GPT-6 vs Claude Fable 5.1: The Rate Cards Match, the Coding Board Doesn't

GPT-6 and Claude Fable 5.1 list at exactly the same rate: $10.00 per million input tokens and $50.00 per million output. That is the whole of the easy part. The two names are not the same kind of thing — GPT-6 is a family of three models with no gpt-6 endpoint behind it, and Claude Fable 5.1 is one weighable model with one rate card — so the price match tells you almost nothing until you decide which member of the GPT-6 family is doing the answering. On the board that matters most for this bracket, Fable 5.1 is first and no GPT-6 model is.

Which GPT-6 turns up to this comparison

Start with the naming, because it decides the answer. OpenAI ships the GPT-6 generation as three separate model ids: GPT-6 Astra at the top, GPT-6 Sol in the middle and GPT-6 Luna at the bottom. There is no model called GPT-6 you can call. Ask for openai/gpt-6 on any gateway and you get a 404, not a completion.

Only one of the three carries the $10.00 / $50.00 card that matches Claude Fable 5.1, and that is Astra. Sol is a fifth of the price at $2.00 / $10.00 and Luna is a hundredth of it at $0.10 / $0.50. So "GPT-6 vs Claude Fable 5.1" is really "GPT-6 Astra vs Claude Fable 5.1" if you insist on comparing like-for-like rate cards — and that specific matchup is not the interesting one any more, for a reason that only appeared at the end of September.

Anthropic's side has no such ambiguity. Claude Fable 5.1 is a single model, released on 1 September 2026, with a 1,000,000-token context window, a 128,000-token output ceiling, and text, image and file input. It is served under the model id anthropic/claude-fable-5.1. Quoting a price for "Fable 5.1" is unambiguous in a way that quoting a price for "GPT-6" never is.

Where Fable 5.1 is actually ahead, and by how much

The gap that decides this comparison is not the general index. It is the coding board. Read off Artificial Analysis and carried in the OrcaRouter catalogue entry for each model on 8 October 2026:

• AA Coding Index — Claude Fable 5.1 81.6, ranked 1st of the models on that board; GPT-6 Astra 76.9, ranked 4th
• AA Intelligence Index — Claude Fable 5.1 53.4, rank 8; GPT-6 Astra 52.7, rank 9
• GPQA Diamond — Claude Fable 5.1 93.7 vs GPT-6 Astra 96.1
• Humanity's Last Exam — Claude Fable 5.1 59.1 vs GPT-6 Astra 54.7
• SciCode — Claude Fable 5.1 63.1 vs GPT-6 Astra 56.5
• Terminal-Bench v2.1 — Claude Fable 5.1 91.4 vs GPT-6 Astra 88.4
• Terminal-Bench v4.0 — Claude Fable 5.1 52.0 vs GPT-6 Astra 59.1
• Long-context recall — Claude Fable 5.1 85.3 vs GPT-6 Astra 80.7
• Context and output — both 1,000,000 tokens in for Fable 5.1 against 1,050,000 for Astra; both 128,000 tokens out

The pattern is not "one model is better". Fable 5.1 wins the two boards that correspond to writing and long-horizon software work — SciCode and Terminal-Bench 2.1 — and Astra wins Terminal-Bench 4.0 and GPQA Diamond. Fable 5.1 carries a 4.4-point lead on Humanity's Last Exam and a 4.6-point lead on long-context recall. On the general index the two are 0.7 points apart, which is inside the noise you would expect from a benchmark refresh.

One caveat applies to every cross-model number in this piece and it is worth stating rather than burying: Artificial Analysis does not guarantee that two model pages are rendered against the same index revision on the same day, and it now splits its peer groups — open-weights models are ranked against open-weights models of the same size class, proprietary models against a proprietary price band. A score read off one page and a score read off another are indicative, not a controlled measurement. Both figures above come from the same evaluator, but treat the sub-point differences as direction rather than precision.

The complication that arrived on 29 September

If you priced this comparison a month ago you would have fielded Astra, accepted a 4.7-point coding deficit and paid $10.00 / $50.00 for it. That is no longer the obvious move, because GPT-6.1 Sol exists — released 29 September 2026, three weeks after Astra and one week after the rest of the family.

