Bändi oli energinen loppuun asti.

Oli is the past tense of olla (to be).

• on = is
• oli = was

So Bändi oli energinen means The band was energetic.

After olla (to be), Finnish usually uses the adjective in the nominative form when it describes what something is/was.

So:

• Bändi oli energinen. = The band was energetic.

Here energinen is the basic dictionary form of the adjective.

A learner may expect a different case ending, but in this kind of sentence, the predicate adjective is normally nominative.

Yes, in the sense that it stays in the form that matches this kind of predicate structure.

Here:

• bändi is singular
• energinen is also singular nominative

Finnish does not have article agreement like a/the, but adjectives do appear in forms that fit the grammar of the sentence.

For example:

• Bändi oli energinen. = The band was energetic.
• Bändit olivat energisiä. = The bands were energetic.

So yes, the adjective changes when the noun changes.

Loppuun asti means until the end, all the way to the end, or right to the end.

It is a very common expression in Finnish.

Breakdown:

• loppu = end
• loppuun = into/to the end
• asti = until / as far as

Together, loppuun asti expresses that something continued without stopping before the end.

Because loppuun asti is about reaching an endpoint, not just being located at the end.

Compare:

• lopussa = at the end
• loppuun = to the end / into the end-point

So:

• elokuvan lopussa = at the end of the movie
• elokuvan loppuun asti = until the end of the movie

In your sentence, the idea is that the band stayed energetic all the way through, so loppuun is the right form.

It is the illative form of loppu.

The illative often expresses movement into something or movement toward an endpoint.

• loppu → loppuun

In this expression, the illative works with asti to mean up to the end or until the end.

Sometimes yes, but loppuun asti is the more complete and idiomatic expression here.

Compare:

• Luin kirjan loppuun. = I read the book to the end / finished the book.
• Hän jaksoi loppuun asti. = He/She kept going until the end.

In your sentence, asti adds the sense of all the way until that final point. It sounds very natural.

Finnish does not have articles like a or the.

So bändi can mean:

• a band
• the band

The exact meaning depends on context.

In this sentence, English would often say the band, but Finnish just says bändi.

It is a normal Finnish word, but yes, it is a loanword ultimately related to English band.

In Finnish it is spelled and pronounced in a Finnish way:

• bändi

It is very common in everyday language for a music group. Another word is yhtye, which is a bit more neutral or formal.

So:

• bändi = band
• yhtye = band / ensemble / group

This is the most neutral Finnish word order here:

• Bändi = subject
• oli = verb
• energinen = predicate adjective
• loppuun asti = adverbial phrase

So the structure is:

subject + verb + description + time/extent phrase

Finnish word order is fairly flexible, but this version sounds natural and straightforward.

For example, you could also say:

• Loppuun asti bändi oli energinen.

But that puts more emphasis on until the end.

It would be:

• Bändi on energinen loppuun asti.

Here:

• on = is
• oli = was

So the only change is the verb tense.

That would be:

• Bändit olivat energisiä loppuun asti.

Changes:

• bändi → bändit (band → bands)
• oli → olivat (was → were)
• energinen → energisiä

This is a good example of how both the verb and adjective change in plural.

It can be used more generally for an endpoint, not only time.

Examples:

• Katsoin elokuvan loppuun asti. = I watched the movie until the end.
• Hän pysyi rauhallisena loppuun asti. = He/She stayed calm until the end.
• Juoksimme loppuun asti. = We ran all the way to the end.

So in your sentence, it means the band’s energy lasted through the whole event or performance.