Why the default changed, July 24, 2026
Opus 5 shipped as the default on Claude Max and the strongest model on Pro, and Anthropic now recommends starting with it. Fable 5 remains available and is not deprecated — it is just no longer the default starting point.
Opus 5: specs and pricingDecision guide · updated August 2026
When to use Claude Fable 5
Since Opus 5 launched on July 24, 2026, most work should start with Opus 5 at half the price. Fable 5 is now a narrow-scope upgrade worth paying for in four specific situations. Here is the decision tree.
The short answer
Since 2026-07-24, Claude Opus 5 is the default model on Claude Max and the strongest model on Claude Pro. Fable 5 is now a narrow-scope upgrade worth paying for only in 4 situations: (1) long-horizon multi-step agentic tasks, (2) Mythos-grade security-conscious coding, (3) 1M full-repo analysis, and (4) compliance setups where Opus 5's no-retention default isn't required but you specifically need Fable's tighter behavior. For everything else, Opus 5 is cheaper and no worse by every published measure.
Decision tree: pick by what you're doing
Five branches. Everything not listed here starts at Opus 5 — cheaper and no worse by every published measure.
You're starting a new project
Most work — new features, routine coding, enterprise development. Anthropic's own guidance is to start with Opus 5, and it is already the Max default. Opus 5.
You run long-horizon multi-step agents
Multi-hour autonomous runs with many tool calls and file memory — the workload Fable 5 was built for, described by Anthropic as its 'long-running agents' model. Fable 5.
You do safety-critical or security-conscious coding
Mythos-grade security work — exploit-resistant code, defensive tooling. Opus 5 itself 'remains behind Mythos 5' on these domains, and Fable 5 is the widely available tier of that family. Fable 5.
You analyze a full repository in one context
Whole-repo reads that saturate the 1M window. Both models carry 1M context, but Fable 5's published ceiling on the hardest coding tasks (SWE-Bench Pro 80.3%) is the figure on record. Fable 5.
You're asking: is Fable 5 worth it?
Usually only if you hit one of the four cases above. At twice the list price ($10/$50 vs $5/$25) with no published capability edge outside those niches, paying for Fable 5 on generic work is hard to justify. Run your real volume through the cost calculator before deciding.
Decision guide as of August 2026, based on Anthropic's published guidance, published benchmarks and plan documentation. Your own evals beat any default.
Cost per solved task and token budget
List prices from src/lib/model-pricing.ts — Fable $10/$50 per M input/output tokens, Opus 5 $5/$25. Both share a 1M context window and 128K max output.
| Claude Fable 5 | Claude Opus 5 | |
|---|---|---|
| Input / MTok | $10 | $5 |
| Output / MTok | $50 | $25 |
| Context window | 1M | 1M |
| Max output | 128K | 128K |
| Data retention | 30 days (mandatory) | None required |
On cost per solved task, the two models sit in the same capability band, so the 2x list-price gap is the headline. Because Opus 5 can spend more output tokens reaching the same answer, the realised per-task gap is often smaller than list price implies — but it is still real. Budget from cost per solved task, not pass rate: if Fable 5 solves a task in fewer or cheaper tokens, only your own workload tells you which. The 30-day retention figure is the one difference that affects compliance teams directly.
Priced at API list rates, last verified August 2026 against Anthropic's pricing documentation. With caching and batching stacked, both models drop further — the cost calculator has the exact math for your volumes.
Compliance: the deciding factor for many teams
Retention policy, not price, is often what picks the model.
Retention requirement
Fable 5 requires a mandatory 30-day retention window for safety monitoring and is excluded from zero-data-retention agreements. Opus 5 general access has no retention requirement. If your compliance review blocked Fable 5 over ZDR, that blocker does not exist on Opus 5 — and if your policy instead requires retention logs, only Fable 5 provides them. Decide on this axis before you decide on price.
Price your real workload before you decide
Run your actual monthly volume through the calculator at both price points, and check the benchmark table to see where the two models actually part ways.