For Claude Fable 5.2 vs Opus 5.5, start on Opus 5.5: that is Anthropic's own rule and it holds up. Fable 5.2 costs about 1.76 times Opus 5.5 today on Tchavi, and about 2 times at list price (15.453 / 77.273 credits per 1,000 input / output tokens with a 12% discount included, against 8.80 / 44.00). In return, Anthropic's numbers show gains mostly on long, agentic tasks. And the worry that a high effort setting blows up your bill did not hold on our test: on a single question xhigh costs 2x low, not 21x.
A discount to know about: Fable 5.2 carries a 12% discount until 31 December 2026. After that date the prices in this article are out of date: read the current one on the model page.
In short
- Same surface. On 10 November 2026 we compared the Models API objects for
claude-fable-5-2andclaude-opus-5-5field by field: 1M tokens in, 128K out, images and PDF in, structured outputs, batch, citations, context management, web search, code execution, effort from low to max, adaptive thinking only. Every capability field is identical. - Price: Fable 5.2 at 15.453 / 77.273 credits today (list price 17.56 / 87.81), Opus 5.5 at 8.80 / 44.00 with no discount. That is about 1.76x today and about 2x at list price.
- Anthropic's rule: start on Opus 5.5 and move to Fable 5.2 "when your evals on a Claude Opus model at higher effort still don't meet your requirements."
- Our calculation: on the same prompt, going from low to xhigh multiplies the cost by 1.99, not 21.
- One independent test exists, as far as we know, and it has Opus ahead on pass rate at medium effort.
What actually changes when you call the two models?
Almost nothing in your code. Same parameters, same limits. On 10 November 2026, using our own key, we compared the two objects returned by the Models API: every capability is identical. The only difference we found is the price:
| Claude Fable 5.2 | Claude Opus 5.5 | |
|---|---|---|
| Tchavi model id | claude-fable-5-2 | claude-opus-5-5 |
| Input charged (credits per 1,000 tokens) | 15.453 (list price 17.56) | 8.80 |
| Output charged (credits per 1,000 tokens) | 77.273 (list price 87.81) | 44.00 |
| Discount | 12% until 31 December 2026 | none |
| Thinking | adaptive only | adaptive only |
Prices read on Tchavi on 10 November 2026; they can move, so check each model's page: Claude Fable 5.2 and Claude Opus 5.5. For the call details, see the chat completions documentation.
The practical catch: the default effort can differ from one model to the other (check it in Anthropic's documentation; we did not record it for Opus 5.5). An A/B test that doesn't pin effort may therefore compare two different settings. Set the same effort on both sides.
What do Anthropic's numbers say?
The figures below are Anthropic's (system card, Table 8.1.A, p. 207), not ours. Columns: Fable 5.2, Fable 5.1, Opus 5.5 (n/a: figure not reproduced here).
| Evaluation (source: Anthropic) | Fable 5.2 | Fable 5.1 | Opus 5.5 |
|---|---|---|---|
| Remote Labor Index | 41.3 | 17.9 | 21.3 |
| AutomationBench | 51.4 | 31.4 | 42.5 |
| Terminal-Bench-Science 0.1 | 74.6 | 52.6 | 58.7 |
| SWE-bench Multimodal | 74.1 | 54.7 | 61.4 |
| Chartography (no tools) | 73.4 | 44.8 | 64.4 |
| WANDR (relaxed) | 82.1 | 68.7 | 72.3 |
| FrontierCode 2.0 | 49.1 | 32.4 | 45.5 |
| Terminal-Bench 4.0 | 67.6 | 55.8 | 66.4 |
| AA-Briefcase (Elo) | 1,785 | n/a | 1,800 |
| GDPval-AA (Elo) | 1,831 | n/a | 1,866 |
Three caveats that a list of wins would hide:
- Opus 5.5 wins two evaluations: AA-Briefcase (1,800 vs 1,785) and GDPval-AA (1,866 vs 1,831).
- FrontierCode 2.0: Anthropic itself writes that the gap to Opus 5.5 "may not be meaningful". The score peaked at xhigh (49.1, the table figure); at max, Anthropic reports 45.7 against 45.5 for Opus. Anthropic adds that 22 of Fable's 660 attempts at max timed out and were graded anyway: counted as zero, the max score would be 44.4, below Opus. Nothing timed out at lower efforts.
- Terminal-Bench 4.0: 67.6 vs 66.4, with a standard error of ±1.8 for Fable 5.2, ±1.6 for Fable 5.1 and ±2.6 for Opus 5.5. That is within noise.
The big gaps are elsewhere: Remote Labor Index (41.3 vs 21.3) and Terminal-Bench-Science (74.6 vs 58.7). Those are long, tool-heavy work tasks. Keep that in mind for the section on cost.
What is the one independent test, and how much is it worth?
