Claude Fable 5.1:
the complete guide
As of 2026-10-20, Anthropic states that Claude Fable 5.1 and Claude Mythos 5.1 are the same model with different levels of safeguards; Fable 5.1 is generally available, while Mythos 5.1 is available only through trusted access programs. Released 2026-09-01, priced at $10/$50 per MTok, with cache reads down from $1.00 to $0.25 (the announcement says 75% less), 1M context and 128K max output. The QCode model id is claude-fable-5-1.
Updated 2026-10-20
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Four pricing and spec figures
Cache read, per million tokens
Fable 5 charges $1.00, so this is 75% lower. Workloads that re-read long context repeatedly benefit most directly.
Input / output, per million tokens
Identical to Fable 5 — the list price did not move. Only the cache line changed.
Context window / max output
Same as Fable 5. Cache writes also unchanged at $12.50 for the 5-minute tier and $20 for the 1-hour tier.
Official estimate for a typical bill
The announcement puts typical workloads around 25% cheaper than Fable 5, with larger savings on complex, highly agentic tasks.
What actually changed
The headline rates did not move: $10 input and $50 output per million tokens, exactly as Fable 5. What moved is the cache read, from $1.00 to $0.25. That is not a marketing number — it decides the real bill for the "long context, many turns" class of workload. An agent re-reads its whole context on every turn, so cache reads are often the largest line on the invoice; cutting three quarters off that line does far more than trimming the input rate would.
Official wording and rates (verified 2026-09-02)
Checked 2026-10-20: Anthropic says the two are the same model with different levels of safeguards; Fable 5.1 is generally available, while Mythos 5.1 is available only through trusted access programs. The announcement states "Cache reads now cost 75% less, or $0.25 per million tokens" and that "costs are reduced by around 25% relative to Fable 5", with larger savings on complex, highly agentic tasks. The rate table agrees line by line: input $10, output $50, cache read $0.25, cache writes $12.50 for the 5-minute tier and $20 for the 1-hour tier, 1M context and 128K max output.
Timeline of the Fable line
Fable 5 and Mythos 5 released.
Fable 5 was disabled for all customers under a US export control directive and restored on 1 July. Other Claude models were unaffected at the time.
Fable 5.1 and Mythos 5.1 released. Anthropic says they are the same model with different safeguards; Fable 5.1 is generally available, Mythos 5.1 is trusted-access only.
Confirmed vs what you have to measure
Confirmed, with a first-hand source
① Anthropic's wording: Fable 5.1 and Mythos 5.1 are the same model with different levels of safeguards; Fable 5.1 is generally available, Mythos 5.1 is trusted-access only. ② Cache reads moved from $1.00 to $0.25, stated as 75% lower. ③ Input $10 / output $50 unchanged. ④ 1M context and 128K max output. ⑤ The official estimate for typical workloads is about 25% lower cost.
What you have to measure
How much you actually save depends on your cache hit rate, which depends on your prompt structure and call cadence. The official 25% is an estimate for typical workloads, not a commitment. To measure: send one fixed, reasonably long input at least three times, drop the first, and look at what share of usage on the rest is cache reads — that share is what decides how much this price cut is worth to you.
Fable 5.1 vs Fable 5
A different bill shape
Input and output cost the same on both; the whole difference sits in cache reads ($0.25 versus $1.00). The higher your hit rate, the longer your context and the more turns you run, the larger 5.1's advantage. A one-shot short question shows almost no difference.
Specs and migration
1M context and 128K max output are identical, so switching is a matter of changing the model id. Note that 5.1 has some developer-side behaviour changes — for example how thinking content from earlier turns is handled — so run your own regression cases before migrating a long-chain agent.
How to decide whether the switch is worth it
① Measure what share of your current bill is cache reads — this needs no model change, just a look at the composition of the bill you already have. ② If that share is small (short conversations, a different input every time), this price cut barely touches you and there is no urgency. ③ If it is large (long-context agents, repeatedly reading the same codebase), your saving is essentially that line multiplied by 75%. ④ Run your own regression cases before switching; do not decide on price alone.
On QCode
The model id is claude-fable-5-1 (the dotted form claude-fable-5.1 normalises to the same model). Billing is per token, with per-model rates on /models; Anthropic's official cache read is $0.25 while QCode's actual rate is whatever /models says. To check: send the same input several times and compare the cache-read tokens and deduction in usage against /models.
FAQ
How much cheaper is Fable 5.1 than Fable 5?
On list price, only the cache read changed: $1.00 to $0.25 per million tokens, a 75% cut. Input at $10 and output at $50 are unchanged. The official overall estimate is around 25% cheaper for typical workloads and more for complex agentic ones — but the real figure depends entirely on your cache hit rate.
Did the context window or max output change?
No. The context window is 1M and max output 128K, the same as Fable 5. The two cache write tiers ($12.50 for 5 minutes, $20 for an hour) are also unchanged.
Can I call Mythos 5.1?
No. Anthropic says the two are the same model with different levels of safeguards; Mythos 5.1 is available only to vetted organisations through trusted access programs and is not a publicly callable model. Anyone claiming they can open Mythos for you should be asked for evidence.
Which model id should I write?
Write claude-fable-5-1. The dotted form normalises to the same model, but standardising on the hyphenated form keeps your own logs and bills from carrying two spellings of one thing.
Do I need code changes to migrate from Fable 5?
At the interface level, changing the model id is enough. But 5.1 carries some developer-side behaviour changes — for instance how thinking content from earlier turns is treated — so run your own regression cases before switching a long-chain agent wholesale on price alone.
How do I confirm the cut actually reached my bill?
Look at usage. Send one reasonably long fixed input at least three times, drop the first (a cold start), then take the cache read token counts and the matching deductions on the rest and work backwards to the unit price to see whether it lands on the $0.25 tier. That is more direct than any second-hand account.
Sources
Cache-read cut and overall reduction: Anthropic's official announcement page (fetched again 2026-10-20; it says cache reads cost 75% less at $0.25 per million tokens and typical workloads are around 25% cheaper). Per-line rates, context and max output: Anthropic's official model overview and pricing page (fetched 2026-10-20: input $10, output $50, cache read $0.25, cache writes $12.50 for 5 minutes and $20 for 1 hour, 1M context and 128K max output). Mythos 5.1 availability is in the same announcement. Prices can change; QCode's actual rates are on /models.
Measure your cache share first
The larger the cache read share of your bill, the more this cut is worth; if it is small, there is no rush to switch.
Further reading
Claude Fable 5 complete guide
The previous generation's specs, pricing and where it fits.
Claude Fable 5 pricing guide
Per-line rates and how cache pricing is calculated.
Switch Claude Code to Fable 5.2: command, version and CC Switch setup (2026-11)
From the official changelog and model-config: /model fable and /model claude-fable-5-2, the v2.1.321 minimum, the model field in settings.json, ANTHROPIC_MODEL, ANTHROPIC_BASE_URL, and where the model name goes in CC Switch, plus the order to check when the switch does not take effect.
Crypto payment guide
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Prices, specifications and official wording were checked on 2026-10-20 and may change. The official cost reduction is an estimate for typical workloads, not a commitment for yours. QCode's actual rates and model availability are governed by /models.