GPT-6.1 Sol scores 51.8 on the same Artificial Analysis Intelligence Index, against Astra's 52.7, and it lists at $2.00 / $10.00 — one fifth of Astra's rate card. It is not a coding-board leader either; it inherits the same one-point-off-Astra shape rather than closing the gap to Fable 5.1. But it changes the economics of the decision. If the reason you were reaching for a $50-output model was "I need frontier reasoning on a hard task", GPT-6.1 Sol now answers most of that for a tenth of the output cost. If the reason was specifically "I need the best coding index in the room", neither GPT-6 model answers it, and the honest advice is to keep Fable 5.1.

Worth pinning down explicitly: OpenAI has never published GPT-6 Astra and Claude Fable 5.1 against each other, and Anthropic has not published a Fable-5.1-versus-GPT-6 comparison either. Every cross-vendor number in this piece is either an independent evaluator's figure or a vendor's own benchmark of its own model. Nothing here is a head-to-head run by either party.

The bill, rather than the sticker

Identical rate cards do not produce identical invoices, because the meters underneath them differ.

• Cached input, Fable 5.1 — $0.25 per million on the OrcaRouter listing, a 97.5% discount on the input rate
• Cached input, GPT-6 Astra — $1.00 per million, a 90% discount
• Cache writes — Fable 5.1 $12.50 per million, GPT-6 Astra $12.50 per million, a straight tie
• Above 272,000 input tokens — Astra reprices the whole request to $20.00 in / $75.00 out; Fable 5.1 has no equivalent step on the figure the catalogue carries
• Traffic, last 7 days — Fable 5.1 1.73 million tokens; GPT-6 Astra 76.2 million tokens
• Median time to first token — Fable 5.1 4,055 ms; GPT-6 Astra 3,500 ms
• Median output speed — Fable 5.1 90.1 tokens/s; GPT-6 Astra 70.4 tokens/s

The cache line is the one that moves money on a Fable 5.1-shaped workload. A long agent run that re-sends the same 200,000-token repository context twenty times pays $0.25 per million on the cached portion instead of $10.00 — an order of magnitude cheaper than Astra's $1.00 cached read. On that shape of request the identical headline card is not identical at all, and Fable 5.1's coding advantage comes with a cheaper way to use it.

The 272K step does the opposite for Astra. Any request that crosses it reprices from the first token, so a 300,000-token prompt on Astra bills at $20.00 / $75.00 for the whole thing, not just for the 28,000 tokens above the line. On a budget model that step is a rounding error; at $10.00 input it is the difference between a $3.00 request and a $6.00 one.

Running both without picking a winner in advance

The practical version of this comparison is that you probably want both, and you want to be able to move between them per request rather than per quarter. Both Claude Fable 5.1 and every live GPT-6 model sit in the same OrcaRouter catalogue — one API in front of 200+ models, the provider's list price passed through at 0% markup, so a vendor price change is live here the same day rather than at your next invoice — and the routing DSL lets you split traffic by request size or by share. The shape that fits this pair is a size split: send short, coding-shaped requests to Claude Fable 5.1 and route the long-context work that would trip Astra's 272K step to a model whose rate card has no step in it, then widen whichever slice your own evaluations favour.

Automatic failover across providers is the other half of that. Neither of these models is immune to a bad afternoon, and a route that degrades mid-run is not something you want to discover from a client complaint.

What each side is for, in one line each

Claude Fable 5.1 is the best coding model on the independent board and it is priced as a premium tier, with the cheapest cached reads of any model in this bracket. The GPT-6 family does not have a member that beats it on coding, and the family member that shares its rate card — Astra — is the one you are now least likely to pick, because GPT-6.1 Sol delivers within a point of Astra's index for a fifth of the money.

So the answer to "GPT-6 vs Claude Fable 5.1" depends entirely on which GPT-6 you meant. If you meant the family's flagship, Fable 5.1 wins the coding board and loses on price-per-answer to a model one tier down. If you meant the family as a whole, then the current best value on the OpenAI side of this pairing is GPT-6.1 Sol at $2.00 / $10.00 — and it is still not the coding leader. The rate cards match. The boards do not.