diff --git a/.changeset/healthy-moons-type.md b/.changeset/healthy-moons-type.md
new file mode 100644
index 00000000000..1f38000ceda
--- /dev/null
+++ b/.changeset/healthy-moons-type.md
@@ -0,0 +1,6 @@
+---
+'firebase': major
+'@firebase/ai': major
+---
+
+Add support for `anyOf` schemas
diff --git a/common/api-review/ai.api.md b/common/api-review/ai.api.md
index d096d4c27f6..859cfb59688 100644
--- a/common/api-review/ai.api.md
+++ b/common/api-review/ai.api.md
@@ -65,6 +65,17 @@ export interface AIOptions {
     backend: Backend;
 }
 
+// @public
+export class AnyOfSchema extends Schema {
+    constructor(schemaParams: SchemaParams & {
+        anyOf: TypedSchema[];
+    });
+    // (undocumented)
+    anyOf: TypedSchema[];
+    // @internal (undocumented)
+    toJSON(): SchemaRequest;
+}
+
 // @public
 export class ArraySchema extends Schema {
     constructor(schemaParams: SchemaParams, items: TypedSchema);
@@ -776,6 +787,10 @@ export abstract class Schema implements SchemaInterface {
     constructor(schemaParams: SchemaInterface);
     [key: string]: unknown;
     // (undocumented)
+    static anyOf(anyOfParams: SchemaParams & {
+        anyOf: TypedSchema[];
+    }): AnyOfSchema;
+    // (undocumented)
     static array(arrayParams: SchemaParams & {
         items: Schema;
     }): ArraySchema;
@@ -804,12 +819,12 @@ export abstract class Schema implements SchemaInterface {
     static string(stringParams?: SchemaParams): StringSchema;
     // @internal
     toJSON(): SchemaRequest;
-    type: SchemaType;
+    type?: SchemaType;
 }
 
 // @public
 export interface SchemaInterface extends SchemaShared<SchemaInterface> {
-    type: SchemaType;
+    type?: SchemaType;
 }
 
 // @public
@@ -819,13 +834,14 @@ export interface SchemaParams extends SchemaShared<SchemaInterface> {
 // @public
 export interface SchemaRequest extends SchemaShared<SchemaRequest> {
     required?: string[];
-    type: SchemaType;
+    type?: SchemaType;
 }
 
 // @public
 export interface SchemaShared<T> {
     // (undocumented)
     [key: string]: unknown;
+    anyOf?: T[];
     description?: string;
     enum?: string[];
     example?: unknown;
@@ -900,7 +916,7 @@ export interface ToolConfig {
 }
 
 // @public
-export type TypedSchema = IntegerSchema | NumberSchema | StringSchema | BooleanSchema | ObjectSchema | ArraySchema;
+export type TypedSchema = IntegerSchema | NumberSchema | StringSchema | BooleanSchema | ObjectSchema | ArraySchema | AnyOfSchema;
 
