GPT-5.5 Instant vs Mistral Medium 3.5
GPT-5.5 Instant (2026) and Mistral Medium 3.5 (2026) are frontier reasoning models from OpenAI and MistralAI. GPT-5.5 Instant ships a 400K-token context window, while Mistral Medium 3.5 ships a 256K-token context window. On pricing, Mistral Medium 3.5 costs $1.5/1M input tokens versus $5/1M for the alternative. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing.
Mistral Medium 3.5 is ~233% cheaper at $1.5/1M; pay for GPT-5.5 Instant only for coding workflow support.
Decision scorecard
Local evidence first| Signal | GPT-5.5 Instant | Mistral Medium 3.5 |
|---|---|---|
| Decision fit | Coding, RAG, and Agents | Coding, RAG, and Agents |
| Context window | 400K | 256K |
| Cheapest output | $30/1M tokens | $7.5/1M tokens |
| Provider routes | 1 tracked | 2 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- GPT-5.5 Instant has the larger context window for long prompts, retrieval packs, or transcript analysis.
- GPT-5.5 Instant uniquely exposes Code execution in local model data.
- Local decision data tags GPT-5.5 Instant for Coding, RAG, and Agents.
- Mistral Medium 3.5 has the lower cheapest tracked output price at $7.5/1M tokens.
- Mistral Medium 3.5 has broader tracked provider coverage for fallback and procurement flexibility.
- Mistral Medium 3.5 uniquely exposes 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.
GPT-5.5 Instant
$11,500
Cheapest tracked route: OpenAI API
Mistral Medium 3.5
$3,075
Cheapest tracked route: Mistral AI Studio
Estimated monthly gap: $8,425. Batch, cache, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for GPT-5.5 Instant and Mistral Medium 3.5; plan for SDK, billing, or endpoint changes.
- Mistral Medium 3.5 is $22.50/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Code execution before moving production traffic.
- Mistral Medium 3.5 adds Reasoning in local capability data.
- No overlapping tracked provider route is sourced for Mistral Medium 3.5 and GPT-5.5 Instant; plan for SDK, billing, or endpoint changes.
- GPT-5.5 Instant is $22.50/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Reasoning before moving production traffic.
- GPT-5.5 Instant adds Code execution in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-05-05 | 2026-04-29 |
| Context window | 400K | 256K |
| Parameters | — | 128B |
| Architecture | decoder only | decoder only |
| License | Proprietary | Mistral License |
| Knowledge cutoff | 2025-08 | - |
Pricing and availability
| Pricing attribute | GPT-5.5 Instant | Mistral Medium 3.5 |
|---|---|---|
| Input price | $5/1M tokens | $1.5/1M tokens |
| Output price | $30/1M tokens | $7.5/1M tokens |
| Providers |
Capabilities
| Capability | GPT-5.5 Instant | Mistral Medium 3.5 |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | No | Yes |
| Function calling | Yes | Yes |
| Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Code execution | Yes | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on reasoning mode: Mistral Medium 3.5 and code execution: GPT-5.5 Instant. Both models share vision, multimodal input, function calling, and tool use, 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.
For cost, GPT-5.5 Instant lists $5/1M input and $30/1M output tokens, while Mistral Medium 3.5 lists $1.5/1M input and $7.5/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Mistral Medium 3.5 lower by about $9.2 per million blended tokens. Availability is 1 providers versus 2, so concentration risk also matters.
Choose GPT-5.5 Instant when coding workflow support and larger context windows are central to the workload. Choose Mistral Medium 3.5 when reasoning depth, lower input-token cost, 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. It also helps separate model capability from provider packaging, which can change cost and latency.
FAQ
Which has a larger context window, GPT-5.5 Instant or Mistral Medium 3.5?
GPT-5.5 Instant supports 400K tokens, while Mistral Medium 3.5 supports 256K tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, GPT-5.5 Instant or Mistral Medium 3.5?
Mistral Medium 3.5 is cheaper on tracked token pricing. GPT-5.5 Instant costs $5/1M input and $30/1M output tokens. Mistral Medium 3.5 costs $1.5/1M input and $7.5/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is GPT-5.5 Instant or Mistral Medium 3.5 open source?
GPT-5.5 Instant 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, GPT-5.5 Instant or Mistral Medium 3.5?
Both GPT-5.5 Instant and Mistral Medium 3.5 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, GPT-5.5 Instant or Mistral Medium 3.5?
Both GPT-5.5 Instant and Mistral Medium 3.5 expose multimodal input. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Where can I run GPT-5.5 Instant and Mistral Medium 3.5?
GPT-5.5 Instant is available on OpenAI API. 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: 2026-05-14. Data sourced from public model cards and provider documentation.