Fable 5.5 vs Gemini 4 vs GPT-6.1: Which Can You Use Today?

As of October 6, 2026, only one of the three models in "Fable 5.5 vs Gemini 4 vs GPT-6.1" is something you can call: GPT-6.1 Sol. Anthropic has not announced Claude Fable 5.5, so it has no model ID, price or published benchmark. Google announced Gemini 4 Argon on September 30, but it is rolling out only to cyber defenders in its Fairwind Program. And the "GPT-6.1" that leak posts say Fable 5.5 beats is GPT-6.1 Astra, which OpenAI decided not to release.

That means nobody can answer "which is best" with a fair test yet. For work you need to ship this week, choose among models that are actually documented: Claude Opus 5.5, Claude Fable 5.1, GPT-6.1 Sol or GPT-6 Astra. A Fable 5.5 release is rumored for Tuesday, October 6 in the US, and Anthropic has not confirmed it. The status below reflects public pages as of the evening of October 5, Pacific time. The checklist near the end shows how to tell when that changes.

Fable 5.5, Gemini 4 Argon and GPT-6.1 status as of October 6, 2026

Three shipped models fill the gap left by those names. Claude Fable 5.1 (claude-fable-5-1, released September 1) costs $10 input / $50 output per million tokens. Claude Opus 5.5 (claude-opus-5-5, released September 22) costs $4 / $20, and Anthropic says it "performs at the level of Claude Fable 5.1 on most work." GPT-6 Astra (gpt-6-astra, released in September) costs $10 / $50 up to 272K input. Anthropic's most recent model release is Claude Sonnet 5.5, on September 28.

Which GPT-6.1? Sol shipped, Astra was canceled

"GPT-6.1" names two different models, and most confusion this week comes from mixing them up.

GPT-6.1 Sol shipped on September 29. It has a 1,050,000-token context window and 128,000 output tokens. Requests up to 272K input tokens cost $2 input, $0.10 cached input and $10 output per million tokens. Above 272K, the whole request bills at $4 / $0.20 / $15. Tool calls need the Responses API. The GPT-6.1 Sol guide covers where to select it and what breaks when you switch.

GPT-6.1 Astra will not ship. The Wall Street Journal reported on September 28 that OpenAI was scrapping its release, and the BBC quoted Saachi Jain, OpenAI's head of safety systems, saying the model "didn't quite meet the bar." It fell short on "staying within scope and authorisation and how it communicates back to the user about the type of work it's done." OpenAI has given no date for a later Astra release. Don't confuse it with GPT-6 Astra, the agentic model OpenAI released in September, which you can still use. The GPT-6.1 Sol vs GPT-6 Astra comparison covers when the older Astra is worth its higher price.

The "Fable 5.5 > GPT-6.1" claim refers to the canceled Astra. According to OrcaRouter's account of the leak chain, an X user posted "5.5 > 6.1" on October 2, and a widely shared quote post expanded it: "Fable 5.5 is expected to outperform Astra 6.1." The thread includes no screenshot, benchmark, number or date. So the claim compares an unannounced model with a model that won't be released. It tells you nothing about GPT-6.1 Sol.

Is Fable 5.5 real? What users report and what Anthropic has published

Fable 5.5 may exist and be close to launch, but Anthropic hasn't said so. As of October 6, 2026:

• The Anthropic newsroom has no Fable 5.5 post. Its latest model posts are Sonnet 5.5 (September 28), Opus 5.5 (September 22) and Fable 5.1 with Mythos 5.1 (September 1).
• The Claude models overview lists Fable 5.1 as the current Fable. A docs URL ending in fable-5-5 loads only the generic documentation shell, with no model name, specs or prices. A URL that loads is not a hidden model page.
• The Claude API release notes, the Claude apps release notes and the Claude status history contain no Fable 5.5 entry.

What exists is a stream of user reports. Posts on X and Reddit say some accounts on claude.ai and in Claude Code are getting a newer model while the model picker still shows Fable 5.1. Users have shared a pixel-art game, an animated short with a score, motion design and 3D web pages. One tester says it is "outperforming Opus 5.5 and Astra too" in their own testing, especially for motion design and video editing. A Reddit thread notes that Opus 5.5 was "secretly tested" in a similar way 3–5 days before its release. That is a pattern people noticed, not a promise.

None of those posts shows a model ID, a request log or a statement from Anthropic. The demos are chosen by the people posting them, and you can't rerun them. A model that calls itself "Fable 5.5" when asked proves nothing about which model is serving the request. Treat the reports as a reason to expect a launch, not as a measurement. No benchmark of Fable 5.5 exists, and Artificial Analysis has no Fable 5.5 page. Any "Fable 5.5 is X% better" claim has nothing behind it yet.

Don't hardcode a guessed ID such as claude-fable-5-5. If Anthropic releases the model, take the ID from its model page.

Fable 5.2 vs Fable 5.5: why this page once said 5.2

This page first appeared on September 20, when the same kind of rumor used a different number. On September 18–19, testers posted results from a "suspected next Fable" they called Fable 5.2, with claims that requests were moving "Fable 5.1 → 5.2." JAZII's September 18 report said that with the same prompt and high reasoning, the output looked better than GPT-6 Astra's, but runs were slower and expensive. In a follow-up post, the author said "5.2" was their own assumption.

The Gemini side of those sightings came from Arena. A controller SVG that Lumina compared with GPT-6 Astra's was attributed to Gemini 4 but appeared under an entry labeled gemini 3.7 flash. The author called both versions nearly perfect, and said they could not get similar results the next day.

