diff --git a/web/src/components/AssistantChat/StatusBar.tsx b/web/src/components/AssistantChat/StatusBar.tsx
index 7032e7b6..32582ef1 100644
--- a/web/src/components/AssistantChat/StatusBar.tsx
+++ b/web/src/components/AssistantChat/StatusBar.tsx
@@ -10,6 +10,7 @@ import type { AgentState, CodexCollaborationMode, PermissionMode } from '@/types
 import type { ConversationStatus } from '@/realtime/types'
 import type { ThreadGoal } from '@/types/api'
 import { getContextBudgetTokens } from '@/chat/modelConfig'
+import { formatCodexReasoningLabel, shouldShowCodexReasoningLabel } from '@/lib/codexStatusLabels'
 import { isFastServiceTier } from './codexFastMode'
 import { useTranslation } from '@/lib/use-translation'
 
@@ -124,12 +125,6 @@ function formatTokenCount(value: number): string {
     return String(value)
 }
 
-function formatCodexReasoningLabel(effort?: string | null): string {
-    const normalized = effort?.trim().toLowerCase()
-    if (!normalized || normalized === 'default') return 'reasoning default'
-    return `reasoning ${normalized}`
-}
-
 function isCodexFastMode(model?: string | null, effort?: string | null): boolean {
     const normalizedEffort = effort?.trim().toLowerCase()
     if (normalizedEffort === 'none' || normalizedEffort === 'minimal' || normalizedEffort === 'low') {
@@ -212,7 +207,7 @@ export function StatusBar(props: {
     const collaborationModeLabel = displayCollaborationMode
         ? getCodexCollaborationModeLabel(displayCollaborationMode)
         : null
-    const codexReasoningLabel = (props.agentFlavor === 'codex' || props.agentFlavor === 'opencode')
+    const codexReasoningLabel = shouldShowCodexReasoningLabel(props.agentFlavor)
         ? formatCodexReasoningLabel(props.modelReasoningEffort)
         : null
     // Prefer the explicit service tier (the real Fast-mode toggle) when set;
diff --git a/web/src/components/SessionHeader.tsx b/web/src/components/SessionHeader.tsx
index c80ac68a..5470307c 100644
--- a/web/src/components/SessionHeader.tsx
+++ b/web/src/components/SessionHeader.tsx
@@ -8,9 +8,11 @@ import { SessionExportDialog } from '@/components/SessionExportDialog'
 import { RenameSessionDialog } from '@/components/RenameSessionDialog'
 import { ConfirmDialog } from '@/components/ui/ConfirmDialog'
 import { formatReopenError } from '@/lib/reopenError'
+import { formatCodexReasoningLabel, shouldShowCodexReasoningLabel } from '@/lib/codexStatusLabels'
 import { getSessionModelLabel } from '@/lib/sessionModelLabel'
 import { useTranslation } from '@/lib/use-translation'
 import { AgentFlavorIcon } from '@/components/AgentFlavorIcon'
+import { isFastServiceTier } from '@/components/AssistantChat/codexFastMode'
 
 function getSessionTitle(session: Session): string {
     if (session.metadata?.name) {
@@ -111,6 +113,12 @@ export function SessionHeader(props: {
     const title = useMemo(() => getSessionTitle(session), [session])
     const worktreeBranch = session.metadata?.worktree?.branch
     const modelLabel = getSessionModelLabel(session)
+    const agentFlavor = session.metadata?.flavor ?? null
+    const reasoningLabel = shouldShowCodexReasoningLabel(agentFlavor)
+        ? formatCodexReasoningLabel(session.modelReasoningEffort)
+        : null
+    // Match expected Fast badge semantics (#1004): only explicit service tier, no effort/model heuristics.
+    const showFastBadge = agentFlavor === 'codex' && isFastServiceTier(session.serviceTier)
 
     const [menuOpen, setMenuOpen] = useState(false)
     const [menuAnchorPoint, setMenuAnchorPoint] = useState<{ x: number; y: number }>({ x: 0, y: 0 })
@@ -198,6 +206,16 @@ export function SessionHeader(props: {
                                     {t(modelLabel.key)}: {modelLabel.value}
                                 </span>
                             ) : null}
+                            {reasoningLabel ? (
+                                <span data-testid="session-header-reasoning">
+                                    {reasoningLabel}
+                                </span>
+                            ) : null}
+                            {showFastBadge ? (
+                                <span data-testid="session-header-fast" className="text-[#34C759]">
+                                    fast
+                                </span>
+                            ) : null}
                             {worktreeBranch ? (
                                 <span>{t('session.item.worktree')}: {worktreeBranch}</span>
                             ) : null}
diff --git a/web/src/lib/codexStatusLabels.test.ts b/web/src/lib/codexStatusLabels.test.ts
new file mode 100644
index 00000000..779f5a07
--- /dev/null
+++ b/web/src/lib/codexStatusLabels.test.ts
@@ -0,0 +1,23 @@
+import { describe, expect, it } from 'vitest'
+import { formatCodexReasoningLabel, shouldShowCodexReasoningLabel } from './codexStatusLabels'
+
+describe('codexStatusLabels', () => {
+    it('formats unset and default effort as reasoning default', () => {
+        expect(formatCodexReasoningLabel(null)).toBe('reasoning default')
+        expect(formatCodexReasoningLabel(undefined)).toBe('reasoning default')
+        expect(formatCodexReasoningLabel('default')).toBe('reasoning default')
+        expect(formatCodexReasoningLabel('  DEFAULT  ')).toBe('reasoning default')
+    })
+
+    it('formats selected efforts', () => {
+        expect(formatCodexReasoningLabel('xhigh')).toBe('reasoning xhigh')
+        expect(formatCodexReasoningLabel('Ultra')).toBe('reasoning ultra')
+    })
+
+    it('only shows the label for codex and opencode', () => {
+        expect(shouldShowCodexReasoningLabel('codex')).toBe(true)
+        expect(shouldShowCodexReasoningLabel('opencode')).toBe(true)
+        expect(shouldShowCodexReasoningLabel('claude')).toBe(false)
+        expect(shouldShowCodexReasoningLabel(null)).toBe(false)
+    })
+})
diff --git a/web/src/lib/codexStatusLabels.ts b/web/src/lib/codexStatusLabels.ts
new file mode 100644
index 00000000..d4960c6b
--- /dev/null
+++ b/web/src/lib/codexStatusLabels.ts
@@ -0,0 +1,11 @@
+/** Labels shared by SessionHeader and composer StatusBar for Codex/OpenCode. */
+
+export function formatCodexReasoningLabel(effort?: string | null): string {
+    const normalized = effort?.trim().toLowerCase()
+    if (!normalized || normalized === 'default') return 'reasoning default'
+    return `reasoning ${normalized}`
+}
+
+export function shouldShowCodexReasoningLabel(agentFlavor: string | null | undefined): boolean {
+    return agentFlavor === 'codex' || agentFlavor === 'opencode'
+}