@@ -7,9 +7,43 @@ import {
   formatHourShort,
   formatPercent,
   formatRelativeHourShort,
+  formatTokens,
   makeWindow,
 } from "./usageFormat.ts";
 
+describe("formatTokens", () => {
+  it.each([
+    [999_499, "999K"],
+    [999_500, "1M"],
+    [999_999, "1M"],
+    [999_499_999, "999M"],
+    [999_500_000, "1B"],
+    [999_999_999, "1B"],
+    [999_499_999_999, "999B"],
+    [999_500_000_000, "1T"],
+    [999_999_999_999, "1T"],
+    [-999_499, "-999K"],
+    [-999_500, "-1M"],
+    [-999_500_000, "-1B"],
+    [-999_500_000_000, "-1T"],
+  ])("uses the rounded unit for %s tokens", (value, expected) => {
+    expect(formatTokens(value)).toBe(expected);
+  });
+
+  it.each([
+    [0, "0"],
+    [804, "804"],
+    [999, "999"],
+    [1_000, "1K"],
+    [1_500_000, "1.50M"],
+    [76_700_000, "76.7M"],
+    [19_900_000_000, "19.9B"],
+    [999_500_000_000_000, "1000T"],
+  ])("preserves existing formatting for %s tokens", (value, expected) => {
+    expect(formatTokens(value)).toBe(expected);
+  });
+});
+
 describe("formatPercent", () => {
   it("distinguishes a small positive share from zero", () => {
     expect(formatPercent(0)).toBe("0.0%");
 
@@ -22,9 +22,10 @@ export function formatCount(value: number): string {
 
 export function formatTokens(value: number): string {
   const abs = Math.abs(value);
-  if (abs >= 1e12) return `${trim(value / 1e12)}T`;
-  if (abs >= 1e9) return `${trim(value / 1e9)}B`;
-  if (abs >= 1e6) return `${trim(value / 1e6)}M`;
+  // Choose the next suffix when three-digit rounding would otherwise produce 1000.
+  if (abs >= 999_500_000_000) return `${trim(value / 1e12)}T`;
+  if (abs >= 999_500_000) return `${trim(value / 1e9)}B`;
+  if (abs >= 999_500) return `${trim(value / 1e6)}M`;
   if (abs >= 1e3) return `${trim(value / 1e3)}K`;
   return INTEGER.format(Math.round(value));
 }