 // @public
 export interface UsageMetadata {
diff --git a/docs-devsite/_toc.yaml b/docs-devsite/_toc.yaml
index b77a6b5910e..0f9372bf72a 100644
--- a/docs-devsite/_toc.yaml
+++ b/docs-devsite/_toc.yaml
@@ -12,6 +12,8 @@ toc:
     path: /docs/reference/js/ai.aimodel.md
   - title: AIOptions
     path: /docs/reference/js/ai.aioptions.md
+  - title: AnyOfSchema
+    path: /docs/reference/js/ai.anyofschema.md
   - title: ArraySchema
     path: /docs/reference/js/ai.arrayschema.md
   - title: Backend
diff --git a/docs-devsite/ai.anyofschema.md b/docs-devsite/ai.anyofschema.md
new file mode 100644
index 00000000000..6fc0fbc60a1
--- /dev/null
+++ b/docs-devsite/ai.anyofschema.md
@@ -0,0 +1,58 @@
+Project: /docs/reference/js/_project.yaml
+Book: /docs/reference/_book.yaml
+page_type: reference
+
+{% comment %}
+DO NOT EDIT THIS FILE!
+This is generated by the JS SDK team, and any local changes will be
+overwritten. Changes should be made in the source code at
+https://github.com/firebase/firebase-js-sdk
+{% endcomment %}
+
+# AnyOfSchema class
+Schema class representing a value that can conform to any of the provided sub-schemas. This is useful when a field can accept multiple distinct types or structures.
+
+<b>Signature:</b>
+
+```typescript
+export declare class AnyOfSchema extends Schema 
+```
+<b>Extends:</b> [Schema](./ai.schema.md#schema_class)
+
+## Constructors
+
+|  Constructor | Modifiers | Description |
+|  --- | --- | --- |
+|  [(constructor)(schemaParams)](./ai.anyofschema.md#anyofschemaconstructor) |  | Constructs a new instance of the <code>AnyOfSchema</code> class |
+
+## Properties
+
+|  Property | Modifiers | Type | Description |
+|  --- | --- | --- | --- |
+|  [anyOf](./ai.anyofschema.md#anyofschemaanyof) |  | [TypedSchema](./ai.md#typedschema)<!-- -->\[\] |  |
+
+## AnyOfSchema.(constructor)
+
+Constructs a new instance of the `AnyOfSchema` class
+
+<b>Signature:</b>
+
+```typescript
+constructor(schemaParams: SchemaParams & {
+        anyOf: TypedSchema[];
+    });
+```
+
+#### Parameters
+
+|  Parameter | Type | Description |
+|  --- | --- | --- |
+|  schemaParams | [SchemaParams](./ai.schemaparams.md#schemaparams_interface) &amp; { anyOf: [TypedSchema](./ai.md#typedschema)<!-- -->\[\]; } |  |
+
+## AnyOfSchema.anyOf
+
+<b>Signature:</b>
+
+```typescript
+anyOf: TypedSchema[];
+```
diff --git a/docs-devsite/ai.generationconfig.md b/docs-devsite/ai.generationconfig.md
index f9697a07454..3810fdb3621 100644
--- a/docs-devsite/ai.generationconfig.md
+++ b/docs-devsite/ai.generationconfig.md
@@ -28,7 +28,7 @@ export interface GenerationConfig
 |  [presencePenalty](./ai.generationconfig.md#generationconfigpresencepenalty) | number |  |
 |  [responseMimeType](./ai.generationconfig.md#generationconfigresponsemimetype) | string | Output response MIME type of the generated candidate text. Supported MIME types are <code>text/plain</code> (default, text output), <code>application/json</code> (JSON response in the candidates), and <code>text/x.enum</code>. |
 |  [responseModalities](./ai.generationconfig.md#generationconfigresponsemodalities) | [ResponseModality](./ai.md#responsemodality)<!-- -->\[\] | <b><i>(Public Preview)</i></b> Generation modalities to be returned in generation responses. |
-|  [responseSchema](./ai.generationconfig.md#generationconfigresponseschema) | [TypedSchema](./ai.md#typedschema) \| [SchemaRequest](./ai.schemarequest.md#schemarequest_interface) | Output response schema of the generated candidate text. This value can be a class generated with a [Schema](./ai.schema.md#schema_class) static method like <code>Schema.string()</code> or <code>Schema.object()</code> or it can be a plain JS object matching the [SchemaRequest](./ai.schemarequest.md#schemarequest_interface) interface. <br/>Note: This only applies when the specified <code>responseMIMEType</code> supports a schema; currently this is limited to <code>application/json</code> and <code>text/x.enum</code>. |
+|  [responseSchema](./ai.generationconfig.md#generationconfigresponseschema) | [TypedSchema](./ai.md#typedschema) \| [SchemaRequest](./ai.schemarequest.md#schemarequest_interface) | Output response schema of the generated candidate text. This value can be a class generated with a [Schema](./ai.schema.md#schema_class) static method like <code>Schema.string()</code> or <code>Schema.object()</code> or it can be a plain JS object matching the [SchemaRequest](./ai.schemarequest.md#schemarequest_interface) interface. <br/>Note: This only applies when the specified <code>responseMimeType</code> supports a schema; currently this is limited to <code>application/json</code> and <code>text/x.enum</code>. |
 |  [stopSequences](./ai.generationconfig.md#generationconfigstopsequences) | string\[\] |  |
 |  [temperature](./ai.generationconfig.md#generationconfigtemperature) | number |  |
 |  [topK](./ai.generationconfig.md#generationconfigtopk) | number |  |
@@ -93,7 +93,7 @@ responseModalities?: ResponseModality[];
 
