AVXL's short interest rate is not trending up, it is mostly stable. Although it frequently fluctuates up and down by small amounts, they have been minor fluctuations for AVXL for a long time now, and overall it has been trending down, based on IB data.
Smaller brokerages like Fidelity might go up when IB rates are going down, and that could be misleading. When I had accounts at multiple brokers, IB always had the highest rates, sometimes twice or more compared to smaller brokers. For example, Fidelity might offer 10% while IB was offering 25%. Since IB splits SLB revenue 50-50, that would mean the borrower was paying 50% APR, IB was keeping 25% APR and the share lending account was getting 25% APR. Fidelity might be getting 25% APR from IB and passing 10% APR to their share-lending customer.
In such a scenario, while the IB rate might remain stable at about 50%, Fidelity might double what they pay their lending customer from 10% to 20% APR, keeping only 5% APR for themselves. To the Fidelity customer, that looks like a dramatic rise in interest rates, but it does not accurately reflect the overall market.
No organization has complete data on all short selling on a daily basis, but IB has more data than any other organization because they act as the gateway for most transactions from other brokers, hedge funds, etc. Therefore, IB SLB rates are only an approximation, but they are the best approximation available, and often vary significantly from rates paid by other organizations.
The SLB rates for AVXL in the charts I have been posting is for the rates the short sellers are paying IB, before that money is split with IB's share-lending customers. Lately it has been around 25% APR.
