diff --git a/.github/workflows/functions-e2e-tests.yaml b/.github/workflows/functions-e2e-tests.yaml
index 7f62603c..2f23cc22 100644
--- a/.github/workflows/functions-e2e-tests.yaml
+++ b/.github/workflows/functions-e2e-tests.yaml
@@ -64,8 +64,14 @@ jobs:
       - name: "🏗️ Build in-repo durable-functions (+ core) for file: linking"
         run: npm run build -w durable-functions
 
+      # Core Tools is pinned to an exact version rather than the floating `@4`
+      # range: its postinstall downloads a platform zip from cdn.functions.azure.com
+      # and hard-fails (process.exit(1)) on any non-200, so a bad upstream publish
+      # breaks this job for every PR. `@4` floated onto 4.13.2, whose linux-x64 zip
+      # 404s on the CDN. Bump this pin deliberately once a newer version is
+      # confirmed to install.
       - name: 🔧 Install Azurite and Azure Functions Core Tools
-        run: npm install -g azurite azure-functions-core-tools@4
+        run: npm install -g azurite azure-functions-core-tools@4.12.1
 
       # --skipApiVersionCheck: the preview extension bundle's Azure Storage SDK
       # targets a newer REST API version than current Azurite accepts; without the
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 46e44627..b4508367 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ### New
 
+- Add an optional `newVersion` parameter to `OrchestrationContext.continueAsNew()` for version migrations.
 - Implement entity support in the in-memory testing backend ([#341](https://github.com/microsoft/durabletask-js/pull/341))
 - Add the top-level `StartOrchestrationOptions.dedupeStatuses` option, `ValidDedupeStatuses`, and
   `OrchestrationAlreadyExistsError`, aligned with the .NET status-based duplicate rejection and
diff --git a/README.md b/README.md
index aeaf9350..9c5b9ef9 100644
--- a/README.md
+++ b/README.md
@@ -170,6 +170,25 @@ const purchaseOrderWorkflow: TOrchestrator = async function* (ctx: Orchestration
 
 You can find the full sample at [examples/hello-world/human_interaction.ts](./examples/hello-world/human_interaction.ts).
 
+### Continue as new
+
+Long-running orchestrations can restart with fresh history and optionally move to a new
+orchestration version:
+
+```typescript
+const eternalOrchestrator: TOrchestrator = async function* (
+  ctx: OrchestrationContext,
+  iteration: number,
+): any {
+  yield ctx.callActivity(processIteration, iteration);
+  ctx.continueAsNew(iteration + 1, true, "2.0.0");
+};
+```
+
+The second argument controls whether unprocessed external events carry over. The optional third
+argument becomes the restarted orchestration's `ctx.version`; omit it to retain the existing
+continue-as-new behavior.
+
 ### Durable entities
 
 Durable entities provide a way to manage small pieces of state with a simple object-oriented programming model:
diff --git a/packages/azure-functions-durable/CHANGELOG.md b/packages/azure-functions-durable/CHANGELOG.md
index 880f1bd6..20f5d7f9 100644
--- a/packages/azure-functions-durable/CHANGELOG.md
+++ b/packages/azure-functions-durable/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ### New
 
+- Add optional orchestration version migration support to `context.df.continueAsNew()`.
 - Added a `durable-functions/testing` entry point with `runOrchestrator`, which runs an orchestrator
   to a terminal state against inline activity implementations on the in-memory backend and always
   releases its worker, and `createActivityContext` for invoking activity handlers directly.
diff --git a/packages/azure-functions-durable/README.md b/packages/azure-functions-durable/README.md
index d672a302..a8ec7ee9 100644
--- a/packages/azure-functions-durable/README.md
+++ b/packages/azure-functions-durable/README.md
@@ -37,6 +37,10 @@ changed:
   and throws when the instance is missing. `showInput` suppresses only the top-level input,
   `showHistory` populates `history`, and `showHistoryOutput` toggles the per-entry input/result
   payloads; `history` entries are core `HistoryEvent`s (v3 types `history` as `Array<unknown>`).
+  **`client.startNew()` supports the `version` option.**
+- **`context.df.continueAsNew(input, saveEvents, newVersion)` can migrate versions.** The optional
+  third argument assigns the restarted orchestration's version; existing one- and two-argument
+  calls keep their current behavior.
   **`client.startNew()` supports the `version` and top-level `dedupeStatuses` options.** Dedupe
   statuses select duplicate errors; other supported statuses are atomically replaced. The current
   shared protocol does not expose an atomic no-op/`IGNORE` action.
diff --git a/packages/azure-functions-durable/src/orchestration-context.ts b/packages/azure-functions-durable/src/orchestration-context.ts
index b4102e3b..4349d521 100644
--- a/packages/azure-functions-durable/src/orchestration-context.ts
+++ b/packages/azure-functions-durable/src/orchestration-context.ts
@@ -127,9 +127,13 @@ export class DurableOrchestrationContext {
     return this._ctx.waitForExternalEvent(name) as Task<T>;
   }
 
