Deepseek via Anthropic api doesn't show reasoning blocks

[zikajk]

To upvote this issue, give it a thumbs up. See this list for the most upvoted issues.

Describe the bug
When using deepseek-reasoner via openrouter and Openai-chat api, I see reasoning blocks. When I use deepseek official anthropic api I don't.

To Reproduce

1. configure deepseek as a custom provider with anthropic api
2. use deepseek-reasoner model
3. ask something - no thinking blocks visible

Expected behavior
See thinking blocks.

[zikajk]

https://api-docs.deepseek.com/guides/reasoning_model
It will probably be related to response parsing. Similar to the problem we had in openai_chat.