str),
+                requested
+            );
+            assert!(!observations.is_empty());
+            for observation in &observations {
+                assert_eq!(
+                    observation.service_tier(),
+                    requested,
+                    "WebSocket={use_websocket}"
+                );
+            }
+            let metadata: Value = serde_json::from_str(
+                observations
+                    .last()
+                    .expect("final observation")
+                    .provider_metadata()
+                    .expect("metadata")
+                    .as_json(),
+            )
+            .expect("metadata JSON");
+            assert_eq!(
+                metadata.get("requestedServiceTier").and_then(Value::as_str),
+                requested
+            );
+            assert_eq!(
+                metadata.get("upstreamServiceTier").and_then(Value::as_str),
+                reported
+            );
+            assert_eq!(
+                costs,
+                vec![expected_cost],
+                "WebSocket={use_websocket}, requested={requested:?}, reported={reported:?}"
+            );
+            assert_eq!(raw_response, response_frames.as_bytes());
+        }
+    }
+}
+
 #[tokio::test]
 async fn response_failed_before_semantic_output_is_atomic_and_persists_quota_lock() {
     let store = Arc::new(MemoryAccountStore::default());
diff --git a/backend/crates/providers/openai/tests/transport/canonical.rs b/backend/crates/providers/openai/tests/transport/canonical.rs
index 5e6775293..832e8c540 100644
--- a/backend/crates/providers/openai/tests/transport/canonical.rs
+++ b/backend/crates/providers/openai/tests/transport/canonical.rs
@@ -219,7 +219,7 @@ fn decoder_should_emit_calculated_cost_for_complete_known_model_usage() {
 }
 
 #[test]
-fn decoder_should_prefer_response_service_tier_over_requested_tier_for_billing() {
+fn decoder_should_bill_requested_service_tier_despite_default_response() {
     let body = concat!(
         "event: response.created\n",
         "data: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_fast_cost\",\"model\":\"gpt-5.4\",\"service_tier\":\"default\"}}\n\n",
@@ -236,12 +236,12 @@ fn decoder_should_prefer_response_service_tier_over_requested_tier_for_billing()
     assert!(canonical_facts(&events).into_iter().any(|event| matches!(
         event,
         GatewayEvent::CalculatedCost(cost)
-            if cost.total().amount().scaled() == 3_437_500
+            if cost.total().amount().scaled() == 6_875_000
     )));
 }
 
 #[test]
-fn decoder_should_use_response_service_tier_when_request_omits_it() {
+fn decoder_should_bill_standard_when_request_omits_service_tier() {
     let body = concat!(
         "event: response.created\n",
         "data: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_response_tier_cost\",\"model\":\"gpt-5.4\",\"service_tier\":\"priority\"}}\n\n",
@@ -257,7 +257,7 @@ fn decoder_should_use_response_service_tier_when_request_omits_it() {
     assert!(canonical_facts(&events).into_iter().any(|event| matches!(
         event,
         GatewayEvent::CalculatedCost(cost)
-            if cost.total().amount().scaled() == 6_875_000
+            if cost.total().amount().scaled() == 3_437_500
     )));
 }
 
@@ -346,7 +346,7 @@ fn decoder_should_fail_closed_for_fixed_block_web_search_content() {
 }
 
 #[test]
-fn websocket_decoder_should_prefer_response_service_tier_over_requested_tier_for_billing() {
+fn websocket_decoder_should_bill_requested_service_tier_despite_default_response() {
     let created = websocket_event_to_sse_frame(
         r#"{"type":"response.created","response":{"id":"resp_ws_fast_cost","model":"gpt-5.4","service_tier":"default"}}"#,
     )
@@ -366,7 +366,7 @@ fn websocket_decoder_should_prefer_response_service_tier_over_requested_tier_for
     assert!(canonical_facts(&events).into_iter().any(|event| matches!(
         event,
         GatewayEvent::CalculatedCost(cost)
-            if cost.total().amount().scaled() == 3_437_500
+            if cost.total().amount().scaled() == 6_875_000
     )));
 }
 
