diff --git a/benchmarks/compare-app.ts b/benchmarks/compare-app.ts
new file mode 100644
index 0000000..39ac7dd
--- /dev/null
+++ b/benchmarks/compare-app.ts
@@ -0,0 +1,101 @@
+import type { SuperJSONCtor } from './fixtures.js';
+import { isDevalue, prepare, runSteps, selectCases, type Case, type Op } from './suite.js';
+
+interface LibMeta {
+  id: string;
+  label: string;
+  url: string;
+  sha: string;
+  ref: string;
+  kind: string;
+  subject: string;
+}
+
+const $ = (id: string) => {
+  const el = document.getElementById(id);
+  if (!el) throw new Error(`missing #${id}`);
+
+  return el;
+};
+
+const params = new URLSearchParams(location.search);
+
+function calibrate() {
+  const start = performance.now();
+  let x = 0;
+  for (let i = 0; i < 3e7; i++) {
+    x = (x + (i & 7)) | 0;
+  }
+  (globalThis as { __sink?: number }).__sink = x;
+
+  return performance.now() - start;
+}
+
+/** null when the library can run the case, otherwise the first line of its error. */
+function refusal(Lib: SuperJSONCtor, c: Case): string | null {
+  try {
+    prepare(Lib, c)();
+
+    return null;
+  } catch (error) {
+    return (error as Error).message.split('\n')[0];
+  }
+}
+
+async function runCompare(opts: { filter: string; ops: Op[]; timeMs: number; throttle: number; series?: string; run?: string }) {
+  $('status').textContent = 'loading versions…';
+  const libs: LibMeta[] = await (await fetch('/api/compare/libs')).json();
+  const versions: SuperJSONCtor[] = await Promise.all(
+    libs.map(async l => (await import(/* @vite-ignore */ l.url)).default)
+  );
+  const selected = selectCases(opts.filter, opts.ops);
+  const calibrationMs = calibrate();
+  const started = performance.now();
+  const cases = [];
+  for (const [i, c] of selected.entries()) {
+    $('status').textContent = `${i + 1}/${selected.length} ${c.id}`;
+    const refused = versions.map(v => (isDevalue(v) ? refusal(v, c) : null));
+    const timed = versions.flatMap((_, k) => (refused[k] === null ? [k] : []));
+    const { bytes, results } = await runSteps(
+      timed.map(k => versions[k]),
+      0,
+      c,
+      { timeMs: opts.timeMs, minSampleMs: 25 }
+    );
+    const full = versions.map((_, k) => {
+      const at = timed.indexOf(k);
+      if (at < 0) {
+        return { ms: null, rme: null, samples: 0, identical: false, refused: refused[k] };
+      }
+
+      return { ...results[at], refused: null };
+    });
+    cases.push({ id: c.id, fixture: c.fixture.name, group: c.fixture.group, op: c.op, bytes, results: full });
+  }
+
+  const next = {
+    createdAt: new Date().toISOString(),
+    engine: navigator.userAgent,
+    throttle: opts.throttle,
+    calibrationMs,
+    crossOriginIsolated,
+    timeMs: opts.timeMs,
+    series: opts.series,
+    run: opts.run,
+    steps: libs.map(l => ({ id: l.id, sha: l.sha, ref: l.ref, kind: l.kind, subject: l.subject, body: '', parent: null, files: [], diff: '' })),
+    cases,
+  };
+  const saved = await (await fetch('/api/compare', { method: 'POST', body: JSON.stringify(next) })).json();
+  $('status').textContent = `done in ${((performance.now() - started) / 1000).toFixed(0)} s, saved as ${saved.name}`;
+}
+
+if (params.get('autorun') === '1') {
+  runCompare({
+    filter: params.get('filter') ?? '',
