Claude Fable 5.1 vs Claude Opus 5.5: when the pricier model earns it
Anthropic’s launch copy makes this an awkward page for the pricier model: it says Opus 5.5 "performs at the level of Claude Fable 5.1 on most work", then cautions that Opus 5.5’s lead in its own benchmark table is "narrower than these scores suggest". Here is what the vendor figures, the independent ones and the two TulexAI prices each say.
The usual choice
Pick one. Pay one subscription. Live inside one vendor's models.
- Claude Fable 5.1 at 25 PT per 750 tokens, Pro and up
- Claude Opus 5.5 at 10 PT per 750 tokens, from Basic
- Plus 54+ models, one login
Anthropic says Claude Opus 5.5 performs at the level of Claude Fable 5.1 on most work for $4/$20 per 1M tokens, not $10/$50; Artificial Analysis scores it 58 to 53 at max effort (Intelligence Index v4.3.2). Anthropic’s docs still route demanding reasoning to Fable 5.1. On TulexAI, Opus 5.5 is 10 PT per 750 tokens from Basic, Fable 5.1 25 PT from Pro.
Claude Fable 5.1 vs Claude Opus 5.5 vs TulexAI
| Claude Fable 5.1 | Claude Opus 5.5 | TulexAI | |
|---|---|---|---|
| API list price per 1M tokens (input / output) | $10 / $50 | $4 / $20 | 25 PT vs 10 PT per 750 tokens of prompt plus reply |
| What Anthropic’s docs recommend it for | Demanding reasoning and long-horizon agentic work | Most workloads, as the starting point | Both in one chat, Pro ($23/mo) and up |
| Intelligence Index v4.3.2 at max effort (Artificial Analysis) | 53 with fallback, #4 of 212 | 58 with fallback, #1 of 212 | Opus 5.5 runs at medium on TulexAI, not max |
| Intelligence Index v4.3.2 at medium effort (Artificial Analysis) | 49, #15 of 212 | 51, #8 of 212 | Medium is Opus 5.5’s setting on TulexAI |
| Anthropic-reported scores (Terminal-Bench 4.0 / GDPval-AA v2.1 Elo) | 55.8% / 1735 | 66.4% at xhigh / 1846 at max effort | Anthropic says the real gap is narrower than its table suggests |
| Cost and output per Intelligence Index task at max effort (Artificial Analysis) | $7.63, ~78k output tokens | $5.98, ~119k output tokens | Billed in Platform Tokens, not per task |
| Hallucination rate at max / medium effort (Artificial Analysis, lower is better) | 73% / 69% | 59% / 68% | About level at medium, Opus 5.5’s TulexAI setting |
| Output speed and time to first token at medium effort (Artificial Analysis) | 55.0 tok/s, 10.14s | 75.2 tok/s, 22.17s | Not measured on TulexAI |
| Tool use and forced tool choice | Tools; forced choice rejected by Anthropic | Tools; forced choice rejected by Anthropic | Tools on both; a forced choice runs as auto |
| Safeguard refusals in Coding Agent Index v1.5 (Artificial Analysis, max effort) | 8.8% of attempts | 9.1% of attempts | No fallback model: flagged requests are declined |
| Claude plan access | Pro via usage credits; included from Max ($100/mo) | Included from Claude Pro ($20/mo) | Opus 5.5 from Basic ($11/mo), Fable 5.1 from Pro ($23/mo) |
Which should you pick?
Start with Claude Opus 5.5, which is what Anthropic’s own docs recommend for most workloads: it lists at $4/$20 per 1M tokens against Fable 5.1’s $10/$50, Anthropic says it performs at the level of Claude Fable 5.1 on most work, and Artificial Analysis scored it higher on Intelligence Index v4.3.2 at both max effort (58 to 53) and medium (51 to 49). Anthropic itself says the lead in its benchmark table overstates the real gap, so treat Opus 5.5’s edge as small. Reach for Claude Fable 5.1 for demanding reasoning or long-horizon agentic work, which Anthropic’s docs still send to it, or when Opus 5.5 has already fallen short. On TulexAI we send no effort setting, so Opus 5.5 answers at medium; if a hard prompt comes back thin, rerun it on Fable 5.1 in the same chat. Opus 5.5 bills 10 PT per 750 tokens of prompt plus reply from the $11 Basic plan, drawing on the premium text allowance (small on Basic, where requests downgrade once it runs out), and Fable 5.1 bills 25 PT from the $23 Pro plan, metered by the frontier allowance.
Why choose at all? TulexAI includes both
54+ models in one subscription - here are the ones that cover what Claude Fable 5.1 and Claude Opus 5.5 each do best.
Text & Chat
- Claude Opus 5.5Premium
- Claude Fable 5.1Premium
- Claude Opus 5Premium
Frequently asked questions
Anthropic says it "performs at the level of Claude Fable 5.1 on most work", and its own table puts Opus 5.5 ahead on every benchmark it reports for both, with Opus 5.5 run at max effort (xhigh on Terminal-Bench 4.0). It also cautions that at these capability levels benchmark margins are "a less reliable guide to real-world differences". Artificial Analysis puts Opus 5.5 ahead on Intelligence Index v4.3.2 at max effort (58 to 53) and narrowly at medium (51 to 49), while noting it does not lead on CritPt, AA-LCR or GDP.pdf; on AA-LCR it scores 85% at max effort, the same as Fable 5.1.
Anthropic’s docs say to "start with Claude Opus 5.5 for most workloads" and to use Fable 5.1 "for demanding reasoning and long-horizon agentic work", or when evals on Opus 5.5 at higher effort still fall short; its model-choice guide names xhigh and max as those settings. TulexAI sends no effort setting, so Opus 5.5 answers at medium there and cannot be turned up. If a hard prompt comes back short of what you need, the step up on TulexAI is to rerun it on Fable 5.1 in the same chat.
On Anthropic’s API, Fable 5.1 costs 2.5 times as much per token: $10 input and $50 output per 1M tokens against $4 and $20. Per task the gap is smaller. At max effort Opus 5.5 writes more, and Artificial Analysis measured $5.98 per Intelligence Index task against $7.63, with about 119k output tokens against 78k; at medium, where Opus 5.5 used fewer output tokens than Fable 5.1 (38M against 44M to run the index), it was $1.34 against $2.98. On TulexAI, Opus 5.5 bills 10 PT per 750 tokens of prompt plus reply and Fable 5.1 bills 25 PT, reasoning included.
Yes, both take tools on TulexAI. Neither accepts a forced tool choice: Anthropic returns an HTTP 400 when a request insists on any tool or on one named tool, so TulexAI sends that request as auto and the model decides whether to call one. On Opus 5.5, adaptive thinking is always on and draws on the same output budget as the answer, and TulexAI caps replies at 8,192 output tokens, so a long plan plus a long answer can run out of room.
Claude Pro ($20/month, or $17/month on the annual plan) includes Opus, and Claude Code defaults to Opus 5.5 on paid plans. On Pro, Fable 5.1 runs only on usage credits; it is included on Max (from $100/month), Team premium seats and seat-based Enterprise premium seats, where up to 50% of weekly limits can go to Fable models. The Free plan has neither. On TulexAI both sit in one chat from the $23 Pro plan, and Opus 5.5 alone starts on the $11 Basic plan.
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