 ## GenerationConfig.responseSchema
 
-Output response schema of the generated candidate text. This value can be a class generated with a [Schema](./ai.schema.md#schema_class) static method like `Schema.string()` or `Schema.object()` or it can be a plain JS object matching the [SchemaRequest](./ai.schemarequest.md#schemarequest_interface) interface. <br/>Note: This only applies when the specified `responseMIMEType` supports a schema; currently this is limited to `application/json` and `text/x.enum`<!-- -->.
+Output response schema of the generated candidate text. This value can be a class generated with a [Schema](./ai.schema.md#schema_class) static method like `Schema.string()` or `Schema.object()` or it can be a plain JS object matching the [SchemaRequest](./ai.schemarequest.md#schemarequest_interface) interface. <br/>Note: This only applies when the specified `responseMimeType` supports a schema; currently this is limited to `application/json` and `text/x.enum`<!-- -->.
 
 <b>Signature:</b>
 
diff --git a/docs-devsite/ai.md b/docs-devsite/ai.md
index c43c0391ba4..8223c745575 100644
--- a/docs-devsite/ai.md
+++ b/docs-devsite/ai.md
@@ -29,6 +29,7 @@ The Firebase AI Web SDK.
 |  --- | --- |
 |  [AIError](./ai.aierror.md#aierror_class) | Error class for the Firebase AI SDK. |
 |  [AIModel](./ai.aimodel.md#aimodel_class) | Base class for Firebase AI model APIs.<!-- -->Instances of this class are associated with a specific Firebase AI [Backend](./ai.backend.md#backend_class) and provide methods for interacting with the configured generative model. |
+|  [AnyOfSchema](./ai.anyofschema.md#anyofschema_class) | Schema class representing a value that can conform to any of the provided sub-schemas. This is useful when a field can accept multiple distinct types or structures. |
 |  [ArraySchema](./ai.arrayschema.md#arrayschema_class) | Schema class for "array" types. The <code>items</code> param should refer to the type of item that can be a member of the array. |
 |  [Backend](./ai.backend.md#backend_class) | Abstract base class representing the configuration for an AI service backend. This class should not be instantiated directly. Use its subclasses; [GoogleAIBackend](./ai.googleaibackend.md#googleaibackend_class) for the Gemini Developer API (via [Google AI](https://ai.google/)<!-- -->), and [VertexAIBackend](./ai.vertexaibackend.md#vertexaibackend_class) for the Vertex AI Gemini API. |
 |  [BooleanSchema](./ai.booleanschema.md#booleanschema_class) | Schema class for "boolean" types. |
@@ -410,7 +411,7 @@ A type that includes all specific Schema types.
 <b>Signature:</b>
 
 ```typescript
-export type TypedSchema = IntegerSchema | NumberSchema | StringSchema | BooleanSchema | ObjectSchema | ArraySchema;
+export type TypedSchema = IntegerSchema | NumberSchema | StringSchema | BooleanSchema | ObjectSchema | ArraySchema | AnyOfSchema;
 ```
 
