diff --git a/.vscode/settings.json b/.vscode/settings.json
index 8823d9ef0b..3d6eca3019 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -28,7 +28,7 @@
 	"typescript.tsserver.experimental.enableProjectDiagnostics": true,
 	"typescript.tsdk": "./node_modules/typescript/lib",
 	// IF YOU UPDATE THE MOCHA CONFIG HERE, PLEASE ALSO UPDATE package.json/mocha AND ark/repo/mocha.jsonc
-	"mochaExplorer.nodeArgv": ["--conditions", "ark-ts", "--import", "tsx"],
+	"mochaExplorer.nodeArgv": ["--conditions", "ark-ts"],
 	// ignore attest since it requires type information
 	"mochaExplorer.ignore": ["ark/attest/**/*"],
 	"mochaExplorer.require": "ark/repo/mocha.globalSetup.ts",
diff --git a/ark/attest/__tests__/utils.ts b/ark/attest/__tests__/utils.ts
index 5daf26e8ef..703d74d732 100644
--- a/ark/attest/__tests__/utils.ts
+++ b/ark/attest/__tests__/utils.ts
@@ -7,7 +7,7 @@ export const runThenGetContents = (templatePath: string): string => {
 	const tempPath = templatePath + ".temp.ts"
 	copyFileSync(templatePath, tempPath)
 	try {
-		shell(`node --import=tsx ${tempPath}`, {
+		shell(`node ${tempPath}`, {
 			cwd: dirName(),
 			env: {
 				ATTEST_failOnMissingSnapshots: "0"
diff --git a/ark/fast-check/package.json b/ark/fast-check/package.json
index dd844bbaf2..acd8e7d649 100644
--- a/ark/fast-check/package.json
+++ b/ark/fast-check/package.json
@@ -34,7 +34,7 @@
 	],
 	"scripts": {
 		"build": "ts ../repo/build.ts",
-		"test": "tsx ../repo/testPackage.ts"
+		"test": "node ../repo/testPackage.ts"
 	},
 	"dependencies": {
 		"arktype": "workspace:*",
diff --git a/ark/repo/mocha.package.jsonc b/ark/repo/mocha.package.jsonc
index dfde0ace2a..3c5e01c1e6 100644
--- a/ark/repo/mocha.package.jsonc
+++ b/ark/repo/mocha.package.jsonc
@@ -8,6 +8,6 @@
 {
 	"spec": ["__tests__/*.test.*"],
 	"ignore": "node_modules/**/*",
-	"node-option": ["conditions=ark-ts", "import=tsx"],
+	"node-option": ["conditions=ark-ts"],
 	"require": "../repo/mocha.globalSetup.ts"
 }
diff --git a/ark/repo/nodeOptions.js b/ark/repo/nodeOptions.js
index c629a0fdba..9cc86532f5 100644
--- a/ark/repo/nodeOptions.js
+++ b/ark/repo/nodeOptions.js
@@ -1,16 +1,15 @@
 // @ts-check
 
-const [major, minor] = process.version.replace("v", "").split(".").map(Number)
+// Every Node version we support (see `engines.node`) strips TypeScript types
+// natively by default — no flag required. This repo also contains no syntax
+// that needs type *transformation* (no runtime enums, parameter properties, or
+// value-bearing namespaces — only erasable `declare`/type-level forms), so
+// stripping alone is sufficient and we pass no TS-related flags. Notably this
+// avoids `--experimental-transform-types`, which Node >= 26 rejects in
+// NODE_OPTIONS.
 
-const versionedFlags =
-	major > 22 || (major === 22 && minor >= 7) ?
-		"--experimental-transform-types --no-warnings"
-	:	(console.log(
-			"--experimental-transform-types requires Node >= 22.7.0, falling back to tsx..."
-		),
-		"--import tsx")
-
-export const nodeDevOptions = `${process.env.NODE_OPTIONS ?? ""} --conditions ark-ts ${versionedFlags}`
+export const nodeDevOptions =
+	`${process.env.NODE_OPTIONS ?? ""} --conditions ark-ts`.trimEnd()
 
 export const addNodeDevOptions = extraOpts =>
-	(process.env.NODE_OPTIONS = `${nodeDevOptions} ${extraOpts ?? ""}`)
+	(process.env.NODE_OPTIONS = `${nodeDevOptions} ${extraOpts ?? ""}`.trimEnd())
diff --git a/ark/type/__tests__/realWorld.test.ts b/ark/type/__tests__/realWorld.test.ts
index 33539ddc9c..acdd6d08c2 100644
--- a/ark/type/__tests__/realWorld.test.ts
+++ b/ark/type/__tests__/realWorld.test.ts
@@ -1302,10 +1302,13 @@ Right: { x: number, y: number, + (undeclared): delete }`)
 
 	it("described input of morph", () => {
 		class ValidatedUserID {
+			readonly data: string
 			static fromString(value: string): ValidatedUserID {
 				return new ValidatedUserID(value)
 			}
-			private constructor(readonly data: string) {}
+			private constructor(data: string) {
+				this.data = data
+			}
 		}
 
 		const UserID = type("string")
diff --git a/package.json b/package.json
index 8d618bf1db..58130e7c76 100644
--- a/package.json
+++ b/package.json
@@ -74,7 +74,6 @@
 		"mocha": "11.7.4",
 		"prettier": "3.6.2",
 		"tsup": "8.5.0",
-		"tsx": "4.20.6",
 		"typescript": "catalog:",
 		"typescript-eslint": "8.46.1"
 	},
@@ -85,8 +84,7 @@
 		],
 		"ignore": "**/node_modules/**/*",
 		"node-option": [
-			"conditions=ark-ts",
-			"import=tsx"
+			"conditions=ark-ts"
 		],
 		"require": "./ark/repo/mocha.globalSetup.ts",
 		"timeout": 10000
@@ -109,7 +107,7 @@
 		"arrowParens": "avoid"
 	},
 	"engines": {
-		"node": ">=18",
+		"node": ">=22.18.0",
 		"pnpm": ">=10"
 	},
 	"packageManager": "pnpm@10.19.0",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9cab8f6e63..5d4b898043 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -89,9 +89,6 @@ importers:
       tsup:
         specifier: 8.5.0
         version: 8.5.0(jiti@2.6.1)(postcss@8.5.6)(tsx@4.20.6)(typescript@5.9.3)
-      tsx:
-        specifier: 4.20.6
-        version: 4.20.6
       typescript:
         specifier: 'catalog:'
         version: 5.9.3
@@ -8263,6 +8260,7 @@ snapshots:
   get-tsconfig@4.12.0:
     dependencies:
       resolve-pkg-maps: 1.0.0
+    optional: true
 
   github-from-package@0.0.0:
     optional: true
@@ -10099,7 +10097,8 @@ snapshots:
 
   resolve-from@5.0.0: {}
 
-  resolve-pkg-maps@1.0.0: {}
+  resolve-pkg-maps@1.0.0:
+    optional: true
 
   resolve@1.22.10:
     dependencies:
@@ -10668,6 +10667,7 @@ snapshots:
       get-tsconfig: 4.12.0
     optionalDependencies:
       fsevents: 2.3.3
+    optional: true
 
   tunnel-agent@0.6.0:
     dependencies: