diff --git a/.eslintrc.js b/.eslintrc.js
index 2e0a7e4..e243b9f 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -16,10 +16,6 @@ module.exports = {
   rules: {
     "@typescript-eslint/explicit-function-return-type": "off",
     "@typescript-eslint/explicit-module-boundary-types": "off",
-    "@typescript-eslint/member-delimiter-style": [
-      "warn",
-      { multiline: { delimiter: "none" } },
-    ],
     "@typescript-eslint/no-explicit-any": "off",
     "@typescript-eslint/no-var-requires": "off",
     "@typescript-eslint/await-thenable": ["error"],
diff --git a/.ncurc.json b/.ncurc.json
index 1c378c6..3de3741 100644
--- a/.ncurc.json
+++ b/.ncurc.json
@@ -1,6 +1,9 @@
 {
   "reject": [
     "@types/chai",
+    "@types/chai-as-promised",
+    "chai-as-promised",
+    "chai-as-promised why: v8 went to ESM",
     "chai",
     "eslint",
     "rimraf",
diff --git a/.vscode/settings.json b/.vscode/settings.json
index 6af3ca4..45e960a 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -8,6 +8,7 @@
         "rngseed"
     ],
     "cSpell.words": [
+        "sinonjs",
         "zombification"
     ]
 }
diff --git a/package.json b/package.json
index 38ebfcb..d46e6de 100644
--- a/package.json
+++ b/package.json
@@ -49,16 +49,18 @@
   "author": "Matthew McEachen <matthew-batchcluster@photostructure.com>",
   "license": "MIT",
   "devDependencies": {
+    "@sinonjs/fake-timers": "^13.0.3",
     "@types/chai": "^4.3.11",
-    "@types/chai-as-promised": "^8.0.1",
+    "@types/chai-as-promised": "^7",
     "@types/chai-string": "^1.4.5",
     "@types/chai-subset": "^1.3.5",
     "@types/mocha": "^10.0.9",
     "@types/node": "^22.7.7",
+    "@types/sinonjs__fake-timers": "^8.1.5",
     "@typescript-eslint/eslint-plugin": "^8.10.0",
     "@typescript-eslint/parser": "^8.10.0",
     "chai": "^4.3.10",
-    "chai-as-promised": "^8.0.0",
+    "chai-as-promised": "^7.1.2",
     "chai-string": "^1.5.0",
     "chai-subset": "^1.6.0",
     "chai-withintoleranceof": "^1.0.1",
@@ -73,7 +75,6 @@
     "serve": "^14.2.4",
     "source-map-support": "^0.5.21",
     "split2": "^4.2.0",
-    "timekeeper": "^2.3.1",
     "typedoc": "^0.26.10",
     "typescript": "~5.6.3"
   }
diff --git a/src/BatchCluster.spec.ts b/src/BatchCluster.spec.ts
index f3144e5..6031671 100644
--- a/src/BatchCluster.spec.ts
+++ b/src/BatchCluster.spec.ts
@@ -1,14 +1,5 @@
+import FakeTimers from "@sinonjs/fake-timers"
 import process from "node:process"
-import { filterInPlace } from "./Array"
-import { delay, until } from "./Async"
-import { BatchCluster } from "./BatchCluster"
-import { secondMs } from "./BatchClusterOptions"
-import { DefaultTestOptions } from "./DefaultTestOptions.spec"
-import { map, omit, orElse } from "./Object"
-import { isWin } from "./Platform"
-import { toS } from "./String"
-import { Task } from "./Task"
-import { thenOrTimeout } from "./Timeout"
 import {
   currentTestPids,
   expect,
@@ -24,9 +15,18 @@ import {
   times,
   unhandledRejections,
 } from "./_chai.spec"
+import { filterInPlace } from "./Array"
+import { delay, until } from "./Async"
+import { BatchCluster } from "./BatchCluster"
+import { secondMs } from "./BatchClusterOptions"
+import { DefaultTestOptions } from "./DefaultTestOptions.spec"
+import { map, omit, orElse } from "./Object"
+import { isWin } from "./Platform"
+import { toS } from "./String"
+import { Task } from "./Task"
+import { thenOrTimeout } from "./Timeout"
 
