Choose OpenAI: GPT-5.5 if…
- you need seed (reproducible sampling) — to repeat a generation for tests and evals; Sakana: Fugu Ultra v2 does not advertise it
OpenAI: GPT-5.5 vs Sakana: Fugu Ultra v2
Neither wins outright: OpenAI: GPT-5.5 is the pick when you need seed (reproducible sampling), Sakana: Fugu Ultra v2 when you want the newer model.
Key numbers
| Spec | OpenAI: GPT-5.5 | Sakana: Fugu Ultra v2 |
|---|---|---|
| Provider | OpenAI | Sakana |
| Input price (per 1M tokens) | $5.00 | $5.00 |
| Output price (per 1M tokens) | $30.00 | $30.00 |
| Blended price (3:1 input/output) | $11.25 | $11.25 |
| Cheaper than … of all models we track | 5% | 5% |
| Context window | 1.1M tokens (~1,575 pages) | 1M tokens (~1,500 pages) |
| Larger context than … of all models | 92% | 68% |
| Max output per response | 128K tokens (~96,000 words) | 128K tokens (~96,000 words) |
| Input types | file, image, text | text, image, file |
| Output types | text | text |
| Free variant | No | No |
| Listed since | 2026-04-24 | 2026-09-11 |
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What it costs for real workloads
Monthly cost at list price for five common workloads. Token counts per unit are stated so you can scale them to your own traffic. A workload that does not fit a model's context window is marked rather than priced.
| Workload (per month) | OpenAI: GPT-5.5 | Sakana: Fugu Ultra v2 | Difference |
|---|---|---|---|
| Customer-support chatbot 50,000 conversations — each a 6-turn conversation (1,500 in / 400 out tokens) | $975 | $975 | — |
| RAG search over documents 20,000 questions — each a question answered from ~8 retrieved passages (6,000 in / 500 out tokens) | $900 | $900 | — |
| Coding / tool-using agent 2,000 tasks — each a multi-step task with tool calls and file context (60,000 in / 6,000 out tokens) | $960 | $960 | — |
| Batch summarisation 10,000 documents — each a 6,000-word report summarised to a page (8,000 in / 600 out tokens) | $580 | $580 | — |
| Long-document analysis 500 documents — each a 150-page contract or codebase read in one pass (100,000 in / 2,000 out tokens) | $280 | $280 | — |
Capabilities side by side
| Capability | OpenAI: GPT-5.5 | Sakana: Fugu Ultra v2 | What it lets you do |
|---|---|---|---|
| Tool / function calling | ✓ Yes | ✓ Yes | call your APIs and run agent loops |
| Structured output (JSON schema) | ✓ Yes | ✓ Yes | return JSON that validates against your schema |
| Reasoning / thinking mode | ✓ Yes | ✓ Yes | spend extra tokens thinking before answering hard problems |
| Image input | ✓ Yes | ✓ Yes | read screenshots, charts and scanned pages |
| Audio input | — | — | take speech or audio directly |
| File / PDF input | ✓ Yes | ✓ Yes | accept documents without your own parsing step |
| Image output | — | — | generate images, not just text |
| Built-in web search | ✓ Yes | ✓ Yes | answer from live web results |
| Seed (reproducible sampling) | ✓ Yes | — | repeat a generation for tests and evals |
| Log-probabilities | — | — | read token confidence for classification and scoring |
From each model's published parameters and input/output types. “—” means not advertised, not proven absent.
Price history
- OpenAI: GPT-5.5: price unchanged since we started tracking it on 2026-08-06.
- Sakana: Fugu Ultra v2: price unchanged since we started tracking it on 2026-09-12.
Which should you choose?
Choose Sakana: Fugu Ultra v2 if…
- you want the newer model — released 2026-09-11, 5 months after the other
Frequently asked questions
Is OpenAI: GPT-5.5 better than Sakana: Fugu Ultra v2?
Neither wins outright: OpenAI: GPT-5.5 is the pick when you need seed (reproducible sampling), Sakana: Fugu Ultra v2 when you want the newer model. In short: OpenAI: GPT-5.5 when you need seed (reproducible sampling); Sakana: Fugu Ultra v2 when you want the newer model.
Which is cheaper, OpenAI: GPT-5.5 or Sakana: Fugu Ultra v2?
They cost the same: $11.25 per 1M tokens at a 3:1 input/output mix.
How much do OpenAI: GPT-5.5 and Sakana: Fugu Ultra v2 cost per million tokens?
OpenAI: GPT-5.5 costs $5.00 per 1M input tokens and $30.00 per 1M output tokens; Sakana: Fugu Ultra v2 costs $5.00 input and $30.00 output. Output tokens are billed separately, so long answers shift the gap.
Which has the bigger context window, OpenAI: GPT-5.5 or Sakana: Fugu Ultra v2?
OpenAI: GPT-5.5: 1.1M tokens, about 1,575 pages, against 1M (about 1,500 pages) for Sakana: Fugu Ultra v2.
Do OpenAI: GPT-5.5 and Sakana: Fugu Ultra v2 support function calling and JSON output?
Tool calling — OpenAI: GPT-5.5: yes, Sakana: Fugu Ultra v2: yes. JSON-schema structured output — OpenAI: GPT-5.5: yes, Sakana: Fugu Ultra v2: yes.
Can OpenAI: GPT-5.5 or Sakana: Fugu Ultra v2 read images?
Yes, both accept image input.
Is OpenAI: GPT-5.5 or Sakana: Fugu Ultra v2 free to use?
No free variant is listed for either; both are pay-per-token.
What is the maximum output length of OpenAI: GPT-5.5 and Sakana: Fugu Ultra v2?
OpenAI: GPT-5.5 can write up to 128K tokens (about 96,000 words) per response; Sakana: Fugu Ultra v2 up to 128K (about 96,000 words).
When were OpenAI: GPT-5.5 and Sakana: Fugu Ultra v2 released?
OpenAI: GPT-5.5 was listed on 2026-04-24; Sakana: Fugu Ultra v2 on 2026-09-11.
About the two models
OpenAI: GPT-5.5
GPT-5.5 is OpenAI’s frontier model designed for complex professional workloads, building on GPT-5.4 with stronger reasoning, higher reliability, and improved token efficiency on hard tasks. It features a 1M+ token...
Full OpenAI: GPT-5.5 specs →Sakana: Fugu Ultra v2
Fugu Ultra v2 is the higher-performance model in Sakana AI's Fugu family. Rather than a single monolithic model, Fugu is a learned multi-agent orchestration system: a language model trained to...
Full Sakana: Fugu Ultra v2 specs →