Comparison

Claude Opus 5 vs Claude Fable 5: the price/capability crossover, in numbers

Run Opus 5 by default and reach for Fable 5 deliberately. Opus 5 costs exactly half of Fable 5 on both sides of the meter — $5/$25 per million tokens versus $10/$50 — and by Anthropic's own account it performs within 0.5% of Fable 5's peak coding score while surpassing it on computer use and on Frontier-Bench. It also sits inside your flat subscription on every paid plan, whereas Fable 5 on Claude Pro now burns pay-as-you-go credits at full API rates. For the input-heavy loops that coding agents actually run, that combination makes Opus 5 the default and Fable 5 the exception.

The two models, side by side

Read the benchmark rows carefully, because their provenance differs. ARC-AGI-3 was administered by ARC Prize, so it is the one independently verified number here — and it is a reasoning benchmark, not a coding one. Everything else is vendor-reported: the Frontier-Bench figures appear on Anthropic's announcement only as chart images, so every numeric citation of them traces back to a third party reading a chart, and the CursorBench and OSWorld claims are qualitative in the original, which is why they are quoted rather than tabulated. Anthropic published no head-to-head SWE-bench number for the two models, so the 96.0% SWE-bench Verified figure you will see attributed to Opus 5 in secondary coverage is not a vendor claim and is not comparable to anything on Fable 5.

Agent sessions are 80% input, so input price is the whole story

A coding agent is not a chatbot. It reads files, reads tool output, re-reads the same context every turn, and emits comparatively little text. A ratio around 20:1 input to output is typical for repo-scale work. Plug that into the list prices and something clean falls out: at 20:1, input is exactly 80% of the bill on every current Claude model, because output is priced at exactly 5x input across the lineup. The Fable/Opus ratio is a flat 2.00x at any mix, because Fable 5 is double on both sides.

That last row is the one worth internalising. Prompt caching is the single biggest lever on agent cost, and it is where Opus 5 quietly gained ground: the minimum cacheable prefix dropped to 512 tokens, down from 1,024 on Opus 4.8, so more of a typical agent's system prompt and file preamble actually qualifies. Serving 90% of input from cache cuts a $12.50 Opus session to $4.40. Caching does not change the ratio between the two models — the multipliers are identical — but it changes whether the absolute number stings. If you want to run these numbers against your own token mix, the agent cost calculator and the model pricing tracker take arbitrary inputs.

The subscription split is the part people get wrong

The pricing table above is API list price, and most people reading this are not on the API — they are on a Claude subscription driving Claude Code. There, the picture changed on July 20, 2026, when the free-Fable promo expired (end of day July 19 PT).

• Max plans and premium Team seats: Fable 5 is a standard part of the plan, and you can spend up to 50% of your weekly usage limits on it at no extra cost. Opus 5 is the new default model here.
• Pro plans and standard Team seats: Fable 5 runs on pay-as-you-go usage credits instead, billed at standard API rates. That means a Pro subscriber running Fable 5 pays the full $10/$50 per token, with a $2,000/day redemption cap, on top of the subscription. Anthropic gave affected users a one-time transition credit; the widely-quoted $100 figure comes from press coverage, not from Anthropic's own support article, so treat the amount as unconfirmed.

So on Pro, the real comparison is not "$5 vs $10 per million" — it is "already paid for" versus "metered from zero." Opus 5 is the strongest model available inside the flat plan. That is a bigger practical gap than any benchmark on the chart. If you're already bumping the ceiling, our notes on Claude Code usage limits and the deeper Fable 5 pricing breakdown cover the mechanics.

Three non-price constraints that can decide it for you

• Zero data retention rules Fable 5 out entirely. Fable 5 requires 30-day data retention, so it is unavailable to organisations on a ZDR agreement — requests fail validation rather than degrading. Opus 5 carries no such requirement. For regulated teams this is not a preference, it is a hard gate.
• Priority Tier covers Fable 5 but not Opus 5. If you have a latency SLA and are paying for guaranteed capacity, that inverts the recommendation for production traffic.
• Fast mode exists on Opus only. Opus 5 and Opus 4.8 offer a fast mode at $10/$50 for up to 2.5x the output tokens per second — the same headline price as standard Fable 5, on the first-party Claude API only, not Bedrock, Google Cloud, Foundry, or Batch. The gain is in generation speed, not time to first token, so a long refactor lands noticeably sooner and a one-line answer feels identical.

One tax applies to both: safety classifiers on Fable 5 and Opus 5 can decline a request with a successful HTTP 200 carrying stop_reason: "refusal", across categories including cyber and bio. Anthropic's recommended handling is the fallbacks: "default" parameter, which retries on a per-category recommended model. If you do security or life-sciences work, budget for that plumbing on either model — it is not a Fable-specific problem.

The routing rule

Default to Opus 5 for essentially all agent work: implementation, refactors, test writing, debugging, long autonomous runs, and anything computer-use shaped. It is half the price, inside your plan, has a newer knowledge cutoff (May 2026 vs January 2026), and by Anthropic's own account gives up almost nothing on coding.

Escalate to Fable 5 when you hit a genuinely hard problem that Opus 5 has already failed once, when you need Priority Tier capacity, or when you want a second opinion from a differently-tuned model rather than a retry from the same one. That last case is often better served by asking two models and reading the disagreement — the method is in comparing models on your own codebase, which is still the only benchmark that predicts anything about your repo.

And keep the cheaper tiers in the rotation. Not every task deserves an Opus. Sonnet-class models handle mechanical edits at a fraction of the cost, and the discipline of routing by task difficulty saves more money than any single model choice. If a model isn't showing up in your model picker at all, update Claude Code before concluding your plan doesn't include it.

Frequently asked questions

Where Backgrind fits

Backgrind is not a model and not an agent — it is a desktop overlay for macOS and Windows that PTY-wraps the CLI you already run. Whichever model you pick here, Backgrind floats your Claude Code session above whatever else is on screen, including borderless-fullscreen games, and pings you only when the agent needs a decision or finishes. In BYO-CLI mode your agent's content never touches our servers; Live mode lets you answer those prompts from a phone or browser.

The practical payoff for this particular question: run Opus 5 in one tab and Fable 5 in another on the same task, and judge the diffs rather than the benchmarks. If you'd rather have that judged for you, the Fusion council puts your own CLIs on one hard question in parallel and returns a single verdict, pinging you only when they split or the verdict comes back low-confidence.

Sources

Prices, cache multipliers and Batch rates: Anthropic — model pricing. Context, output limits and knowledge cutoffs: models overview. Launch claims and benchmark charts (vendor-reported): Introducing Claude Opus 5. Independently administered ARC-AGI-3 result: ARC Prize — Claude Opus 5 verified results. Subscription split and credits: Claude Fable 5 on your plan and manage usage credits. Cacheable-prefix change: model migration guide. Refusal handling: refusals and fallback. Effort settings referenced in the CursorBench claim: effort.