diff --git a/packages/app/cypress/e2e/ttft-x-axis-toggle.cy.ts b/packages/app/cypress/e2e/ttft-x-axis-toggle.cy.ts
index 1ce282c2f..f499a3a45 100644
--- a/packages/app/cypress/e2e/ttft-x-axis-toggle.cy.ts
+++ b/packages/app/cypress/e2e/ttft-x-axis-toggle.cy.ts
@@ -13,6 +13,8 @@ const interceptDerivedMetrics = () => {
             p90_prefill_tps_per_user: 100 + index,
             p75_normalized_e2e_400_s: 8 + index,
             p90_normalized_e2e_400_s: 12 + index,
+            p75_osl_per_e2el: 40 + index,
+            p90_osl_per_e2el: 25 + index,
           },
         ]),
       ),
@@ -144,6 +146,10 @@ const interceptFixedSequenceData = () => {
 describe('X-Axis Mode Toggle (inference chart)', () => {
   before(() => {
     interceptAgenticData();
+    // Stub derived metrics before the visit: if the agentic DEFAULT x-axis mode
+    // is (or becomes) a derived mode that fetches /derived-agentic-metrics on
+    // mount, the chart must not sit on its loading skeleton.
+    interceptDerivedMetrics();
     cy.visit('/inference?i_seq=agentic-traces', {
       onBeforeLoad(win) {
         win.localStorage.setItem('inferencex-star-modal-dismissed', String(Date.now()));
@@ -165,6 +171,21 @@ describe('X-Axis Mode Toggle (inference chart)', () => {
     cy.get('[data-testid="chart-figure"] h2').should('contain.text', 'Interactivity');
   });
 
+  it('shows the selected percentile in the Interactivity axis label', () => {
+    // Explicitly select the mode — do not rely on the agentic default mode.
+    cy.get('[data-testid="x-axis-mode-interactivity"]').click();
+    cy.get('[data-testid="x-axis-mode-interactivity"]').should(
+      'have.attr',
+      'aria-selected',
+      'true',
+    );
+    // Agentic plots percentile fields (p90_intvty), so the axis label carries it.
+    cy.get('[data-testid="chart-figure"] svg').should(
+      'contain.text',
+      'P90 Interactivity (tok/s/user)',
+    );
+  });
+
   it('defaults to parallelism labels without line labels for the agentic view', () => {
     cy.get('#scatter-parallelism-labels').should('have.attr', 'data-state', 'checked');
     cy.get('#scatter-point-labels').should('have.attr', 'data-state', 'checked');
@@ -195,6 +216,7 @@ describe('X-Axis Mode Toggle (inference chart)', () => {
     cy.get('[data-testid="x-axis-mode-e2e"]').click();
     cy.get('[data-testid="x-axis-mode-e2e"]').should('have.attr', 'aria-selected', 'true');
     cy.get('[data-testid="chart-figure"] h2').should('contain.text', 'End-to-end Latency');
+    cy.get('[data-testid="chart-figure"] svg').should('contain.text', 'P90 End-to-end Latency (s)');
   });
 
   it('switches to request-level normalized E2E at 400 output tokens', () => {
@@ -231,6 +253,11 @@ describe('X-Axis Mode Toggle (inference chart)', () => {
       'true',
     );
     cy.get('[data-testid="chart-figure"] h2').should('contain.text', 'Interactivity');
+    // Percentile was switched to p75 in the previous test — the axis label follows.
+    cy.get('[data-testid="chart-figure"] svg').should(
+      'contain.text',
+      'P75 Interactivity (tok/s/user)',
+    );
   });
 });
 
@@ -246,6 +273,9 @@ describe('Default scenario', () => {
     });
     cy.get('[data-testid="scenario-selector"]').should('contain.text', '8K / 1K');
     cy.get('[data-testid="chart-figure"]').should('have.length.at.least', 1);
+    // Fixed-seq plots the mean field — no percentile prefix on the axis label.
+    cy.get('[data-testid="chart-figure"] svg').should('contain.text', 'Interactivity (tok/s/user)');
+    cy.get('[data-testid="chart-figure"] svg').should('not.contain.text', 'P90 Interactivity');
   });
 });
 
