Robot Inventor Hub (51515) - pybricks.experimental gives AttributeError after pybricks-primehub-v3.6.1.zip flash via pybricksdev (REPL shows 2025 build date)

[KeltosGG]

Hello Pybricks Team and Community,
I'm encountering a persistent issue with my LEGO MINDSTORMS Robot Inventor Hub (51515) where pybricks.experimental appears to be missing or inaccessible. My goal is to use pybricks.experimental.pb_ble_uart for BLE communication with a PC.

After flashing pybricks-primehub-v3.6.1.zip (downloaded from the official v3.6.1 GitHub release) using pybricksdev, the Hub's REPL reports itself as Pybricks MicroPython ci-release-86-v3.6.1 on 2025-03-11. When I try to import pybricks.experimental (which seems to pass without an ImportError initially) and then access any attribute like dir(pybricks.experimental) or use from pybricks.experimental import pb_ble_uart in a script, I get AttributeError: 'module' object has no attribute 'experimental'.
The "About Pybricks Code" dialog in my Pybricks Code web IDE (v2.6.0) also references "v3.6.1".

Steps Taken:
1.Tried the web flasher on code.pybricks.com (using Pybricks Code v2.6.0) multiple times with different browsers (Chrome, Edge, incognito mode). This did not resolve the issue.

2.Downloaded pybricks-primehub-v3.6.1.zip directly from the Pybricks v3.6.1 GitHub release assets page.
Used pybricksdev to flash this file. The flash process reported success (erase and download completed 100%).
pybricksdev Flash Log:

C:\Users\mahir>pybricksdev flash C:\Projects\MyAI_Robot\pybricks-primehub-v3.6.1.zip
Creating firmware...
Could not find hub in standard firmware mode. Trying DFU.
Failed to retrieve string descriptor 5
Failed to retrieve string descriptor 6
Failed to retrieve string descriptor 7
dfu-util 0.10-dev
Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2021 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to http://sourceforge.net/p/dfu-util/tickets/
Multiple alternate interfaces for DfuSe file
Opening DFU capable USB device...
Device ID 0694:0011
Device DFU version 011a
Claiming USB DFU Interface...
Setting Alternate Interface #0 ...
Determining device status...
DFU state(2) = dfuIDLE, status(0) = No error condition is present
DFU mode device DFU version 011a
Device returned transfer size 2048
DfuSe interface name: "LEGO LES HUB "
File contains 1 DFU images
Parsing DFU image 1
Target name: ST...
Image for alternate setting 0, (1 elements, total size = 279752)
Setting Alternate Interface #0 ...
Parsing element 1, address = 0x08008000, size = 279744
Erase           [=========================] 100%       279744 bytes
Erase    done.
Download        [=========================] 100%       279744 bytes
Download done.
Done parsing DfuSe file

REPL Output After Local Flash:
The REPL output after a successful pybricksdev flash and connecting to the Hub via Pybricks Code is as follows:

Pybricks MicroPython ci-release-86-v3.6.1 on 2025-03-11; SPIKE Prime Hub with STM32F413VG
Type "help()" for more information.
>>> import pybricks.experimental
>>> dir(pybricks.experimental)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'experimental'
>>> _

The REPL string Pybricks MicroPython ci-release-86-v3.6.1 on 2025-03-11 is particularly concerning. While the version tag is v3.6.1, the build date of 2025-03-11 seems anomalous for a firmware that was officially released around March 2024. Could this indicate an issue with the specific build artifact for pybricks-primehub-v3.6.1.zip in that release, or that I'm somehow getting a development/mislabeled build?

1.Is pybricks-primehub-v3.6.1.zip from the v3.6.1 release the correct and latest stable firmware for the LEGO MINDSTORMS Robot Inventor Hub (51515)?
2.Should pybricks.experimental (and specifically pb_ble_uart within it) be present and accessible in this official v3.6.1 firmware for this hub?
3.Is the 2025-03-11 build date reported by the Hub's REPL expected for the official pybricks-primehub-v3.6.1.zip firmware, or does this suggest a potential issue with the build/artifact?
4.Given the successful pybricksdev flash log, why might pybricks.experimental still be inaccessible? Are there any known issues or alternative steps for the Robot Inventor Hub?

I've been very careful with the flashing process and seem to have hit a roadblock. Any insights or guidance would be greatly appreciated!
Thank you,
KeltosGG

[laurensvalk]

There exists no function called pb_ble_uart, so it cannot be imported. What makes you think it exists?

[dlech]

AttributeError: 'module' object has no attribute 'experimental'

MicroPython imports don't work quite the same as regular Python. The only thing you could do right now is:

from pybricks.experimental import hello_world

There isn't anything else in the experimental module currently.

To be able to use dir() on the module, you can also import this way:

exp = __import__("pybricks.experimental")
print(dir(exp))

[KeltosGG]

Hi @laurensvalk and @dlech,
Thank you so much for the quick and very helpful clarifications! This definitely explains why my previous attempts to import pb_ble_uart directly from pybricks.experimental were failing.
My main goal is to establish a simple BLE UART-like communication channel between my Robot Inventor Hub and a Python script running on my PC (using bleak) so I can send string commands to the hub and have it react.

What is the current recommended/official method in Pybricks to create a custom BLE service that can receive data from a PC?
Is there another Pybricks module or specific example project I should be looking at for this kind of PC-to-hub BLE communication?
I'm eager to get the communication working. Any pointers to the correct modules, examples, or documentation for setting up a simple command-receiving BLE service on the hub would be fantastic!
Thanks again for your time and expertise.

[dlech]

What is the current recommended/official method in Pybricks to create a custom BLE service that can receive data from a PC?

https://pybricks.com/projects/tutorials/wireless/hub-to-device/

[KeltosGG]

I forgot one thing. Is the pybricks-primehub-v3.6.1.zip released in 2025-03-11 the right version for the Lego Inventor Hub (51515)?