Long Context Claude keeps failing or "running out of conversation length"

Claude Sonnet and Opus (and Fable while it lasted) feature 1M long context for a while now. I work with big contexts through the chat (I know it’s niche), and it really doesn’t feel like 1M context.

It got especially bad recently, when not even 100 pages of text are “too long” for the context. This used to be fine with Opus until recently, and it’s fine with Deepseek v4 for example.

Did something change? Are the models hooked up 1M context?

This bug is Browser and OS independent.