+    ops: (params.get('ops') ?? 'stringify,parse,serialize,deserialize').split(',').map(s => s.trim()) as Op[],
+    timeMs: Number(params.get('time') ?? 6000),
+    throttle: Number(params.get('throttle') ?? 1),
+    series: params.get('series') ?? undefined,
+    run: params.get('run') ?? undefined,
+  });
+}
diff --git a/benchmarks/compare.html b/benchmarks/compare.html
new file mode 100644
index 0000000..cc292ae
--- /dev/null
+++ b/benchmarks/compare.html
@@ -0,0 +1,16 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <title>superjson vs devalue</title>
+    <style>
+      body { font: 14px/1.45 ui-sans-serif, system-ui, sans-serif; margin: 24px; }
+      pre { white-space: pre-wrap; }
+    </style>
+  </head>
+  <body>
+    <h1>superjson (base and PR) against devalue, interleaved</h1>
+    <pre id="status">loading…</pre>
+    <script type="module" src="/compare.js"></script>
+  </body>
+</html>
diff --git a/benchmarks/devalue-features.ts b/benchmarks/devalue-features.ts
new file mode 100644
index 0000000..67758b5
--- /dev/null
+++ b/benchmarks/devalue-features.ts
@@ -0,0 +1,83 @@
+/**
+ * Round-trips one value per feature through superjson (current src) and devalue, and prints ok, lossy or throws.
+ * Run: bun benchmarks/devalue-features.ts
+ */
+import { isDeepStrictEqual } from 'node:util';
+import { currentEntry, writeBundle } from './build.js';
+import { parse, stringify } from 'devalue';
+
+const SuperJSON = (await import(await writeBundle('probe-features', currentEntry, 'bun'))).default;
+
+class Point {
+  constructor(public x: number, public y: number) {}
+}
+
+const cyclic: Record<string, unknown> = { name: 'loop' };
+cyclic.self = cyclic;
+const shared = { id: 1 };
+
+const cases: [string, unknown][] = [
+  ['Date', new Date('2026-10-22T10:00:00.000Z')],
+  ['undefined in object and array', { a: undefined, b: [undefined, 1] }],
+  ['NaN, Infinity, -0', { n: NaN, i: Infinity, z: -0 }],
+  ['BigInt', { big: 12345678901234567890n }],
+  ['Map and Set', { m: new Map([[1, 'a']]), s: new Set([1, 2]) }],
+  ['RegExp', /ab+c/gi],
+  ['URL', new URL('https://example.com/a?b=1')],
+  ['URLSearchParams', new URLSearchParams('a=1&b=2')],
+  ['ArrayBuffer', new ArrayBuffer(4)],
+  ['Uint8Array and Float64Array', { u: new Uint8Array([1, 2]), f: new Float64Array([1.5]) }],
+  ['BigInt64Array', new BigInt64Array([1n, -1n])],
+  ['Error with message', new Error('boom')],
+  ['Error with cause', new Error('outer', { cause: new Error('inner') })],
+  ['class instance (not registered)', new Point(1, 2)],
+  ['symbol (unregistered)', { s: Symbol.for('app.key') }],
+  ['cycle', cyclic],
+  ['shared references', { a: shared, b: shared }],
+  ['own __proto__ key', JSON.parse('{"__proto__": {"polluted": true}, "x": 1}')],
+  ['sparse array', [1, , 3]],
+  ['Promise', Promise.resolve(1)],
+  ['Temporal.Instant', globalThis.Temporal ? globalThis.Temporal.Instant.from('2026-10-22T10:00:00Z') : 'no Temporal in this runtime'],
+];
+
+const rows: string[] = [];
+for (const [name, value] of cases) {
+  let sj: string;
+  try {
+    const sjs = new SuperJSON({ dedupe: true });
+    const back = sjs.parse(sjs.stringify(value));
+    sj = isDeepStrictEqual(back, value) ? 'ok' : 'lossy';
+  } catch (error) {
+    sj = `throws: ${(error as Error).message.split('\n')[0].slice(0, 70)}`;
+  }
+  let dv: string;
+  try {
