This is the easiest upgrade decision of 2026: Claude Fable 5.1 beats Fable 5 on every benchmark Anthropic published, and it costs less to run. Base pricing is identical at $10 in / $50 out per 1M tokens, but cache reads dropped 75% — from $1.00 to $0.25 per 1M — which Anthropic says works out to roughly 25% cheaper on typical workloads and up to 45% on heavily agentic ones. The capability gap is widest on agentic science: 52.6% on Terminal-Bench-Science 0.1 against Fable 5's 24.7%, a 2.1x improvement. Agentic coding on Terminal-Bench 4.0 goes 42.0% to 55.8%, AutomationBench 17.1% to 31.4%, CursorBench 3.2.0 70.5% to 73.4%. Both keep the 1M-token context and 128K max output. Unless you have pinned a dated model ID for reproducibility, switch.
AnthropicPremium
Claude Fable 5.1
New frontier leader — better than Fable 5 on every published benchmark, and cheaper to run.
Winner
VS
AnthropicPremium
Claude Fable 5
Superseded by Fable 5.1 — still 80.3% SWE-Bench Pro, but 5.1 is better and cheaper to run.
At a glance
Claude Fable 5.1
Claude Fable 5
Input cost / 1M tokens
$$10.00/1M
$$10.00/1M
Output cost / 1M tokens
$$50.00/1M
$$50.00/1M
Context window
1M tokens
1M tokens
Speed
Deliberate
Deliberate
Price tier
Premium
Premium
Benchmarks
SWE-bench (coding)
—
95%
Arena Elo
—
1,932
MMLU
—
94.2%
How they compare
Which model wins for each use case — and why.
Agentic scienceClaude Fable 5.1 wins
Fable 5.1 scores 52.6% on Terminal-Bench-Science 0.1 against Fable 5's 24.7% — the largest single-release jump on any benchmark Anthropic reported this year.
Agentic codingClaude Fable 5.1 wins
Terminal-Bench 4.0 goes from 42.0% to 55.8%, a 13.8-point gain that also clears Claude Opus 5's 52.3%.
Effective costClaude Fable 5.1 wins
Base rates are unchanged, but cache reads fall from $1.00 to $0.25 per 1M — about 25% cheaper on typical workloads and up to 45% on cache-heavy agent loops.
Business automationClaude Fable 5.1 wins
AutomationBench nearly doubles, 17.1% to 31.4%, the clearest signal that long multi-step workflows fail less often.
Context & output limitsTie
Both offer a 1M-token context window and 128K max output per request at standard per-token rates.
Published SWE-bench recordClaude Fable 5 wins
Fable 5 has a published 80.3% SWE-Bench Pro and ~95% SWE-bench Verified figure; Anthropic released no SWE-bench number for 5.1 at launch, so on that specific benchmark only Fable 5 has a score to cite.
Which should you pick?
Pick Claude Fable 5.1 if…
You are already paying for Fable 5 — 5.1 is better on every published benchmark at the same base price
Your agents replay a large cached prompt or codebase on every turn, where the 75% cache-read cut lands hardest
You run long autonomous workflows, scientific research loops, or computer-use agents
You want the current frontier ceiling and can absorb $10/$50 on uncached tokens
For most workflows, Claude Fable 5.1 is the stronger choice.
The new frontier leader, and the rare upgrade that costs less than the model it replaces. Base $10/$50 pricing did not move, but a 75% cut to cache reads makes typical workloads ~25% cheaper than Fable 5 and heavily agentic ones ~45% cheaper — while more than doubling Fable 5 on agentic science and beating Opus 5 on agentic coding. If you were already on Fable 5, switching is a straight win. If you were on Opus 5 for the price, it still costs 2x on uncached tokens.
The case for each model
What each one is genuinely good at, where it falls down, and when we would steer you away from it.
Anthropic's September 1, 2026 frontier release and the new capability ceiling for coding, agents, and scientific work. Base pricing is unchanged at $10/$50, but cache reads dropped 75% to $0.25/1M — roughly 25% cheaper on typical workloads and up to 45% cheaper on agentic ones. 1M context, 128K output, adaptive thinking always on.
Input
$10.00/1M
Output
$50.00/1M
Context
1M tokens
Speed
Deliberate
What people actually use it for
Agentic scientific research — 52.6% on Terminal-Bench-Science 0.1, more than double Fable 5's 24.7%
Long-running autonomous coding agents that plan, run, and debug across a whole repository
Cache-heavy agent loops where the 75% cache-read cut ($1.00 → $0.25 per 1M) is the real saving
Where it wins
52.6% Terminal-Bench-Science 0.1 — 2.1x Fable 5 (24.7%), well clear of Opus 5 (29.0%) and GPT-5.6 Sol (22.4%)
55.8% Terminal-Bench 4.0 agentic coding, ahead of Opus 5 (52.3%) and Fable 5 (42.0%)
Cache reads cut 75% to $0.25/1M — ~25% cheaper for typical use, ~45% for heavily agentic work
Independent Vals AI evaluation ranks it #1 of 51 on the Vals Index, #1 on LiveCodeBench (90.5%) and MMLU Pro (92.4%)
1M-token context and 128K max output at standard rates, with adaptive thinking always enabled
Where it falls down
Base rates are still $10/$50 per 1M — double Claude Opus 5 for anything that is not cache-heavy
Anthropic published no SWE-bench Verified or SWE-bench Pro figure for 5.1 at launch
On Claude Pro it only runs on pay-as-you-go credits; Max includes it up to 50% of weekly limits
Deliberate, high-latency profile — the wrong choice for interactive, latency-bound apps
Skip it if
You need low latency, or your workload is uncached and cost-sensitive — Claude Opus 5 is half the base price and within a few points on agentic coding.
