What's this about?
dotey noticed that `claude-fable-5-1[1m]` and `claude-fable-5-1` appear to be two different model IDs, and asks whether they are actually different models.
Why would a context window get its own model ID?
Because a 1M-context variant is often a different deployment rather than a flag: different serving infrastructure, potentially different attention handling, and certainly different pricing. Exposing it as a distinct ID is honest, and it also means "which model am I using" has an answer more specific than the name on the box. dotey's finding yesterday that disabling the 1M context makes tokens last noticeably longer is the practical consequence — the two IDs behave differently enough to matter to your bill.
Why is it worth noticing?
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- If you are pinning model IDs in production code, the bracket suffix is not cosmetic.
- It connects directly to his `CLAUDE_CODE_DISABLE_1M_CONTEXT` finding — that setting is choosing between these.
- Small, precise observations like this are how the practical documentation of these products gets written.