diff --git a/packages/orm/src/client/contract.ts b/packages/orm/src/client/contract.ts
index 4a451e203..4d54c2e49 100644
--- a/packages/orm/src/client/contract.ts
+++ b/packages/orm/src/client/contract.ts
@@ -28,15 +28,20 @@ import type {
     FindUniqueArgs,
     GroupByArgs,
     GroupByResult,
+    OmitWhere,
     ProcedureFunc,
     SelectSubset,
+    SelectSubsetWithWhere,
     SimplifiedPlainResult,
     Subset,
+    SubsetWithWhere,
     TypeDefResult,
     UpdateArgs,
     UpdateManyAndReturnArgs,
     UpdateManyArgs,
     UpsertArgs,
+    WhereInput,
+    WhereUniqueInput,
 } from './crud-types';
 import type { Diagnostics } from './diagnostics';
 import type { ClientOptions, QueryOptions } from './options';
@@ -405,8 +410,8 @@ export type AllModelOperations<
                * });
                * ```
                */
-              updateManyAndReturn<T extends UpdateManyAndReturnArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>(
-                  args: Subset<T, UpdateManyAndReturnArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
+              updateManyAndReturn<T extends OmitWhere<UpdateManyAndReturnArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>(
+                  args: { where?: WhereInput<Schema, Model, Options> } & SubsetWithWhere<T, OmitWhere<UpdateManyAndReturnArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>,
               ): ZenStackPromise<Schema, SimplifiedPlainResult<Schema, Model, T, Options, ExtResult>[]>;
           });
 
@@ -498,8 +503,8 @@ type CommonModelOperations<
      * }); // result: `{ _count: { posts: number } }`
      * ```
      */
-    findMany<T extends FindManyArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>(
-        args?: SelectSubset<T, FindManyArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
+    findMany<T extends OmitWhere<FindManyArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>(
+        args?: { where?: WhereInput<Schema, Model, Options> } & SelectSubset<T, FindManyArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
     ): ZenStackPromise<Schema, SimplifiedPlainResult<Schema, Model, T, Options, ExtResult>[]>;
 
     /**
@@ -508,8 +513,8 @@ type CommonModelOperations<
      * @returns a single entity or null if not found
      * @see {@link findMany}
      */
-    findUnique<T extends FindUniqueArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>(
-        args: SelectSubset<T, FindUniqueArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
+    findUnique<T extends OmitWhere<FindUniqueArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>(
+        args: { where: WhereUniqueInput<Schema, Model, Options> } & SelectSubset<T, FindUniqueArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
     ): ZenStackPromise<Schema, SimplifiedPlainResult<Schema, Model, T, Options, ExtResult> | null>;
 
     /**
@@ -518,8 +523,8 @@ type CommonModelOperations<
      * @returns a single entity
      * @see {@link findMany}
      */
-    findUniqueOrThrow<T extends FindUniqueArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>(
-        args: SelectSubset<T, FindUniqueArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
+    findUniqueOrThrow<T extends OmitWhere<FindUniqueArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>(
+        args: { where: WhereUniqueInput<Schema, Model, Options> } & SelectSubset<T, FindUniqueArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
     ): ZenStackPromise<Schema, SimplifiedPlainResult<Schema, Model, T, Options, ExtResult>>;
 
     /**
@@ -528,8 +533,8 @@ type CommonModelOperations<
      * @returns a single entity or null if not found
      * @see {@link findMany}
      */
-    findFirst<T extends FindFirstArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>(
-        args?: SelectSubset<T, FindFirstArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
+    findFirst<T extends OmitWhere<FindFirstArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>(
+        args?: { where?: WhereInput<Schema, Model, Options> } & SelectSubset<T, FindFirstArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
     ): ZenStackPromise<Schema, SimplifiedPlainResult<Schema, Model, T, Options, ExtResult> | null>;
 
     /**
@@ -538,8 +543,8 @@ type CommonModelOperations<
      * @returns a single entity
      * @see {@link findMany}
      */
-    findFirstOrThrow<T extends FindFirstArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>(
-        args?: SelectSubset<T, FindFirstArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
+    findFirstOrThrow<T extends OmitWhere<FindFirstArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>(
+        args?: { where?: WhereInput<Schema, Model, Options> } & SelectSubset<T, FindFirstArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
     ): ZenStackPromise<Schema, SimplifiedPlainResult<Schema, Model, T, Options, ExtResult>>;
 
