Even the crashed Blue Scarab, early on, doesn't display much in the way of sentience. It doesn't do anything that a tactical database with a voice command couldn't - "Situation X occurs, suggest solution Y."

It doesn't adapt "Solution Y" to the fact that Jamie clearly and obviously prefers some solutions to others, or make allowances for a certain style of combat, or learn not to suggest things that its symbiote dislikes, or anything that would indicate learning or emotions. It barely displays life, let alone sentience.

It doesn't display any real kind of learning until after it is dominated by the Reach itself, when it acknowledges that it might have been comfortable with Hymie after all. I honestly think of it as being closer to a pet than a sentient being.