diff --git a/CHANGELOG.md b/CHANGELOG.md
index c655fdb..eea8945 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,11 +8,13 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 
 ### Added
 
+- `examples/` directory with sync and async downstream-SDK integration scripts demonstrating the extension API against the free `simulator`.
 - `QctrlQaoaJobCreationPayload` and `QctrlQaoaJobInput` for submitting Q-CTRL QAOA maxcut combinatorial-optimization jobs via `create_job`. The `create_job` body union now also accepts `QctrlQaoaJobCreationPayload`.
-- `cost_model` optional field on `BaseJob`, `GetCircuitJobResponse`, and `GetJobResponse`, typed as `CostModel` (`"quantum_compute_time"` or `"execution_time"`).
+- `cost_model` optional field on `BaseJob`, `GetCircuitJobResponse`, and `GetJobResponse`, typed as `CostModel` (`"quantum_compute_time"`, `"execution_time"`, `"QCT"`, or `"2QGE_operations"`).
 
 ### Changed
 
+- Extended the local OpenAPI overlay so `CostModel` accepts live API values (`QCT`, `2QGE_operations`) returned by completed jobs; fixes `get_job` deserialization failures during polling.
 - `NativeCircuitInput.qubits` and `JsonMultiCircuitInput.qubits` are now `int | Unset` (previously `float | Unset`), matching upstream's tightening to `format: int32, minimum: 1`. `QisCircuitInput.qubits` already had this type locally via the OpenAPI overlay; that overlay action has been removed now that upstream is correct natively.
 
 ## [0.1.1] - 2026-04-30
diff --git a/README.md b/README.md
index 992bbde..69b8437 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,15 @@ Each generated endpoint module exposes four callables: `sync`, `sync_detailed`,
 
 For options (`api_key`, `base_url`, `max_retries`, `timeout`, `extension`), error classes, retry behavior, pagination, polling, sessions, and downstream-SDK extension hooks, see the [API reference](https://ionq.github.io/ionq-core-python/).
 
+## Examples
+
+Runnable scripts for downstream SDK integration live in [`examples/`](examples/):
+
+- [`downstream_integration.py`](examples/downstream_integration.py) — sync `ClientExtension` integration (event hooks, error mapping, Bell-state job).
+- [`downstream_integration_async.py`](examples/downstream_integration_async.py) — the same flow on the async path.
+
+See [`examples/README.md`](examples/README.md) for setup (`pip install ionq-core`, `export IONQ_API_KEY=...`).
+
 ## Versioning
 