+    const back = parse(stringify(value));
+    dv = isDeepStrictEqual(back, value) ? 'ok' : 'lossy';
+  } catch (error) {
+    dv = `throws: ${(error as Error).message.split('\n')[0].slice(0, 70)}`;
+  }
+  rows.push(`${name}\t${sj}\t${dv}`);
+}
+
+const custom = { p: new Point(3, 4) };
+let dvCustom: string;
+try {
+  const text = stringify(custom, { Point: (v: unknown) => v instanceof Point && [v.x, v.y] });
+  const back = parse(text, { Point: ([x, y]: number[]) => new Point(x, y) });
+  dvCustom = isDeepStrictEqual(back, custom) ? 'ok (reducer and reviver)' : 'lossy';
+} catch (error) {
+  dvCustom = `throws: ${(error as Error).message.split('\n')[0].slice(0, 70)}`;
+}
+let sjCustom: string;
+try {
+  const sjs = new SuperJSON();
+  sjs.registerClass(Point);
+  const back = sjs.parse(sjs.stringify(custom));
+  sjCustom = isDeepStrictEqual(back, custom) ? 'ok (registerClass)' : 'lossy';
+} catch (error) {
+  sjCustom = `throws: ${(error as Error).message.split('\n')[0].slice(0, 70)}`;
+}
+rows.push(`custom class with registration (superjson) or reducer and reviver (devalue)\t${sjCustom}\t${dvCustom}`);
+
+console.log(rows.join('\n'));
diff --git a/benchmarks/devalue-lib.ts b/benchmarks/devalue-lib.ts
new file mode 100644
index 0000000..9993f30
--- /dev/null
+++ b/benchmarks/devalue-lib.ts
@@ -0,0 +1,27 @@
+import { parse, stringify } from 'devalue';
+
+/**
+ * devalue behind the SuperJSON call shape, so the harness can time it next to superjson.
+ * devalue has no class, symbol or custom-type registry, so the harness skips fixture setup for it.
+ */
+export default class DevalueCodec {
+  static readonly format = 'devalue';
+
+  constructor(_options?: { dedupe?: boolean }) {}
+
+  serialize(value: unknown) {
+    return { json: stringify(value) };
+  }
+
+  deserialize(payload: { json: string }) {
+    return parse(payload.json);
+  }
+
+  stringify(value: unknown) {
+    return stringify(value);
+  }
+
+  parse(text: string) {
+    return parse(text);
+  }
+}
diff --git a/benchmarks/ledger-run.ts b/benchmarks/ledger-run.ts
index 310f9ff..7f32643 100644
--- a/benchmarks/ledger-run.ts
+++ b/benchmarks/ledger-run.ts
@@ -18,6 +18,7 @@ const { values } = parseArgs({
     time: { type: 'string', default: '6000' },
     headed: { type: 'boolean', default: false },
     repeat: { type: 'string', default: '1' },
+    page: { type: 'string', default: '/steps' },
   },
 });
 
@@ -103,7 +104,7 @@ async function runOnce(run: number): Promise<any> {
     `# ${values.browser}: fixed loop ${unthrottled.toFixed(0)} ms unthrottled, ${throttled.toFixed(0)} ms at rate ${rate} (${(throttled / unthrottled).toFixed(2)}× measured)`
   );
 
-  const url = new URL('/steps', server.url);
+  const url = new URL(values.page!, server.url);
   url.search = new URLSearchParams({
     autorun: '1',
     throttle: String(rate),
@@ -138,8 +139,9 @@ for (const c of cases) {
   console.error(`\n${c.fixture} · ${c.op}`);
   steps.forEach((s: any, i: number) => {
     const r = c.results[i];
+    const shown = r.ms === null ? `${'refused'.padStart(8)}   ` : `${r.ms.toFixed(2).padStart(8)} ms  ${(c.results[base].ms / r.ms).toFixed(2)}×`;
     console.error(
-      `  ${String(i).padStart(2)} ${s.kind.padEnd(9)} ${s.sha} ${r.ms.toFixed(2).padStart(8)} ms  ${(c.results[base].ms / r.ms).toFixed(2)}×${r.identical ? '' : '  ✗ OUTPUT DIFFERS'}  ${s.subject.slice(0, 70)}`
