Just put in 100 shares after your post, came back to me at 491%
Haven't looked at May options, maybe that's suggesting this high rate is very short term. I would also love to see a comparison of rates across brokers.
High borrow like this is usually always heavily concentrated in the front of the term structure. Brokers sometimes gouge on borrow but in more liquid names I think they are usually fairly accurate and uniformly concentrated around the borrow implied by the shortest option expirations in the chain.
One aspect is that demand for shares to borrow is probably highly driven by long warrant holders. Even paying ~500% borrow until they can exercise has them close to breakeven but with the additional benefit of being long the downside tail.
Therefore, even [rational] bullish spot holders who think the stock + borrow collected will outperform selling pressure, should start to price fair value of spot lower as time erodes the total amount of borrow to be collected from this pool of demand.
This dynamic, let alone how high above any reasonable valuation the stock is floating, should inevitably create a reflexive crash within the month, of at least 50% I think. The real losers are sadly always uninformed retail holding toxic positions without realizing it. Like holding long spot with lending disabled and/or the broker taking the majority of the interest. Instead of buying the synthetic long forward commensurate to their holding period.