Opus 5.5 vs Fable 5.1 vs Sonnet 5.5 for Coding (2026)
Opus 5.5 vs Fable 5.1 vs Sonnet 5.5 for coding: Anthropic's own benchmarks, real cost per task, plan access in Claude Code, and which model to pick when.
By AI Tool Verdicts Editorial Team · Published
Bottom line: Opus 5.5 for most coding, Sonnet 5.5 when speed and cost matter, Fable 5.1 only for multi-hour agent runs where Opus at high effort still fails.
Opus 5.5 vs Fable 5.1 vs Sonnet 5.5 for coding comes down to this: Claude Opus 5.5 is the right default, and Claude Fable 5.1 is rarely worth its price. On Anthropic's own coding benchmarks, Opus 5.5 beats Fable 5.1 while costing 60% less per token, and Sonnet 5.5 even tops both on Terminal-Bench. Fable 5.1 earns its place only on very long agent sessions where Opus 5.5 at high effort keeps falling short.
If you searched for "Fable 5.5" or "Fable 5.5 vs Opus 5.5": there's no Fable 5.5 as of November 2026. Fable 5.1 is the newest Fable model, and the 5.5 number belongs to Opus, Sonnet and Haiku.
Anthropic says the same thing. Its own model guide says most workloads should start with Opus 5.5 and move to Fable 5.1 only "if your evals at xhigh or max effort still fall short."
How we researched this: Anthropic's model docs, pricing pages, launch posts and Claude Code docs as of October 2026. All benchmark numbers are Anthropic's own; we haven't run our own benchmarks.
Opus 5.5 vs Fable 5.1 vs Sonnet 5.5 at a glance
| Opus 5.5 | Fable 5.1 | Sonnet 5.5 | |
|---|---|---|---|
| Released | Sep 22, 2026 | Sep 1, 2026 | Sep 28, 2026 |
| Anthropic's pitch | Long-running agentic coding and knowledge work | Demanding reasoning and long-horizon agentic work | Best mix of speed and intelligence |
| API price (input / output per 1M tokens) | $4 / $20 | $10 / $50 | $2 / $10 |
| Cache reads per 1M tokens | $0.20 | $0.25 | $0.10 |
| Speed (Anthropic's label) | Moderate | Slower | Fast |
| Context / max output | 1M / 128K | 1M / 128K | 1M / 128K |
| Default effort in Claude Code | Medium | Must be picked manually | Medium |
| On Claude Pro | Included | Only with usage credits | Included |
Specs and prices come from Anthropic's models overview and pricing page. All three share the same June 2026 knowledge cutoff.
Opus 5.5 vs Fable 5.1 benchmarks
Anthropic published three coding benchmarks with all of these models in its launch posts. Higher is better.
| Benchmark | Opus 5.5 | Fable 5.1 | Sonnet 5.5 |
|---|---|---|---|
| Terminal-Bench 4.0 | 66.4% | 55.8% | 70.6% |
| FrontierCode v1.1 | 54.4% | 50.3% | 52.1% |
| CursorBench 4.0 | 57.8% | 51.8% | 55.5% |
Sources: the Opus 5.5 launch post for Opus and Fable, and the Sonnet 5.5 launch post for Sonnet. Sonnet's FrontierCode figure is at xhigh effort; at max effort Anthropic reports 46.2%.
Two caveats matter here. First, these are vendor numbers, and the effort settings differ: Opus 5.5 ran Terminal-Bench at xhigh, and Anthropic notes a margin of error of about 2.6 points on that test. Second, short benchmarks favor fast, focused models. Fable's pitch is work that runs for hours, which none of these tests measure well.
Even with those caveats, the pattern is clear. On tasks a typical developer runs every day, the most expensive model does not come out on top.
Sonnet 5.5 vs Opus 5.5: when the cheaper model wins
Sonnet 5.5 costs half as much as Opus 5.5 per token, runs faster, and scored higher on Terminal-Bench 4.0. Opus 5.5 still leads on FrontierCode and CursorBench, which lean on larger, multi-file changes.
In practice that splits cleanly:
- Pick Sonnet 5.5 for shell work, scripts, small fixes, tests and anything you run many times a day.
