Anthropic Support straight up mentioned that Claude Code just doesn't handle this case correctly and erroneously gives you the impression that it's supported against your billing method
spondyl on Hacker News
In the thread “Claude: Elevated errors across many models [resolved]”, replying to this comment
Got in the way: Undocumented incompatibility between AWS Marketplace billing and Fast Mode.
… It turns out that for all of the matrices on the documentation site, there is a secret "other" set of infrastructure for those who bill Enterprise via AWS Marketplace where certain features like Fast Mode are incompatible when using "aws routing" Anthropic Support straight up mentioned that Claude Code just doesn't handle this case correctly and erroneously gives you the impression that it's supported against your billing method, and that it's all effectively undocumented. I suppose this means there are like 5 different AWS methods of use: …