Fix Vitest 5 bench No Longer Top-Level Export

Why the top-level bench import stops working

Vitest’s own migration guide states this plainly under “Benchmarking API Rewrite”:

bench is no longer a top-level import from vitest; it is a test-context fixture accessed from inside a regular test().

That’s a structural change, not a rename. The old form:

import { bench } from "vitest";

bench("sort", () => {
  [3, 1, 2].sort();
});

no longer resolves to a working benchmark call in Vitest 5, because vitest stops exporting a bench symbol at the module level at all. Exactly how that surfaces depends on your bundler and TypeScript setup: some configs throw at import time, others fail type-checking first, and a few just silently run nothing because bench resolves to undefined. Vitest’s guide doesn’t publish one canonical error string for this case, so treat the exact wording you see as environment-specific rather than a fixed message to search for. The mechanical cause is the same either way: bench isn’t there to import anymore.

The guide also confirms bench.skip, bench.only, and bench.todo are removed in the same rewrite. Any suite using those modifiers needs the same migration as a plain bench call.

What happens to benchmark.reporters, outputFile, compare, and outputJson

This is the part of the change that breaks a CI pipeline quietly instead of loudly. A benchmark suite that imports bench correctly can still fail to produce the output a workflow expects, because four benchmark.* config options are removed entirely in the same rewrite, not renamed:

• benchmark.reporters and benchmark.outputFile are gone. The migration guide says that output now ships through the standard reporter pipeline instead of a dedicated benchmark reporter, so there’s no separate config to point at a custom output stream anymore.
• benchmark.compare and the matching --compare CLI flag are removed, with no direct 1:1 replacement documented.
• benchmark.outputJson and the --outputJson CLI flag are removed. The guide’s replacement is --reporter=json --outputFile=<path>, run through Vitest’s general reporter system instead of a benchmark-specific option.

None of these throw an import error the way the bench removal does. A vitest.config.ts that still sets benchmark.compare just has that setting silently ignored, so the first sign of trouble is usually a CI step that expects a comparison artifact or a JSON file and doesn’t get one.

Fix it: move bench into the test context fixture

Rewrite each benchmark to destructure bench from the test() callback’s context object, call it, then call .run() on the result:

import { bench } from "vitest"; // BROKEN: no longer exported at module scope

bench("sort", () => {
  [3, 1, 2].sort();
});

import { test } from "vitest";

test("sort", async ({ bench }) => {
  // FIXED: bench is a fixture on the test context now, and .run() is required
  await bench("sort", () => {
    [3, 1, 2].sort();
  }).run();
});

The .run() call is not optional decoration. Without it, bench(...) just constructs the benchmark and returns without ever executing it, so a half-migrated call site can look correct while producing no timing data at all.

Confirmed version range

This is documented in Vitest’s own current migration guide, under “Benchmarking API Rewrite,” as an intentional Vitest 5 change, corroborated as in-window against the beta release available at research time (v5.0.0-beta.7). This repo’s own vitest.config.ts is pinned to vitest@^3.0.0 and doesn’t use the benchmarking API, so this specific removal wasn’t independently reproducible against this repo’s own build. Treat the mechanics above as documented behavior from Vitest’s primary source, not a first-party reproduction. Browse more posts like this in the Guides & Fixes archive.