     /**
@@ -744,8 +749,8 @@ type CommonModelOperations<
      * });
      * ```
      */
-    update<T extends UpdateArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>(
-        args: SelectSubset<T, UpdateArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
+    update<T extends OmitWhere<UpdateArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>(
+        args: { where: WhereUniqueInput<Schema, Model, Options> } & SelectSubsetWithWhere<T, OmitWhere<UpdateArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>,
     ): ZenStackPromise<Schema, SimplifiedPlainResult<Schema, Model, T, Options, ExtResult>>;
 
     /**
@@ -768,8 +773,8 @@ type CommonModelOperations<
      *     limit: 10
      * });
      */
-    updateMany<T extends UpdateManyArgs<Schema, Model, Options, ExtQueryArgs>>(
-        args: Subset<T, UpdateManyArgs<Schema, Model, Options, ExtQueryArgs>>,
+    updateMany<T extends OmitWhere<UpdateManyArgs<Schema, Model, Options, ExtQueryArgs>>>(
+        args: { where?: WhereInput<Schema, Model, Options> } & SubsetWithWhere<T, OmitWhere<UpdateManyArgs<Schema, Model, Options, ExtQueryArgs>>>,
     ): ZenStackPromise<Schema, BatchResult>;
 
     /**
@@ -792,8 +797,8 @@ type CommonModelOperations<
      * });
      * ```
      */
-    upsert<T extends UpsertArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>(
-        args: SelectSubset<T, UpsertArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
+    upsert<T extends OmitWhere<UpsertArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>(
+        args: { where: WhereUniqueInput<Schema, Model, Options> } & SelectSubsetWithWhere<T, OmitWhere<UpsertArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>,
     ): ZenStackPromise<Schema, SimplifiedPlainResult<Schema, Model, T, Options, ExtResult>>;
 
     /**
@@ -815,8 +820,8 @@ type CommonModelOperations<
      * }); // result: `{ id: string; email: string }`
      * ```
      */
-    delete<T extends DeleteArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>(
-        args: SelectSubset<T, DeleteArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
+    delete<T extends OmitWhere<DeleteArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>>(
+        args: { where: WhereUniqueInput<Schema, Model, Options> } & SelectSubset<T, DeleteArgs<Schema, Model, Options, ExtQueryArgs, ExtResult>>,
     ): ZenStackPromise<Schema, SimplifiedPlainResult<Schema, Model, T, Options, ExtResult>>;
 
     /**
@@ -838,8 +843,8 @@ type CommonModelOperations<
      * });
      * ```
      */
-    deleteMany<T extends DeleteManyArgs<Schema, Model, Options, ExtQueryArgs>>(
-        args?: Subset<T, DeleteManyArgs<Schema, Model, Options, ExtQueryArgs>>,
+    deleteMany<T extends OmitWhere<DeleteManyArgs<Schema, Model, Options, ExtQueryArgs>>>(
+        args?: { where?: WhereInput<Schema, Model, Options> } & Subset<T, DeleteManyArgs<Schema, Model, Options, ExtQueryArgs>>,
     ): ZenStackPromise<Schema, BatchResult>;
 
     /**
diff --git a/packages/orm/src/client/crud-types.ts b/packages/orm/src/client/crud-types.ts
index d29822209..8c8108089 100644
--- a/packages/orm/src/client/crud-types.ts
+++ b/packages/orm/src/client/crud-types.ts
@@ -347,6 +347,22 @@ export type WhereInput<
     AND?: OrArray<WhereInput<Schema, Model, Options, ScalarOnly>>;
     OR?: WhereInput<Schema, Model, Options, ScalarOnly>[];
     NOT?: OrArray<WhereInput<Schema, Model, Options, ScalarOnly>>;
+} & (IsDelegateModel<Schema, Model> extends true
+    ? { $is?: SubModelWhereInput<Schema, Model, Options, ScalarOnly> }
+    : object);
+
+/**
+ * Where filter that targets a specific sub-model of a delegate (polymorphic) base model.
+ * Keys are direct sub-model names; values are `WhereInput` for that sub-model.
+ * Multiple sub-model entries are combined with OR semantics.
+ */
+export type SubModelWhereInput<
+    Schema extends SchemaDef,
+    Model extends GetModels<Schema>,
+    Options extends QueryOptions<Schema> = QueryOptions<Schema>,
+    ScalarOnly extends boolean = false,
+> = {
+    [SubModel in GetSubModels<Schema, Model>]?: WhereInput<Schema, SubModel, Options, ScalarOnly> | null;
 };
 
 type FieldFilter<
@@ -1088,6 +1104,42 @@ export type SelectSubset<T, U> = {
       ? 'Please either choose `select` or `omit`.'
       : {});
 
