Yes, available as a retrofit to existing cars

No, new hardware will be released but not required

EDIT: Clarified what counts as "existing cars"

Tesla has made multiple changes to its cars' autopilot/FSD hardware over the years. This includes both upgrading the compute, and both adding and removing sensors. Elon Musk and Tesla have promised that existing cars will be able to use "full" FSD (completely autonomous level 5 operation), but they have also made claims about the hardware (and, especially, the time lines) before that were later walked back. Some older cars already can't use the current FSD beta features.

On October 10th, Tesla has scheduled a "Robotaxi" event, at which it is expected to announce... Something relating to self-driving vehicles.

This market resolves based on the last relevant claims officially made during or in the week prior to the event. Contradictory official claims will be taken based on what the last official claim was, not who made them. Insider leaks don't count unless confirmed. It doesn't matter for this market when or if the feature becomes available, only what is announced; this means if e.g. new hardware is announced as getting true FSD sooner but Tesla maintains that existing cars will eventually qualify, this resolves as not a new requirement. All official statements, including Q&A responses, Tweets, and so on qualify.

This market will be extended if Tesla again reschedules the event, or it runs past midnight without clearly ending. If Tesla cancels the event, it will resolve based on any announcements made by midnight of the last scheduled day of the event. I will not trade on this market.