@@ -340,6 +370,9 @@ const interceptAgenticDataWithOverlay = () => {
 describe('X-Axis Mode Toggle — overlay path (finding #8 regression guard)', () => {
   before(() => {
     interceptAgenticDataWithOverlay();
+    // Same as the main suite: keep the visit independent of the agentic default
+    // x-axis mode (a derived default fetches /derived-agentic-metrics on mount).
+    interceptDerivedMetrics();
     cy.visit(`/inference?unofficialrun=${OVERLAY_RUN_ID}&i_seq=agentic-traces`, {
       onBeforeLoad(win) {
         win.localStorage.setItem('inferencex-star-modal-dismissed', String(Date.now()));
@@ -352,10 +385,22 @@ describe('X-Axis Mode Toggle — overlay path (finding #8 regression guard)', ()
   });
 
   it('shows overlay (unofficial-run) watermark SVG when an overlay is loaded', () => {
+    // Explicitly select Interactivity — do not rely on the agentic default mode.
+    cy.get('[data-testid="x-axis-mode-interactivity"]').click();
+    cy.get('[data-testid="x-axis-mode-interactivity"]').should(
+      'have.attr',
+      'aria-selected',
+      'true',
+    );
     // The unofficial-run pattern watermark appears when isUnofficialRun is true.
     cy.get('[data-testid="inference-chart-display"] svg pattern[id^="unofficial-pattern-"]').should(
       'exist',
     );
+    // Overlay shares the chartDefinition label — the percentile prefix applies here too.
+    cy.get('[data-testid="chart-figure"] svg').should(
+      'contain.text',
+      'P90 Interactivity (tok/s/user)',
+    );
   });
 
   it('switches to ttft x-axis mode and renders SVG with overlay points', () => {
diff --git a/packages/app/src/components/inference/hooks/useChartData.test.ts b/packages/app/src/components/inference/hooks/useChartData.test.ts
index c4998add0..fe0452129 100644
--- a/packages/app/src/components/inference/hooks/useChartData.test.ts
+++ b/packages/app/src/components/inference/hooks/useChartData.test.ts
@@ -1,6 +1,7 @@
 import { describe, it, expect } from 'vitest';
 
 import {
+  applyAgenticPercentileToXLabel,
   buildComparisonDates,
   dedupeRowsToLatestPerConfig,
   filterByGPU,
@@ -139,6 +140,54 @@ describe('filterByGPU', () => {
   });
 });
 
