[BUG] RADKit 1.9.5 — fail with FastAPI > 0.131.0

MarcoZaurus — Sat, 28 Feb 2026 12:09:51 GMT

# [BUG] RADKit 1.9.5 — `create_devices` / `create_device` fail with FastAPI > 0.131.0

**Category:** RADKit / Python SDK / Control API

**RADKit version:** 1.9.5

**Affected methods:** `ControlAPI.create_devices()`, `ControlAPI.create_device()`

**Root cause:** Incompatibility with FastAPI >= 0.132.0

---

## Summary

When using the RADKit Python SDK (`cisco_radkit_service==1.9.5`) in an environment where FastAPI has been upgraded beyond version `0.131.0`, all write operations through `ControlAPI` fail silently with a Pydantic body-validation error. Read operations (`list_devices`, `get_service_status`) are unaffected.

This post was written with the help of Claude (Anthropic) who assisted in debugging and isolating the root cause.

---

## Symptoms

Calling `service.control_api.create_devices(devices)` with a valid `list[NewDevice]` returns an error result instead of raising a Python exception:

```

Input Validation Error

root=Error(

success=False,

message='Input should be a valid list',

detail=[{'type': 'list_type', 'msg': 'Input should be a valid list', 'loc': 'body'}]

)

```

Similarly, `create_device(device)` (singular) returns:

```

root=Error(

success=False,

message='Input should be a valid dictionary or object to extract fields from',

detail=[{'type': 'model_attributes_type', 'msg': '...', 'loc': 'body'}]

)

```

The Python call does **not** raise an exception — the error is embedded in the return value, making it easy to miss.

---

## Reproduction

### Environment that works

```

cisco_radkit_service==1.9.5

fastapi==0.131.0

starlette==0.52.1

pydantic==2.11.7

```

### Environment that fails

```

cisco_radkit_service==1.9.5

fastapi==0.134.0 ← any version > 0.131.0 is affected

starlette==0.52.1

pydantic==2.11.7

```

All versions of FastAPI strictly greater than `0.131.0` up to at least `0.134.0` are affected (tested exhaustively).

### Minimal reproduction script

```python

from radkit_client.sync import Client

from radkit_common.types import DeviceType

from radkit_service.webserver.models.devices import NewDevice, NewTerminal

terminal = NewTerminal(username="admin", password="Cisco123")

device = NewDevice(

name="test-device",

host="test-device.example.com",

deviceType=DeviceType.GENERIC,

terminal=terminal,

enabled=True,

)

with Client.create() as client:

service = client.create_service(

radkit_directory="local_radkit",

autobootstrap=True,

superadmin_password="<your_password>",

)

result = service.control_api.create_devices([device])

print(result)

# With fastapi==0.131.0 → BulkResult with success_count=1

# With fastapi>=0.132.0 → Error(success=False, message='Input should be a valid list')

```

---

## Root Cause Analysis

`service.control_api` is a synchronous proxy object (`radkit_service.control_api.ControlAPI`) that serializes Python calls into HTTP requests directed at RADKit's internal FastAPI webserver. The device objects (`NewDevice`, `NewTerminal`) use Pydantic `CustomSecretStr` fields for sensitive values (passwords, keys).

Between FastAPI `0.131.0` and `0.132.0`, the framework changed how it validates and deserializes request bodies containing Pydantic models with custom secret types. The internal HTTP layer can no longer correctly serialize `list[NewDevice]` into a valid JSON body, causing the FastAPI endpoint to reject it with a body-validation error before the actual logic is reached.

The error originates server-side inside RADKit's own webserver process, which is why no Python exception is raised — the call completes successfully from the SDK's perspective, but carries a failure payload.

**Key evidence:**

- `type(service.control_api)` → `<class 'radkit_service.control_api.ControlAPI'>` ✓ correct type

- `inspect.signature(service.control_api.create_devices)` → `(devices: Sequence[NewDevice]) -> BulkResult[StoredDeviceWithMetadata]` ✓ correct signature

- Passing `list[NewDevice]` → body validation error (FastAPI rejects it)

- Passing `list[dict]` (via `model_dump()`) → same error

- Downgrading to `fastapi==0.131.0` → works immediately, no code changes needed

---

## Workaround

Pin FastAPI to `0.131.0` until a fix is released:

```bash

pip install "fastapi==0.131.0"

```

Or in `pyproject.toml` / `requirements.txt`:

```

fastapi==0.131.0

```

---

## Request

Please pin or constrain the FastAPI version in RADKit's dependencies so that `pip install cisco_radkit_service` does not silently pull in an incompatible version. A constraint such as `fastapi>=0.100.0,<=0.131.0` (or whatever upper bound is validated) would prevent this issue for new installs.

Ideally, the incompatibility with FastAPI >= 0.132.0 should be investigated and fixed so that RADKit works with current releases of the framework.

---

*Tested on: Windows 11, Python 3.13, RADKit 1.9.5, integrated (bootstrap) service mode.*

*Debugging assisted by Claude (Anthropic).*

topic [BUG] RADKit 1.9.5 — fail with FastAPI > 0.131.0 in RADKit Discussions

[BUG] RADKit 1.9.5 — fail with FastAPI > 0.131.0