Colosseum 355B vs Mistral Medium 3.5
Colosseum 355B (2025) and Mistral Medium 3.5 (2026) are frontier reasoning models from iGenius and MistralAI. Colosseum 355B ships a 131K-token context window, while Mistral Medium 3.5 ships a 256K-token context window. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing. The goal is to make the tradeoff clear before deeper testing.
Mistral Medium 3.5 is safer overall; choose Colosseum 355B when provider fit matters.
Decision scorecard
Local evidence first| Signal | Colosseum 355B | Mistral Medium 3.5 |
|---|---|---|
| Decision fit | Long context | Coding, RAG, and Agents |
| Context window | 131K | 256K |
| Cheapest output | - | $7.5/1M tokens |
| Provider routes | 0 tracked | 2 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Local decision data tags Colosseum 355B for Long context.
- Mistral Medium 3.5 has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Mistral Medium 3.5 has broader tracked provider coverage for fallback and procurement flexibility.
- Mistral Medium 3.5 uniquely exposes Vision, Multimodal, and Reasoning in local model data.
- Local decision data tags Mistral Medium 3.5 for Coding, RAG, and Agents.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output prices on this page.
Colosseum 355B
Unavailable
No complete token price in local provider data
Mistral Medium 3.5
$3,075
Cheapest tracked route: Mistral AI Studio
Cost delta unavailable until both models have sourced input and output token prices.
Switch friction
- No overlapping tracked provider route is sourced for Colosseum 355B and Mistral Medium 3.5; plan for SDK, billing, or endpoint changes.
- Mistral Medium 3.5 adds Vision, Multimodal, and Reasoning in local capability data.
- No overlapping tracked provider route is sourced for Mistral Medium 3.5 and Colosseum 355B; plan for SDK, billing, or endpoint changes.
- Check replacement coverage for Vision, Multimodal, and Reasoning before moving production traffic.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-03-10 | 2026-04-29 |
| Context window | 131K | 256K |
| Parameters | 355B | 128B |
| Architecture | - | decoder only |
| License | Proprietary | Mistral License |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | Colosseum 355B | Mistral Medium 3.5 |
|---|---|---|
| Input price | - | $1.5/1M tokens |
| Output price | - | $7.5/1M tokens |
| Providers | - |
Capabilities
| Capability | Colosseum 355B | Mistral Medium 3.5 |
|---|---|---|
| Vision | No | Yes |
| Multimodal | No | Yes |
| Reasoning | No | Yes |
| Function calling | No | Yes |
| Tool use | No | Yes |
| Structured outputs | No | Yes |
| Code execution | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on vision: Mistral Medium 3.5, multimodal input: Mistral Medium 3.5, reasoning mode: Mistral Medium 3.5, function calling: Mistral Medium 3.5, tool use: Mistral Medium 3.5, and structured outputs: Mistral Medium 3.5. Both models share the core language-model surface, 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: Colosseum 355B has no token price sourced yet and Mistral Medium 3.5 has $1.5/1M input tokens. Provider availability is 0 tracked routes versus 2. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose Colosseum 355B when provider fit are central to the workload. Choose Mistral Medium 3.5 when reasoning depth, larger context windows, and broader provider choice are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions.
FAQ
Which has a larger context window, Colosseum 355B or Mistral Medium 3.5?
Mistral Medium 3.5 supports 256K tokens, while Colosseum 355B supports 131K tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Is Colosseum 355B or Mistral Medium 3.5 open source?
Colosseum 355B is listed under Proprietary. Mistral Medium 3.5 is listed under Mistral License. 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, Colosseum 355B or Mistral Medium 3.5?
Mistral Medium 3.5 has the clearer documented vision signal in this comparison. If vision is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for multimodal input, Colosseum 355B or Mistral Medium 3.5?
Mistral Medium 3.5 has the clearer documented multimodal input signal in this comparison. If multimodal input is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for reasoning mode, Colosseum 355B or Mistral Medium 3.5?
Mistral Medium 3.5 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 Colosseum 355B and Mistral Medium 3.5?
Colosseum 355B is available on the tracked providers still being sourced. Mistral Medium 3.5 is available on Mistral AI Studio and OpenRouter. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-05-19. Data sourced from public model cards and provider documentation.