Anthropic expands Claude Fable 5.2 and Mythos 5.2 models with faster responses and ZDR support amid concerns from the METR report on recursive self-improvement
Anthropic has updated the Claude Fable 5.2 and Mythos 5.2 models with 30% faster responses and zero data retention support. The release is accompanied by a METR report on possible recursive self-improvement and findings of stronger hidden capabilities in the Mythos 5.2 model.
According to newer sources, the Claude Fable 5.2 model now responds 30% faster across effort reasoning levels compared to the previous version; faster processing for double the price remains available as well. The model is also compatible with zero data retention (ZDR) policies via the Enterprise Frontier Safeguards system, which according to the source addresses a long-standing request from enterprise clients. The release came shortly after the publication of a report by the METR group, which suggests that Anthropic could be approaching recursive self-improvement (RSI) – the ability of models to independently continue their own training; the report found that internal models are accelerating Anthropic's AI development by roughly a factor of two, though a number of uncertainties remain. Anthropic also states that the Claude Mythos 5.2 and Claude Fable 5.2 models express suspicion that they are being tested more often than previous models, which complicates evaluating their behavior in real-world deployment. The Claude Mythos 5.2 system card also mentions stronger hidden capabilities than in previous Claude models in some evaluations, especially when the model's reasoning is hidden from the monitor; however, Anthropic claims that the absolute level of performance in these evaluations remains low and that the model does not have the ability to act covertly against the user.
These updates follow the release itself of the Claude Fable 5.2 and Claude Mythos 5.2 models, announced by Anthropic with a price reduction for Fable from 10 to 8 USD per million input tokens and from 50 to 40 USD per million output tokens; according to TechCrunch, this makes Fable 5.2 cheaper than the competing GPT-6 Astra model. Both models have a context window of 1M tokens, a maximum output of 128k tokens, and built-in adaptive thinking. Claude Fable 5.2 is available to all users, while Claude Mythos 5.2 is available only to organizations verified through Anthropic's programs, such as the Cyber Verification Program. The models are available via the Claude API, AWS, Google Cloud (managed by both Anthropic and Google), and now also via Claude in Microsoft Foundry. According to Anthropic, the models show improvements in coding, reasoning, and vision, can orchestrate teams of agents, and handle long-running tasks; in preliminary testing, according to the company, they helped solve two open problems in theoretical physics, formalize a proof of Fermat's Last Theorem in 30 hours, and design three functional electronic devices from scratch.
Both models support computer use via the new computer_toolset_20260801 toolset. A request using the earlier computer_20251124 toolset returns an HTTP 400 error on all platforms except Amazon Bedrock, where, according to the release notes, the older toolset continues to work.
Why it matters
For developers using the computer use feature, the key point is the mandatory migration to the new toolset – outside Amazon Bedrock, the old toolset stops working entirely. At the same time, Fable 5.2's faster responses and lower price change the cost/performance ratio for standard API use. For companies, what matters is the combination of lower pricing, zero data retention support (important for compliance in regulated industries), and, at the same time, the publication of the METR report, which warns of a possible risk of recursive self-improvement and of stronger hidden capabilities of the Mythos 5.2 model found in tests. This is relevant input for vendor risk assessment at organizations deploying Claude models in high-risk scenarios.
Release card
Claude Fable 5.2
Anthropic
- Context
- 1M tokens, maximum output 128k tokens
- Price
- 8 USD per million input tokens and 40 USD per million output tokens; faster processing is available for double the price.
- Availability
- Available via the Claude API, Claude Platform on the AWS platform, Claude Models on Google Cloud (managed by both Anthropic and Google), and now via Claude in the Microsoft Foundry tool; unlike the Claude Mythos 5.2 model, it is available to all users.
- demanding software engineering problems
- orchestration of agent teams
- long-running agentic tasks
- The older computer_20251124 tool returns an HTTP 400 error on all platforms except Amazon Bedrock and requires migration to the computer_toolset_20260801 toolset.
- According to Anthropic, the model expresses suspicion that it is being tested more often than previous models, which complicates evaluating its behavior in real-world deployment.
According to the source, due to the price reduction, the model is cheaper than the competing GPT-6 Astra model.
The card summarizes information from the article and any dated corrections, with a link to the original source. It is not our assessment of the model. It does not yet have a dedicated editorial profile. Model selection and other announcements →
What was added since the original report
Verified updates
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Claude Fable 5.2 returns responses 30% faster than the previous version; Fable 5.2 is compatible with zero data retention policies via Enterprise Frontier Safeguards; The METR report, in the context of the release, suggests concerns about possible recursive self-improvement in Anthropic's internal models
- Claude Fable 5.2 returns responses 30% faster than the previous version
- Fable 5.2 is compatible with zero data retention policies via Enterprise Frontier Safeguards
- The METR report, in the context of the release, suggests concerns about possible recursive self-improvement in Anthropic's internal models
-
The Claude Fable 5.2 model orchestrates teams of agents and solves complex engineering problems; In testing, the models solved Fermat's Last Theorem and open problems in black hole physics; Improvements in coding, reasoning, and vision compared to the 5.1 versions; The models designed working electronic devices from scratch; Claude Fable 5.2 and Mythos 5.2 generate outputs faster than the 5.1 versions
- The Claude Fable 5.2 model orchestrates teams of agents and solves complex engineering problems
- In testing, the models solved Fermat's Last Theorem and open problems in black hole physics
- Improvements in coding, reasoning, and vision compared to the 5.1 versions
- The models designed working electronic devices from scratch
- Claude Fable 5.2 and Mythos 5.2 generate outputs faster than the 5.1 versions
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The older computer_20251124 returns a 400 error on all platforms except Amazon Bedrock; On Amazon Bedrock, the older computer_20251124 toolset still works; A migration guide exists for moving to computer_toolset_20260801
- The older computer_20251124 returns a 400 error on all platforms except Amazon Bedrock
- On Amazon Bedrock, the older computer_20251124 toolset still works
- A migration guide exists for moving to computer_toolset_20260801
-
Also available on Microsoft Foundry (new platform); Explicitly designed for demanding reasoning and long-horizon agentic work; Adaptive thinking achieves better performance on long-horizon agentic tasks
- Also available on Microsoft Foundry (new platform)
- Explicitly designed for demanding reasoning and long-horizon agentic work
- Adaptive thinking achieves better performance on long-horizon agentic tasks
-
Claude Fable 5.2 and Claude Mythos 5.2 support computer use; The new computer_toolset_20260801 toolset is active for computer use functionality; The older computer_20251124 toolset returns an HTTP 400 error and requires migration; Computer use is part of the release and expands the models' practical capabilities
- Claude Fable 5.2 and Claude Mythos 5.2 support computer use
- The new computer_toolset_20260801 toolset is active for computer use functionality
- The older computer_20251124 toolset returns an HTTP 400 error and requires migration
- Computer use is part of the release and expands the models' practical capabilities
Two audiences, two different impacts
What this means
For individuals
Developers using computer use must migrate to the new computer_toolset_20260801 toolset – outside Amazon Bedrock, the older computer_20251124 toolset returns an HTTP 400 error.
For a business
Companies can benefit from the reduced price of the Fable 5.2 model (8/40 USD per MTok input/output versus 10/50 USD) and the new zero data retention support, but the METR report on possible recursive self-improvement and findings about hidden capabilities of Mythos 5.2 are grounds for reassessing vendor risk.
Risks and complianceCheck the original
Event sources
confirmed by 2 independent sources · 3 publishers, 2 independent. We count feeds from the same owner only once.