adverb, noun which may take the genitive case particle 'no'
more than expected; beyond expectations
Used adverbially or with の to describe a result that exceeds what was anticipated. Often appears with verbs like なる, だ, or 難しい.
The exam was more difficult than expected.
The exam was more difficult than I expected.
We achieved results beyond expectations.
The new product got a bigger response than expected.
The construction took more time than expected.
予想外 emphasizes surprise at something unforeseen, while 予想以上 neutrally states that a result exceeded the expected level.
案外 expresses personal surprise that something turned out differently than thought, whereas 予想以上 specifically measures a result as exceeding a prior estimate.
Compound of 予想 (expectation) + 以上 (more than, above). The meaning is transparent from its parts.