Intelligence is the casting ability

Spell attack rolls and spell save DC use Intelligence. A low-Intelligence Arcane Trickster can still choose useful spells that do not require an attack roll or saving throw, but control-focused builds benefit greatly from higher Intelligence.

Spells known, not daily preparation

The subclass learns a limited set of Wizard spells. It does not prepare a new list after every long rest and does not gain the Wizard's spellbook system.

The 2014 school restriction matters

Most Arcane Trickster spells learned through the subclass must come from enchantment or illusion. A smaller number of spell choices gained at specified Rogue levels can come from any Wizard school. This is the 2014 restriction; the 2024 Arcane Trickster uses different rules.

Mage hand is special

Mage hand is part of the subclass's identity because Mage Hand Legerdemain expands what it can do and later Versatile Trickster uses the hand to create combat advantage.

Spellcasting and Sneak Attack use different engines

A spell attack does not normally deliver Sneak Attack. The strongest Arcane Trickster turns often use magic to set up or protect a weapon attack rather than trying to stack Sneak Attack onto a spell.