Claude Fable 5.2 changelog

Claude Fable 5.2 becomes available in the Perplexity Agent API

The Agent API now supports anthropic/claude-fable-5-2. The changelog entry gives no pricing.

Claude Fable 5.2 is available on AWS, Google Cloud and Microsoft Foundry

Claude Fable 5.2 is available on the Claude API, Claude Platform on AWS, and Claude Models on Google Cloud (Anthropic managed). It is also available on Claude in Amazon Bedrock, Claude Models on Google Cloud (Google managed), and Claude in Microsoft Foundry.

Claude Fable 5.2 and Mythos 5.2 return 400 errors when the prefix changes

Both models enforce the prefix check for every account. Requests that edit the system prompt, tools, or an earlier message, then send back a thinking block from a later turn, return a 400 error.

Who is affected:

Apps that edit earlier context while reusing thinking blocks will fail on these models.

Suggested next step:

Check whether your code edits the prefix before you switch models.

Claude Code makes Claude Fable 5.2 the default Fable model

Claude Fable 5.2 has 1M context and costs $8/$40 per Mtok with $0.20/Mtok cache reads. It is now the default Fable model in Claude Code.

Who is affected:

Claude Code users who run the default Fable model get Claude Fable 5.2 in new sessions.

Suggested next step:

No action needed unless you want Fable 5.1, which you can select with /model claude-fable-5-1.

Claude Fable 5.2 costs $8 per million input tokens, down from $10

Claude Fable 5.2 costs $8 USD per MTok of input and $40 USD per MTok of output. Claude Fable 5.1 cost $10 USD per MTok of input and $50 USD per MTok of output.

Claude Fable 5.2 fast mode costs $16 per million input tokens

Fast mode delivers up to 2.5x higher output tokens per second, at $16 USD per MTok of input and $80 USD per MTok of output. Requests opt in by setting speed to fast.

Who is affected:

Developers who need faster output pay a higher rate than standard Claude Fable 5.2 pricing.

Suggested next step:

Set speed to fast only on requests where faster output is worth the higher rate.

Claude Fable 5.2 launches with a 1M token context window and 128k max output

Claude Fable 5.2 is built for demanding reasoning and long-horizon agentic work. It has a 1M token context window, 128k max output tokens, and always-on adaptive thinking.

Who is affected:

Developers building long-running reasoning and agent workloads can move to the new model.

Suggested next step:

Read the migration guide before switching, since the prefix check and computer use changes apply.

Claude Fable 5.2 and Mythos 5.2 launch with outputs up to 30% faster

Claude Fable 5.2 and Claude Mythos 5.2 are upgrades that show improvements in coding, reasoning, and vision. Testers found they generate outputs up to 30% faster than Claude Fable 5.1 and Claude Mythos 5.1.

Claude Fable 5.2 becomes available in GitHub Copilot

GitHub Copilot adds Claude Fable 5.2 as a model option.