 This package follows [SemVer 2.0](https://semver.org/spec/v2.0.0.html), independent of the upstream REST API version - pass an explicit `base_url` to `IonQClient` to pin against a different API. Print the installed version with:
diff --git a/examples/README.md b/examples/README.md
new file mode 100644
index 0000000..21047f2
--- /dev/null
+++ b/examples/README.md
@@ -0,0 +1,49 @@
+# ionq-core examples
+
+Runnable scripts that demonstrate how downstream SDKs integrate with `ionq-core`
+through the [extension API](https://ionq.github.io/ionq-core-python/ionq_core/extensions.html).
+
+## Setup
+
+```sh
+pip install ionq-core
+export IONQ_API_KEY=your-api-key
+```
+
+Create a free account at [identity.ionq.com/create-account](https://identity.ionq.com/create-account) if you need an API key. Both scripts target the free `simulator` backend.
+
+On Windows PowerShell:
+
+```powershell
+$env:IONQ_API_KEY = "your-api-key"
+python examples/downstream_integration.py
+```
+
+From a clone of this repository you can also use:
+
+```sh
+uv run python examples/downstream_integration.py
+```
+
+## Scripts
+
+| Script | What it demonstrates |
+| --- | --- |
+| [`downstream_integration.py`](downstream_integration.py) | Sync `ClientExtension`: `user_agent_token`, `default_headers`, `EventHook`, `error_mapper`, Bell-state job lifecycle |
+| [`downstream_integration_async.py`](downstream_integration_async.py) | Same flow with `AsyncEventHook`, `async_wait_for_job`, and `asyncio` endpoints |
+
+Each script configures a `ClientExtension` with:
+
+- `user_agent_token` — downstream SDK identity in the `User-Agent` header
+- `default_headers` — SDK-specific headers on every request
+- `EventHook` / `AsyncEventHook` — request, response, and error logging
+- `error_mapper` — wraps `APIError` and `RateLimitError` (including `request_id`) into SDK types when a real API call fails
+
+After submitting a Bell-state circuit and waiting for completion, the scripts print
+the job id, status, and measured probabilities (expect roughly equal weight on
+`|00⟩` and `|11⟩`).
+
+```sh
+python examples/downstream_integration.py
+python examples/downstream_integration_async.py
+```
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diff --git a/examples/__pycache__/sdk_shared.cpython-311.pyc b/examples/__pycache__/sdk_shared.cpython-311.pyc
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diff --git a/examples/downstream_integration.py b/examples/downstream_integration.py
new file mode 100644
index 0000000..5c14b64
--- /dev/null
+++ b/examples/downstream_integration.py
@@ -0,0 +1,135 @@
+# SPDX-FileCopyrightText: 2026 IonQ, Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+"""Sync downstream-SDK example: ClientExtension + Bell state on simulator.
+
+Shows how a higher-level SDK wraps ionq-core with ``user_agent_token``,
+``default_headers``, an ``EventHook``, and an ``error_mapper`` that translates
+``APIError`` / ``RateLimitError`` into SDK-defined exception types.
+
+Extension API reference:
+https://ionq.github.io/ionq-core-python/ionq_core/extensions.html
+"""
+
+from __future__ import annotations
+
+import logging
+import sys
+
+import httpx
+
+from ionq_core import APIError, ClientExtension, EventHook, IonQClient, RateLimitError, wait_for_job
+from ionq_core.api.default import create_job, get_job_probabilities
+from ionq_core.models.circuit_job_creation_payload import CircuitJobCreationPayload
+
+SDK_NAME = "example-sdk/0.1.0"
+logger = logging.getLogger(__name__)
+
+BELL_CIRCUIT = CircuitJobCreationPayload.from_dict(
+    {
+        "type": "ionq.circuit.v1",
+        "backend": "simulator",
+        "shots": 100,
+        "input": {
+            "gateset": "qis",
+            "qubits": 2,
+            "circuit": [
+                {"gate": "h", "target": 0},
+                {"gate": "cnot", "control": 0, "target": 1},
+            ],
+        },
+    }
+)
+
+
+class ExampleSDKError(Exception):
+    """Base exception for this example downstream SDK."""
+
+
+class ExampleAPIError(ExampleSDKError):
+    """SDK wrapper around ionq-core HTTP API errors."""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        status_code: int | None = None,
+        request_id: str | None = None,
+    ) -> None:
+        self.status_code = status_code
+        self.request_id = request_id
+        super().__init__(message)
+
+
+class ExampleRateLimitError(ExampleAPIError):
+    """SDK wrapper around ionq-core rate-limit errors."""
+
+    def __init__(self, message: str, *, retry_after: float | None = None) -> None:
+        self.retry_after = retry_after
+        super().__init__(message, status_code=429)
+
+
+class LoggingHook(EventHook):
+    """Sync event hook: log requests, responses, and transport failures."""
+
+    def on_request(self, request: httpx.Request) -> None:
+        logger.info("--> %s %s", request.method, request.url)
+
+    def on_response(self, request: httpx.Request, response: httpx.Response) -> None:
+        logger.info("<-- %s %s", response.status_code, request.url)
+
+    def on_error(self, request: httpx.Request, error: Exception) -> None:
+        logger.warning("!! %s %s failed: %s", request.method, request.url, error)
+
+
+def map_ionq_error(exc: Exception) -> Exception:
+    if isinstance(exc, RateLimitError):
+        return ExampleRateLimitError(f"IonQ rate limit: {exc.message}", retry_after=exc.retry_after)
+    if isinstance(exc, APIError):
+        return ExampleAPIError(
+            f"IonQ API {exc.status_code}: {exc.message}",
+            status_code=exc.status_code,
+            request_id=exc.request_id,
+        )
+    return exc
+
+
+def main() -> int:
+    logging.basicConfig(level=logging.INFO, format="%(levelname)s %(message)s")
+    logging.getLogger("httpx").setLevel(logging.WARNING)
+
+    extension = ClientExtension(
+        user_agent_token=SDK_NAME,
+        default_headers={"X-Example-SDK": SDK_NAME},
