This update adds more efficient ways for Odoo to combine groups of records internally. It can help developers and system processes handle record collections with less overhead, supporting better performance without changing everyday user workflows.

As the title says:

``` python
recs0.concat(recs1, ..., recsn)     # same as recs0 + recs1 + ... + recsn
recs0.union(recs1, ..., recsn)      # same as recs0 | recs1 | ... | recsn
```