+/**
+ * Strips the `where` field from an args type so the remaining fields can be used as
+ * the generic type parameter `T` in CRUD methods, allowing `where` to be typed directly
+ * and benefit from TypeScript's excess property checking.
+ * @internal
+ */
+export type OmitWhere<T> = Omit<T, 'where'>;
+
+/**
+ * Like {@link Subset} but maps the `where` key to `unknown` (instead of `never`) when
+ * `where` is not present in `U`. This is used in CRUD method signatures where `where`
+ * is separately typed as `{ where: WhereXxxInput }`: because TypeScript infers T from
+ * the full argument object (including the `where` field), a naive `Subset<T, OmitWhere<U>>`
+ * would produce `where: never` in the mapped result, collapsing the `where` type in the
+ * intersection to `never`. Mapping to `unknown` instead gives
+ * `{ where: W } & { where: unknown }` = `{ where: W }`, preserving both the correct type
+ * and TypeScript's excess-property checking on `where`.
+ * @internal
+ */
+export type SubsetWithWhere<T, U> = {
+    [key in keyof T]: key extends keyof U ? T[key] : key extends 'where' ? unknown : never;
+};
+
+/**
+ * Like {@link SelectSubset} but maps the `where` key to `unknown` (instead of `never`) when
+ * `where` is not present in `U`. See {@link SubsetWithWhere} for the rationale.
+ * @internal
+ */
+export type SelectSubsetWithWhere<T, U> = {
+    [key in keyof T]: key extends keyof U ? T[key] : key extends 'where' ? unknown : never;
+} & (T extends { select: any; include: any }
+    ? 'Please either choose `select` or `include`.'
+    : T extends { select: any; omit: any }
+      ? 'Please either choose `select` or `omit`.'
+      : {});
+
 type ToManyRelationFilter<
     Schema extends SchemaDef,
     Model extends GetModels<Schema>,
diff --git a/packages/orm/src/client/crud/dialects/base-dialect.ts b/packages/orm/src/client/crud/dialects/base-dialect.ts
index b525ac486..3a7ddbf38 100644
--- a/packages/orm/src/client/crud/dialects/base-dialect.ts
+++ b/packages/orm/src/client/crud/dialects/base-dialect.ts
@@ -23,6 +23,7 @@ import {
     ensureArray,
     flattenCompoundUniqueFilters,
     getDelegateDescendantModels,
+    getDiscriminatorField,
     getManyToManyRelation,
     getModelFields,
     getRelationForeignKeyFieldPairs,
@@ -224,6 +225,11 @@ export abstract class BaseCrudDialect<Schema extends SchemaDef> {
             result = this.and(result, _where['$expr'](this.eb));
         }
 
+        // handle $is filter for delegate (polymorphic) base models
+        if ('$is' in _where && _where['$is'] != null && typeof _where['$is'] === 'object') {
+            result = this.and(result, this.buildIsFilter(model, modelAlias, _where['$is'] as Record<string, any>));
+        }
+
         return result;
     }
 
@@ -319,6 +325,59 @@ export abstract class BaseCrudDialect<Schema extends SchemaDef> {
             .exhaustive();
     }
 
