diff --git a/src/ask/ask.ts b/src/ask/ask.ts
index 655fe69f..939d99fd 100644
--- a/src/ask/ask.ts
+++ b/src/ask/ask.ts
@@ -17,7 +17,7 @@ import { existsSync, readdirSync, readFileSync } from "node:fs";
 import { join, resolve } from "node:path";
 import { matter } from "../util/front-matter.js";
 import { contextDirFor } from "../context/node-file.js";
-import { withSavings, savingsFor, savingsTurnNudge, type Savings } from "../context/savings.js";
+import { withSavings, savingsFor, savingsTurnNudge, groupDigits, type Savings } from "../context/savings.js";
 import { loadGraphCached, loadAskIndexCached } from "../graph/load.js";
 import {
   assertPrefixIndexed,
@@ -1553,9 +1553,9 @@ function askSavingsLine(r: AskResult, body: string): string {
   const saved = base - pack;
   const pct = Math.round((saved / base) * 100);
   return (
-    `${tag()} tokens saved ≈ ${saved.toLocaleString()} (${pct}%) — this pack ≈ ` +
-    `${pack.toLocaleString()} tok vs reading the ${r.saved.files} source file(s) whole ≈ ` +
-    `${base.toLocaleString()} tok. Estimate (baseline = those files read in full).` +
+    `${tag()} tokens saved ≈ ${groupDigits(saved)} (${pct}%) — this pack ≈ ` +
+    `${groupDigits(pack)} tok vs reading the ${r.saved.files} source file(s) whole ≈ ` +
+    `${groupDigits(base)} tok. Estimate (baseline = those files read in full).` +
     savingsTurnNudge(saved)
   );
 }
diff --git a/src/claude/format.ts b/src/claude/format.ts
index 211262d6..55254f6a 100644
--- a/src/claude/format.ts
+++ b/src/claude/format.ts
@@ -6,6 +6,7 @@ import type { GraphV1, EdgeV1 } from '../graph/types.js';
 // question in both places, and one set of calibrated numbers beats two.
 import { HIGH_FLOOR, STRONG_FLOOR } from '../ask/fuse.js';
 import { dollarsSaved, formatDollars } from '../context/price.js';
+import { groupDigits } from '../context/savings.js';
 import { brand, cmd, tag } from '../brand.js';
 import { formatNoteHits, learningCredit, learningSavingsLine, PR_SPEEDUP, sectionLead, type Note, type NoteHit } from '../notes/notes.js';
 
@@ -43,7 +44,7 @@ export function renderStatusline(
     // stands alone rather than carrying a rate nobody measured.
     const usd = dollarsSaved(saved, session?.inputCostMicros, session?.inputTokensBilled);
     const money = usd === null ? '' : ` · ~${formatDollars(usd)}`;
-    top.push(C.indigo(`~${saved.toLocaleString()} tok saved${money}`));
+    top.push(C.indigo(`~${groupDigits(saved)} tok saved${money}`));
   }
 
   const bottom: string[] = [];
@@ -167,9 +168,9 @@ export function formatRetrieval(ask: AskJson, cap = 5): string | null {
   const base = tokensOf(ask.saved!.baselineChars);
   const pct = Math.round((saved / base) * 100);
   return (
-    `${body}\n${tag()} tokens saved ≈ ${saved.toLocaleString()} (${pct}%); this pack ≈ ` +
-    `${tokensOf(body.length).toLocaleString()} tok vs reading the ${ask.saved!.files} file(s) whole ≈ ` +
-    `${base.toLocaleString()} tok (estimate).`
+    `${body}\n${tag()} tokens saved ≈ ${groupDigits(saved)} (${pct}%); this pack ≈ ` +
+    `${groupDigits(tokensOf(body.length))} tok vs reading the ${ask.saved!.files} file(s) whole ≈ ` +
+    `${groupDigits(base)} tok (estimate).`
   );
 }
 