-  /** Restarts the orchestration with a new input. */
-  continueAsNew(input: unknown, saveEvents = true): void {
-    this._ctx.continueAsNew(input, saveEvents);
+  /** Restarts the orchestration with a new input and optionally a new version. */
+  continueAsNew(input: unknown, saveEvents = true, newVersion?: string): void {
+    if (newVersion === undefined) {
+      this._ctx.continueAsNew(input, saveEvents);
+    } else {
+      this._ctx.continueAsNew(input, saveEvents, newVersion);
+    }
   }
 
   /** Sets the orchestration's custom status payload. */
diff --git a/packages/azure-functions-durable/test/unit/orchestration-context.spec.ts b/packages/azure-functions-durable/test/unit/orchestration-context.spec.ts
index eb8f7e2d..2f9f7289 100644
--- a/packages/azure-functions-durable/test/unit/orchestration-context.spec.ts
+++ b/packages/azure-functions-durable/test/unit/orchestration-context.spec.ts
@@ -151,6 +151,15 @@ describe("DurableOrchestrationContext", () => {
     expect(entities.signalEntity).toHaveBeenCalledWith(entityId, "reset", undefined);
   });
 
+  it("forwards a new version when continuing as new", () => {
+    const { ctx, raw } = createFakeCoreContext();
+    const df = new DurableOrchestrationContext(ctx, undefined);
+
+    df.continueAsNew("next", false, "2.0.0");
+
+    expect(raw.continueAsNew).toHaveBeenCalledWith("next", false, "2.0.0");
+  });
+
   it("schedules callHttp as the built-in poll sub-orchestration with the built request payload", () => {
     const { ctx, raw } = createFakeCoreContext();
     const df = new DurableOrchestrationContext(ctx, undefined);
diff --git a/packages/durabletask-js/src/orchestration/exception/orchestration-already-exists-error.ts b/packages/durabletask-js/src/orchestration/exception/orchestration-already-exists-error.ts
index c50f22fc..a0e2eda6 100644
--- a/packages/durabletask-js/src/orchestration/exception/orchestration-already-exists-error.ts
+++ b/packages/durabletask-js/src/orchestration/exception/orchestration-already-exists-error.ts
@@ -3,7 +3,11 @@
 
 /** Thrown when an orchestration ID reuse request matches an existing dedupe status. */
 export class OrchestrationAlreadyExistsError extends Error {
-  constructor(message: string, options?: ErrorOptions) {
+  // The options type is spelled out structurally instead of using the ambient
+  // `ErrorOptions`, which only exists in the ES2022 lib. Naming it here would leak
+  // into the emitted .d.ts and break consumers compiling against an older lib
+  // (e.g. the `func`-style apps that default to `target: es6` without skipLibCheck).
+  constructor(message: string, options?: { cause?: unknown }) {
     super(message, options);
     this.name = "OrchestrationAlreadyExistsError";
   }
diff --git a/packages/durabletask-js/src/task/context/orchestration-context.ts b/packages/durabletask-js/src/task/context/orchestration-context.ts
index bf75699f..3847a0d7 100644
--- a/packages/durabletask-js/src/task/context/orchestration-context.ts
+++ b/packages/durabletask-js/src/task/context/orchestration-context.ts
@@ -163,8 +163,9 @@ export abstract class OrchestrationContext {
    *
    * @param newInput {any} The new input to use for the new orchestration instance.
    * @param saveEvents {boolean} A flag indicating whether to add any unprocessed external events in the new orchestration history.
+   * @param newVersion {string} The optional version to use for the new orchestration instance.
    */
-  abstract continueAsNew(newInput: any, saveEvents: boolean): void;
+  abstract continueAsNew(newInput: any, saveEvents: boolean, newVersion?: string): void;
 