+    /**
+     * Builds a filter expression for the `$is` operator on a delegate (polymorphic) base model.
+     * Each key in `payload` is a direct sub-model name; the value is an optional `WhereInput` for
+     * that sub-model. Multiple sub-model entries are combined with OR semantics.
+     */
+    private buildIsFilter(model: string, modelAlias: string, payload: Record<string, any>): Expression<SqlBool> {
+        const discriminatorField = getDiscriminatorField(this.schema, model);
+        if (!discriminatorField) {
+            throw createInvalidInputError(
+                `"$is" filter is only supported on delegate models; "${model}" is not a delegate model. ` +
+                    `Only models with a @@delegate attribute support the "$is" filter.`,
+            );
+        }
+
+        const discriminatorFieldDef = requireField(this.schema, model, discriminatorField);
+        const discriminatorTableAlias = discriminatorFieldDef.originModel ?? modelAlias;
+        const discriminatorRef = this.eb.ref(`${discriminatorTableAlias}.${discriminatorField}`);
+
+        const conditions: Expression<SqlBool>[] = [];
+
+        for (const [subModelName, subWhere] of Object.entries(payload)) {
+            // discriminator must equal the sub-model name
+            const discriminatorCheck = this.eb(discriminatorRef, '=', subModelName);
+
+            if (subWhere == null || (typeof subWhere === 'object' && Object.keys(subWhere).length === 0)) {
+                // no sub-model field filter — just check the discriminator
+                conditions.push(discriminatorCheck);
+            } else {
+                // build a correlated EXISTS subquery for sub-model-specific field filters
+                const subAlias = tmpAlias(`${modelAlias}__is__${subModelName}`);
+                const idFields = requireIdFields(this.schema, model);
+
+                // correlate sub-model rows to the outer model rows via primary key
+                const joinConditions = idFields.map((idField) =>
+                    this.eb(this.eb.ref(`${subAlias}.${idField}`), '=', this.eb.ref(`${modelAlias}.${idField}`)),
+                );
+
+                const subWhereFilter = this.buildFilter(subModelName, subAlias, subWhere);
+
+                const existsSubquery = this.eb
+                    .selectFrom(`${subModelName} as ${subAlias}`)
+                    .select(this.eb.lit(1).as('__exists'))
+                    .where(this.and(...joinConditions, subWhereFilter));
+
+                conditions.push(this.and(discriminatorCheck, this.eb.exists(existsSubquery)));
+            }
+        }
+
+        if (conditions.length === 0) return this.true();
+        if (conditions.length === 1) return conditions[0]!;
+        return this.or(...conditions);
+    }
+
     private buildRelationFilter(model: string, modelAlias: string, field: string, fieldDef: FieldDef, payload: any) {
         if (!fieldDef.array) {
             return this.buildToOneRelationFilter(model, modelAlias, field, fieldDef, payload);
diff --git a/packages/orm/src/client/zod/factory.ts b/packages/orm/src/client/zod/factory.ts
index 0f8b22701..3db45a192 100644
--- a/packages/orm/src/client/zod/factory.ts
+++ b/packages/orm/src/client/zod/factory.ts
@@ -484,6 +484,23 @@ export class ZodSchemaFactory<
         // expression builder
         fields['$expr'] = z.custom((v) => typeof v === 'function', { error: '"$expr" must be a function' }).optional();
 
+        // $is sub-model filter for delegate (polymorphic) base models
+        const modelDef = requireModel(this.schema, model);
+        if (modelDef.isDelegate && modelDef.subModels && modelDef.subModels.length > 0) {
+            const subModelSchema = z.object(
+                Object.fromEntries(
+                    modelDef.subModels.map((subModel) => [
+                        subModel,
+                        z
+                            .lazy(() => this.makeWhereSchema(subModel, false, false, false, options))
+                            .nullish()
+                            .optional(),
+                    ]),
+                ),
+            );
+            fields['$is'] = subModelSchema.optional();
+        }
+
         // logical operators
         fields['AND'] = this.orArray(
             z.lazy(() => this.makeWhereSchema(model, false, withoutRelationFields, false, options)),
diff --git a/tests/e2e/orm/client-api/delegate.test.ts b/tests/e2e/orm/client-api/delegate.test.ts
index e325aaa5b..b4075a88c 100644
--- a/tests/e2e/orm/client-api/delegate.test.ts
+++ b/tests/e2e/orm/client-api/delegate.test.ts
@@ -557,6 +557,69 @@ describe('Delegate model tests ', () => {
                 }),
             ).toResolveFalsy();
         });
+
+        it('works with $is sub-model filter on base model', async () => {
+            // add an Image so we can test OR semantics of $is
+            await client.image.create({
+                data: { format: 'png', viewCount: 2 },
+            });
+
+            // $is: { Video: {} } — all assets that are Videos (2 RatedVideos)
+            await expect(
+                client.asset.findMany({
+                    where: { $is: { Video: {} } },
+                }),
+            ).toResolveWithLength(2);
+
+            // $is: { Video: null } — null value also means "is a Video"
+            await expect(
+                client.asset.findMany({
+                    where: { $is: { Video: null } },
+                }),
+            ).toResolveWithLength(2);
+
+            // $is: { Video: { duration: { gt: 100 } } } — only v2
+            await expect(
+                client.asset.findMany({
+                    where: { $is: { Video: { duration: { gt: 100 } } } },
+                }),
+            ).toResolveWithLength(1);
+
+            // $is combined with base-model field filter
+            await expect(
+                client.asset.findMany({
+                    where: { viewCount: { gt: 0 }, $is: { Video: { duration: { gt: 100 } } } },
+                }),
+            ).toResolveWithLength(1);
+
+            // $is: { Video: { duration: { gte: 100 } } } — both videos
+            await expect(
+                client.asset.findMany({
+                    where: { $is: { Video: { duration: { gte: 100 } } } },
+                }),
+            ).toResolveWithLength(2);
+
+            // $is with multiple sub-models → OR semantics (1 Video with viewCount>0 OR the Image)
+            await expect(
+                client.asset.findMany({
+                    where: { $is: { Video: { duration: { gt: 100 } }, Image: { format: 'png' } } },
+                }),
+            ).toResolveWithLength(2);
+
+            // $is on Video (which is itself a delegate) — filter on its sub-model RatedVideo
+            await expect(
+                client.video.findMany({
+                    where: { $is: { RatedVideo: { rating: 5 } } },
+                }),
+            ).toResolveWithLength(1);
+
+            // nested $is: Asset.$is.Video.$is.RatedVideo
+            await expect(
+                client.asset.findMany({
+                    where: { $is: { Video: { $is: { RatedVideo: { rating: 5 } } } } },
+                }),
+            ).toResolveWithLength(1);
+        });
     });
 