diff --git a/src/claude/session-metrics.ts b/src/claude/session-metrics.ts
index 3e970024..272f0861 100644
--- a/src/claude/session-metrics.ts
+++ b/src/claude/session-metrics.ts
@@ -31,7 +31,7 @@
  */
 import { statSync } from 'node:fs';
 import { join } from 'node:path';
-import { sumSavingsFooters } from '../context/savings.js';
+import { groupDigits, sumSavingsFooters } from '../context/savings.js';
 import { dollarsSaved, formatDollars } from '../context/price.js';
 import { readSession, writeSession, sessionDir, listSessionIds, type SessionState } from './state.js';
 import type { AgentHost } from '../telemetry/contract.js';
@@ -202,7 +202,7 @@ export function formatSessionStats(s: SessionSummary | null): string {
     `  graft reads:   ${graft}`,
     `  source reads:  ${source}   (Read / Grep / Glob)`,
     `  mix:           ${mix}`,
-    `  tokens saved:  ~${saved.toLocaleString()}`,
+    `  tokens saved:  ~${groupDigits(saved)}`,
   ];
   // Omitted, not zeroed, when no turn has been billed yet: a host whose hooks
   // name no transcript can't know what a token costs here, and a made-up rate
diff --git a/src/context/savings.ts b/src/context/savings.ts
index 75c3daf9..d6ef86a4 100644
--- a/src/context/savings.ts
+++ b/src/context/savings.ts
@@ -107,6 +107,25 @@ export function savingsTurnNudge(savedTokens: number): string {
   );
 }
 
