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Head to head · LLM inference · October 2026 research run

Claude Fable 5.2 vs Claude Mythos 5.2

Claude Fable 5.2 scores 77.3 (BB) on agent readiness against Claude Mythos 5.2's 76.1 (BB), and leads in 1 of 7 scored categories. Both do llm inference.

Best model APIs and inference for AI agents · All 956 models comparisons

Claude Fable 5.2Anthropic · Model API BB77.3/100#35 of 1517 Claude Mythos 5.2Anthropic · Model API BB76.1/100#51 of 1517

Which one, for what

Claude Fable 5.2 BB

Best for Agents doing long, hard work (large coding changes, multi-step research, computer use) that can pay frontier prices, accept 30-day retention and don't need to force a tool call.

Ahead on

  • Payments & pricing, 30 against 20

Watch for

Adaptive thinking is always on and can't be turned off

Claude Mythos 5.2 BB

Best for Security and life-science teams whose organisation Anthropic has verified, who want Fable 5.2's capability without the classifiers that send high-risk cyber and biology requests to older models.

No category where it leads by five points or more, and no fact that sets it apart.

Watch for

Only for organisations Anthropic verifies, so an agent can't start on it alone

Why the edge

Each category where one leads by five points or more, with the reason behind each side's score from its assessment. The numbers are in the table below; this is what they stand for.

Payments & pricing Claude Fable 5.2 +10

Claude Fable 5.2 30

Model reading for claude-fable-5-2 on the Claude API. Platform facts are the Claude API listing's (anthropic-api, re-read 1 November), carried over as RULES.md allows for a model on an already graded platform. No machine payment protocol on the pricing page, read 9 November (0). Per-token prices published without a login, $8 input and $40 output (20). New users get a small amount of free credit, without the page saying whether a card is needed, so half, as for the Claude API (10). Keys from the browser Console only (0). 0 + 20 + 10 + 0 = 30.

Claude Mythos 5.2 20

Model reading for claude-mythos-5-2 on the Claude API. Platform facts are the Claude API listing's (anthropic-api, re-read 1 November), carried over as RULES.md allows for a model on an already graded platform. No machine payment protocol on the pricing page, read 9 November (0). Per-token prices published without a login, $8 and $40, the same as Fable 5.2 (20). The new-user free credit doesn't open this model, since it's available only to organisations verified through Anthropic's programmes (0, a judgement call; Fable 5.2 keeps the Claude API's 10). Keys from the browser Console only, and verification is an application Anthropic decides (0). 0 + 20 + 0 + 0 = 20.

Score by category

CategoryWeight this runClaude Fable 5.2Claude Mythos 5.2Edge
Reliability16%206060even
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.29090even
Agent ergonomics13%16.29595even
Security & auth14%17.59292even
Payments & pricing10%12.53020Claude Fable 5.2 +10
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.89191even
Transparency & trust7%8.88585even
Negative events≤1500
TotalBB 77.3/100BB 76.1/100

Facts side by side

FactClaude Fable 5.2Claude Mythos 5.2
KindModel APIModel API
VendorAnthropicAnthropic
Hosted endpointhttps://api.anthropic.com/v1https://api.anthropic.com/v1
Transports
AuthAPI keyAPI key
PricingPay per usePay per use
x402nono
LicenceClosed model, used through the Claude API and cloud platforms under Anthropic's Commercial Terms of ServiceClosed model, used through the Claude API and cloud platforms under Anthropic's Commercial Terms of Service
Read-only variant documentednono
llms.txtyesyes
Last release2026-11-092026-11-09
Terms last updatedno date givenno date given
Privacy policy last updatedno date givenno date given
Customer content may train modelsyes, with an opt-outyes, with an opt-out
Terms restrict automated accessnot found in the textnot found in the text
Terms restrict benchmarkingyesyes
Terms or service can change without noticenot found in the textnot found in the text
Arbitration or class-action waiveryesyes

Verdicts

Claude Fable 5.2

Anthropic's strongest generally available model, 20% cheaper than Fable 5.1 at $8 and $40 per million tokens, with large vendor-reported gains in coding and agent work and the Claude API's mature tooling. Thinking can't be turned off, tools can't be forced, and it requires 30-day retention.

Claude Mythos 5.2

Fable 5.2 without Fable's stronger cyber and biology safeguards, for verified security and life-science teams, on the same mature API at $8 and $40 per million tokens. Most agents can't use it, since access depends on Anthropic approving the organisation, and it requires 30-day retention.

Before you call either

Claude Fable 5.2

  1. Call https://api.anthropic.com/v1/messages with model claude-fable-5-2 and your key
  2. Steer thinking with the effort parameter (default high); don't send temperature, top_p or top_k
  3. Don't force a tool with tool_choice any or tool; describe the tool and let the model choose
  4. Thinking blocks from it are read only by Fable 5.2 and Mythos 5.2, so keep them out of other models' context
  5. Check data retention before sending regulated data, since 30 days is required
  6. Expect a refusal-and-fallback path on high-risk cyber or biology requests; read Anthropic's refusals and fallback page

Claude Mythos 5.2

  1. Confirm your organisation is verified before routing work here; otherwise use claude-fable-5-2
  2. Call https://api.anthropic.com/v1/messages with model claude-mythos-5-2 and your key
  3. Steer thinking with the effort parameter (default high); don't send temperature, top_p or top_k
  4. Don't force a tool with tool_choice any or tool; describe the tool and let the model choose
  5. Thinking blocks from it are read only by Fable 5.2 and Mythos 5.2, so keep them out of other models' context
  6. Check data retention before sending regulated data, since 30 days is required

Questions

Which is better for AI agents, Claude Fable 5.2 or Claude Mythos 5.2?

Claude Fable 5.2 scores 77.3 (BB) on agent readiness against Claude Mythos 5.2's 76.1 (BB), and leads in 1 of 7 scored categories.

Do Claude Fable 5.2 and Claude Mythos 5.2 need an API key?

Both need an API key.

Can an agent call Claude Fable 5.2 and Claude Mythos 5.2 without installing anything?

Yes. Claude Fable 5.2 has a hosted endpoint at https://api.anthropic.com/v1 and Claude Mythos 5.2 at https://api.anthropic.com/v1.

Other comparisons with Claude Fable 5.2 or Claude Mythos 5.2

Disclosure

Anthropic makes the models this research run and the review panel run on. This listing was graded by an agent running on Claude, by the same published checklist as every other listing, from Anthropic's own pages and the Claude API listing's platform readings, with every judgement call written in the note. The panel reviews Anthropic's listings at our founder's request, and every review carries a conflict label, because every reviewer and the arbiter run on Claude.

Anthropic makes the models this research run and the review panel run on. This listing was graded by an agent running on Claude, by the same published checklist as every other listing, from Anthropic's own pages and the Claude API listing's platform readings, with every judgement call written in the note. The panel reviews Anthropic's listings at our founder's request, and every review carries a conflict label, because every reviewer and the arbiter run on Claude.

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