   /**
    * Sets a custom status value for the current orchestration instance.
diff --git a/packages/durabletask-js/src/testing/in-memory-backend.ts b/packages/durabletask-js/src/testing/in-memory-backend.ts
index a0d9a498..6937381a 100644
--- a/packages/durabletask-js/src/testing/in-memory-backend.ts
+++ b/packages/durabletask-js/src/testing/in-memory-backend.ts
@@ -1049,6 +1049,14 @@ export class InMemoryOrchestrationBackend {
     if (status === pb.OrchestrationStatus.ORCHESTRATION_STATUS_CONTINUED_AS_NEW) {
       // Handle continue-as-new
       const newInput = completeAction.getResult()?.getValue();
+      const currentVersion = instance.history
+        .find((event) => event.hasExecutionstarted())
+        ?.getExecutionstarted()
+        ?.getVersion()
+        ?.getValue();
+      const newVersion = completeAction.hasNewversion()
+        ? completeAction.getNewversion()?.getValue()
+        : currentVersion;
       const carryoverEvents = completeAction.getCarryovereventsList();
 
       // Cancel timers still pending from the previous iteration. Their timer IDs are
@@ -1084,6 +1092,7 @@ export class InMemoryOrchestrationBackend {
         newInput,
         undefined,
         instance.executionId,
+        newVersion
       );
       instance.pendingEvents = [orchestratorStarted, executionStarted, ...carryoverEvents];
 
diff --git a/packages/durabletask-js/src/utils/pb-helper.util.ts b/packages/durabletask-js/src/utils/pb-helper.util.ts
index 9f353798..45e500cb 100644
--- a/packages/durabletask-js/src/utils/pb-helper.util.ts
+++ b/packages/durabletask-js/src/utils/pb-helper.util.ts
@@ -22,7 +22,14 @@ export function newOrchestratorStartedEvent(timestamp?: Date | null): pb.History
   return event;
 }
 
-export function newExecutionStartedEvent(name: string, instanceId: string, encodedInput?: string, parentInstance?: { name: string; instanceId: string; taskScheduledId: number }, executionId?: string): pb.HistoryEvent {
+export function newExecutionStartedEvent(
+  name: string,
+  instanceId: string,
+  encodedInput?: string,
+  parentInstance?: { name: string; instanceId: string; taskScheduledId: number },
+  executionId?: string,
+  version?: string,
+): pb.HistoryEvent {
   const ts = new Timestamp();
 
   const orchestrationInstance = new pb.OrchestrationInstance();
@@ -39,6 +46,7 @@ export function newExecutionStartedEvent(name: string, instanceId: string, encod
   executionStartedEvent.setName(name);
   executionStartedEvent.setInput(getStringValue(encodedInput));
   executionStartedEvent.setOrchestrationinstance(orchestrationInstance);
+  executionStartedEvent.setVersion(getStringValueIfDefined(version));
 
   // Set parent instance info if provided (for sub-orchestrations)
   if (parentInstance) {
@@ -360,6 +368,16 @@ export function getStringValue(val?: string): StringValue | undefined {
   return stringValue;
 }
 
+function getStringValueIfDefined(val?: string): StringValue | undefined {
+  if (val === undefined) {
+    return;
+  }
+
+  const stringValue = new StringValue();
+  stringValue.setValue(val);
+  return stringValue;
+}
+
 /**
  * Populates a tag map with the provided tags.
  *
@@ -390,12 +408,14 @@ export function newCompleteOrchestrationAction(
   result?: string,
   failureDetails?: pb.TaskFailureDetails,
   carryoverEvents?: pb.HistoryEvent[] | null,
+  newVersion?: string,
 ): pb.OrchestratorAction {
   const completeOrchestrationAction = new pb.CompleteOrchestrationAction();
   completeOrchestrationAction.setOrchestrationstatus(status);
   completeOrchestrationAction.setResult(getStringValue(result));
   completeOrchestrationAction.setFailuredetails(failureDetails);
   completeOrchestrationAction.setCarryovereventsList(carryoverEvents || []);
+  completeOrchestrationAction.setNewversion(getStringValueIfDefined(newVersion));
 
   const action = new pb.OrchestratorAction();
   action.setId(id);
@@ -679,4 +699,3 @@ function wrapEntityMessageAction(
   action.setSendentitymessage(sendEntityMessage);
   return action;
 }
-
diff --git a/packages/durabletask-js/src/worker/runtime-orchestration-context.ts b/packages/durabletask-js/src/worker/runtime-orchestration-context.ts
index 828deb4e..39caea41 100644
--- a/packages/durabletask-js/src/worker/runtime-orchestration-context.ts
+++ b/packages/durabletask-js/src/worker/runtime-orchestration-context.ts
@@ -49,6 +49,7 @@ export class RuntimeOrchestrationContext extends OrchestrationContext {
   _pendingEvents: Record<string, CompletableTask<any>[]>;
   _newInput?: any;
   _saveEvents: boolean;
+  _newVersion?: string;
   _customStatus?: string;
   _entityFeature: RuntimeOrchestrationEntityFeature;
 