+describe('applyAgenticPercentileToXLabel', () => {
+  it('prefixes the percentile when the interactivity label has no statistic word', () => {
+    expect(applyAgenticPercentileToXLabel('Interactivity (tok/s/user)', 'P90')).toBe(
+      'P90 Interactivity (tok/s/user)',
+    );
+  });
+
+  it('prefixes the percentile when the e2e latency label has no statistic word', () => {
+    expect(applyAgenticPercentileToXLabel('End-to-end Latency (s)', 'P90')).toBe(
+      'P90 End-to-end Latency (s)',
+    );
+  });
+
+  it('follows the selected percentile (p75)', () => {
+    expect(applyAgenticPercentileToXLabel('Interactivity (tok/s/user)', 'P75')).toBe(
+      'P75 Interactivity (tok/s/user)',
+    );
+  });
+
+  it('replaces an existing percentile prefix instead of doubling it', () => {
+    expect(applyAgenticPercentileToXLabel('P90 Time To First Token (s)', 'P75')).toBe(
+      'P75 Time To First Token (s)',
+    );
+  });
+
+  it('replaces Median/Mean statistic prefixes', () => {
+    expect(applyAgenticPercentileToXLabel('Median Time To First Token (s)', 'P90')).toBe(
+      'P90 Time To First Token (s)',
+    );
+    expect(applyAgenticPercentileToXLabel('Mean Interactivity (tok/s/user)', 'P75')).toBe(
+      'P75 Interactivity (tok/s/user)',
+    );
+  });
+
+  it('is a no-op when the label already carries the selected percentile', () => {
+    expect(applyAgenticPercentileToXLabel('P90 Interactivity (tok/s/user)', 'P90')).toBe(
+      'P90 Interactivity (tok/s/user)',
+    );
+  });
+
+  it('does not touch mid-label statistic words', () => {
+    // Only a LEADING statistic word is a prefix; words later in the label are content.
+    expect(applyAgenticPercentileToXLabel('Normalized E2E @ 400 output tokens (s)', 'P90')).toBe(
+      'P90 Normalized E2E @ 400 output tokens (s)',
+    );
+  });
+});
+
 describe('flipRooflineDirection', () => {
   it('flips left/right while preserving upper/lower', () => {
     expect(flipRooflineDirection('upper_left')).toBe('upper_right');
diff --git a/packages/app/src/components/inference/hooks/useChartData.ts b/packages/app/src/components/inference/hooks/useChartData.ts
index 197fcd6b2..c125e9e9e 100644
--- a/packages/app/src/components/inference/hooks/useChartData.ts
+++ b/packages/app/src/components/inference/hooks/useChartData.ts
@@ -139,6 +139,25 @@ export function flipRooflineDirection(dir: RooflineDirection): RooflineDirection
   return FLIP_MAP[dir];
 }
 
+// Statistic words that may already prefix an x-axis label (from chart config
+// or the TTFT override label). Trailing whitespace is consumed so a replace
+// never doubles the separator space.
+const X_LABEL_STAT_PREFIX_RE = /^(?:Median|Mean|P75|P90|P95|P99(?:\.9)?)\b\s*/iu;
+
+/**
+ * Agentic sequences plot percentile fields (e.g. `p90_intvty`, `p75_e2el`),
+ * so the x-axis label must carry the selected percentile. Replaces an
+ * existing leading statistic word (e.g. the TTFT override's "P90 Time To
+ * First Token (s)") or prefixes the percentile when the configured label has
+ * none (e.g. "Interactivity (tok/s/user)" → "P90 Interactivity (tok/s/user)").
+ * Only call for agentic sequences — fixed-seq labels must stay untouched.
+ */
+export function applyAgenticPercentileToXLabel(label: string, pctlWord: string): string {
+  return X_LABEL_STAT_PREFIX_RE.test(label)
+    ? label.replace(X_LABEL_STAT_PREFIX_RE, `${pctlWord} `)
+    : `${pctlWord} ${label}`;
+}
+
 /** The dedup key fields a chart series is identified by. */
 interface DedupeRow {
   hardware: string;
@@ -409,13 +428,15 @@ export function useChartData(
 
         // Agentic: relabel to the chosen percentile (the resolver already
         // rewrote the field) — xAxisLabel still carries the raw chartDef
-        // prefix. The chart heading ("vs. <latency>") is also rewritten so the
-        // title above the plot reflects what's drawn.
+        // prefix (or none: the base Interactivity / E2E Latency config labels
+        // have no statistic word, so the percentile is prefixed). The chart
+        // heading ("vs. <latency>") is also rewritten so the title above the
+        // plot reflects what's drawn.
         const headingKey = `${selectedYAxisMetric}_heading` as keyof ChartDefinition;
         let chartHeading = (chartDef[headingKey] as string) || chartDef.heading;
         if (isAgentic) {
           const pctlWord = selectedPercentile.toUpperCase();
-          xAxisLabel = xAxisLabel.replace(/^(?:Median|Mean|P75|P90|P95|P99(?:\.9)?)\b/iu, pctlWord);
+          xAxisLabel = applyAgenticPercentileToXLabel(xAxisLabel, pctlWord);
           chartHeading = chartHeading.replace(
             /^(?<vsPrefix>vs\.\s+)(?:(?:Median|Mean|P75|P90|P95|P99(?:\.9)?)\s+)?/iu,
             `$1${pctlWord} `,