     describe('Delegate update tests', () => {
diff --git a/tests/e2e/orm/schemas/delegate/typecheck.ts b/tests/e2e/orm/schemas/delegate/typecheck.ts
index 76e36115f..c17981818 100644
--- a/tests/e2e/orm/schemas/delegate/typecheck.ts
+++ b/tests/e2e/orm/schemas/delegate/typecheck.ts
@@ -176,11 +176,48 @@ async function queryBuilder() {
     client.$qb.selectFrom('Video').select(['viewCount']).execute();
 }
 
+async function whereEPC() {
+    // unknown fields in `where` clause should produce a TypeScript error
+    await client.asset.findMany({
+        where: {
+            viewCount: 1,
+            // @ts-expect-error notExistsColumn is not a valid field
+            notExistsColumn: 1,
+        },
+    });
+
+    await client.asset.findFirst({
+        where: {
+            viewCount: 1,
+            // @ts-expect-error notExistsColumn is not a valid field
+            notExistsColumn: 1,
+        },
+    });
+
+    // valid fields should not produce errors
+    await client.asset.findMany({
+        where: {
+            viewCount: { gt: 0 },
+        },
+    });
+
+    // unknown fields in `where` clause for update should also produce TypeScript errors
+    await client.asset.update({
+        where: {
+            id: 1,
+            // @ts-expect-error notExistsColumn is not a valid field
+            notExistsColumn: 1,
+        },
+        data: { viewCount: 2 },
+    });
+}
+
 async function main() {
     await create();
     await update();
     await find();
     await queryBuilder();
+    await whereEPC();
 }
 
 main();
diff --git a/tests/e2e/orm/schemas/typing/typecheck.ts b/tests/e2e/orm/schemas/typing/typecheck.ts
index 9f8b2aa86..d28059153 100644
--- a/tests/e2e/orm/schemas/typing/typecheck.ts
+++ b/tests/e2e/orm/schemas/typing/typecheck.ts
@@ -220,6 +220,30 @@ async function find() {
     console.log(u.posts[0]?.author?.role);
     // @ts-expect-error
     console.log(u.posts[0]?.author?.email);
+
+    // unknown fields in `where` clause should produce TypeScript errors
+    await client.user.findMany({
+        where: {
+            email: 'test@test.com',
+            // @ts-expect-error notExistsColumn is not a valid field
+            notExistsColumn: 1,
+        },
+    });
+
+    await client.user.findFirst({
+        where: {
+            email: 'test@test.com',
+            // @ts-expect-error notExistsColumn is not a valid field
+            notExistsColumn: 1,
+        },
+    });
+
+    // valid where fields should not produce errors
+    await client.user.findMany({
+        where: {
+            email: { contains: '@test.com' },
+        },
+    });
 }
 
 async function create() {
@@ -554,6 +578,35 @@ async function update() {
             email: 'alex@zenstack.dev',
         },
     });
+
+    // unknown fields in `where` clause should produce TypeScript errors for update/upsert/updateMany
+    await client.user.update({
+        where: {
+            id: 1,
+            // @ts-expect-error notExistsColumn is not a valid field
+            notExistsColumn: 1,
+        },
+        data: { name: 'Alex' },
+    });
+
+    await client.user.upsert({
+        where: {
+            id: 1,
+            // @ts-expect-error notExistsColumn is not a valid field
+            notExistsColumn: 1,
+        },
+        create: { name: 'Alex', email: 'alex@zenstack.dev' },
+        update: { name: 'Alex New' },
+    });
+
+    await client.user.updateMany({
+        where: {
+            email: 'test@test.com',
+            // @ts-expect-error notExistsColumn is not a valid field
+            notExistsColumn: 1,
+        },
+        data: { name: 'Alex' },
+    });
 }
 
 async function del() {