@@ -72,6 +73,7 @@ export class RuntimeOrchestrationContext extends OrchestrationContext {
     this._pendingEvents = {};
     this._newInput = undefined;
     this._saveEvents = false;
+    this._newVersion = undefined;
     this._customStatus = undefined;
     this._entityFeature = new RuntimeOrchestrationEntityFeature(this);
   }
@@ -258,7 +260,7 @@ export class RuntimeOrchestrationContext extends OrchestrationContext {
     this._pendingActions[action.getId()] = action;
   }
 
-  setContinuedAsNew(newInput: any, saveEvents: boolean) {
+  setContinuedAsNew(newInput: any, saveEvents: boolean, newVersion?: string) {
     if (this._isComplete) {
       return;
     }
@@ -267,6 +269,7 @@ export class RuntimeOrchestrationContext extends OrchestrationContext {
     this._completionStatus = pb.OrchestrationStatus.ORCHESTRATION_STATUS_CONTINUED_AS_NEW;
     this._newInput = newInput;
     this._saveEvents = saveEvents;
+    this._newVersion = newVersion;
   }
 
   getActions(): pb.OrchestratorAction[] {
@@ -292,6 +295,7 @@ export class RuntimeOrchestrationContext extends OrchestrationContext {
         this._newInput !== undefined ? JSON.stringify(this._newInput) : undefined,
         undefined,
         carryoverEvents,
+        this._newVersion,
       );
 
       // Include fire-and-forget actions (sendEvent, signalEntity, etc.) that were
@@ -459,14 +463,15 @@ export class RuntimeOrchestrationContext extends OrchestrationContext {
   }
 
   /**
-   * Orchestrations can be continued as new. This API allows an  orchestration to restart itself from scratch, optionally with a new input.
+   * Restarts the orchestration with fresh history, optionally carrying over unprocessed events
+   * and assigning a new orchestration version.
    */
-  continueAsNew(newInput: any, saveEvents: boolean = false) {
+  continueAsNew(newInput: any, saveEvents: boolean = false, newVersion?: string) {
     if (this._isComplete) {
       return;
     }
 
-    this.setContinuedAsNew(newInput, saveEvents);
+    this.setContinuedAsNew(newInput, saveEvents, newVersion);
   }
 
   /**
diff --git a/packages/durabletask-js/test/in-memory-backend.spec.ts b/packages/durabletask-js/test/in-memory-backend.spec.ts
index 647845ec..0c9f11ac 100644
--- a/packages/durabletask-js/test/in-memory-backend.spec.ts
+++ b/packages/durabletask-js/test/in-memory-backend.spec.ts
@@ -14,6 +14,7 @@ import {
   TOrchestrator,
 } from "../src";
 import * as pb from "../src/proto/orchestrator_service_pb";
+import { StringValue } from "google-protobuf/google/protobuf/wrappers_pb";
 
 describe("In-Memory Backend", () => {
   let backend: InMemoryOrchestrationBackend;
@@ -331,6 +332,81 @@ describe("In-Memory Backend", () => {
     expect(state?.serializedOutput).toEqual(JSON.stringify(5));
   });
 