+        event_hooks=(LoggingHook(),),
+        error_mapper=map_ionq_error,
+    )
+
+    try:
+        with IonQClient(extension=extension) as client:
+            job = create_job.sync(client=client, body=BELL_CIRCUIT)
+            if job is None:
+                raise ExampleSDKError("create_job returned no job")
+
+            completed = wait_for_job(client, job.id, timeout=120)
+            probs = get_job_probabilities.sync(uuid=job.id, client=client)
+            if probs is None:
+                raise ExampleSDKError(f"get_job_probabilities returned no data for job {job.id}")
+
+            print()
+            print("Bell-state job on simulator")
+            print(f"  job_id:  {completed.id}")
+            print(f"  status:  {completed.status}")
+            print(f"  results: {probs.additional_properties}")
+    except ExampleSDKError:
+        logger.exception("downstream SDK call failed")
+        return 1
+    except ValueError as exc:
+        logger.error("%s", exc)
+        return 1
+
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/examples/downstream_integration_async.py b/examples/downstream_integration_async.py
new file mode 100644
index 0000000..e4ed2c0
--- /dev/null
+++ b/examples/downstream_integration_async.py
@@ -0,0 +1,142 @@
+# SPDX-FileCopyrightText: 2026 IonQ, Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+"""Async downstream-SDK example: ClientExtension + Bell state on simulator.
+
+Same flow as ``downstream_integration.py`` using ``AsyncEventHook``,
+``async_wait_for_job``, and the ``asyncio`` endpoint variants.
+
+Extension API reference:
+https://ionq.github.io/ionq-core-python/ionq_core/extensions.html
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+import sys
+
+import httpx
+
+from ionq_core import (
+    APIError,
+    AsyncEventHook,
+    ClientExtension,
+    IonQClient,
+    RateLimitError,
+    async_wait_for_job,
+)
+from ionq_core.api.default import create_job, get_job_probabilities
+from ionq_core.models.circuit_job_creation_payload import CircuitJobCreationPayload
+
+SDK_NAME = "example-sdk/0.1.0"
+logger = logging.getLogger(__name__)
+
+BELL_CIRCUIT = CircuitJobCreationPayload.from_dict(
+    {
+        "type": "ionq.circuit.v1",
+        "backend": "simulator",
+        "shots": 100,
+        "input": {
+            "gateset": "qis",
+            "qubits": 2,
+            "circuit": [
+                {"gate": "h", "target": 0},
+                {"gate": "cnot", "control": 0, "target": 1},
+            ],
+        },
+    }
+)
+
+
+class ExampleSDKError(Exception):
+    """Base exception for this example downstream SDK."""
+
+
+class ExampleAPIError(ExampleSDKError):
+    """SDK wrapper around ionq-core HTTP API errors."""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        status_code: int | None = None,
+        request_id: str | None = None,
+    ) -> None:
+        self.status_code = status_code
+        self.request_id = request_id
+        super().__init__(message)
+
+
+class ExampleRateLimitError(ExampleAPIError):
+    """SDK wrapper around ionq-core rate-limit errors."""
+
+    def __init__(self, message: str, *, retry_after: float | None = None) -> None:
+        self.retry_after = retry_after
+        super().__init__(message, status_code=429)
+
+
+class AsyncLoggingHook(AsyncEventHook):
+    """Async event hook: log requests, responses, and transport failures."""
+
+    async def on_request(self, request: httpx.Request) -> None:
+        logger.info("--> %s %s", request.method, request.url)
+
+    async def on_response(self, request: httpx.Request, response: httpx.Response) -> None:
+        logger.info("<-- %s %s", response.status_code, request.url)
+
+    async def on_error(self, request: httpx.Request, error: Exception) -> None:
+        logger.warning("!! %s %s failed: %s", request.method, request.url, error)
+
+
+def map_ionq_error(exc: Exception) -> Exception:
+    if isinstance(exc, RateLimitError):
+        return ExampleRateLimitError(f"IonQ rate limit: {exc.message}", retry_after=exc.retry_after)
+    if isinstance(exc, APIError):
+        return ExampleAPIError(
+            f"IonQ API {exc.status_code}: {exc.message}",
+            status_code=exc.status_code,
+            request_id=exc.request_id,
+        )
+    return exc
+
+
+async def main() -> int:
+    logging.basicConfig(level=logging.INFO, format="%(levelname)s %(message)s")
+    logging.getLogger("httpx").setLevel(logging.WARNING)
+
+    extension = ClientExtension(
+        user_agent_token=SDK_NAME,
+        default_headers={"X-Example-SDK": SDK_NAME},
+        async_event_hooks=(AsyncLoggingHook(),),
+        error_mapper=map_ionq_error,
+    )
+
+    try:
+        async with IonQClient(extension=extension) as client:
+            job = await create_job.asyncio(client=client, body=BELL_CIRCUIT)
+            if job is None:
+                raise ExampleSDKError("create_job returned no job")
+
+            completed = await async_wait_for_job(client, job.id, timeout=120)
+            probs = await get_job_probabilities.asyncio(uuid=job.id, client=client)
+            if probs is None:
+                raise ExampleSDKError(f"get_job_probabilities returned no data for job {job.id}")
+
+            print()
+            print("Bell-state job on simulator")
+            print(f"  job_id:  {completed.id}")
+            print(f"  status:  {completed.status}")
+            print(f"  results: {probs.additional_properties}")
+    except ExampleSDKError:
+        logger.exception("downstream SDK call failed")
+        return 1
+    except ValueError as exc:
+        logger.error("%s", exc)
+        return 1
+
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(asyncio.run(main()))
diff --git a/ionq_core/models/cost_model.py b/ionq_core/models/cost_model.py
index c464277..3348e36 100644
--- a/ionq_core/models/cost_model.py
+++ b/ionq_core/models/cost_model.py
@@ -4,9 +4,9 @@
 
