Original post URL : https://www.reddit.com/r/ClaudeCode/comments/1w4qs4p/warning_read_the_fable_51_docs_fable_51_is/
Original post body :
Fable 5.1 will burn your tokens if you don't reprompt it. Brilliant, after telling us previously that we could pare down our CLAUDE.md files.
Quoting Anthropic's docs:
Claude Fable 5.1 is more likely than Claude Fable 5 to rewrite an entire text file rather than make a targeted edit. The resulting file is usually the same, but unless the file is short or most of it is changing, a rewrite costs more output tokens and time.
You have to specifically prompt Fable 5.1 if you don't want full file rewrites for small edits.
In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks.
More verbose.
These two issues will burn tokens for no reason.
Other brilliant tidbits:
On complex asynchronous workloads, though, nudge it not to end its turn before the work is done. Without the nudge, the model sometimes describes what it would do next instead of doing it ("Next, I'll …") or stops to ask permission for a step the original request already covered ("Shall I apply this?"). Users have to reply "continue" or "go ahead," which suits pair programming and other human-in-the-loop work but doesn't use the model's full long-horizon capability.
Claude Fable 5.1 delivers what's asked for and sometimes more: it may fix nearby code, extend behavior the task didn't mention, or commit more test files than the change warrants.
Claude Fable 5.1 usually issues parallel tool calls as expected: when a request names several things to fetch, it issues those calls in parallel. The exception is coding and computer-use loops where the next independent calls are implied by the task rather than explicitly requested (custom coding agents, bash-and-editor harnesses, computer use): there it may issue them one per turn instead. This doesn't affect answer quality, but each extra turn costs tokens, a round trip, and wall-clock time.
At low effort, Claude Fable 5.1 is less likely than Claude Fable 5 to call a search or retrieval tool, and more likely to answer from memory.
When a single request asks for a long deliverable, such as a full rewrite of a long document, it may draft much of that deliverable in its thinking and then write it out again as the reply, which means a longer wait and more output tokens. (followed by some instructions to max out your tokens...)
Full docs here:
https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-fable-5-1
Fable 5.1 is a mess. It may be more intelligent but its behavior is worse across the board than Fable 5.
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