 ## VertexAI
diff --git a/docs-devsite/ai.schema.md b/docs-devsite/ai.schema.md
index b0681b0cdf3..ce90cf9c805 100644
--- a/docs-devsite/ai.schema.md
+++ b/docs-devsite/ai.schema.md
@@ -33,12 +33,13 @@ export declare abstract class Schema implements SchemaInterface
 |  [example](./ai.schema.md#schemaexample) |  | unknown | Optional. The example of the property. |
 |  [format](./ai.schema.md#schemaformat) |  | string | Optional. The format of the property. Supported formats:<br/> <ul> <li>for NUMBER type: "float", "double"</li> <li>for INTEGER type: "int32", "int64"</li> <li>for STRING type: "email", "byte", etc</li> </ul> |
 |  [nullable](./ai.schema.md#schemanullable) |  | boolean | Optional. Whether the property is nullable. Defaults to false. |
-|  [type](./ai.schema.md#schematype) |  | [SchemaType](./ai.md#schematype) | Optional. The type of the property. [SchemaType](./ai.md#schematype)<!-- -->. |
+|  [type](./ai.schema.md#schematype) |  | [SchemaType](./ai.md#schematype) | Optional. The type of the property. [SchemaType](./ai.md#schematype)<!-- -->. This can only be undefined when using <code>anyOf</code> schemas, which do not have an explicit type in the . |
 
 ## Methods
 
 |  Method | Modifiers | Description |
 |  --- | --- | --- |
+|  [anyOf(anyOfParams)](./ai.schema.md#schemaanyof) | <code>static</code> |  |
 |  [array(arrayParams)](./ai.schema.md#schemaarray) | <code>static</code> |  |
 |  [boolean(booleanParams)](./ai.schema.md#schemaboolean) | <code>static</code> |  |
 |  [enumString(stringParams)](./ai.schema.md#schemaenumstring) | <code>static</code> |  |
@@ -105,14 +106,34 @@ nullable: boolean;
 
 ## Schema.type
 
-Optional. The type of the property. [SchemaType](./ai.md#schematype)<!-- -->.
+Optional. The type of the property. [SchemaType](./ai.md#schematype)<!-- -->. This can only be undefined when using `anyOf` schemas, which do not have an explicit type in the .
 
 <b>Signature:</b>
 
 ```typescript
-type: SchemaType;
+type?: SchemaType;
 ```
 
+## Schema.anyOf()
+
+<b>Signature:</b>
+
+```typescript
+static anyOf(anyOfParams: SchemaParams & {
+        anyOf: TypedSchema[];
+    }): AnyOfSchema;
+```
+
+#### Parameters
+
+|  Parameter | Type | Description |
+|  --- | --- | --- |
+|  anyOfParams | [SchemaParams](./ai.schemaparams.md#schemaparams_interface) &amp; { anyOf: [TypedSchema](./ai.md#typedschema)<!-- -->\[\]; } |  |
+
+<b>Returns:</b>
+
+[AnyOfSchema](./ai.anyofschema.md#anyofschema_class)
+
 ## Schema.array()
 
 <b>Signature:</b>
diff --git a/docs-devsite/ai.schemainterface.md b/docs-devsite/ai.schemainterface.md
index 6dd33e69e18..11e3542b357 100644
--- a/docs-devsite/ai.schemainterface.md
+++ b/docs-devsite/ai.schemainterface.md
@@ -23,14 +23,14 @@ export interface SchemaInterface extends SchemaShared<SchemaInterface>
 
 |  Property | Type | Description |
 |  --- | --- | --- |
-|  [type](./ai.schemainterface.md#schemainterfacetype) | [SchemaType](./ai.md#schematype) | The type of the property. [SchemaType](./ai.md#schematype)<!-- -->. |
+|  [type](./ai.schemainterface.md#schemainterfacetype) | [SchemaType](./ai.md#schematype) | The type of the property. this can only be undefined when using <code>anyof</code> schemas, which do not have an explicit type in the . |
 
 ## SchemaInterface.type
 
-The type of the property. [SchemaType](./ai.md#schematype)<!-- -->.
+The type of the property. this can only be undefined when using `anyof` schemas, which do not have an explicit type in the .
 
