As a 1st-level character, the Warlock cantrip eldritch blast can be used with the Twinned Spell Metamagic feature of the sorcerer.
However, when a character reaches 5th level, eldritch blast becomes a spell with two possible targets, and can no longer be twinned.
Can a 5th-level character cast the 1st-level version of a cantrip?
Best Answer
When you cast a spell that has an actual level given below its name, you choose (and expend) a slot equal to the spell's level or higher and the spell is cast at that level. This is all better explained on page 201 of the PHB. Some spells have additional effects that happen when you cast them using a higher level slot.
Cantrips however are a slightly different story; their spell level is 0, they don't expend spell slots and as such they can't be cast at a higher, or lower, level (PHB pg.201).
This means that there is no choosing the level at which it's cast because its spell level is always constant.
The extra effects gained by a cantrip aren't based on slot level but on your character level and are worded in such a way that doesn't give you a choice of whether they happen or not.
For example:
or
As opposed to spells that use slots: