# Claude Fable 5.1 is out: cheaper in practice, same price on paper > Anthropic released Claude Fable 5.1 on 1 September 2026, cutting repeat-context costs by 75%. *Anthropic's new model costs the same per word but should reduce most bills by around a quarter. Here's the trick, and what it means for you.* By The SuggestedTech Team · SuggestedTech Canonical: https://suggestedtech.com/news/claude-fable-5-1-explained Anthropic released a new version of its most capable model on 1 September 2026, and did something slightly unusual with the pricing: it left the advertised numbers exactly as they were, then cut a different cost that most people never look at but almost everyone pays. The net effect for most users is a bill roughly a quarter smaller. ## The pricing trick, explained When you have a long conversation with an AI, or when an AI tool works through a big task, the same background information gets sent to the model again and again — the instructions, the documents, everything said so far. Providers store that repeated material in a cache so it does not have to be processed from scratch each time, and they charge a reduced rate for reading from it. That cache rate is where a surprising share of real bills come from. Anthropic cut it by three quarters. > Cache reads now cost 75% less, or $0.25 per million tokens. > — [Anthropic](https://www.anthropic.com/claude-fable-and-mythos-5-1), 2026-09-01 In practice, Anthropic estimates that works out to about 25% less than the previous version for typical use, and as much as 45% less for tasks where an AI works through something long and complicated — writing and testing software, for example, or researching across many documents. > Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads, wherever usage is billed by token. > — [Anthropic](https://www.anthropic.com/claude-fable-and-mythos-5-1), 2026-09-01 ## Effort levels: a genuinely useful idea The new version also lets you choose how hard it thinks. At low or medium effort, Anthropic says it performs as well as or better than the previous model while costing considerably less. At high effort it goes further than the old model could. Different products pick sensible defaults: high effort in Claude Code, where the tasks are demanding, and medium in the general chat interface. > **Info:** This is worth knowing even as a casual user. Not every question needs maximum deliberation, and being able to spend more thinking on the hard ones and less on the easy ones is how these tools stop being expensive by default. ## Why there are two names Anthropic released two models with different names that are, underneath, the same thing. Fable 5.1 is the version everyone can use. Mythos 5.1 is the identical model with fewer restrictions, available only to organisations that have been vetted — mainly in cybersecurity and life sciences, where legitimate work sometimes runs into safety filters designed to stop misuse. > Claude Mythos 5.1 is identical to Fable 5.1, but it offers more permissive safeguards for vetted individuals and organizations. > — [Anthropic](https://www.anthropic.com/claude-fable-and-mythos-5-1), 2026-09-01 For everyone else, that means the standard version sometimes declines requests touching cybersecurity, biology and chemistry, or copying other AI models — and those requests get handled by a less capable model instead. It is a sensible compromise, and it is becoming the industry norm: OpenAI runs a comparable vetted-access programme for security work. One more thing worth knowing if you compare models: Anthropic says these safety measures can affect benchmark scores, so published test results may not exactly match what a normal user experiences. That is an honest disclosure and a good reminder that benchmark tables deserve a pinch of salt regardless of who publishes them. ## One result that isn't about coding Among the performance claims, one stands out because it can be checked against real human work. Anthropic says that on three targets, the model designed proteins that bound to their targets ten times more strongly than the best entries submitted to a competition run by a company called Adaptyv Bio. Protein design matters because it underpins drug development: if you can design a molecule that attaches tightly and specifically to a target in the body, you have the starting point for a medicine. A result ten times better than the best human-submitted entries is a meaningful signal that these systems are becoming genuinely useful in laboratory science, not just in writing and coding. It is also a reminder of why the restricted Mythos version exists. The same capability that designs a useful protein is capability worth being careful with, which is why access to the less-restricted version is limited to vetted organisations in fields like life sciences and cybersecurity. The trade-off is real and the industry is, for now, handling it by checking who is asking. ## Key takeaways - Anthropic released Claude Fable 5.1 on 1 September 2026, alongside a restricted version called Mythos 5.1. - The advertised price did not change, but the cost of re-reading stored context fell by 75%. - Anthropic estimates most users will pay about 25% less, and heavy automated tasks up to about 45% less. - The model now has effort levels — lower settings match the old model at lower cost, higher ones go further. - It is available in Claude, Claude Code, Cursor and through Amazon, Google and Microsoft's cloud platforms. ## FAQ ### Is Claude Fable 5.1 cheaper than Fable 5? The advertised price is the same at $10/$50 per million tokens, but cache reads cost 75% less. Anthropic estimates about 25% lower cost for typical use and up to 45% for long automated tasks. ### What is the difference between Fable and Mythos? They are the same model. Mythos has fewer restrictions and is only available to vetted organisations, mainly in cybersecurity and life sciences. ### Where can I use Claude Fable 5.1? In Claude, Claude Code and Cursor, and through the Claude API, Amazon Web Services, Google Cloud and Microsoft Azure. ### What are effort levels? A setting controlling how much thinking the model does. Low and medium match the previous model at lower cost; high goes further. Claude Code defaults to high, Claude.ai to medium. ## Sources - [Introducing Claude Fable 5.1 and Claude Mythos 5.1](https://www.anthropic.com/claude-fable-and-mythos-5-1) — Anthropic, 2026-09-01 - [Anthropic's Claude Fable 5.1 and Mythos 5.1 arrive with a 75% cost reduction for Fable cache reads](https://venturebeat.com/technology/anthropics-claude-fable-5-1-and-mythos-5-1-arrive-with-a-75-cost-reduction-for-fable-cache-reads) — VentureBeat, 2026-09-01 - [Anthropic releases Claude Fable 5.1 and Mythos 5.1](https://sdtimes.com/claude-fable-5-1/61089/) — SD Times, 2026-09-02 - [Anthropic Launches Claude Fable 5.1 With Lower Costs and Fewer False Positives](https://www.macrumors.com/2026/09/01/anthropic-claude-fable-5-1/) — MacRumors, 2026-09-01