The Metro! It says the source at the bottom of the story. But as you asked, below is the link again. I've deleted the stats, as it seems they're probably wrong. Most of the British press thought this announcement was newsworthy, apparently. I thought people might be interested.

https://www.msn.com/en-gb/news/world/us-announces-deadly-new-nuclear-weapon-days-after-china-announced-warhead-expansion/ar-AA1j8KqQ