 <b>Signature:</b>
 
 ```typescript
-type: SchemaType;
+type?: SchemaType;
 ```
diff --git a/docs-devsite/ai.schemarequest.md b/docs-devsite/ai.schemarequest.md
index e71d24a6b1a..15423f967a4 100644
--- a/docs-devsite/ai.schemarequest.md
+++ b/docs-devsite/ai.schemarequest.md
@@ -24,7 +24,7 @@ export interface SchemaRequest extends SchemaShared<SchemaRequest>
 |  Property | Type | Description |
 |  --- | --- | --- |
 |  [required](./ai.schemarequest.md#schemarequestrequired) | string\[\] | Optional. Array of required property. |
-|  [type](./ai.schemarequest.md#schemarequesttype) | [SchemaType](./ai.md#schematype) | The type of the property. [SchemaType](./ai.md#schematype)<!-- -->. |
+|  [type](./ai.schemarequest.md#schemarequesttype) | [SchemaType](./ai.md#schematype) | The type of the property. this can only be undefined when using <code>anyof</code> schemas, which do not have an explicit type in the . |
 
 ## SchemaRequest.required
 
@@ -38,10 +38,10 @@ required?: string[];
 
 ## SchemaRequest.type
 
-The type of the property. [SchemaType](./ai.md#schematype)<!-- -->.
+The type of the property. this can only be undefined when using `anyof` schemas, which do not have an explicit type in the .
 
 <b>Signature:</b>
 
 ```typescript
-type: SchemaType;
+type?: SchemaType;
 ```
diff --git a/docs-devsite/ai.schemashared.md b/docs-devsite/ai.schemashared.md
index eba57f82935..fd903b34395 100644
--- a/docs-devsite/ai.schemashared.md
+++ b/docs-devsite/ai.schemashared.md
@@ -22,6 +22,7 @@ export interface SchemaShared<T>
 
 |  Property | Type | Description |
 |  --- | --- | --- |
+|  [anyOf](./ai.schemashared.md#schemasharedanyof) | T\[\] | An array of [Schema](./ai.schema.md#schema_class)<!-- -->. The generated data must be valid against any of the schemas listed in this array. This allows specifying multiple possible structures or types for a single field. |
 |  [description](./ai.schemashared.md#schemashareddescription) | string | Optional. The description of the property. |
 |  [enum](./ai.schemashared.md#schemasharedenum) | string\[\] | Optional. The enum of the property. |
 |  [example](./ai.schemashared.md#schemasharedexample) | unknown | Optional. The example of the property. |
@@ -30,6 +31,16 @@ export interface SchemaShared<T>
 |  [nullable](./ai.schemashared.md#schemasharednullable) | boolean | Optional. Whether the property is nullable. |
 |  [properties](./ai.schemashared.md#schemasharedproperties) | { \[k: string\]: T; } | Optional. Map of <code>Schema</code> objects. |
 
+## SchemaShared.anyOf
+
+An array of [Schema](./ai.schema.md#schema_class)<!-- -->. The generated data must be valid against any of the schemas listed in this array. This allows specifying multiple possible structures or types for a single field.
+
+<b>Signature:</b>
+
+```typescript
+anyOf?: T[];
+```
+
 ## SchemaShared.description
 
 Optional. The description of the property.
diff --git a/packages/ai/src/requests/schema-builder.test.ts b/packages/ai/src/requests/schema-builder.test.ts
index d05b81381ea..451fdca8a54 100644
--- a/packages/ai/src/requests/schema-builder.test.ts
+++ b/packages/ai/src/requests/schema-builder.test.ts
@@ -15,10 +15,16 @@
  * limitations under the License.
  */
 
+import { AIError } from '../errors';
 import { expect, use } from 'chai';
 import sinonChai from 'sinon-chai';
-import { Schema } from './schema-builder';
-import { AIErrorCode } from '../types';
+import {
+  AnyOfSchema,
+  NumberSchema,
+  Schema,
+  StringSchema
+} from './schema-builder';
+import { AIErrorCode, SchemaType } from '../types';
 
 use(sinonChai);
 
