diff --git a/src/index.ts b/src/index.ts
index ac4fdbf..78673ad 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,3 +1,62 @@
+// SDK type re-exports — every SDK type used in this package's public API
+// so consumers don't need to depend on @openrouter/sdk directly.
+
+export type { RequestOptions } from '@openrouter/sdk/lib/sdks';
+
+export type {
+  // Core request/response
+  BaseInputsUnion,
+  // Message & item types
+  ChatAssistantMessage,
+  ChatMessages,
+  EasyInputMessage,
+  EasyInputMessageContentUnion1,
+  EasyInputMessageRoleUnion,
+  // Error event
+  ErrorEvent,
+  FunctionCallItem,
+  FunctionCallOutputItem,
+  // Content input types (multimodal)
+  InputAudio,
+  InputFile,
+  InputImage,
+  InputMessageItem,
+  InputsUnion,
+  InputText,
+  InputVideo,
+  OpenResponsesResult,
+  // Output item types (StreamableOutputItem members)
+  OutputFileSearchCallItem,
+  OutputFunctionCallItem,
+  OutputImageGenerationCallItem,
+  OutputMessage,
+  OutputReasoningItem,
+  OutputWebSearchCallItem,
+  // Response output content
+  ResponseOutputText,
+  ResponsesRequest,
+  StreamEvents,
+  Usage,
+} from '@openrouter/sdk/models';
+
+// Clean item type aliases
+export type {
+  AssistantMessageItem,
+  CallFileSearchItem,
+  CallFunctionToolItem,
+  CallImageGenerationItem,
+  CallWebSearchItem,
+  DeveloperMessageItem,
+  ErrorItem,
+  FunctionProgressItem,
+  FunctionResultItem,
+  Item,
+  NewUserMessageItem,
+  ReasoningItem,
+  SystemMessageItem,
+  UserMessageItem,
+} from './lib/item-types.js';
+
 // Message format compatibility helpers
 
 // High-level model calling
diff --git a/src/lib/item-types.ts b/src/lib/item-types.ts
new file mode 100644
index 0000000..9720d99
--- /dev/null
+++ b/src/lib/item-types.ts
@@ -0,0 +1,100 @@
+import type {
+  EasyInputMessage,
+  ErrorEvent,
+  FunctionCallOutputItem,
+  OutputFileSearchCallItem,
+  OutputFunctionCallItem,
+  OutputImageGenerationCallItem,
+  OutputMessage,
+  OutputReasoningItem,
+  OutputWebSearchCallItem,
+} from '@openrouter/sdk/models';
+import type { ToolPreliminaryResultEvent } from './tool-types.js';
+
+/**
+ * Adds a required `id` field to a type, representing an item that has been
+ * persisted in conversation history (as opposed to newly created input).
+ * This is a local convention — the SDK's `EasyInputMessage` has no `id` field.
+ */
+type WithID<T> = T & {
+  id: string;
+};
+
+/** A function call initiated by the model */
+export type CallFunctionToolItem = OutputFunctionCallItem;
+
+/** An assistant message in the response output */
+export type AssistantMessageItem = OutputMessage;
+
+/** A new user message for input (not yet persisted, no id) */
+export type NewUserMessageItem = EasyInputMessage & {
+  role: 'user';
+};
+
+/** A user message from conversation history (has an assigned id) */
+export type UserMessageItem = WithID<EasyInputMessage> & {
+  role: 'user';
+};
+
+/** A system message from conversation history (has an assigned id) */
+export type SystemMessageItem = WithID<EasyInputMessage> & {
+  role: 'system';
+};
+
+/** A developer message from conversation history (has an assigned id) */
+export type DeveloperMessageItem = WithID<EasyInputMessage> & {
+  role: 'developer';
+};
+
+/** Reasoning output from the model */
+export type ReasoningItem = OutputReasoningItem;
+
+/** A file search call in the response output */
+export type CallFileSearchItem = OutputFileSearchCallItem;
+
+/**
+ * The output from a function call execution.
+ * `FunctionCallOutputItem` already declares `id?: string | null | undefined`,
+ * so no `WithID` wrapper is needed.
+ */
+export type FunctionResultItem = FunctionCallOutputItem;
+
+/**
+ * A preliminary result event emitted during tool execution.
+ * `ToolPreliminaryResultEvent` uses `toolCallId` (not `id`) for identification.
+ */
+export type FunctionProgressItem = ToolPreliminaryResultEvent;
+
+/** A web search call in the response output */
+export type CallWebSearchItem = OutputWebSearchCallItem;
+
+/** An image generation call in the response output */
+export type CallImageGenerationItem = OutputImageGenerationCallItem;
+
+/**
+ * A streaming error event.
+ * `ErrorEvent` has no `id` field; it uses `code`, `message`, `param`, and `sequenceNumber`.
+ */
+export type ErrorItem = ErrorEvent;
+
+/**
+ * Union of all item types used by this package.
+ *
+ * This is not exhaustive over every possible SDK output item type —
+ * server tool items (e.g. `OutputDatetimeItem`, `OutputServerToolItem`)
+ * are not included. Extend this union if you need to handle those.
+ */
+export type Item =
+  | AssistantMessageItem
+  | UserMessageItem
+  | SystemMessageItem
+  | DeveloperMessageItem
+  | NewUserMessageItem
+  | CallFunctionToolItem
+  | ReasoningItem
+  | CallFileSearchItem
+  | FunctionResultItem
+  | FunctionProgressItem
+  | CallWebSearchItem
+  | CallImageGenerationItem
+  | ErrorItem;