 const isCI = process.env.CI === "1"
-const tk = require("timekeeper")
 
 function arrayEqualish<T>(a: T[], b: T[], maxAcceptableDiffs: number) {
   const common = a.filter((ea) => b.includes(ea))
@@ -901,11 +901,20 @@ describe("BatchCluster", function () {
 
   describe("maxProcAgeMillis (recycling procs)", () => {
     let bc: BatchCluster
+    let clock: FakeTimers.InstalledClock
+
+    beforeEach(() => {
+      clock = FakeTimers.install({
+        shouldClearNativeTimers: true,
+        shouldAdvanceTime: true,
+      })
+    })
 
     afterEach(() => {
-      tk.reset()
+      clock.uninstall()
       return shutdown(bc)
     })
+
     for (const { maxProcAgeMillis, ctx, exp } of [
       {
         maxProcAgeMillis: 0,
@@ -929,8 +938,6 @@ describe("BatchCluster", function () {
       it("(" + maxProcAgeMillis + "): " + ctx, async function () {
         // TODO: look into why this fails in CI on windows
         if (isWin && isCI) return this.skip()
-        const start = Date.now()
-        tk.freeze(start)
         setFailratePct(0)
 
         bc = listen(
@@ -944,7 +951,7 @@ describe("BatchCluster", function () {
         )
         assertExpectedResults(await Promise.all(runTasks(bc, 2)))
         const pidsBefore = bc.pids()
-        tk.freeze(start + 7000)
+        clock.tick(7000)
         assertExpectedResults(await Promise.all(runTasks(bc, 2)))
         const pidsAfter = bc.pids()
         console.dir({ maxProcAgeMillis, pidsBefore, pidsAfter })
diff --git a/src/BatchClusterEmitter.ts b/src/BatchClusterEmitter.ts
index ec186ee..b12e7b6 100644
--- a/src/BatchClusterEmitter.ts
+++ b/src/BatchClusterEmitter.ts
@@ -23,7 +23,7 @@ export interface TypedEventEmitter<T> {
   ): this
   emit<E extends keyof T>(eventName: E, ...args: Args<T[E]>): boolean
 
-  // eslint-disable-next-line @typescript-eslint/ban-types
+  // eslint-disable-next-line @typescript-eslint/no-unsafe-function-type
   listeners<E extends keyof T>(event: E): Function[]
 
   removeAllListeners(eventName?: keyof T): this
diff --git a/src/BatchProcess.ts b/src/BatchProcess.ts
index a6d7eb0..50239de 100644
--- a/src/BatchProcess.ts
+++ b/src/BatchProcess.ts
@@ -365,7 +365,7 @@ export class BatchProcess {
         })
         return true
       }
-    } catch (err) {
+    } catch {
       // child process went away. We should too.
       this.end(false, "stdin.error")
       return false
diff --git a/src/Error.ts b/src/Error.ts
index 9100aa8..7bce9bd 100644
--- a/src/Error.ts
+++ b/src/Error.ts
@@ -8,7 +8,7 @@ export function tryEach(arr: (() => void)[]): void {
   for (const f of arr) {
     try {
       f()
-    } catch (_) {
+    } catch {
       //
     }
   }
diff --git a/src/Rate.spec.ts b/src/Rate.spec.ts
index 82f7b71..c2c6c1a 100644
--- a/src/Rate.spec.ts
+++ b/src/Rate.spec.ts
@@ -1,20 +1,22 @@
+import FakeTimers from "@sinonjs/fake-timers"
 import { minuteMs } from "./BatchClusterOptions"
 import { Rate } from "./Rate"
 import { expect, times } from "./_chai.spec"
 
-const tk = require("timekeeper")
-
 describe("Rate", () => {
   const now = Date.now()
   const r = new Rate()
+  let clock: FakeTimers.InstalledClock
 
   beforeEach(() => {
-    tk.freeze(now)
-    // clear() must be called _after_ freezing time
+    clock = FakeTimers.install({ now: now })
+    // clear() must be called _after_ setting up fake timers
     r.clear()
   })
 