Whether the September "5.2" model and today's "5.5" reports describe the same model is unknown. Whether the Arena output came from what Google later named Argon is also unknown. Anthropic has not renamed anything publicly. Both reports point to the same lesson: a stronger-looking first result can come with a longer wait and a higher bill, and one striking output is not a repeatable result.

This image summarizes the September 18–20 sightings. "Alleged Gemini 4" and "Suspected next Fable" are the labels used before Google named Argon and before the current Fable 5.5 reports.

Is Gemini 4 Argon out? Announced, but limited to Fairwind and not free

No. Google announced Gemini 4 Argon on September 30 and said it is "rolling out to a set of trusted cyber defenders through our Fairwind Program." Broader access will come "as soon as possible," "starting with paid API customers and Google AI Ultra subscribers." Google has given no date, no model ID and no rate limits. As of October 6, 2026, the Gemini API models page and the Gemini API pricing page still have no Gemini 4 or Argon entry. Posts claiming Argon is "now available for developers" contradict Google's own text. "Gemini 4 Pro" was an earlier rumored name; the announced model is Gemini 4 Argon.

It won't be free on the API either. Google announced an introductory price of $2 input and $10 output per million tokens, with cached input 95% off ($0.10). After an introductory period of unannounced length, the price becomes $4 / $20. Google states a 1M-token output limit, while Vals' Gemini 4 Argon page lists 262K. Opus 5.5, Fable 5.1, GPT-6.1 Sol and GPT-6 Astra all cap output at 128K.

Fairwind is the same program Google used for earlier cyber models. The Gemini 3.8 Flash Cyber Fairwind guide explains how that program worked for 3.8 Flash Cyber. Google has not published separate application steps for Argon.

The published scores are strong but mixed:

• Google's own table compares Argon with GPT-6 Astra, Claude Fable 5.1 and Claude Opus 5.5. GPT-6.1 Sol is not in it. Argon leads Opus 5.5 on the Vals Index (68.9 vs 67.0) and DeepSWE v1.1 (77.9 vs 74.2). Opus 5.5 leads on FrontierSWE v2 (62.3 vs 55.0) and Terminal-bench 4.0 (66.4 vs 57.4).
• Artificial Analysis Intelligence Index v4.3.2 at "high" effort scores Argon 53 at $1.99 per index task, Opus 5.5 54 at $1.82 and GPT-6.1 Sol 50 at $0.32. Argon and Sol share the same $2 / $10 token price, yet $1.99 ÷ $0.32 ≈ 6.2, so Argon costs about six times more per task because it uses far more tokens. Sol at max effort scores 52 for $0.72, within one point of Argon at high for about 36% of the cost.
• The Vals Index ranks Argon first of 41 models at 68.90%, ahead of Opus 5.5 (66.97%), Fable 5.1 (65.83%), GPT-6 Astra (63.13%) and GPT-6.1 Sol (61.15%). Vals also lists Argon weak on CUA-bench, at 4.83%.

The Gemini 4 Argon vs Claude Opus 5.5 vs GPT-6.1 Sol comparison works through the cost per task and benchmark details.

What to run now while Fable 5.5 and Argon are out of reach

Don't pause real work waiting for either model. Pick from the documented models by workload:

Use the Claude Fable 5.1 vs Opus 5.5 comparison if the choice is between the two Claude models, and Claude Fable 5.1 API pricing for its full billing details.

The useful thing to do while you wait is to build your test set now. When Fable 5.5 or Argon becomes available, you can run it against your current model right away instead of starting the evaluation from scratch.

Release-day checklist: signs Fable 5.5 or Argon is actually available

Count a model as released only when it appears on the vendor's own pages and in your account.

For Claude Fable 5.5:

1. A launch post in the Anthropic newsroom.
2. A model page with real content and a pricing row on the Claude Platform docs, with an exact model ID.
3. An entry in the Claude API release notes.
4. The ID in the GET /v1/models response for your own API key. The list is paginated, so check every page before deciding the model is missing.
5. For app users, the name in the claude.ai model picker. Output that seems better, or a model that names itself, doesn't count.

For Gemini 4 Argon:

1. A Gemini 4 Argon entry with a model ID on the Gemini API models page, or in the Vertex AI Model Garden.
2. A pricing row on the Gemini API pricing page, including how long the introductory price lasts.
3. For Google AI Ultra subscribers, Argon in the Gemini app's model menu.

Social posts about being routed to a new model, leaked screenshots and URLs that merely load don't meet any of these checks.

How to compare Fable 5.5, Argon and your current model fairly

Once a model is on that checklist, compare it on your own work rather than on demos:

• Identified models. Use the documented model ID for every run, and record it with the results.
• Matched tasks. Use the same task description, files, tools and permissions for every model.
• Matched effort or budget. Comparing one model at max effort with another at high effort shows you the effort setting, not the model.
• Acceptance criteria written in advance. Decide what counts as done, such as passing tests, following the required format or needing only minimal edits, before you see any output.
• Every attempt counted. Record retries, total cost and wall-clock time, not just the best run.

Then compare cost per accepted task, which equals the cost of all attempts divided by the number of accepted tasks. For example, if 25 attempts cost $30 in total and 20 tasks pass review, the cost is $30 ÷ 20 = $1.50 per accepted task. A pricier model can come out cheaper on this measure if it needs fewer retries. A model that produces richer output can come out more expensive if the extra material has to be removed.

This chart was made in September with GPT-6 Astra as the comparison model, and its note about "Fable 5.2" refers to the earlier rumor name. The same steps apply with Opus 5.5, Fable 5.1 or GPT-6.1 Sol as your baseline and Fable 5.5 or Argon as the challenger.

A launch announcement settles the names, the IDs and the prices. Only a repeatable improvement on your own tasks tells you whether to switch.