Fugu vs Qwen3.5-4B
Fugu (2026) and Qwen3.5-4B (2026) are frontier reasoning models from Sakana AI and Alibaba. Fugu ships a 1m-token context window, while Qwen3.5-4B ships a 262k-token context window. On Google-Proof Q&A, Fugu leads by 19.3 pts. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads. It focuses on practical selection signals rather than broad model-family marketing.
Fugu is safer overall; choose Qwen3.5-4B when vision-heavy evaluation matters.
Decision scorecard
Local evidence first| Signal | Fugu | Qwen3.5-4B |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and tool-calling agents | multimodal apps |
| Decision fit | Coding, RAG, and Agents | Coding, Agents, and Long context |
| Context window | 1m | 262k |
| Cheapest output | - | - |
| Provider routes | 1 tracked | 0 tracked |
| Shared benchmarks | Google-Proof Q&A leader | 2 shared |
Decision tradeoffs
- Fugu holds a shared-benchmark lead on Google-Proof Q&A, ahead by 19.3 points.
- Fugu has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Fugu has broader tracked provider coverage for fallback and procurement flexibility.
- Fugu uniquely exposes Reasoning, Function calling, and Tool use in local model data.
- Local decision data tags Fugu for Coding, RAG, and Agents.
- Local decision data tags Qwen3.5-4B for Coding, Agents, and Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Fugu
Unavailable
No complete token price in local provider data
Qwen3.5-4B
Unavailable
No complete token price in local provider data
Cost delta unavailable until both models have sourced input and output token prices.
Switch friction
- No overlapping tracked provider route is sourced for Fugu and Qwen3.5-4B; plan for SDK, billing, or endpoint changes.
- Check replacement coverage for Reasoning, Function calling, and Tool use before moving production traffic.
- No overlapping tracked provider route is sourced for Qwen3.5-4B and Fugu; plan for SDK, billing, or endpoint changes.
- Fugu adds Reasoning, Function calling, and Tool use in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-06-22 | 2026-03-02 |
| Context window | 1m | 262k |
| Parameters | — | 4B |
| Architecture | Composition of Experts | - |
| License | Proprietary | Apache 2.0OSI-approved |
| Openness | Proprietary | Open source |
| Commercial use | Commercial use: conditional | Commercial use: permitted |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | Fugu | Qwen3.5-4B |
|---|---|---|
| Input price | - | - |
| Output price | - | - |
| Providers | - |
Pricing not yet sourced for either model.
Capabilities
| Capability | Fugu | Qwen3.5-4B |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | Yes | No |
| Function calling | Yes | No |
| Tool use | Yes | No |
| Structured outputs | Yes | No |
| Code execution | No | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
| Benchmark | Fugu | Qwen3.5-4B |
|---|---|---|
| Google-Proof Q&A | 95.5 | 76.2 |
| LiveCodeBench | 92.9 | 55.8 |
Deep dive
On shared benchmark coverage, Google-Proof Q&A has Fugu at 95.5 and Qwen3.5-4B at 76.2, with Fugu ahead by 19.3 points; LiveCodeBench has Fugu at 92.9 and Qwen3.5-4B at 55.8, with Fugu ahead by 37.1 points. The largest visible gap is 37.1 points on LiveCodeBench, which matters most when that benchmark mirrors your workload. Treat isolated benchmark wins as directional, because provider routing, prompt style, and tool access can move real application results.
The capability footprint differs most on reasoning mode: Fugu, function calling: Fugu, tool use: Fugu, and structured outputs: Fugu. Both models share vision and multimodal input, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
Pricing coverage is uneven: Fugu has no token price sourced yet and Qwen3.5-4B has no token price sourced yet. Provider availability is 1 tracked routes versus 0. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose Fugu when reasoning depth, larger context windows, and broader provider choice are central to the workload. Choose Qwen3.5-4B when vision-heavy evaluation are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship.
FAQ
Which has a larger context window, Fugu or Qwen3.5-4B?
Fugu supports 1m tokens, while Qwen3.5-4B supports 262k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Is Fugu or Qwen3.5-4B open source?
Fugu is listed under Proprietary. Qwen3.5-4B is listed under Apache 2.0. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for vision, Fugu or Qwen3.5-4B?
Both Fugu and Qwen3.5-4B expose vision. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for multimodal input, Fugu or Qwen3.5-4B?
Both Fugu and Qwen3.5-4B expose multimodal input. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for reasoning mode, Fugu or Qwen3.5-4B?
Fugu has the clearer documented reasoning mode signal in this comparison. If reasoning mode is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run Fugu and Qwen3.5-4B?
Fugu is available on Sakana AI. Qwen3.5-4B is available on the tracked providers still being sourced. Provider coverage can affect latency, region availability, compliance posture, and fallback options. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Continue comparing
Last reviewed: 2026-06-22. Data sourced from public model cards and provider documentation.