Learn Dutch: We denken jullie komen bijtijds aan. - We think you guys are arriving in good time.

This is an example of complementizer drop, which is common in spoken Dutch. We have omitted the word dat (that). When you drop dat after verbs of thought or speech like denken, the following clause stops acting like a subordinate clause and reverts to normal V2 (verb-second) main clause word order.

How would this sentence look if we did include the word dat?

It would be We denken dat jullie bijtijds aankomen. With dat, the second part becomes a standard subordinate clause, which pushes the conjugated verb to the very end and reconnects it with the separable prefix aan to form aankomen.

Why is aan at the very end of the sentence?

It is the separable prefix of the verb aankomen (to arrive). Because the dropped dat causes the second clause to use main clause word order, the conjugated part (komen) takes the second position, and the prefix (aan) gets sent to the end of the clause.

Can I use this dropped dat structure in formal writing?

It is best to avoid it in formal writing. While dropping dat and using V2 word order is very natural in spoken Dutch or casual texting, formal written Dutch still strongly prefers keeping dat and using the standard subordinate clause word order.