GPT-5.1 Codex Max vs Qwen3.5-4B
GPT-5.1 Codex Max (2025) and Qwen3.5-4B (2026) compare a coding-specialized model against a standalone API model. GPT-5.1 Codex Max ships a not-yet-sourced context window, while Qwen3.5-4B ships a 262K-token context window. This page treats the result as workflow and deployment fit, not a universal model winner.
Treat this as a product-type comparison: GPT-5.1 Codex Max is coding-specialized model, while Qwen3.5-4B is standalone API model. Choose based on workflow fit before reading any benchmark or price row as decisive.
Decision scorecard
Local evidence first| Signal | GPT-5.1 Codex Max | Qwen3.5-4B |
|---|---|---|
| Product type | Coding-specialized model | Standalone API model |
| Best for | custom coding agents, code generation, and tool loops | multimodal apps |
| Decision fit | Coding, Agents, and Vision | Long context and Vision |
| Context window | — | 262K |
| Cheapest output | $10/1M tokens | - |
| Provider routes | 2 tracked | 0 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- GPT-5.1 Codex Max has broader tracked provider coverage for fallback and procurement flexibility.
- GPT-5.1 Codex Max uniquely exposes Reasoning, Function calling, and Tool use in local model data.
- Local decision data tags GPT-5.1 Codex Max for Coding, Agents, and Vision.
- Qwen3.5-4B has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Qwen3.5-4B uniquely exposes Vision in local model data.
- Local decision data tags Qwen3.5-4B for Long context and Vision.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
GPT-5.1 Codex Max
$3,500
Cheapest tracked route/tier: OpenRouter
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 GPT-5.1 Codex Max 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.
- Qwen3.5-4B adds Vision in local capability data.
- No overlapping tracked provider route is sourced for Qwen3.5-4B and GPT-5.1 Codex Max; plan for SDK, billing, or endpoint changes.
- Check replacement coverage for Vision before moving production traffic.
- GPT-5.1 Codex Max adds Reasoning, Function calling, and Tool use in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-11-19 | 2026-03-02 |
| Context window | — | 262K |
| Parameters | — | 4B |
| Architecture | - | - |
| License | Proprietary | Apache 2.0 |
| Knowledge cutoff | 2024-09 | - |
Pricing and availability
| Pricing attribute | GPT-5.1 Codex Max | Qwen3.5-4B |
|---|---|---|
| Input price | $1.25/1M tokens | - |
| Output price | $10/1M tokens | - |
| Providers | - |
Capabilities
| Capability | GPT-5.1 Codex Max | Qwen3.5-4B |
|---|---|---|
| Vision | No | 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
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on vision: Qwen3.5-4B, reasoning mode: GPT-5.1 Codex Max, function calling: GPT-5.1 Codex Max, tool use: GPT-5.1 Codex Max, and structured outputs: GPT-5.1 Codex Max. Both models share 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: GPT-5.1 Codex Max has $1.25/1M input tokens and Qwen3.5-4B has no token price sourced yet. Provider availability is 2 tracked routes versus 0. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose GPT-5.1 Codex Max when coding workflow support 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. 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
Is GPT-5.1 Codex Max or Qwen3.5-4B open source?
GPT-5.1 Codex Max 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, GPT-5.1 Codex Max or Qwen3.5-4B?
Qwen3.5-4B 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. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for multimodal input, GPT-5.1 Codex Max or Qwen3.5-4B?
Both GPT-5.1 Codex Max 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, GPT-5.1 Codex Max or Qwen3.5-4B?
GPT-5.1 Codex Max 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.
Which is better for function calling, GPT-5.1 Codex Max or Qwen3.5-4B?
GPT-5.1 Codex Max has the clearer documented function calling signal in this comparison. If function calling is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run GPT-5.1 Codex Max and Qwen3.5-4B?
GPT-5.1 Codex Max is available on OpenRouter and Vercel AI Gateway. Qwen3.5-4B is available on the tracked providers still being sourced. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-05-22. Data sourced from public model cards and provider documentation.