diff --git a/gui/src/i18n/de.ts b/gui/src/i18n/de.ts
index f0eb85fcee..07100850ac 100644
--- a/gui/src/i18n/de.ts
+++ b/gui/src/i18n/de.ts
@@ -742,6 +742,10 @@ export const de: Record<TKey, string> = {
   "logs.modelTooltip.configuredTier": "konfigurierte Stufe",
   "logs.modelTooltip.responseTier": "Antwortstufe",
   "logs.modelTooltip.supportsTier": "Stufenunterstützung",
+  "logs.modelTooltip.tierOutcome.confirmed": "bestätigt",
+  "logs.modelTooltip.tierOutcome.assumed": "angenommen",
+  "logs.modelTooltip.tierOutcome.downgraded": "herabgestuft",
+  "logs.modelTooltip.tierOutcome.unknown": "unbekannt",
   "logs.tokens.reported": "gemeldet",
   "logs.tokens.unreported": "nicht gemeldet",
   "logs.tokens.unsupported": "nicht unterstützt",
diff --git a/gui/src/i18n/en.ts b/gui/src/i18n/en.ts
index 8c49a81248..95a68e618c 100644
--- a/gui/src/i18n/en.ts
+++ b/gui/src/i18n/en.ts
@@ -775,6 +775,10 @@ export const en = {
   "logs.modelTooltip.configuredTier": "configured tier",
   "logs.modelTooltip.responseTier": "response tier",
   "logs.modelTooltip.supportsTier": "tier support",
+  "logs.modelTooltip.tierOutcome.confirmed": "confirmed",
+  "logs.modelTooltip.tierOutcome.assumed": "assumed",
+  "logs.modelTooltip.tierOutcome.downgraded": "downgraded",
+  "logs.modelTooltip.tierOutcome.unknown": "unknown",
   "logs.tokens.reported": "reported",
   "logs.tokens.unreported": "unreported",
   "logs.tokens.unsupported": "unsupported",
diff --git a/gui/src/i18n/fr.ts b/gui/src/i18n/fr.ts
index a05872c155..540675641e 100644
--- a/gui/src/i18n/fr.ts
+++ b/gui/src/i18n/fr.ts
@@ -756,6 +756,10 @@ export const fr: Record<TKey, string> = {
   "logs.modelTooltip.configuredTier": "niveau configuré",
   "logs.modelTooltip.responseTier": "niveau de réponse",
   "logs.modelTooltip.supportsTier": "prise en charge du niveau",
+  "logs.modelTooltip.tierOutcome.confirmed": "confirmé",
+  "logs.modelTooltip.tierOutcome.assumed": "supposé",
+  "logs.modelTooltip.tierOutcome.downgraded": "rétrogradé",
+  "logs.modelTooltip.tierOutcome.unknown": "inconnu",
   "logs.tokens.reported": "communiqués",
   "logs.tokens.unreported": "non communiqués",
   "logs.tokens.unsupported": "non pris en charge",
diff --git a/gui/src/i18n/ja.ts b/gui/src/i18n/ja.ts
index ce861c5c47..7005308026 100644
--- a/gui/src/i18n/ja.ts
+++ b/gui/src/i18n/ja.ts
@@ -718,6 +718,10 @@ export const ja: Record<TKey, string> = {
   "logs.modelTooltip.configuredTier": "設定ティア",
   "logs.modelTooltip.responseTier": "応答ティア",
   "logs.modelTooltip.supportsTier": "ティア対応",
+  "logs.modelTooltip.tierOutcome.confirmed": "確認済み",
+  "logs.modelTooltip.tierOutcome.assumed": "推定",
+  "logs.modelTooltip.tierOutcome.downgraded": "降格",
+  "logs.modelTooltip.tierOutcome.unknown": "不明",
   "logs.tokens.reported": "報告済み",
   "logs.tokens.unreported": "未報告",
   "logs.tokens.unsupported": "非対応",
