Reciprocal Rank Fusion on free Elasticsearch: licensing, workarounds, and the OpenSearch alternative

Reciprocal Rank Fusion (RRF) on Elasticsearch's free tier returns a 403 due to licensing restrictions. To work around this, implement RRF in application code, combine BM25 and vector results, or switch to OpenSearch. RRF is a ranking technique that combines multiple ranked result sets into a single ranking. It's useful for hybrid search as it sidesteps normalization problems without requiring tuning. Consider upgrading to the Enterprise tier or using OpenSearch for access to RRF.