Is there a method to make claude (sonnet 3.5) output desired amount of words?

It is my goal to create a summary of several news articles. I give claude some articles from news sites and want it to summarize them. Some important articles should have more length (300 words) and some less important ones 100 words. Ideally I can input for example 5 articles (3x 300 words, 2x 100 words) and claude gives me one answer with all articles matching my wished summary length.

I feel like I tried everything from telling claude the word count, the amount of characters and an estimation of the tokens 300 words would equal. I know LLMs dont think in words but there has to be a way to get a somewhat correctly sized answer. At the moment the answers seem to be around 50% of wished word count.

Have you found a reliable method / prompting technique to get the answer length you want? Would appreciate some tips