diff --git a/gui/src/i18n/ko.ts b/gui/src/i18n/ko.ts
index bf7fe01e24..e1ac145324 100644
--- a/gui/src/i18n/ko.ts
+++ b/gui/src/i18n/ko.ts
@@ -761,6 +761,10 @@ export const ko: Record<TKey, string> = {
   "logs.modelTooltip.configuredTier": "설정 티어",
   "logs.modelTooltip.responseTier": "응답 티어",
   "logs.modelTooltip.supportsTier": "티어 지원",
+  "logs.modelTooltip.tierOutcome.confirmed": "확인됨",
+  "logs.modelTooltip.tierOutcome.assumed": "추정됨",
+  "logs.modelTooltip.tierOutcome.downgraded": "강등됨",
+  "logs.modelTooltip.tierOutcome.unknown": "알 수 없음",
   "logs.tokens.reported": "측정됨",
   "logs.tokens.unreported": "미보고",
   "logs.tokens.unsupported": "미지원",
diff --git a/gui/src/i18n/ru.ts b/gui/src/i18n/ru.ts
index 19ebbf68b2..868dc32720 100644
--- a/gui/src/i18n/ru.ts
+++ b/gui/src/i18n/ru.ts
@@ -759,6 +759,10 @@ export const ru: Record<TKey, string> = {
   "logs.modelTooltip.configuredTier": "настроенный уровень",
   "logs.modelTooltip.responseTier": "уровень ответа",
   "logs.modelTooltip.supportsTier": "поддержка уровня",
+  "logs.modelTooltip.tierOutcome.confirmed": "подтверждено",
+  "logs.modelTooltip.tierOutcome.assumed": "предполагается",
+  "logs.modelTooltip.tierOutcome.downgraded": "понижено",
+  "logs.modelTooltip.tierOutcome.unknown": "неизвестно",
   "logs.tokens.reported": "сообщено",
   "logs.tokens.unreported": "не сообщено",
   "logs.tokens.unsupported": "не поддерживается",
diff --git a/gui/src/i18n/tr.ts b/gui/src/i18n/tr.ts
index 21c70d54fd..297a4812af 100644
--- a/gui/src/i18n/tr.ts
+++ b/gui/src/i18n/tr.ts
@@ -766,6 +766,10 @@ export const tr: Record<TKey, string> = {
   "logs.modelTooltip.configuredTier": "yapılandırılan katman",
   "logs.modelTooltip.responseTier": "yanıt katmanı",
   "logs.modelTooltip.supportsTier": "katman desteği",
+  "logs.modelTooltip.tierOutcome.confirmed": "doğrulandı",
+  "logs.modelTooltip.tierOutcome.assumed": "varsayıldı",
+  "logs.modelTooltip.tierOutcome.downgraded": "düşürüldü",
+  "logs.modelTooltip.tierOutcome.unknown": "bilinmiyor",
   "logs.tokens.reported": "bildirilen",
   "logs.tokens.unreported": "bildirilmeyen",
   "logs.tokens.unsupported": "desteklenmeyen",
diff --git a/gui/src/i18n/zh-TW.ts b/gui/src/i18n/zh-TW.ts
index 588b09cac0..c47cae1f87 100644
--- a/gui/src/i18n/zh-TW.ts
+++ b/gui/src/i18n/zh-TW.ts
@@ -594,6 +594,10 @@ export const zhTW: Record<TKey, string> = {
   "logs.modelTooltip.configuredTier": "設定層級",
   "logs.modelTooltip.responseTier": "回應層級",
   "logs.modelTooltip.supportsTier": "支援層級",
+  "logs.modelTooltip.tierOutcome.confirmed": "已確認",
+  "logs.modelTooltip.tierOutcome.assumed": "假定",
+  "logs.modelTooltip.tierOutcome.downgraded": "已降級",
+  "logs.modelTooltip.tierOutcome.unknown": "未知",
   "logs.tokens.reported": "已上報",
   "logs.tokens.unreported": "未上報",
   "logs.tokens.unsupported": "不支援",
diff --git a/gui/src/i18n/zh.ts b/gui/src/i18n/zh.ts