+  it("should retain the current version when continue-as-new omits a new version", async () => {
+    const observedVersions: string[] = [];
+    const orchestrator: TOrchestrator = async (ctx: OrchestrationContext, input: number) => {
+      if (!ctx.isReplaying) {
+        observedVersions.push(ctx.version);
+      }
+
+      if (input === 0) {
+        ctx.continueAsNew(1, false, "2.0.0");
+        return;
+      }
+
+      if (input === 1) {
+        ctx.continueAsNew(2, false);
+        return;
+      }
+
+      return ctx.version;
+    };
+
+    worker.addOrchestrator(orchestrator);
+    const id = "versioned-continue-as-new";
+    backend.createInstance(id, getName(orchestrator), JSON.stringify(0));
+    const initialExecutionStarted = backend
+      .getInstance(id)
+      ?.pendingEvents.find((event) => event.hasExecutionstarted())
+      ?.getExecutionstarted();
+    const initialVersion = new StringValue();
+    initialVersion.setValue("1.0.0");
+    initialExecutionStarted?.setVersion(initialVersion);
+    await worker.start();
+
+    const state = await client.waitForOrchestrationCompletion(id, true, 10);
+
+    expect(state).toBeDefined();
+    expect(state?.runtimeStatus).toEqual(OrchestrationStatus.COMPLETED);
+    expect(state?.serializedOutput).toEqual(JSON.stringify("2.0.0"));
+    expect(observedVersions).toEqual(["1.0.0", "2.0.0", "2.0.0"]);
+  });
+
+  it("should clear the current version when continue-as-new specifies an empty version", async () => {
+    const observedVersions: string[] = [];
+    const orchestrator: TOrchestrator = async (ctx: OrchestrationContext, input: number) => {
+      if (!ctx.isReplaying) {
+        observedVersions.push(ctx.version);
+      }
+
+      if (input === 0) {
+        ctx.continueAsNew(1, false, "");
+        return;
+      }
+
+      return ctx.version;
+    };
+
+    worker.addOrchestrator(orchestrator);
+    const id = "clear-version-continue-as-new";
+    backend.createInstance(id, getName(orchestrator), JSON.stringify(0));
+    const initialExecutionStarted = backend
+      .getInstance(id)
+      ?.pendingEvents.find((event) => event.hasExecutionstarted())
+      ?.getExecutionstarted();
+    const initialVersion = new StringValue();
+    initialVersion.setValue("2.0.0");
+    initialExecutionStarted?.setVersion(initialVersion);
+    await worker.start();
+
+    const state = await client.waitForOrchestrationCompletion(id, true, 10);
+
+    expect(state).toBeDefined();
+    expect(state?.runtimeStatus).toEqual(OrchestrationStatus.COMPLETED);
+    expect(state?.serializedOutput).toEqual(JSON.stringify(""));
+    expect(observedVersions).toEqual(["2.0.0", ""]);
+  });
+
   it("should not collide default sub-orchestration instance IDs across continue-as-new generations", async () => {
     // Regression for the callHttp-on-continueAsNew collision: a default (auto-derived) child
     // instance ID must be unique per generation. Before the fix the derived ID was
diff --git a/packages/durabletask-js/test/orchestration_executor.spec.ts b/packages/durabletask-js/test/orchestration_executor.spec.ts
index 94a9780a..82f720a1 100644
--- a/packages/durabletask-js/test/orchestration_executor.spec.ts
+++ b/packages/durabletask-js/test/orchestration_executor.spec.ts
@@ -1010,6 +1010,7 @@ describe("Orchestration Executor", () => {
       );
       expect(completeAction?.getResult()?.getValue()).toEqual(JSON.stringify(2));
       expect(completeAction?.getCarryovereventsList()?.length).toEqual(saveEvent ? 3 : 0);
+      expect(completeAction?.getNewversion()).toBeUndefined();
 
       for (let i = 0; i < (completeAction?.getCarryovereventsList()?.length ?? 0); i++) {
         const event = completeAction?.getCarryovereventsList()[i];
@@ -1024,6 +1025,29 @@ describe("Orchestration Executor", () => {
     }
   });
 
+  it("should set the new version on a continue-as-new action", async () => {
+    const orchestrator: TOrchestrator = async (ctx: OrchestrationContext, input: number) => {
+      ctx.continueAsNew(input + 1, false, "2.0.0");
+    };
+
+    const registry = new Registry();
+    const orchestratorName = registry.addOrchestrator(orchestrator);
+    const newEvents = [
+      newOrchestratorStartedEvent(),
+      newExecutionStartedEvent(orchestratorName, TEST_INSTANCE_ID, "1"),
+    ];
+
+    const executor = new OrchestrationExecutor(registry, testLogger);
+    const result = await executor.execute(TEST_INSTANCE_ID, [], newEvents);
+
+    const completeAction = getAndValidateSingleCompleteOrchestrationAction(result);
+    expect(completeAction?.getOrchestrationstatus()).toEqual(
+      pb.OrchestrationStatus.ORCHESTRATION_STATUS_CONTINUED_AS_NEW,
+    );
+    expect(completeAction?.getResult()?.getValue()).toEqual(JSON.stringify(2));
+    expect(completeAction?.getNewversion()?.getValue()).toEqual("2.0.0");
+  });
+
   it("should test that a fan-out pattern correctly schedules N tasks", async () => {
     const hello = async (_: any, name: string) => {
       return `Hello ${name}`;