Type instantiation is excessively deep and possibly infinite

[kudretdonmez]

Description

I am using it with express.js on the node.js side. on functions like streamText, tool:

Type instantiation is excessively deep and possibly infinite.ts(2589)

and I can't start the server.

backend:dev: D:\projects\autocad-ai-tool\node_modules\.pnpm\ts-node@10.9.2_@types+node@24.1.0_typescript@5.9.2\node_modules\ts-node\src\index.ts:859
backend:dev:     return new TSError(diagnosticText, diagnosticCodes, diagnostics);
backend:dev:            ^
backend:dev: TSError: ⨯ Unable to compile TypeScript:
backend:dev: src/controllers/prompt.controller.ts(78,26): error TS2589: Type instantiation is excessively deep and possibly infinite.
backend:dev:
backend:dev:     at createTSError (D:\projects\autocad-ai-tool\node_modules\.pnpm\ts-node@10.9.2_@types+node@24.1.0_typescript@5.9.2\node_modules\ts-node\src\index.ts:859:12)        
backend:dev:     at reportTSError (D:\projects\autocad-ai-tool\node_modules\.pnpm\ts-node@10.9.2_@types+node@24.1.0_typescript@5.9.2\node_modules\ts-node\src\index.ts:863:19)        
backend:dev:     at getOutput (D:\projects\autocad-ai-tool\node_modules\.pnpm\ts-node@10.9.2_@types+node@24.1.0_typescript@5.9.2\node_modules\ts-node\src\index.ts:1077:36)
backend:dev:     at Object.compile (D:\projects\autocad-ai-tool\node_modules\.pnpm\ts-node@10.9.2_@types+node@24.1.0_typescript@5.9.2\node_modules\ts-node\src\index.ts:1433:41)      
backend:dev:     at Module.m._compile (D:\projects\autocad-ai-tool\node_modules\.pnpm\ts-node@10.9.2_@types+node@24.1.0_typescript@5.9.2\node_modules\ts-node\src\index.ts:1617:30)   
backend:dev:     at node:internal/modules/cjs/loader:1699:10
backend:dev:     at Object.require.extensions.<computed> [as .ts] (D:\projects\autocad-ai-tool\node_modules\.pnpm\ts-node@10.9.2_@types+node@24.1.0_typescript@5.9.2\node_modules\ts-node\src\index.ts:1621:12)
backend:dev:     at Module.load (node:internal/modules/cjs/loader:1313:32)
backend:dev:     at Function._load (node:internal/modules/cjs/loader:1123:12)
backend:dev:     at TracingChannel.traceSync (node:diagnostics_channel:322:14) {
backend:dev:   diagnosticCodes: [ 2589 ]
backend:dev: }
backend:dev: [nodemon] app crashed
backend:dev:  ELIFECYCLE  Command failed with exit code 1.
backend:dev: ERROR: command finished with error: command (D:\projects\autocad-ai-tool\backend) C:\Users\kayak\AppData\Local\pnpm\.tools\pnpm\10.13.1\bin\pnpm.CMD run dev exited (1)
backend#dev: command (D:\projects\autocad-ai-tool\backend) C:\Users\kayak\AppData\Local\pnpm\.tools\pnpm\10.13.1\bin\pnpm.CMD run dev exited (1)

AI SDK Version

package.json:

{
  "name": "backend",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "build": "tsc",
    "start": "node dist/server.js",
    "dev": "nodemon --exitcrash --watch src -e ts --exec \"ts-node src/server.ts\"",
    "lint": "eslint 'src/**/*.ts'"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "packageManager": "pnpm@10.12.4",
  "dependencies": {
    "@ai-sdk/google": "^2.0.0",
    "@google/generative-ai": "^0.24.1",
    "ai": "5.0.0",
    "cors": "^2.8.5",
    "dotenv": "^17.2.1",
    "express": "^5.1.0",
    "zod": "^3.25.76"
  },
  "devDependencies": {
    "@types/cors": "^2.8.19",
    "@types/express": "^5.0.3",
    "nodemon": "^3.1.10",
    "prettier": "^3.6.2",
    "ts-node": "^10.9.2",
    "typescript": "catalog:"
  }
}

[lgrammel]

Which Zod version are you using? please make sure to import either import { z } from 'zod/v4'; or import { z } from 'zod/v3' but not import { z } from 'zod';

[Aschen]

Thanks @lgrammel !

[colinhacks]

If you have been experiencing this, it's because you're using legacy tsconfig settings, namely moduleResolution: "node". There's no reason to be using this anymore. The root cause was a very subtle resolution bug that caused both ESM and CJS versions of Zod to be loaded in the codebase simultaneously. TypeScript considers these independent constructs, resulting in assignability issues and associated slow TS performance and occasionally OOM errors.

The simplest fix for this is to upgrade to a modern moduleResolution setting: https://www.typescriptlang.org/tsconfig/#moduleResolution. The old "node" setting mirrored the behavior of Node 10 which hit EOL in 2021.

That said, I found a mitigation on Zod's end that also resolves this issue. Upgrade to zod@4.1.6 and you won't hit this anymore: colinhacks/zod#5222

[Aschen]

Thanks @colinhacks, I really appreciate the investigation you made and I didn't know my moduleResolution config was obsolete !

Also thanks for the great work on Zod, I love it