+      `  ${String(i).padStart(2)} ${s.kind.padEnd(9)} ${s.sha} ${shown}${r.identical ? '' : '  ✗ OUTPUT DIFFERS'}  ${s.subject.slice(0, 70)}`
     );
   });
 }
diff --git a/benchmarks/server.ts b/benchmarks/server.ts
index 98e33cb..42c241c 100644
--- a/benchmarks/server.ts
+++ b/benchmarks/server.ts
@@ -26,6 +26,7 @@ export async function startServer({ port, baselineRef, onResults, onLedger }: Se
   const baseline = await ensureBaseline(baselineRef);
   const resultsDir = join(BENCH, '.results');
   const ledgersDir = join(resultsDir, 'ledgers');
+  const compareDir = join(resultsDir, 'compare');
   mkdirSync(ledgersDir, { recursive: true });
   const savedFile = async (dir: string, encoded: string) => {
     const name = basename(decodeURIComponent(encoded));
@@ -61,6 +62,37 @@ export async function startServer({ port, baselineRef, onResults, onLedger }: Se
             return new Response(Bun.file(join(BENCH, 'steps.html')), { headers });
           case '/steps.js':
             return js(await bundle(join(BENCH, 'steps-app.ts'), 'browser'));
+          case '/compare':
+            return new Response(Bun.file(join(BENCH, 'compare.html')), { headers });
+          case '/compare.js':
+            return js(await bundle(join(BENCH, 'compare-app.ts'), 'browser'));
+          case '/lib/devalue.js':
+            return js(await bundle(join(BENCH, 'devalue-lib.ts'), 'browser'));
+          case '/api/compare/libs': {
+            const ours = (await $`git -C ${ROOT} rev-parse perf/faster-serialize`.text()).trim();
+            const raw = (await $`git -C ${ROOT} rev-list -n 1 v2.2.3`.text()).trim();
+            const devalueVersion = JSON.parse(await Bun.file(join(ROOT, 'node_modules/devalue/package.json')).text()).version;
+
+            return Response.json(
+              [
+                { id: 'raw', label: 'superjson 2.2.3 (col-web)', url: `/lib/ref/${raw}.js`, sha: raw, ref: 'v2.2.3', kind: 'baseline', subject: 'superjson 2.2.3, the version col-web ships' },
+                { id: 'base', label: 'superjson origin/main', url: `/lib/ref/${baseline.sha}.js`, sha: baseline.sha, ref: baseline.ref, kind: 'reference', subject: 'superjson origin/main (2.2.5)' },
+                { id: 'ours', label: 'superjson PR #364', url: `/lib/ref/${ours}.js`, sha: ours, ref: 'perf/faster-serialize', kind: 'step', subject: 'superjson perf/faster-serialize (PR #364)' },
+                { id: 'devalue', label: `devalue ${devalueVersion}`, url: '/lib/devalue.js', sha: `devalue@${devalueVersion}`, ref: `npm devalue ${devalueVersion}`, kind: 'lib', subject: `devalue ${devalueVersion} through a SuperJSON-shaped adapter` },
+              ],
+              { headers }
+            );
+          }
+          case '/api/compare': {
+            const body = await req.json();
+            const stamp = new Date().toISOString().replace(/[:.]/g, '-');
+            const name = `${stamp}-x${body.throttle ?? 1}.json`;
+            mkdirSync(compareDir, { recursive: true });
+            await Bun.write(join(compareDir, name), JSON.stringify(body));
+            onLedger?.(body);
+
+            return Response.json({ ok: true, name }, { headers });
+          }
           case '/api/steps':
