Citi - Thank You Rewards has certain policies regarding the transfer of points, which can vary depending on the partner to whom the points are being transferred. Generally, there is no universal cap on the total number of points that one can transfer at any time; however, specific partner programs may impose their own limits. It is also important to note that points must be transferred in increments determined by the partner program, which may affect how many points you can transfer in a single transaction.
You can find detailed information about the exact limits and transfer policies by visiting the appropriate sections on their website. This will provide you with the most current and comprehensive guidelines regarding point transfers. Additionally, you may find that the transfer options can sometimes change, so checking the website periodically is a good practice.