@@ -975,14 +975,19 @@ fn pricing_response_cost(
 }
 
 #[test]
-fn billing_should_follow_actual_tier_and_only_fall_back_when_it_is_absent() {
+fn billing_should_follow_requested_tier_independently_of_response_tier() {
     for (requested, actual, expected) in [
-        (Some("fast"), Some("default"), Some(1_000_000_000)),
-        (Some("auto"), Some("fast"), Some(2_000_000_000)),
-        (Some("default"), Some("flex"), Some(500_000_000)),
+        (Some("priority"), Some("default"), Some(2_000_000_000)),
+        (Some("fast"), Some("default"), Some(2_000_000_000)),
+        (Some("auto"), Some("fast"), None),
+        (Some("default"), Some("flex"), Some(1_000_000_000)),
+        (Some("flex"), Some("priority"), Some(500_000_000)),
         (Some("fast"), None, Some(2_000_000_000)),
         (Some("auto"), None, None),
-        (Some("default"), Some("future"), None),
+        (Some("default"), Some("future"), Some(1_000_000_000)),
+        (Some("future"), Some("default"), None),
+        (None, Some("priority"), Some(1_000_000_000)),
+        (None, None, Some(1_000_000_000)),
     ] {
         assert_eq!(
             pricing_response_cost(requested, actual, json!([]), &[]),
@@ -1002,8 +1007,8 @@ fn billing_should_add_file_and_web_search_fees_without_tier_markup() {
     for (tier, expected) in [("default", 1_150_000_000), ("fast", 2_150_000_000)] {
         assert_eq!(
             pricing_response_cost(
-                None,
                 Some(tier),
+                Some("default"),
                 output.clone(),
                 &[json!({"type": "web_search"})]
             ),
diff --git a/docs/api.md b/docs/api.md
index a345ea7f9..81d746164 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -884,13 +884,16 @@ Dashboard 的 `accountUsage[]` 由后端提供 `usageWindow`、`metricLabel`、`
 和本地用量由 Provider/Admin 投影。前端不得从套餐缺失推断免费套餐，也不得从显示时舍入的百分比推断
 触顶。滚动窗口使用相应时间范围的本地用量，独立于 Dashboard 的今日统计范围。
 
-OpenAI 的 `serviceTier` 只接受上游响应生命周期事件确认的实际 `response.service_tier`；请求里的
-期望档位只保留在 request summary，不能冒充响应事实。计费展示把 `priority`/`fast` 映射为 `Fast`，
-`flex` 映射为 `Flex`，缺失或 `default` 映射为 `Default`；未知非空值原样展示。各模型、档位及长上下文
-区间使用明确登记的价格；缺少对应价格时不估算，不以固定倍数兜底。展示的倍率由所选档位与标准档位
-费用之比计算，托管工具调用费不随 Token 档位倍增。
-响应未报告实际档位时，本地费用估算回退到请求档位；该推测不写入响应 `serviceTier`，也不能确认
-上游最终采用了该档位，因此本地费用不能代替官方账单。
+OpenAI Responses 用量记录的 `serviceTier` 与本地费用估算统一采用 Provider 最终发给上游的请求
+`service_tier`，不使用响应档位覆盖或回退。例如发送 `priority`、响应回显 `default` 时，仍显示
+`Fast` 并按 Priority 价格估算。未发送档位时，`serviceTier` 保持缺失，展示与估算按标准档处理。
+计费展示把 `priority`/`fast` 映射为 `Fast`，`flex` 映射为 `Flex`，缺失或 `default`/`standard`
+映射为 `Standard`；其他非空值以首字母大写展示。各模型、档位及长上下文区间使用明确登记的价格；缺少对应
+价格时不估算（包括 `auto` 和未知档位），不以固定倍数兜底。展示的倍率由所选档位与标准档位费用之比
+计算，托管工具调用费不随 Token 档位倍增。
+Provider metadata 分别保留 `requestedServiceTier` 与 `upstreamServiceTier` 供诊断；发送给客户端的
+原始 `response.service_tier` 不变。用量中的 Fast 仅表示发送档位，不能证明上游实际加速，本地费用
+估算也不能代替官方账单。该口径仅作用于新记录，不回填历史档位或重算已存储费用。
 
 本地计价规则只保留尚在服务的型号；已过官方关闭日期的型号不再新增本地估价。清理计价规则不删除或
 重新计算已存储的历史费用；缺少当前计价规则时，历史总额仍保留，但无法再据此补充费用拆分。
diff --git a/docs/architecture.md b/docs/architecture.md
index 6f3ee9aa7..4d6fe74f9 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -427,7 +427,9 @@ observation、调用 metadata；最终失败的关联头不与 opening 身份混
 `generate: false` 将连接与上下文准备归类为 `prewarm`，不信任客户端单独声明的同名 metadata。
 Store 的共享用量口径排除这些预热记录，账号用量与额度预测复用同一规则；原始请求审计、响应额度
 观测和费用事实仍保留，不将未知费用改写为零，也不影响 Client Key 结算账本。
-实际 `service_tier` 只接受上游响应事件确认，不能用请求期望值替代。
+OpenAI Responses 的统计档位与本地费用估算统一使用 Provider 最终发给上游的请求 `service_tier`，
+不由响应回显覆盖；未发送档位时保留缺失值，展示与估算按标准档处理。上游响应档位独立保留在
+Provider metadata 的 `upstreamServiceTier`，不改写客户端收到的响应，也不据此断言实际加速效果。
 
 Worker 由各 Bundle 贡献、由 Host 统一监督：