You can choose to continue using the @slash decorator while splitting your code into multiple classes / files if you like, just that you will still need to instantiate each class in __main__.py and pass the required BDK services along with ActivityRegistry.

# __main__.py
from .my_file import MyClass

async def run():
    config = BdkConfigLoader.load_from_file(Path.joinpath(current_dir, 'resources', 'config.yaml'))

    async with SymphonyBdk(config) as bdk:
        datafeed_loop = bdk.datafeed()
        datafeed_loop.subscribe(MessageListener())

        MyClass(bdk.activities(), bdk.messages())

        await datafeed_loop.start()

# my_file.py
class MyClass():
    def __init__(self, activities: ActivityRegistry, messages: MessageService):
        @activities.slash("/mycommand")
        async def do_something(context: CommandContext):
            await messages.send_message(context.stream_id, "Hello!")