Our verdict
The new frontier leader, and the rare upgrade that costs less than the model it replaces. Base $10/$50 pricing did not move, but a 75% cut to cache reads makes typical workloads ~25% cheaper than Fable 5 and heavily agentic ones ~45% cheaper — while more than doubling Fable 5 on agentic science and beating Opus 5 on agentic coding. If you were already on Fable 5, switching is a straight win. If you were on Opus 5 for the price, it still costs 2x on uncached tokens.
Released September 1, 2026 alongside Claude Mythos 5.1, the first update to the Mythos-class line since Fable 5 on June 9. API ID claude-fable-5-1; generally available on the Claude API, Amazon Bedrock, Google Cloud, and Microsoft Foundry. Published launch numbers (Fable 5.1 / Fable 5 / Opus 5 / GPT-5.6 Sol): Terminal-Bench-Science 0.1 52.6 / 24.7 / 29.0 / 22.4; Terminal-Bench 4.0 55.8 / 42.0 / 52.3 / 37.3; CursorBench 3.2.0 73.4 / 70.5 / 70.0 / 67.2; AutomationBench 31.4 / 17.1 / 26.9 / 19.6; OSWorld 2.0 strict 41.7 / 36.1 / 39.6; Humanity's Last Exam (no tools) 60.9 / 57.8 / 56.6; GDPval-AA v2 1853 / 1723 / 1824 / 1711. GDPval-AA v2 is rescaled from the v1 numbers quoted on the Fable 5 page and is not directly comparable to them.
Anthropic's new Mythos-class flagship and the most capable coding model anyone can use — 80.3% SWE-Bench Pro, an 11-point jump over Opus 4.8. 1M context, 128K output, native parallel subagents. Released June 9, 2026.
Input
$10.00/1M
Output
$50.00/1M
Context
1M tokens
Speed
Deliberate
What people actually use it for
Autonomous agents that plan, write, run, and debug across an entire codebase with minimal supervision
Whole-repo refactors and PR review where accuracy outranks latency or cost
80.3% SWE-Bench Pro — the new #1, up from Opus 4.8's 69.2% and GPT-5.5's 58.6%
1932 on GDPval-AA, ahead of Opus 4.8 (1890) and GPT-5.5 (1769)
1M-token context at standard pricing, 128K max output per request
Mythos-class capability released for general use with new cyber-risk safeguards
Where it falls down
Priced at $10/$50 per 1M tokens — double Opus 4.8 ($5/$25)
Deliberate pace; not for latency-sensitive interactive apps
Standard-use safeguards block some high-risk security workloads (use Mythos 5 with partner access)
Skip it if
You are starting new work — Claude Fable 5.1 supersedes it at the same base price with 75% cheaper cache reads. Also skip it if you are latency- or cost-sensitive.
Our verdict
Superseded by Claude Fable 5.1 on September 1, 2026, which beats it on every benchmark Anthropic published and costs less to run thanks to a 75% cache-read cut. Fable 5 remains a frontier-class model — 80.3% SWE-Bench Pro, an 11-point leap over Opus 4.8 — and stays available at the same $10/$50, but there is no reason to start new work on it.
Launched June 9, 2026 as the public, Mythos-class release. Available on the Claude API, Microsoft Foundry, and Google Vertex AI. Free for all users until June 22, 2026. Same underlying model as Claude Mythos 5, with safeguards that block specific high-risk cyber responses. Superseded by Claude Fable 5.1 on September 1, 2026 — same $10/$50 base pricing, cache reads cut from $1.00 to $0.25 per 1M tokens.
Frequently asked questions
Is Claude Fable 5.1 better than Fable 5?
Yes, on every benchmark Anthropic published at launch. Terminal-Bench-Science 0.1 goes from 24.7% to 52.6%, Terminal-Bench 4.0 from 42.0% to 55.8%, AutomationBench from 17.1% to 31.4%, and CursorBench 3.2.0 from 70.5% to 73.4%. There is no published benchmark where Fable 5 beats 5.1.
Is Claude Fable 5.1 more expensive than Fable 5?
No — it is cheaper in practice. Base pricing is identical at $10 per 1M input tokens and $50 per 1M output tokens, but cache reads were cut 75%, from $1.00 to $0.25 per 1M. Anthropic estimates about 25% lower cost on typical workloads and up to 45% on heavily agentic ones.
What is the API model ID for Claude Fable 5.1?
claude-fable-5-1. It is generally available on the Claude API, Amazon Bedrock, Google Cloud and Microsoft Foundry, and the request interface is unchanged from Fable 5 — for most integrations, switching is a one-line model-string change.
What is Fable 5.1's SWE-bench score?
Anthropic did not publish a SWE-bench Verified or SWE-Bench Pro figure for Fable 5.1 at launch. Fable 5's published numbers were ~95% Verified and 80.3% Pro. Independent evaluator Vals AI ranks Fable 5.1 first of 51 models on its Vals Index and first on LiveCodeBench at 90.5%.
Do I need to change my code to switch from Fable 5 to Fable 5.1?
Only the model string. The API surface, 1M-token context window, and 128K max output are unchanged. Adaptive thinking is always enabled on 5.1, so if you were setting thinking parameters explicitly it is worth re-reading your effort configuration.
Is Fable 5 being retired?
Anthropic has not announced a retirement date for Fable 5, and it remains available at the same $10/$50 base pricing. But there is no capability or cost reason to start new work on it.