index 136c60b254..340b7cc31f 100644
--- a/gui/src/i18n/zh.ts
+++ b/gui/src/i18n/zh.ts
@@ -754,6 +754,10 @@ export const zh: Record<TKey, string> = {
   "logs.modelTooltip.configuredTier": "配置层级",
   "logs.modelTooltip.responseTier": "响应层级",
   "logs.modelTooltip.supportsTier": "支持层级",
+  "logs.modelTooltip.tierOutcome.confirmed": "已确认",
+  "logs.modelTooltip.tierOutcome.assumed": "假定",
+  "logs.modelTooltip.tierOutcome.downgraded": "已降级",
+  "logs.modelTooltip.tierOutcome.unknown": "未知",
   "logs.tokens.reported": "已上报",
   "logs.tokens.unreported": "未上报",
   "logs.tokens.unsupported": "不支持",
diff --git a/gui/src/pages/Logs.tsx b/gui/src/pages/Logs.tsx
index 384231f698..358f06a217 100644
--- a/gui/src/pages/Logs.tsx
+++ b/gui/src/pages/Logs.tsx
@@ -15,7 +15,7 @@ import Debug from "./Debug";
 
 import type { LogsTab } from "./logs-tab-keydown";
 import { logsTabKeyDown, readTabFromHash, selectLogsTab } from "./logs-tab-keydown";
-import { modelTitle } from "./logs-model-title";
+import { modelTitle, type ModelTitleTierOutcome } from "./logs-model-title";
 import { speedLabel } from "./logs-speed-label";
 import { formatEstimatedUsd, formatEstimatedUsdValue, summarizeEstimatedCosts } from "./logs-cost-format";
 import { cacheSplit, isCursorUsageProvider, tokensTitle } from "./logs-token-title";
@@ -152,6 +152,9 @@ export interface LogEntry {
   configuredServiceTier?: string;
   configuredSpeedLabel?: string;
   responseServiceTier?: string;
+  // #2455: qualifies responseServiceTier in the model tooltip — the echoed tier alone
+  // cannot say whether Fast was granted on a backend whose echo is not authoritative.
+  tierOutcome?: ModelTitleTierOutcome;
   resolvedModel?: string;
   modelSupportsServiceTier?: boolean;
   status: number;
diff --git a/gui/src/pages/logs-model-title.ts b/gui/src/pages/logs-model-title.ts
index 77b1fe0577..8bcf314119 100644
--- a/gui/src/pages/logs-model-title.ts
+++ b/gui/src/pages/logs-model-title.ts
@@ -1,5 +1,10 @@
 import type { TFn } from "../i18n/shared";
 
+export interface ModelTitleTierOutcome {
+  confirmation?: "confirmed" | "assumed" | "downgraded" | "unknown";
+  fastDowngradeReason?: string;
+}
+
 export interface ModelTitleEntry {
   model: string;
   resolvedModel?: string;
@@ -7,6 +12,28 @@ export interface ModelTitleEntry {
   configuredServiceTier?: string;
   responseServiceTier?: string;
   modelSupportsServiceTier?: boolean;
+  tierOutcome?: ModelTitleTierOutcome;
+}
+
+/**
+ * #2455: the echoed tier alone does not say whether Fast was granted. The ChatGPT
+ * backend answers `default` on turns it in fact scheduled as priority, so its echo is
+ * marked non-authoritative and the outcome stays `assumed` (#2558) — which is the
+ * honest answer, but only if the operator can see it. Qualify the echoed value with
+ * how much it is worth, and name the reason when the tier was actually declined.