- Pick Opus 5.5 for refactors that touch many files, tricky bugs, architecture questions and long agent sessions.
Claude Code has a built-in way to get both: the opusplan model setting uses Opus while planning and switches to Sonnet to carry out the plan, per the Claude Code model docs.
What each model costs per coding task
Per-token prices hide how much an agent actually spends. Here is the same agent task priced on each model at list API prices. Our assumptions: 30 requests, each reading 55K tokens from the prompt cache, writing 5K new tokens to the cache and producing 1.5K output tokens.
| Model | Cache reads | Cache writes | Output | Cost per task |
|---|---|---|---|---|
| Sonnet 5.5 | $0.17 | $0.38 | $0.45 | about $0.99 |
| Opus 5.5 | $0.33 | $0.75 | $0.90 | about $1.98 |
| Fable 5.1 | $0.41 | $1.88 | $2.25 | about $4.54 |
So Fable 5.1 costs about 2.3 times as much as Opus 5.5 and 4.6 times as much as Sonnet 5.5 for the same work. The real gap is likely wider, because thinking tokens bill as output and Fable runs at high effort by default. Our Claude Code pricing guide shows how these task costs add up over a month.
If you use Claude Code on a subscription rather than the API, the cost shows up as plan limits instead of dollars, which brings us to access.
Which plans include Fable 5.1, Opus 5.5 and Sonnet 5.5
As of October 2026, per Claude's pricing page:
- Pro ($20 a month): Opus 5.5 and Sonnet 5.5 are included. Fable 5.1 runs only on paid usage credits.
- Max (from $100 a month): all three, but Fable 5.1 is capped at 50% of your weekly limits.
- Team: Fable 5.1 only on premium seats, also capped at 50% of weekly limits.
- Enterprise: full Fable access.
In Claude Code, Opus 5.5 is the default model on every paid plan. Fable 5.1 is never the default: you pick it with /model fable, and you need Claude Code v2.1.257 or later. On plans where Fable bills to credits, Claude Code asks before it spends them in interactive sessions, but in non-interactive -p mode it bills credits without asking, according to the model config docs. Watch that one if you run scripted jobs.
When Fable 5.1 is worth it
Anthropic positions Fable 5.1 as its most capable model open to all customers, built for agent sessions that run for hours, multistep research and work carried through to a finished document. For coding, that points to a narrow set of jobs:
- An agent that has to work on its own for hours, such as a large migration across a big codebase.
- Hard reasoning where Opus 5.5 at xhigh or max effort has already failed on your own tests.
- Work where getting it right once matters far more than the token bill.
For everything else, Opus 5.5 gives you better scores on the published coding tests for well under half the price.
Which should you choose?
- Choose Opus 5.5 if you want one model for serious coding work. It's the default in Claude Code for a reason.
- Choose Sonnet 5.5 if you run lots of small tasks, care about speed, or pay per token through the API.
- Choose Fable 5.1 if your multi-hour agent runs fail on Opus 5.5 even at high effort, and you have Max, a premium Team seat, Enterprise or credits to spare.
Not sure Claude is the right family at all? Our best AI for coding roundup compares it with GPT and Gemini models, and Cursor vs Claude Code covers what changes when you use these models inside Cursor.
FAQ
Is Fable 5.1 better than Opus 5.5 for coding?
Not on Anthropic's published coding benchmarks: Opus 5.5 scores higher on Terminal-Bench 4.0, FrontierCode and CursorBench. Fable 5.1 targets very long agent sessions, which those tests don't capture.
Is Sonnet 5.5 good enough for coding?
Yes for most everyday work. It beat Opus 5.5 on Terminal-Bench 4.0 and trails it by only a few points on the other two tests, at half the price.
How much does Opus 5.5 cost?
On the API, $4 per million input tokens and $20 per million output tokens, with cache reads at $0.20. On a subscription, it's included from Claude Pro at $20 a month.
Can I use Fable 5.1 on Claude Pro?
Only with usage credits, which are billed on top of the plan. Max plans include Fable 5.1 up to 50% of the weekly limits.
Which model does Claude Code use by default?
Opus 5.5 on Pro, Max, Team and Enterprise. Switch any time with /model sonnet, /model opus or /model fable.