Items have to be added one by one using [`add_collection_item`]. You only need to know the `collection_slug`, `item_id` and `item_type`. Optionally, you can also add a `note` to the item (500 characters maximum).  
```py
>>> from huggingface_hub import create_collection, add_collection_item

>>> collection = create_collection(title="OS Week Highlights - Sept 18 - 24", namespace="osanseviero")
>>> collection.slug
"osanseviero/os-week-highlights-sept-18-24-650bfed7f795a59f491afb80"

>>> add_collection_item(collection.slug, item_id="coqui/xtts", item_type="space")
>>> add_collection_item(
...     collection.slug,
...     item_id="warp-ai/wuerstchen",
...     item_type="model",
...     note="Würstchen is a new fast and efficient high resolution text-to-image architecture and model"
... )
>>> add_collection_item(collection.slug, item_id="lmsys/lmsys-chat-1m", item_type="dataset")
>>> add_collection_item(collection.slug, item_id="warp-ai/wuerstchen", item_type="space") # same item_id, different item_type
```  
If an item already exists in a collection (same `item_id`/`item_type` pair), an HTTP 409 error will be raised. You can choose to ignore this error by setting `exists_ok=True`.