@@ -242,9 +248,149 @@ describe('Schema builder', () => {
         population: Schema.integer({ nullable: true })
       },
       optionalProperties: ['cat']
-    });
+    }) as any; // Cast to any to bypass TypedSchema check for testing purposes
+    expect(() => schema.toJSON()).to.throw(
+      AIError,
+      /Property "cat" specified in "optionalProperties" does not exist./
+    );
+    // Check the error code as well
     expect(() => schema.toJSON()).to.throw(AIErrorCode.INVALID_SCHEMA);
   });
+
+  describe('AnyOfSchema', () => {
+    it('builds an anyOf schema with basic types using Schema.anyOf()', () => {
+      const schema: AnyOfSchema = Schema.anyOf({
+        anyOf: [Schema.string(), Schema.number()]
+      });
+
+      expect(schema).to.be.instanceOf(AnyOfSchema);
+      expect(schema.type).to.be.undefined;
+      expect(schema.nullable).to.be.false; // Default from SchemaParams
+      expect(schema.anyOf).to.be.an('array').with.lengthOf(2);
+      expect(schema.anyOf[0]).to.be.instanceOf(StringSchema);
+      expect(schema.anyOf[1]).to.be.instanceOf(NumberSchema);
+
+      expect(schema.toJSON()).to.eql({
+        type: undefined,
+        anyOf: [
+          { type: 'string', nullable: false },
+          { type: 'number', nullable: false }
+        ],
+        nullable: false
+      });
+    });
+
+    it('builds an anyOf schema with complex types and options', () => {
+      const schema = Schema.anyOf({
+        description: 'Can be a string or a detailed object',
+        nullable: true,
+        anyOf: [
+          Schema.string({ description: 'A simple string' }),
+          Schema.object({
+            properties: {
+              id: Schema.integer(),
+              name: Schema.string()
+            },
+            description: 'A detailed object',
+            nullable: false // Explicitly set for the object schema itself
+          })
+        ]
+      });
+
+      expect(schema.description).to.equal(
+        'Can be a string or a detailed object'
+      );
+      expect(schema.nullable).to.be.true;
+      expect(schema.anyOf).to.be.an('array').with.lengthOf(2);
+
+      expect(schema.toJSON()).to.eql({
+        type: undefined,
+        description: 'Can be a string or a detailed object',
+        nullable: true,
+        anyOf: [
+          { type: 'string', description: 'A simple string', nullable: false },
+          {
+            type: 'object',
+            description: 'A detailed object',
+            properties: {
+              id: { type: 'integer', nullable: false },
+              name: { type: 'string', nullable: false }
+            },
+            required: ['id', 'name'],
+            nullable: false
+          }
+        ]
+      });
+    });
+
+    it('correctly overrides type to undefined even if type is passed in params', () => {
+      const schema = Schema.anyOf({
+        type: SchemaType.STRING,
+        anyOf: [Schema.string(), Schema.number()]
+      });
+      expect(schema.toJSON().type).to.be.undefined;
+      expect(schema.toJSON()).to.eql({
+        type: undefined, // Explicitly undefined for anyOf
+        anyOf: [
+          { type: 'string', nullable: false },
+          { type: 'number', nullable: false }
+        ],
+        nullable: false // Default from SchemaParams
+      });
+    });
+
+    it('toJSON() correctly serializes nested complex schemas within anyOf', () => {
+      const schema = Schema.anyOf({
+        anyOf: [
+          Schema.object({
+            properties: { name: Schema.string() },
+            optionalProperties: ['name']
+          }),
+          Schema.array({ items: Schema.integer() })
+        ]
+      });
+      expect(schema.toJSON()).to.eql({
+        type: undefined,
+        anyOf: [
+          {
+            type: 'object',
+            properties: { name: { type: 'string', nullable: false } },
+            nullable: false
+          },
+          {
+            type: 'array',
+            items: { type: 'integer', nullable: false },
+            nullable: false
+          }
+        ],
+        nullable: false
+      });
+    });
+
+    it('throws an error if the anyOf array is empty', () => {
+      expect(() => Schema.anyOf({ anyOf: [] })).to.throw(
+        AIErrorCode.INVALID_SCHEMA
+      );
+    });
+  });
+
+  describe('ObjectSchema toJSON() optionalProperties edge cases', () => {
+    it('handles empty optionalProperties array (all properties required)', () => {
+      const schema = Schema.object({
+        properties: { a: Schema.string(), b: Schema.integer() },
+        optionalProperties: []
+      });
+      expect(schema.toJSON().required).to.deep.equal(['a', 'b']);
+    });
+
+    it('handles all properties being optional (empty required array)', () => {
+      const schema = Schema.object({
+        properties: { a: Schema.string(), b: Schema.integer() },
+        optionalProperties: ['a', 'b']
+      });
+      expect(schema.toJSON().required).to.be.undefined; // or empty array, depending on implementation
+    });
+  });
 });
 
