With thinking mode on, you can even just ask Claude in web to add thinking blocks by wrapping them with <antml:thinking> xml tags (or cut it’s thinking early), the web UI will also put them in thinking blocks.
This post prompted me to check the conversation where I discovered this, and I noticed Anthropic made it so all thinking blocks are stuck together at the top rather than having them interleaved the order that the model generates them. You can clearly see that the model is able to think in one coherent chain where the “CoT” doesn’t delimit a strict “thinking” then “responding” portion, in the example below it even reflects on “am I inside a thinking block, or the response?”
Screenshot from ~2 months ago
Same chat, screenshot from today
Very nice, Claude seems really excited to play with its boundaries. I also just checked on mobile and saw that they intersperse the thinking blocks there as before, so having all the blocks on top seems like a new/inconsistent web feature