+/**
+ * Digits grouped for display, pinned to en-US.
+ *
+ * Not a style choice: the `[graft] tokens saved ≈ N` line below is read back by
+ * {@link sumSavingsFooters}, whose regex knows `,` and nothing else. Rendered
+ * with the machine's locale instead, a de-DE or tr-TR box wrote `1.990` and
+ * graft parsed its own footer as `1` — every savings total downstream, and the
+ * dollar value beside it, off by a factor of a thousand (#338). fr-FR and ru-RU
+ * group with a narrow no-break space and lost it the same way.
+ *
+ * Every number graft renders goes through here, not only the parsed one: a
+ * statusline that grouped differently from the footer right above it would be
+ * its own small bug. `src/cli-epilogue.ts` pins the same way, for the same
+ * reason.
+ */
+export function groupDigits(n: number): string {
+  return n.toLocaleString('en-US');
+}
+
 /** The one-line savings estimate for a command's text output, so the agent gets
  * the number for free — no extra tool call. `body` is the exact rendered output
  * the agent reads (the pack). Returns "" when there's nothing honest to claim:
@@ -120,9 +139,9 @@ export function savingsLine(body: string, saved: Savings | undefined): string {
   const delta = base - pack;
   const pct = Math.round((delta / base) * 100);
   return (
-    `${tag()} tokens saved ≈ ${delta.toLocaleString()} (${pct}%) — this output ≈ ` +
-    `${pack.toLocaleString()} tok vs reading the ${saved.files} file(s) it covers whole ≈ ` +
-    `${base.toLocaleString()} tok (estimate).` +
+    `${tag()} tokens saved ≈ ${groupDigits(delta)} (${pct}%) — this output ≈ ` +
+    `${groupDigits(pack)} tok vs reading the ${saved.files} file(s) it covers whole ≈ ` +
+    `${groupDigits(base)} tok (estimate).` +
     savingsTurnNudge(delta)
   );
 }
diff --git a/test/savings-locale.test.ts b/test/savings-locale.test.ts
new file mode 100644
index 00000000..0e944061
--- /dev/null
+++ b/test/savings-locale.test.ts
@@ -0,0 +1,67 @@
+/**
+ * #338: graft rendered its savings footer with the machine's locale and read it
+ * back with a regex that knows only `,`, so a `de-DE`/`tr-TR` box wrote `1.990`
+ * and parsed it as `1`.
+ *
+ * A process cannot change its own ambient locale — Node takes it from the
+ * environment on posix and from the OS on Windows — so these tests move the
+ * *default* instead: `toLocaleString()` with no argument answers the way a
+ * `.`-grouping locale would, while calls that name a locale are left alone.
+ * That is exactly the difference the fix turns on, and it behaves identically on
+ * an en-US CI runner, which is why CI never caught the original.
+ */
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { savingsLine, sumSavingsFooters } from '../src/context/savings.js';
+import { formatSessionStats } from '../src/claude/session-metrics.js';
+import { formatAsk, type AskResult } from '../src/ask/ask.js';
+
+/** Run `fn` on a machine whose default locale groups thousands with `locale`'s
+ *  separator. Restores the real method even if `fn` throws. */
+function withDefaultLocale<T>(locale: string, fn: () => T): T {
+  const real = Number.prototype.toLocaleString;
+  Number.prototype.toLocaleString = function (
+    this: number,
+    locales?: string | string[],
+    options?: Intl.NumberFormatOptions,
+  ): string {
+    return real.call(this, locales ?? locale, options);
+  };
+  try {
+    return fn();
+  } finally {
+    Number.prototype.toLocaleString = real;
+  }
+}
+
+test('#338: the savings footer round-trips on a machine that is not en-US', () => {
+  // Sanity: the stand-in really does change what an unqualified call renders,
+  // or the rest of this file would pass for the wrong reason.
+  assert.equal(withDefaultLocale('de-DE', () => (1990).toLocaleString()), '1.990');
+
+  const line = withDefaultLocale('de-DE', () => savingsLine('x'.repeat(40), { files: 2, baselineChars: 8000 }));
+  assert.match(line, /tokens saved ≈ 1,990/, 'grouped for the reader, not for the machine');
+  assert.equal(sumSavingsFooters(line), 1990, 'and read back whole, not as its first group');
+});
+
+test('#338: what graft displays groups the same way as what it parses', () => {
+  const out = withDefaultLocale('de-DE', () =>
+    formatSessionStats({ id: 'abc', perAgentQuery: {}, graftReads: 8, sourceReads: 2, savedTokens: 12345 }),
+  );
+  assert.match(out, /tokens saved:\s+~12,345/);
+});
+
+test('#338: `graft ask` writes a footer its own reader can parse, on a machine that is not en-US', () => {
+  // The third writer of the parsed line, and the one no other test renders: ask.ts
+  // has its own wording of the footer, so a revert there would bring the bug back
+  // for every `graft ask` while the other two writers stayed green.
+  const result: AskResult = {
+    query: 'probe',
+    mode: 'lexical',
+    hits: [{ kind: 'symbol', title: 'probe', pointer: 'src/probe.ts:L1-L2', snippet: '', score: 1 }],
+    saved: { files: 3, baselineChars: 8000 }, // ≈ 2000 tok against a pack of a few dozen
+  };
+  const out = withDefaultLocale('de-DE', () => formatAsk(result));
+  assert.match(out, /tokens saved ≈ \d{1,3},\d{3} /, 'grouped for the reader, not for the machine');
+  assert.ok(sumSavingsFooters(out) >= 1000, `read back whole, not as its first group (got ${sumSavingsFooters(out)})`);
+});
diff --git a/test/savings.test.ts b/test/savings.test.ts
index 4a9596bf..4c862e57 100644
--- a/test/savings.test.ts
+++ b/test/savings.test.ts
@@ -4,7 +4,7 @@
  */
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { savingsFor, savingsLine, withSavings, toTokens, setInputRate } from '../src/context/savings.js';
+import { savingsFor, savingsLine, withSavings, toTokens, setInputRate, groupDigits } from '../src/context/savings.js';
 import { hasSavingsTally } from '../src/claude/tally.js';
 import type { GraphV1, NodeV1 } from '../src/graph/types.js';
 
@@ -49,7 +49,10 @@ test('savingsLine: reports saved tokens and percent when the output is smaller',
   assert.match(footer, /tokens saved ≈ [\d,]+ \(\d+%\)/);
   assert.match(footer, /2 file\(s\)/);
   const base = toTokens(8000);
-  assert.ok(footer.includes((base - toTokens(body.length)).toLocaleString()));
+  // Through the same pinned formatter the footer uses: rendered with the test
+  // machine's locale instead, this asserted `1.990` against a footer that says
+  // `1,990` — the mirror image of #338, and just as invisible on an en-US runner.
+  assert.ok(footer.includes(groupDigits(base - toTokens(body.length))));
   // The nudge rides along so the agent reports the turn total without SKILL.md.
   assert.match(footer, /end of your reply/i);
   assert.match(footer, /graft saved ~N tokens this turn/);