Wizard multiclass can scribe the level of spells they have slots for.
Half and one-third caster classes are rounded UP, not down, when determining spell slots.
My Eldritch Knight started double Fireballing enemies with Action Surge at lvl 8, Fighter 5 / Wizard 3. Spell slots 4 3 2. In 5e you would have to be 10th level 5/5. Eldritch Knight needed a buff, but certainly not like this. And this affects all caster classes.
A Cleric 11 / Wizard 1 will get access to both 6th level Cleric spells AND 6th level Wizard spells. By having one level of Wizard. (Probably Cleric 10 / Wizard 1 already gets 11th level spells from Cleric list as well.)
That was my understanding from what I have read and seen online since launch.
Larian completely borked the system and are probably very satisfied with the exploitable mess of a situation they created because class identity is dissolved into a classless caster system. A Wizard should always dip in 1 level Cleric for Heavy Armor and the entire Divine spell list. A Wizard can freely dip into Sorcerer for their metamagic abilities (and pick only spells that don't require Cha, like Shield) without losing anything except 1 prepared spell per non-Wizard level which is not a big deal. It's really stupid but there it is now. WotC should have more say about Larian messing things up so badly but I doubt their contract allows it.
Except my understanding is this only works when multiclassing out of wizard. I don't believe one could roll cleric 1/wizard 11 and achieve a similar effect.
