diff --git a/openworkflow/hello-world.ts b/openworkflow/hello-world.ts
index 8093fe33..e407e4f1 100644
--- a/openworkflow/hello-world.ts
+++ b/openworkflow/hello-world.ts
@@ -14,7 +14,9 @@ import { defineWorkflow } from "openworkflow";
  */
 export const helloWorld = defineWorkflow(
   { name: "hello-world" },
-  async ({ step }) => {
+  async ({ step, run }) => {
+    console.log(`[run ${run.id}]`);
+
     const greeting = await step.run({ name: "greet" }, () => {
       return "Hello, World!";
     });
diff --git a/packages/docs/docs/workflows.mdx b/packages/docs/docs/workflows.mdx
index 198639cf..343f6954 100644
--- a/packages/docs/docs/workflows.mdx
+++ b/packages/docs/docs/workflows.mdx
@@ -211,18 +211,20 @@ create a separate run.
 
 ## Workflow Function Parameters
 
-The workflow function receives an object with three properties:
+The workflow function receives an object with four properties:
 
-| Parameter | Type             | Description                                       |
-| --------- | ---------------- | ------------------------------------------------- |
-| `input`   | Generic          | The input data passed when starting the workflow  |
-| `step`    | `StepApi`        | API for defining steps (`step.run`, `step.sleep`) |
-| `version` | `string \| null` | The workflow version, if specified                |
+| Parameter | Type                  | Description                                       |
+| --------- | --------------------- | ------------------------------------------------- |
+| `input`   | Generic               | The input data passed when starting the workflow  |
+| `step`    | `StepApi`             | API for defining steps (`step.run`, `step.sleep`) |
+| `version` | `string \| null`      | The workflow version, if specified                |
+| `run`     | `WorkflowRunMetadata` | Read-only run metadata snapshot (`run.id`, etc.)  |
 
 ```ts
-defineWorkflow({ name: "example" }, async ({ input, step, version }) => {
+defineWorkflow({ name: "example" }, async ({ input, step, version, run }) => {
   console.log("Input:", input);
   console.log("Version:", version);
+  console.log("Run ID:", run.id);
 
   await step.run({ name: "my-step" }, async () => {
     // step logic
diff --git a/packages/openworkflow/execution.test.ts b/packages/openworkflow/execution.test.ts
index 7871ae49..6823f355 100644
--- a/packages/openworkflow/execution.test.ts
+++ b/packages/openworkflow/execution.test.ts
@@ -540,6 +540,116 @@ describe("executeWorkflow", () => {
       expect(result).toEqual({ receivedVersion: null });
     });
   });
+
+  describe("run", () => {
+    test("exposes run metadata from workflow run", async () => {
+      const backend = await createBackend();
+      const client = new OpenWorkflow({ backend });
+      const deadlineAt = new Date(Date.now() + 60_000);
+      const idempotencyKey = "run-metadata-idempotency";
+
+      const workflow = client.defineWorkflow(
+        { name: "run-metadata", version: "1.2.3" },
+        ({ run }) => {
+          return {
+            id: run.id,
+            workflowName: run.workflowName,
+            createdAtIsDate: run.createdAt instanceof Date,
+            startedAtIsDate: run.startedAt instanceof Date,
+            createdAtMs: run.createdAt.getTime(),
+            startedAtMs: run.startedAt?.getTime() ?? null,
+          };
+        },
+      );
+
+      const worker = client.newWorker();
+      const handle = await workflow.run(
+        {},
+        {
+          deadlineAt,
+          idempotencyKey,
+        },
+      );
+      await worker.tick();
+      const result = await handle.result();
+
+      expect(result.id).toBe(handle.workflowRun.id);
+      expect(result.workflowName).toBe("run-metadata");
+      expect(result.createdAtIsDate).toBe(true);
+      expect(result.startedAtIsDate).toBe(true);
+      expect(result.startedAtMs).not.toBeNull();
+      if (result.startedAtMs === null) {
+        throw new Error("expected startedAtMs");
+      }
+      expect(result.startedAtMs).toBeGreaterThanOrEqual(result.createdAtMs);
