Claude Fable 5 vs Opus 4.8 vs GPT-5.5 vs Gemini 3.5: The 2026 Benchmark Table

Claude Fable 5 tops every published benchmark in this comparison (SWE-Bench Pro 80.3%, Humanity's Last Exam 64.5%, OSWorld 85.0%), but a US government export-control order suspended Fable 5 worldwide on June 12, 2026, so almost no developer can call it today. Among models you can actually use right now, Claude Opus 4.8 leads the Artificial Analysis Intelligence Index at 61.4 versus GPT-5.5 at 60.2, and Gemini 3.5 Pro has not shipped publicly at all. The honest answer: the benchmark winner is off the market, and Opus 4.8 is the real production pick.

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Why this matters to you

If you are choosing a model for an AI agent, a coding tool, or a SaaS feature, you want the best model you can actually call from your code. A benchmark table that crowns a model you cannot access wastes your time. So this post splits the four models into two groups: the one that is blocked (Fable 5) and the three you can ship on today (Opus 4.8, GPT-5.5, Gemini 3.5 Flash). A "benchmark" here just means a standardized test that scores how well a model handles a task, like fixing real software bugs or solving hard math.

The benchmark table (June 28, 2026)

Rows marked with a red asterisk are not usable in production today. Read the table with that in mind.

Notes: "MTok" means one million tokens (a token is roughly three quarters of a word). The context window is how much text the model can read at once. Figures are from Artificial Analysis and each lab's published model cards as of June 28, 2026. SWE-Bench Pro scores are the agentic coding numbers cited in the research brief; treat lab-reported numbers as reported, not independently re-run.

The lead story: Fable 5 is blocked

Fable 5 is the strongest model on paper, and it is the one you cannot use. A US government national security directive suspended Fable 5 globally on June 12, 2026. As of June 28 that is day 16 of the blackout. A verification gate is reported to open on July 8 that limits access to verified US citizens only. Until then, building a product around Fable 5 means building on a model your users cannot reach. Bookmark it for later. Do not ship on it now.

This is why the table has an asterisk. The "best" model and the "best model you can deploy" are two different answers in June 2026.

Opus 4.8: the top available model

Among models you can call today, Claude Opus 4.8 ranks first on the Artificial Analysis Intelligence Index at 61.4. Two things stand out:

• Coding. Opus 4.8 leads agentic coding (SWE-Bench Pro 69.2% versus GPT-5.5 at 58.6%). Agentic coding means the model edits files, runs tests, and fixes its own mistakes across many steps, not just writing one snippet.
• Math. Opus 4.8 scored 96.7% on USAMO 2026, up from 69.3% on Opus 4.7. That is a 27.4 point jump in 41 days, the steepest math gain reported in 2026.

Opus 4.8 also lets you set "reasoning effort" as a parameter, so you can trade speed and cost against depth in your pipeline. On Claude Code it defaults to high. Pricing is $5 input and $25 output per million tokens, with a faster mode at $10 / $50.

GPT-5.5: the long-context pick

GPT-5.5 (codename Spud) is the choice when your job depends on reading a lot of text at once. It has a 1M-token context window and strong long-context retrieval: it scored 74.0% on MRCR v2 at 1M tokens, up from 36.6% on GPT-5.4. MRCR is a test of finding the right needle in a giant haystack of text. If you are building RAG (retrieval-augmented generation, where the model answers using documents you feed it), GPT-5.5 holds up better as the document pile grows. Standard pricing is $5 / $30 per million tokens, with a $30 / $180 pro tier and a free Instant variant.

Gemini 3.5: Flash only, and that is the point

In this comparison, "Gemini 3.5" means Gemini 3.5 Flash. Gemini 3.5 Pro was announced at Google I/O on May 19 but stays in a limited Vertex AI enterprise preview with no confirmed general-availability date. Many competitor articles compare against "Gemini 3.5" as if Pro shipped. That is a factual error. The only public option is Flash, and Flash earns its place on speed and price: around 807 characters per second (about 4x faster than frontier peers) at $1.50 / $9.00 per million tokens. Use it when throughput and budget matter more than peak reasoning.

How to pick (a 3-step rule)

1. Need the best coding and reasoning you can deploy? Use Opus 4.8.
2. Need to read huge documents or run RAG at 1M tokens? Use GPT-5.5.
3. Need cheap, high-volume, fast responses? Use Gemini 3.5 Flash.

Whatever you pick, the model is only half the build. The other half is the harness around it: the auth, payments, database security, and agent wiring that turn a model into a real app. That is what the Build This Now $29 Code Kit gives you, a build system for Claude Code with a production SaaS skeleton (auth, Stripe payments, PostgreSQL with row-level security on every table). It runs on Claude Code with Opus 4.8 today, and swapping models later is a config change, not a rewrite.

If you are wiring an agent, the model is one decision. The rest is your Claude Code subagents, your CLAUDE.md project rules, your MCP servers, and row-level security on your data. Get those right and you can change the model behind them whenever the leaderboard shifts.

FAQ

Is Fable 5 available to use right now?

No. Fable 5 was suspended worldwide on June 12, 2026 by a US government export-control directive. As of June 28 it is still unavailable to the public. A US-citizen-only ID verification gate is reported for July 8 before any access resumes.

Claude Opus 4.8 vs GPT-5.5, which is better in 2026?

On the Artificial Analysis Intelligence Index, Claude Opus 4.8 leads slightly at 61.4 versus GPT-5.5 at 60.2. Opus 4.8 wins on agentic coding (SWE-Bench Pro 69.2% vs 58.6%) and math (USAMO 96.7%). GPT-5.5 wins on long-context retrieval (MRCR v2 74.0% at 1M tokens). Both cost $5 input per million tokens.

Is Gemini 3.5 Pro released?

Not publicly. Only Gemini 3.5 Flash is generally available as of June 28, 2026. Gemini 3.5 Pro was announced at Google I/O on May 19 but remains in a limited Vertex AI enterprise preview with no confirmed GA date.

What model should I use for my AI agent or SaaS in June 2026?

Claude Opus 4.8 is the strongest available option for reasoning-heavy and coding-heavy agentic pipelines. Use GPT-5.5 if your workflow depends on a 1M-token context window for RAG. Use Gemini 3.5 Flash if throughput and cost are your main constraints.