I can't see a date on their website but this comes up on a search that appears to confirm things.

Good news about your membership

We’ve been through a lot together recently and we’d like to thank you for your continued loyalty and support during this challenging time.

We’ve already reduced the number of Tier Points needed to renew your Silver status or upgrade to Gold by 25%, until 31 December 2022.

We’re now going a step further and temporarily reducing the threshold to renew your Silver status by 50% for the remainder of your current Tier Point Collection Year. If you earn a total of 300 Tier Points by your next Tier Point Collection Year end date, your Silver status will automatically be renewed for another year.

Your Tier Point tracker on ba.com and the British Airways app will continue to show a threshold of 450 Tier Points. Please rest assured we have activated your reduced Tier Point threshold.