+ *
+ * The confirmation word is this proxy's own judgement about the turn, not a value the
+ * upstream returned, so it is translated like any other visible string. The downgrade
+ * reason stays verbatim: it is a diagnostic identifier (`response-declined`) that maps
+ * to `fastDowngradeReason` in the source, and translating it would break that link.
+ */
+function tierConfirmationSuffix(outcome: ModelTitleEntry["tierOutcome"], t: TFn): string {
+  const confirmation = outcome?.confirmation;
+  if (!confirmation) return "";
+  const reason = confirmation === "downgraded" && outcome?.fastDowngradeReason
+    ? `: ${outcome.fastDowngradeReason}`
+    : "";
+  return ` (${t(`logs.modelTooltip.tierOutcome.${confirmation}`)}${reason})`;
 }
 
 export function modelTitle(log: ModelTitleEntry, t: TFn): string {
@@ -15,7 +42,9 @@ export function modelTitle(log: ModelTitleEntry, t: TFn): string {
     log.resolvedModel ? `${t("logs.modelTooltip.resolvedModel")}=${log.resolvedModel}` : undefined,
     log.requestedServiceTier ? `${t("logs.modelTooltip.requestedTier")}=${log.requestedServiceTier}` : undefined,
     log.configuredServiceTier ? `${t("logs.modelTooltip.configuredTier")}=${log.configuredServiceTier}` : undefined,
-    log.responseServiceTier ? `${t("logs.modelTooltip.responseTier")}=${log.responseServiceTier}` : undefined,
+    log.responseServiceTier
+      ? `${t("logs.modelTooltip.responseTier")}=${log.responseServiceTier}${tierConfirmationSuffix(log.tierOutcome, t)}`
+      : undefined,
     log.modelSupportsServiceTier !== undefined
       ? `${t("logs.modelTooltip.supportsTier")}=${log.modelSupportsServiceTier}`
       : undefined,
diff --git a/tests/logs-model-tier-confirmation.test.ts b/tests/logs-model-tier-confirmation.test.ts
new file mode 100644
index 0000000000..995b76f793
--- /dev/null
+++ b/tests/logs-model-tier-confirmation.test.ts
@@ -0,0 +1,124 @@
+import { describe, expect, test } from "bun:test";
+import { modelTitle, type ModelTitleEntry } from "../gui/src/pages/logs-model-title";
+import { readFileSync, readdirSync } from "node:fs";
+import { join } from "node:path";
+
+/**
+ * #2455: a user routing gpt-5.x through the proxy asked for `service_tier: priority`,
+ * saw the backend echo something else, and had no way to tell whether Fast was granted.
+ *
+ * The echo alone cannot answer it. The ChatGPT-internal Codex backend returns
+ * `service_tier: "default"` on turns it in fact scheduled as priority, so its echo is
+ * marked non-authoritative and the outcome stays `assumed` rather than being read as a
+ * downgrade (#2558). That is the honest answer — but it was computed in `tierOutcome`
+ * and never shown, so the tooltip printed a bare echoed value that looked like a denial.
+ */
+
+/**
+ * Stub translator. The tier-outcome labels are marked with a `t:` prefix on purpose: a
+ * hardcoded English label would render the same bare word as a translated one, so
+ * without the marker these assertions could not tell the two apart. The real catalogs
+ * are checked separately, by file, in the locale-coverage test.