 const layeredSchemaOutputPartial = {
diff --git a/packages/ai/src/requests/schema-builder.ts b/packages/ai/src/requests/schema-builder.ts
index 524cfdb1c20..0f46f0b098c 100644
--- a/packages/ai/src/requests/schema-builder.ts
+++ b/packages/ai/src/requests/schema-builder.ts
@@ -35,9 +35,10 @@ import {
 export abstract class Schema implements SchemaInterface {
   /**
    * Optional. The type of the property. {@link
-   * SchemaType}.
+   * SchemaType}. This can only be undefined when using `anyOf` schemas, which do not have an
+   * explicit type in the {@link OpenAPI specification | https://swagger.io/docs/specification/v3_0/data-models/data-types/#any-type}.
    */
-  type: SchemaType;
+  type?: SchemaType;
   /** Optional. The format of the property.
    * Supported formats:<br/>
    * <ul>
@@ -60,12 +61,22 @@ export abstract class Schema implements SchemaInterface {
   [key: string]: unknown;
 
   constructor(schemaParams: SchemaInterface) {
+    // TODO(dlarocque): Enforce this with union types
+    if (!schemaParams.type && !schemaParams.anyOf) {
+      throw new AIError(
+        AIErrorCode.INVALID_SCHEMA,
+        "A schema must have either a 'type' or an 'anyOf' array of sub-schemas."
+      );
+    }
     // eslint-disable-next-line guard-for-in
     for (const paramKey in schemaParams) {
       this[paramKey] = schemaParams[paramKey];
     }
     // Ensure these are explicitly set to avoid TS errors.
     this.type = schemaParams.type;
+    this.format = schemaParams.hasOwnProperty('format')
+      ? schemaParams.format
+      : undefined;
     this.nullable = schemaParams.hasOwnProperty('nullable')
       ? !!schemaParams.nullable
       : false;
@@ -77,7 +88,7 @@ export abstract class Schema implements SchemaInterface {
    * @internal
    */
   toJSON(): SchemaRequest {
-    const obj: { type: SchemaType; [key: string]: unknown } = {
+    const obj: { type?: SchemaType; [key: string]: unknown } = {
       type: this.type
     };
     for (const prop in this) {
@@ -133,6 +144,12 @@ export abstract class Schema implements SchemaInterface {
   static boolean(booleanParams?: SchemaParams): BooleanSchema {
     return new BooleanSchema(booleanParams);
   }
+
+  static anyOf(
+    anyOfParams: SchemaParams & { anyOf: TypedSchema[] }
+  ): AnyOfSchema {
+    return new AnyOfSchema(anyOfParams);
+  }
 }
 
 /**
@@ -145,7 +162,8 @@ export type TypedSchema =
   | StringSchema
   | BooleanSchema
   | ObjectSchema
-  | ArraySchema;
+  | ArraySchema
+  | AnyOfSchema;
 
