About a quarter of US jurisdictions follow the same basic rule as California, where exceeding a posted speed limit is prima facie, but rebuttable, evidence of a violation.

So it's not a 49/1 rule.

And, in any case, 100% of US jurisdictions prohibit driving at a speed above the safe and reasonable speed if that is lower than the posted and/or statutory limit, so you need to be able to determine what is safe for conditions anyway; it's just a minority of states where that is a relevant determination when the results are above the posted limit.

Autonomous cars will need to be able to determine a safe and prudent speed in every state. I'm pretty sure every state has laws saying that speeds must be lower that the limit in bad conditions, and even if they don't, the car will have to do this just for basic safety. It shouldn't need any special casing for California.

You have it backwards. Everyone is going to drive fast regardless of the law. Cali is just a state that recognizes this. Writing the law for humans should be celebrated. You can either take that into account or you close your eyes and plug your ears to reality and release a shitty autonomous car.

You may be underestimating the market of Californians who want to drive fast. For a long time, to sell a car in California at all, you had to put a special emissions package together, with was a lot of overhead, but manufacturers still did it, because losing the California market to save overhead doesn't make sense when selling cars.