             return Response.json(await resolveSteps(), { headers });
           case '/api/ledgers': {
diff --git a/benchmarks/suite.ts b/benchmarks/suite.ts
index 6615faf..8662ebe 100644
--- a/benchmarks/suite.ts
+++ b/benchmarks/suite.ts
@@ -45,13 +45,31 @@ const dataOf = (fixture: Fixture) => {
   return dataCache.get(fixture);
 };
 
+/** devalue exposes `format = 'devalue'` and has no registries, so it skips fixture setup and fidelity is checked instead of bytes. */
+export const isDevalue = (Lib: SuperJSONCtor): boolean => 'format' in Lib && Lib.format === 'devalue';
+
 const instance = (Lib: SuperJSONCtor, fixture: Fixture) => {
   const sj = new Lib({ dedupe: fixture.dedupe });
-  fixture.setup?.(sj);
+  if (!isDevalue(Lib)) {
+    fixture.setup?.(sj);
+  }
 
   return sj;
 };
 
+/** devalue's text differs from superjson's, so it counts as identical when its round trip keeps superjson's canonical form. */
+export function fidelityMatches(reference: SuperJSONCtor, lib: SuperJSONCtor, c: Case): boolean {
+  const ref = instance(reference, c.fixture);
+  const sj = instance(lib, c.fixture);
+  const data = dataOf(c.fixture) as any;
+  const canon = (v: any) => JSON.stringify(ref.serialize(v), stableBigint);
+  try {
+    return canon(sj.parse(sj.stringify(data))) === canon(data);
+  } catch {
+    return false;
+  }
+}
+
 /** Returns the function to time. All inputs are prepared up front so only the op itself is measured. */
 export function prepare(Lib: SuperJSONCtor, c: Case): () => unknown {
   const sj = instance(Lib, c.fixture);
@@ -215,7 +233,9 @@ export async function runSteps(
 ): Promise<{ bytes: number; results: StepResult[] }> {
   const reference = versions[referenceIndex];
   const expected = outputSignature(reference, reference, c);
-  const identical = versions.map(v => outputSignature(reference, v, c) === expected);
+  const identical = versions.map(v =>
+    isDevalue(v) ? fidelityMatches(reference, v, c) : outputSignature(reference, v, c) === expected
+  );
   const fns = versions.map(v => prepare(v, c));
   fns.forEach(fn => timeIt(fn, 2));
   const counts = fns.map(fn => calibrate(fn, opts.minSampleMs));
diff --git a/package-lock.json b/package-lock.json
index de4ee07..17fb514 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -15,6 +15,7 @@
         "benchmark": "^2.1.4",
         "copy-anything": "4.0.5",
         "decimal.js": "^10.3.1",
+        "devalue": "^6.0.3",
         "mongodb": "^3.6.6",
         "tsdx": "^0.14.1",
         "typescript": "^5.9.3",
@@ -5452,6 +5453,16 @@
         "node": ">=8"
       }
     },
+    "node_modules/devalue": {
+      "version": "6.0.3",
+      "resolved": "https://registry.npmjs.org/devalue/-/devalue-6.0.3.tgz",
+      "integrity": "sha512-3woMEITftG1wKeO/4d/QXH1DVKctTSZg3jNGPpjp9hNr5Hos8MCFF5McTML5ZtgKDObm2R591B0spRp2IVernA==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/diff-sequences": {
       "version": "25.2.6",
       "resolved": "https://registry.npmjs.org/diff-sequences/-/diff-sequences-25.2.6.tgz",
diff --git a/package.json b/package.json
index eb34491..58f2864 100644
--- a/package.json
+++ b/package.json
@@ -55,6 +55,7 @@
     "benchmark": "^2.1.4",
     "copy-anything": "4.0.5",
     "decimal.js": "^10.3.1",
+    "devalue": "^6.0.3",
     "mongodb": "^3.6.6",
     "tsdx": "^0.14.1",
     "typescript": "^5.9.3",