In some places of our project we are using toMultimap() method which is marked as @Beta and consequently is considered as an unstable API.

See:
https://github.com/google/guava/blob/d7a26416109381a6770681bc6c299567615e8341/guava/src/com/google/common/collect/Multimaps.java#L108

So. There is already 29.0 version of Google Guava. When does it gonna be considered as a "stable API"?
I would provide you more examples of  similar "unstable API" methods from Guava...
}
    @Override
    public void clear() {
      map.clear();
    }
    @Override
    Set<K> createKeySet() {
      return map.keySet();
    }
    @Override
    Collection<V> createValues() {
      return map.values();
    }
    @Override
    public Set<Entry<K, V>> entries() {
      return map.entrySet();
    }
    @Override
    Collection<Entry<K, V>> createEntries() {
      throw new AssertionError("unreachable");
    }
    @Override
    Multiset<K> createKeys() {
      return new Multimaps.Keys<K, V>(this);
    }
    @Override
    Iterator<Entry<K, V>> entryIterator() {
      return map.entrySet().iterator();
    }
    @Override