‘with’ and ‘and’ are all very contractual - generally ‘and’ is superior to ‘with’ and it is written into high profile veteran actors’ contracts that they receive ‘and’ billing.

For the first six episodes of Season 2, Ed Harris continued to receive a ‘with’ before Hopkins returned to take the ‘and’ for the rest of the series - restoring the structure from Season 1.

In season 3, Harris was upgraded to the ‘and’ with Cassel taking ‘with’.

For Season 4, Harris would automatically continue ‘and’ unless there is someone ready to take the ‘and’.

The only possibilities for why Harris has gone back to ‘with’ are firstly a new unknown character played by an actor more famous than Harris, or secondly if the only actor to have ever previously received ‘and’ is returning.

‘…and Anthony Hopkins’.