 /**
  * Schema class for "integer" types.
@@ -290,3 +308,37 @@ export class ObjectSchema extends Schema {
     return obj as SchemaRequest;
   }
 }
+
+/**
+ * Schema class representing a value that can conform to any of the provided sub-schemas. This is
+ * useful when a field can accept multiple distinct types or structures.
+ * @public
+ */
+export class AnyOfSchema extends Schema {
+  anyOf: TypedSchema[]; // Re-define field to narrow to required type
+  constructor(schemaParams: SchemaParams & { anyOf: TypedSchema[] }) {
+    if (schemaParams.anyOf.length === 0) {
+      throw new AIError(
+        AIErrorCode.INVALID_SCHEMA,
+        "The 'anyOf' array must not be empty."
+      );
+    }
+    super({
+      ...schemaParams,
+      type: undefined // anyOf schemas do not have an explicit type
+    });
+    this.anyOf = schemaParams.anyOf;
+  }
+
+  /**
+   * @internal
+   */
+  toJSON(): SchemaRequest {
+    const obj = super.toJSON();
+    // Ensure the 'anyOf' property contains serialized SchemaRequest objects.
+    if (this.anyOf && Array.isArray(this.anyOf)) {
+      obj.anyOf = (this.anyOf as TypedSchema[]).map(s => s.toJSON());
+    }
+    return obj;
+  }
+}
diff --git a/packages/ai/src/types/requests.ts b/packages/ai/src/types/requests.ts
index 67f45095c2a..8abe74363f5 100644
--- a/packages/ai/src/types/requests.ts
+++ b/packages/ai/src/types/requests.ts
@@ -99,7 +99,7 @@ export interface GenerationConfig {
    * value can be a class generated with a {@link Schema} static method
    * like `Schema.string()` or `Schema.object()` or it can be a plain
    * JS object matching the {@link SchemaRequest} interface.
-   * <br/>Note: This only applies when the specified `responseMIMEType` supports a schema; currently
+   * <br/>Note: This only applies when the specified `responseMimeType` supports a schema; currently
    * this is limited to `application/json` and `text/x.enum`.
    */
   responseSchema?: TypedSchema | SchemaRequest;
diff --git a/packages/ai/src/types/schema.ts b/packages/ai/src/types/schema.ts
index e9fe9286b61..314cb33a57e 100644
--- a/packages/ai/src/types/schema.ts
+++ b/packages/ai/src/types/schema.ts
@@ -42,6 +42,12 @@ export enum SchemaType {
  * @public
  */
 export interface SchemaShared<T> {
+  /**
+   * An array of {@link Schema}. The generated data must be valid against any of the schemas
+   * listed in this array. This allows specifying multiple possible structures or types for a
+   * single field.
+   */
+  anyOf?: T[];
   /** Optional. The format of the property.
    * When using the Gemini Developer API ({@link GoogleAIBackend}), this must be either `'enum'` or
    * `'date-time'`, otherwise requests will fail.
@@ -77,10 +83,10 @@ export interface SchemaParams extends SchemaShared<SchemaInterface> {}
  */
 export interface SchemaRequest extends SchemaShared<SchemaRequest> {
   /**
-   * The type of the property. {@link
-   * SchemaType}.
+   * The type of the property. this can only be undefined when using `anyof` schemas,
+   * which do not have an explicit type in the {@link OpenAPI specification | https://swagger.io/docs/specification/v3_0/data-models/data-types/#any-type}.
    */
-  type: SchemaType;
+  type?: SchemaType;
   /** Optional. Array of required property. */
   required?: string[];
 }
@@ -91,10 +97,10 @@ export interface SchemaRequest extends SchemaShared<SchemaRequest> {
  */
 export interface SchemaInterface extends SchemaShared<SchemaInterface> {
   /**
-   * The type of the property. {@link
-   * SchemaType}.
+   * The type of the property. this can only be undefined when using `anyof` schemas,
+   * which do not have an explicit type in the {@link OpenAPI specification | https://swagger.io/docs/specification/v3_0/data-models/data-types/#any-type}.
    */
-  type: SchemaType;
+  type?: SchemaType;
 }
 
 /**