From 4c9ab954ee62040287fd17f3bea82b35b653d3ff Mon Sep 17 00:00:00 2001
From: LeCarbonator <18158911+LeCarbonator@users.noreply.github.com>
Date: Thu, 13 Aug 2026 10:22:22 +0200
Subject: [PATCH 1/2] fix: tighten schema output type

---
 packages/form-core/src/validation.public.ts   | 17 ++++-
 packages/form-core/tests/validation.test-d.ts | 66 +++++++++++++++++++
 2 files changed, 80 insertions(+), 3 deletions(-)

diff --git a/packages/form-core/src/validation.public.ts b/packages/form-core/src/validation.public.ts
index 655a4621d5..457fb865ed 100644
--- a/packages/form-core/src/validation.public.ts
+++ b/packages/form-core/src/validation.public.ts
@@ -636,6 +636,19 @@ type TryGetSchemaOutput<TValidator> = TValidator extends {
   ? TOutput
   : undefined
 
+type TryGetSubmitSchemaOutput<TValidator> =
+  TryGetSchemaOutput<TValidator> extends infer TOutput
+    ? TValidator extends { readonly runOnSubmit: infer TRunOnSubmit }
+      ? [TRunOnSubmit] extends [false]
+        ? undefined // User explicitly set runOnSubmit: false -> guaranteed undefined
+        : TRunOnSubmit extends (...args: Array<any>) => boolean
+          ? TOutput | undefined // Callback could dynamically be true or false -> union
+          : false extends TRunOnSubmit
+            ? TOutput | undefined // the explicit variable is boolean, so also dynamic -> union
+            : TOutput
+      : TOutput // default, which is guaranteed present
+    : never
+
 type ValidatorTriggers<TValidator> = TValidator extends {
   readonly triggers: infer TTriggers
 }
@@ -667,9 +680,7 @@ type MappedSchemaOutputs<in out TValidators extends ReadonlyArray<unknown>> = {
   [K in keyof TValidators]: TValidators[K] extends {
     readonly run: any
   }
-    ? TValidators[K] extends { readonly runOnSubmit: false }
-      ? undefined
-      : TryGetSchemaOutput<TValidators[K]>
+    ? TryGetSubmitSchemaOutput<TValidators[K]>
     : never
 }
 
diff --git a/packages/form-core/tests/validation.test-d.ts b/packages/form-core/tests/validation.test-d.ts
index bc1b8c0b9d..71b099acab 100644
--- a/packages/form-core/tests/validation.test-d.ts
+++ b/packages/form-core/tests/validation.test-d.ts
@@ -1285,6 +1285,72 @@ describe('validator type transforms', () => {
     >()
   })
 
+  it('makes schema outputs optional when runOnSubmit is dynamic', () => {
+    const dynamicRunOnSubmit = true as boolean
+    const vs = defineFormValidators([
+      {
+        run: z.object({ name: z.string() }),
+        triggers: [],
+      },
+      {
+        run: z.object({ name: z.string() }),
+        triggers: [],
+        runOnSubmit: true,
+      },
+      {
+        run: z.object({ name: z.string() }),
+        triggers: [],
+        runOnSubmit: false,
+      },
+      {
+        run: z.object({ name: z.string() }),
+        triggers: [],
+        runOnSubmit: dynamicRunOnSubmit,
+      },
+      {
+        run: z.object({ name: z.string() }),
+        triggers: [],
+        runOnSubmit: () => true,
+      },
+      {
+        run: z.object({ name: z.string() }),
+        triggers: [],
+        runOnSubmit: () => false,
+      },
+      {
+        run: z.object({ name: z.string() }),
+        triggers: [],
+        runOnSubmit: () => dynamicRunOnSubmit,
+      },
+      {
+        run: z.object({ name: z.string() }),
+        triggers: [],
+        runOnSubmit: undefined,
+      },
+    ])
+
+    type Output = { name: string }
+    type Outputs = ToFormSchemaOutputs<typeof vs>
+    type Expected = readonly [
+      // An omitted runOnSubmit defaults to true, so the output is guaranteed.
+      Output,
+      // A literal true always runs the validator during submit.
+      Output,
+      // A literal false always skips the validator during submit.
+      undefined,
+      // A broad boolean may skip the validator at runtime.
+      Output | undefined,
+      // Predicates currently always assume dynamic results. Types are here if you plan to tighten it in the future.
+      Output | undefined,
+      Output | undefined,
+      Output | undefined,
+      // An explicit undefined receives the same true default as an omitted property.
+      Output,
+    ]
+
+    expectTypeOf<Outputs>().toEqualTypeOf<Expected>()
+  })
+
   it('should transform field validators', () => {
     const vs = defineFieldValidators([
       {

From 504e0efec505d409a91f9c8ce21d4d6fffee91f5 Mon Sep 17 00:00:00 2001
From: LeCarbonator <18158911+LeCarbonator@users.noreply.github.com>
Date: Thu, 13 Aug 2026 15:44:02 +0200
Subject: [PATCH 2/2] chore: add changeset

---
 .changeset/odd-comics-push.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/odd-comics-push.md

diff --git a/.changeset/odd-comics-push.md b/.changeset/odd-comics-push.md
new file mode 100644
index 0000000000..25de60ef11
--- /dev/null
+++ b/.changeset/odd-comics-push.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/form-core': patch
+---
+
+Fix: Schema output type now properly guards against dynamically enabled validators