Starting from 1st January 2020, the Alaska Mileage Plan will be cutting Alaska miles earning rates on selected Qantas Economy Class booking fares. Here are the details:
Current Earning Rates

Future Earning Rates

In summary, only certain booking fare classes that fall under Economy Class are affected. The rest remains status quo.
No matter what the changes are, you should always take reference from wheretocredit.com. This website will show you how many miles you will be earning across multiple frequent flyer programs. Here is an example:
Suppose you are booked on Qantas Economy Class for your SIN-SYD-SIN flight and your booking fare class is N, here are the miles that you will earn before 1st January:

The Alaska Mileage Plan will be offering 1955 miles (25%) instead of 7822 miles (100%) from 1st January. It will no longer be the frequent flyer program that offers the most number of miles.
For miles beginners, this is not the end of the story. You should not blindly credit your miles to a frequent flyer program just because it gives you the most number of miles. Generally speaking, you should pick the frequent flyer program that:
1)Gives you most number of miles, AND
2)Requires the lowest amount of miles to redeem a flight from their frequent flyer program.
When the new earning rates kick in, here is my personal preference (in descending order):
1)Alaska Mileage Plan
2)British Airways/American Airlines
As I am based in Singapore, your personal preference may differ from mine as we are exposed to different credit card markets and different flight redemption preferences.



I doubt that this is of Alaska’s doing. As you know, American Airlines and QANTAS entered into a joint venture. I suspect this has more to do with American Airlines’ relationship with Alaska. the same thing happened when Alaska was partners with Delta. We lost Air France and KLM as partners as the partnership with Delta ended.