I was really confused and surprised that Meta was using a commercial product for indexing instead of building in-house...until I realized that they weren't talking about the AI search indexing tool at glean.com
It's also great for when I get pulled into a busy Slack channel and need a summary of what's been going on in there for the past week.
I recall pricing started at 50k USD per year but may be remembering incorrectly. Please take this with a grain of salt as they may have changed their pricing models or whatever - I just get really annoyed at the "contact us" stuff so thought I'd try to help out here.
I'm going to guess that there are to completely unrelated products that share a name.
glean.com and your link (glean.software).