+    });
+
+    test("keeps run metadata frozen at runtime", async () => {
+      const backend = await createBackend();
+      const client = new OpenWorkflow({ backend });
+      let mutationError: unknown = null;
+
+      const workflow = client.defineWorkflow(
+        { name: "run-frozen" },
+        async ({ run, step }) => {
+          await step.run({ name: "mutate-run" }, () => {
+            try {
+              Object.assign(run as unknown as Record<string, unknown>, {
+                id: "mutated",
+              });
+            } catch (error) {
+              mutationError = error;
+            }
+            return null;
+          });
+          return run.id;
+        },
+      );
+
+      const worker = client.newWorker();
+      const handle = await workflow.run();
+      await worker.tick();
+
+      const result = await handle.result();
+      expect(result).toBe(handle.workflowRun.id);
+      if (mutationError !== null) {
+        expect(mutationError).toBeInstanceOf(TypeError);
+      }
+    });
+
+    test("keeps id and timestamps stable across replay", async () => {
+      const backend = await createBackend();
+      const client = new OpenWorkflow({ backend });
+      const snapshots: {
+        id: string;
+        createdAt: number;
+        startedAt: number | null;
+      }[] = [];
+
+      const workflow = client.defineWorkflow(
+        { name: "run-replay-stable" },
+        async ({ run, step }) => {
+          snapshots.push({
+            id: run.id,
+            createdAt: run.createdAt.getTime(),
+            startedAt: run.startedAt?.getTime() ?? null,
+          });
+          await step.sleep("pause", "10ms");
+          return null;
+        },
+      );
+
+      const worker = client.newWorker();
+      const handle = await workflow.run();
+      await worker.tick();
+      await sleep(50);
+      await worker.tick();
+      await handle.result();
+
+      expect(snapshots.length).toBe(2);
+      expect(snapshots[0]).toEqual(snapshots[1]);
+    });
+  });
 });
 
 describe("createStepExecutionStateFromAttempts", () => {
diff --git a/packages/openworkflow/execution.ts b/packages/openworkflow/execution.ts
index 18bac5ac..dbf5a520 100644
--- a/packages/openworkflow/execution.ts
+++ b/packages/openworkflow/execution.ts
@@ -52,6 +52,14 @@ export type StepFunction<Output> = () =>
   | Output
   | undefined;
 
+/**
+ * Read-only workflow run metadata exposed to workflow functions.
+ */
+export type WorkflowRunMetadata = Pick<
+  WorkflowRun,
+  "id" | "workflowName" | "createdAt" | "startedAt"
+>;
+
 /**
  * Params passed to a workflow function for the user to use when defining steps.
  */
@@ -59,6 +67,7 @@ export interface WorkflowFunctionParams<Input> {
   input: Input;
   step: StepApi;
   version: string | null;
+  run: WorkflowRunMetadata;
 }
 
 /**
@@ -364,7 +373,6 @@ export async function executeWorkflow(
       }
     }
 
-    // create step executor
     const executor = new StepExecutor({
       backend,
       workflowRunId: workflowRun.id,
@@ -372,11 +380,19 @@ export async function executeWorkflow(
       attempts,
     });
 
+    const run = Object.freeze<WorkflowRunMetadata>({
+      id: workflowRun.id,
+      workflowName: workflowRun.workflowName,
+      createdAt: workflowRun.createdAt,
+      startedAt: workflowRun.startedAt,
+    });
+
     // execute workflow
     const output = await workflowFn({
       input: workflowRun.input as unknown,
       step: executor,
       version: workflowVersion,
+      run,
     });
 
     // mark success
diff --git a/packages/openworkflow/index.ts b/packages/openworkflow/index.ts
index fa0d6304..ec7636d6 100644
--- a/packages/openworkflow/index.ts
+++ b/packages/openworkflow/index.ts
@@ -2,6 +2,9 @@
 export type { OpenWorkflowOptions } from "./client.js";
 export { OpenWorkflow } from "./client.js";
 
+// execution
+export type { WorkflowRunMetadata } from "./execution.js";
+
 // worker
 export type { WorkerOptions } from "./worker.js";
 export { Worker } from "./worker.js";