+ */
+const t = ((key: string) => {
+  const leaf = key.split(".").pop() ?? key;
+  return key.includes("tierOutcome.") ? `t:${leaf}` : leaf;
+}) as never;
+
+const CONFIRMATIONS = ["confirmed", "assumed", "downgraded", "unknown"] as const;
+
+function entry(over: Partial<ModelTitleEntry> = {}): ModelTitleEntry {
+  return { model: "gpt-5.6-terra", ...over };
+}
+
+describe("model tooltip tier confirmation (#2455)", () => {
+  test("qualifies the echoed tier with the outcome", () => {
+    const title = modelTitle(
+      entry({ responseServiceTier: "default", tierOutcome: { confirmation: "assumed" } }),
+      t,
+    );
+    expect(title).toContain("=default (t:assumed)");
+  });
+
+  test("names the reason when the tier was actually declined", () => {
+    const title = modelTitle(
+      entry({
+        responseServiceTier: "default",
+        tierOutcome: { confirmation: "downgraded", fastDowngradeReason: "response-declined" },
+      }),
+      t,
+    );
+    expect(title).toContain("=default (t:downgraded: response-declined)");
+  });
+
+  test("a confirmed grant reads as confirmed", () => {
+    const title = modelTitle(
+      entry({ responseServiceTier: "priority", tierOutcome: { confirmation: "confirmed" } }),
+      t,
+    );
+    expect(title).toContain("=priority (t:confirmed)");
+  });
+
+  test("no outcome leaves the existing tooltip unchanged", () => {
+    const before = modelTitle(entry({ responseServiceTier: "default" }), t);
+    expect(before).toContain("=default");
+    expect(before).not.toContain("(");
+  });
+
+  test("an outcome without an echoed tier adds nothing", () => {
+    // The qualifier explains an echoed value; with nothing echoed there is nothing to
+    // qualify, and a lone parenthesis would read as a malformed field.
+    const title = modelTitle(entry({ tierOutcome: { confirmation: "assumed" } }), t);
+    expect(title).not.toContain("assumed");
+    expect(title).toBe("model=gpt-5.6-terra");
+  });
+
+  test("a downgrade with no recorded reason omits the colon", () => {
+    const title = modelTitle(
+      entry({ responseServiceTier: "default", tierOutcome: { confirmation: "downgraded" } }),
+      t,
+    );
+    expect(title).toContain("=default (t:downgraded)");
+    expect(title).not.toContain("downgraded:");
+  });
+
+  test("every confirmation value is translated in every locale", () => {
+    // The label is this proxy's own judgement about the turn, so it is visible text and
+    // must not fall back to a raw key in any dashboard language. Read the catalogs as
+    // files: importing the barrel pulls in the whole GUI dependency graph.
+    // Named explicitly: the directory also holds label modules that are not catalogs,
+    // and this list is the same one LOCALES declares in i18n/shared.ts.
+    const LOCALE_FILES = [
+      "en.ts", "de.ts", "fr.ts", "ko.ts", "zh.ts", "zh-TW.ts", "ru.ts", "ja.ts", "tr.ts",
+    ];
+    const dir = join(import.meta.dir, "..", "gui", "src", "i18n");
+    const present = readdirSync(dir);
+    for (const file of LOCALE_FILES) {
+      expect(present, `${file} disappeared from i18n/`).toContain(file);
+    }
+
+    for (const file of LOCALE_FILES) {
+      const text = readFileSync(join(dir, file), "utf8");
+      for (const confirmation of CONFIRMATIONS) {
+        const key = `"logs.modelTooltip.tierOutcome.${confirmation}":`;
+        const line = text.split("\n").find(l => l.includes(key));
+        expect(line, `${file} is missing ${key}`).toBeTruthy();
+        const value = line!.slice(line!.indexOf(key) + key.length).trim().replace(/^"|",?$/g, "");
+        expect(value.length, `${file} ${key} is empty`).toBeGreaterThan(0);
+      }
+    }
+  });
+
+  test("the downgrade reason stays a verbatim identifier", () => {
+    // `response-declined` maps to fastDowngradeReason in the source; translating it
+    // would break the link between what the operator reads and what to grep for.
+    const title = modelTitle(
+      entry({
+        responseServiceTier: "default",
+        tierOutcome: { confirmation: "downgraded", fastDowngradeReason: "wire-unavailable" },
+      }),
+      t,
+    );
+    expect(title).toContain("wire-unavailable");
+  });
+});