Anthropic launches Claude Fable 5.1 after Bedrock exposed its model slug
The official release confirms a pre-launch API clue that distinguished Fable 5.1 from invalid Anthropic model identifiers.
By Ryan Merket · Published · Updated
Primary source: X
Why it matters
Bedrock staging can precede a model launch. The 404 gives developers an early clue that Anthropic may be preparing its first Fable point release after months of safeguard tuning.
Anthropic has launched Claude Fable 5.1, confirming a release that surfaced a day earlier through an unusual Amazon Bedrock API response.
The pre-launch finding came from Leo (@synthwavedd), who tested a Fable 5.1 model slug against Bedrock and received a 404 response stating "Model not found." The same endpoint returned a 400 response stating "The provided model identifier is invalid" for an Opus 5.1 slug and a deliberately nonsensical Anthropic identifier, Leo wrote.…