Invalid discriminator errors in Zod 4 do not list possible options like Zod 3

In Zod 3, if you received an error for an invalid discriminator, you received a list of possible options. In Zod 4, it just gives you a invalid_union code with no sub-errors or list of possible values. If the error map had access to the actual schema, it could theoretically use the discriminator to loop through the options, but this seems impossible at this point.

This is a pretty limiting regression in Zod 4, since without this information we can't tell users what they should be doing.

The script below logs the following:

Zod 4
[
  {
    code: 'invalid_union',
    errors: [],
    note: 'No matching discriminator',
    discriminator: 'type',
    path: [ 'type' ],
    message: 'Invalid input'
  }
]

Zod 3
[
  {
    code: 'invalid_union_discriminator',
    options: [ 'fruit', 'vegetable' ],
    path: [ 'type' ],
    message: "Invalid discriminator value. Expected 'fruit' | 'vegetable'"
  }
]

import { z } from 'zod';
import { z as z3 } from 'zod/v3';

console.log('Zod 4');
const schema = z.discriminatedUnion('type', [
  z.object({ type: z.literal('fruit') }),
  z.object({ type: z.literal('vegetable') }),
]);

console.log(schema.safeParse({ type: 'hi' }).error?.issues);

console.log('Zod 3');

const schema2 = z3.discriminatedUnion('type', [
  z3.object({ type: z3.literal('fruit') }),
  z3.object({ type: z3.literal('vegetable') }),
]);

console.log(schema2.safeParse({ type: 'hi' }).error?.issues);

Issue Reproduction Confirmed ✅

I reproduced the issue and verified the difference between Zod 3 and Zod 4:

Zod 4 output:

[
  {
    "code": "invalid_union",
    "errors": [],
    "note": "No matching discriminator",
    "discriminator": "type",
    "path": ["type"],
    "message": "Invalid input"
  }
]

Zod 3 output:

[
  {
    "code": "invalid_union_discriminator",
    "options": ["fruit", "vegetable"],
    "path": ["type"],
    "message": "Invalid discriminator value. Expected 'fruit' | 'vegetable'"
  }
]

Analysis

This is a valid regression. Zod 3 provided:

A dedicated invalid_union_discriminator error code
An options field listing valid discriminator values
A descriptive error message

Zod 4 consolidates this into the generic invalid_union code but loses the options information. The discriminator map (disc.value in packages/zod/src/v4/core/schemas.ts:2297-2312) already contains all valid discriminator values—they're just not being included in the error.

Suggested Fix

In packages/zod/src/v4/core/schemas.ts at line ~2337, add an options field:

payload.issues.push({
  code: "invalid_union",
  errors: [],
  note: "No matching discriminator",
  discriminator: def.discriminator,
  options: Array.from(disc.value.keys()),  // ← Add this
  input,
  path: [def.discriminator],
  inst,
});

Then update packages/zod/src/v4/locales/en.ts to produce a better message when options is present on invalid_union issues.

This would restore the Zod 3 behavior while keeping the unified invalid_union error code.

^{｜ Triggered by Pullfrog ｜ Using Claude Code ｜ View workflow run ｜ pullfrog.com ｜ 𝕏}

See #5086 for a related discussion.

I'd like to work on this issue. Can you assign it to me?

fix: add options to invalid discriminator errors

fix: add options to invalid discriminator errors (colinhacks#5723)

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Invalid discriminator errors in Zod 4 do not list possible options like Zod 3 #5670

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Invalid discriminator errors in Zod 4 do not list possible options like Zod 3 #5670

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pullfrog commented on Jan 28, 2026

Issue Reproduction Confirmed ✅

Analysis

Suggested Fix

BrendanC23 commented on Jan 29, 2026

Danielchinasa commented on Feb 18, 2026

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