-  after(() => tk.reset())
+  afterEach(() => {
+    clock.uninstall()
+  })
 
   function expectRate(rate: Rate, epm: number, tol = 0.1) {
     expect(rate.eventsPerMs).to.be.withinToleranceOf(epm, tol)
@@ -27,7 +29,7 @@ describe("Rate", () => {
   })
 
   it("maintains a rate of 0 after time with no events", () => {
-    tk.freeze(now + minuteMs)
+    clock.tick(minuteMs)
     expectRate(r, 0)
   })
 
@@ -37,38 +39,39 @@ describe("Rate", () => {
       () => {
         times(cnt, () => r.onEvent())
         expectRate(r, 0)
-        tk.freeze(now + 100)
+        clock.tick(100)
         expectRate(r, 0)
-        tk.freeze(now + r.warmupMs + 1)
+        clock.tick(r.warmupMs - 100 + 1)
         expectRate(r, cnt / r.warmupMs)
-        tk.freeze(now + 2 * r.warmupMs)
+        clock.tick(r.warmupMs)
         expectRate(r, cnt / (2 * r.warmupMs))
-        tk.freeze(now + 3 * r.warmupMs)
+        clock.tick(r.warmupMs)
         expectRate(r, cnt / (3 * r.warmupMs))
-        tk.freeze(now + r.periodMs)
+        clock.tick(r.periodMs - 3 * r.warmupMs)
         expectRate(r, 0)
-        expect(r.msSinceLastEvent).to.eql(minuteMs)
+        expect(r.msSinceLastEvent).to.be.closeTo(r.periodMs, 5)
       },
     )
   }
 
-  for (const events of [5, 10, 100, 1000]) {
+  for (const events of [4, 32, 256, 1024]) {
     it(
       "calculates average rate for " + events + " events, and then decays",
       () => {
         const period = r.periodMs
-        times(events, (i) => {
-          tk.freeze(now + (period * i) / events)
+        times(events, () => {
+          clock.tick(r.periodMs / events)
           r.onEvent()
         })
+        const tickMs = r.periodMs / 4
         expectRate(r, events / period, 0.3)
-        tk.freeze(now + 1.25 * r.periodMs)
+        clock.tick(tickMs)
         expectRate(r, 0.75 * (events / period), 0.3)
-        tk.freeze(now + 1.5 * r.periodMs)
+        clock.tick(tickMs)
         expectRate(r, 0.5 * (events / period), 0.3)
-        tk.freeze(now + 1.75 * r.periodMs)
-        expectRate(r, 0.25 * (events / period), 0.3)
-        tk.freeze(now + 2 * r.periodMs)
+        clock.tick(tickMs)
+        expectRate(r, 0.25 * (events / period), 0.5)
+        clock.tick(tickMs)
         expectRate(r, 0)
       },
     )
diff --git a/src/_chai.spec.ts b/src/_chai.spec.ts
index e761fce..de29a8d 100644
--- a/src/_chai.spec.ts
+++ b/src/_chai.spec.ts
@@ -1,3 +1,4 @@
+/* eslint-disable @typescript-eslint/no-require-imports */
 try {
   require("source-map-support").install()
 } catch {
diff --git a/src/test.ts b/src/test.ts
index fe985e9..afee866 100644
--- a/src/test.ts
+++ b/src/test.ts
@@ -40,7 +40,8 @@ function toF(s: string | undefined) {
 const failrate = toF(process.env.failrate) ?? 0
 const rng =
   process.env.rngseed != null
-    ? require("seedrandom")(process.env.rngseed)
+    ? // eslint-disable-next-line @typescript-eslint/no-require-imports
+      require("seedrandom")(process.env.rngseed)
     : Math.random
 
 async function onLine(line: string): Promise<void> {
@@ -148,5 +149,6 @@ async function onLine(line: string): Promise<void> {
 const m = new Mutex()
 
 process.stdin
+  // eslint-disable-next-line @typescript-eslint/no-require-imports
   .pipe(require("split2")())
   .on("data", (ea: string) => m.serial(() => onLine(ea)))