As far as we know, just one: paddo.dev, "Marked Down for Being Right", published on 10 November 2026 (link). It is one person's work, not a study.
| In that test | Fable 5.2 | Opus 5.5 |
|---|---|---|
| Passing runs (out of 52 each) | 40 | 44 |
| Total cost, at list price | $127.93 | $78.44 |
| Reviewing Opus's passing fix: routing gap caught | 4 of 4 | 1 of 4 |
Setup: a TypeScript monorepo of about 3,700 files, Claude Code, medium effort on both sides. Fable cost about 1.6x more and passed slightly fewer runs. As a reviewer, it spotted a routing gap that Opus's fix left in place, four times out of four against one, but on four attempts only: a signal, not proof.
The author's own caveat matters: every run was at medium effort, while Anthropic's reported gains are at high effort and above. So this test doesn't contradict Anthropic; it doesn't cover the zone where Fable is supposed to stand out.
How much does a higher effort really cost?
Anthropic publishes a cost curve (system card, §8.4, FrontierCode 2.0) in which effort moves the cost per task by about 21x: $2.10 at low, $44.70 at max. That is right for that task, which is long and agentic. But it is not what a single call sees.
We sent the same prompt to claude-fable-5-2 at three efforts on 10 November 2026; the credits are calculated at Tchavi's rate card, discount included, not read off an invoice. All three stopped at end_turn: complete answers, not cut-offs.
| Effort | Input tokens | Output tokens | Credits calculated | Approx. KES |
|---|---|---|---|---|
| low | 119 | 888 | 70.458 | ≈ KES 5.20 |
| high | 120 | 1,174 | 92.573 | ≈ KES 6.84 |
| xhigh | 120 | 1,789 | 140.096 | ≈ KES 10.35 |
KES figures use the rate read on 2026-11-10 (1 credit ≈ KES 0.07385; for reference 2.2871 UGX, 0.8431 RWF, 0.0116 ZMW), which moves with the market. One run per effort: a test, not a benchmark.
xhigh costs 1.99 times low (140.096 vs 70.458), and that ratio does not depend on the discount. What effort costs here is the output: 888 output tokens at low against 1,789 at xhigh (of which 1,123 were thinking). The input barely moves.
Our reading, which you should check on your own prompts: the 21x multiplier is a property of long, agentic tasks, with more turns, more tool calls and more subagents. It doesn't come from the effort setting alone. On a single question, xhigh costs about double low. Many calls look like that second case. For an agent that loops for an hour, Anthropic's curve is the one to look at.
To measure on your side, the X-Credits-Used header on every response gives the exact cost of the call.
When to stay on Opus 5.5, and when to move to Fable 5.2?
| Your situation | Pick | Why |
|---|---|---|
| You have no evaluation yet | Opus 5.5 | Anthropic's rule, and a lower price |
| Chat, extraction, writing, short calls | Opus 5.5 | Same capabilities, no published gain on this kind of call |
| Your Opus at high effort still fails your evals | Fable 5.2 | That is Anthropic's stated condition |
| Long agent with tools on full work tasks | Fable 5.2, to test | Anthropic's biggest gaps are here |
| Code review, defect spotting | Fable 5.2, to test | Signal from the paddo.dev test, on 4 attempts |
| Tight budget | Opus 5.5 | Fable costs about 1.76x today, 2x at list price |
The only fair judge is your own evaluations, with the same effort pinned on both sides.
FAQ
Claude Fable 5.2 vs Opus 5.5: which one is better?
Fable 5.2 beats Opus 5.5 on most of the evaluations Anthropic published, mainly long work tasks, but Opus 5.5 wins two (AA-Briefcase and GDPval-AA) and several gaps are within noise. "Better" depends on your task. Start on Opus 5.5.
How much more does Fable 5.2 cost than Opus 5.5 on Tchavi?
About 1.76 times today: 15.453 / 77.273 credits per 1,000 tokens (input / output) against 8.80 / 44.00, thanks to a 12% discount that ends on 31 December 2026. At list price (17.56 / 87.81) the gap is about 2x (1.9957). Read on 10 November 2026: check the model page on the day you decide.
Does setting effort to xhigh multiply the bill by 21?
Not on our single-call test. Anthropic shows a factor of about 21 ($2.10 to $44.70) on a long agentic task. On one prompt, xhigh cost 140.096 calculated credits against 70.458 at low, which is 1.99 times.
Do the two models have the same capabilities?
Yes, on every field we compared on 10 November 2026: context, output, images, PDF, structured outputs, batch, citations, web search, code execution, effort levels. The difference we found is the price.
Do I need to pin effort to compare them?
Yes. The default effort can differ from one model to the other: set the same effort on both sides so your test is fair.
Is Fable 5.2 always right?
No. In the paddo.dev test (52 runs each, medium effort), Opus passed 44 runs and Fable 40. That is one person's measurement, on one repository, at one effort.
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Ready to call it? First call with Claude Fable 5.2, and the four parameters that return a 400. Read next: Claude Sonnet 5.5 is now on Tchavi and cost vs quality, choosing the right model.
This article is part of the series "Building an AI product from Africa". Tchavi is an OpenAI-compatible AI API gateway: one key gives access to over 100 text, image, audio and video models, and you pay for it with mobile money, no bank card (countries and operators). More guides on the blog. Follow us: LinkedIn and X.