 from typing import Literal, cast
 
-CostModel = Literal['execution_time', 'quantum_compute_time']
+CostModel = Literal['2QGE_operations', 'execution_time', 'QCT', 'quantum_compute_time']
 
-COST_MODEL_VALUES: set[CostModel] = { 'execution_time', 'quantum_compute_time',  }
+COST_MODEL_VALUES: set[CostModel] = { '2QGE_operations', 'execution_time', 'QCT', 'quantum_compute_time',  }
 
 def check_cost_model(value: str) -> CostModel:
     if value in COST_MODEL_VALUES:
diff --git a/openapi-overlay.yaml b/openapi-overlay.yaml
index d371a15..6ce154a 100644
--- a/openapi-overlay.yaml
+++ b/openapi-overlay.yaml
@@ -1,7 +1,7 @@
 overlay: 1.0.0
 info:
   title: ionq-core-python local OpenAPI fixes
-  version: 0.2.0
+  version: 0.3.0
   description: |
     Patches applied to openapi.json before client generation. The upstream
     spec marks QisCircuitInput.qubits as optional, but the simulator
@@ -13,6 +13,9 @@ info:
     (and extended it to NativeCircuitInput and JsonMultiCircuitInput), so
     that action was removed.
 
+    CostModel is extended with live API values (``QCT``, ``2QGE_operations``)
+    that the platform returns but the vendored spec has not yet adopted.
+
 actions:
   - target: $.components.schemas.QisCircuitInput.required
     remove: true
@@ -22,3 +25,12 @@ actions:
         - circuit
         - gateset
         - qubits
+  - target: $.components.schemas.CostModel.enum
+    remove: true
+  - target: $.components.schemas.CostModel
+    update:
+      enum:
+        - quantum_compute_time
+        - execution_time
+        - QCT
+        - 2QGE_operations