Learn Finnish: Tämä versio on yhtä kehittynyt kuin tuo. - This version is as advanced as that one.

We use the word yhtä (which usually means "equally") before the adjective, and kuin (as / than) after it. So, yhtä kehittynyt kuin literally translates to "equally advanced as".

Is kehittynyt an adjective or a verb here?

It acts as an adjective meaning "advanced", but it is actually the past participle (the NUT-participle) of the verb kehittyä (to develop or progress). Using verb participles as adjectives is very common in Finnish, and they behave just like normal adjectives.

Why is there no word for "one" after tuo at the end of the sentence?

In English, we often add "one" (like "that one") to avoid repeating the noun. In Finnish, demonstrative pronouns like tämä (this) and tuo (that) stand perfectly fine on their own. Translating "that one" literally by adding the word yksi would sound completely unnatural.

Does the adjective between yhtä and kuin ever change its form?

Yes, it must still agree with the noun it describes! Because the subject Tämä versio is in the basic nominative case, the adjective kehittynyt is too. If the sentence required a different case, the adjective would change its ending to match, but the comparison words yhtä and kuin are frozen and never change.