GPT-4o (11-20) vs Step 3.5 Flash
GPT-4o (11-20) (2024) and Step 3.5 Flash (2026) are frontier reasoning models from OpenAI and StepFun. GPT-4o (11-20) ships a 128k-token context window, while Step 3.5 Flash 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.
Step 3.5 Flash is safer overall; choose GPT-4o (11-20) when coding workflow support matters.
Decision scorecard
Local evidence first| Signal | GPT-4o (11-20) | Step 3.5 Flash |
|---|---|---|
| Best for | multimodal apps | reasoning-heavy apps |
| Decision fit | Coding, Agents, and Long context | Long context |
| Context window | 128k | 256k |
| Cheapest output | - | $0.30/1M tokens |
| Provider routes | 0 tracked | 1 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- GPT-4o (11-20) uniquely exposes Vision and Code execution in local model data.
- Local decision data tags GPT-4o (11-20) for Coding, Agents, and Long context.
- Step 3.5 Flash has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Step 3.5 Flash has broader tracked provider coverage for fallback and procurement flexibility.
- Step 3.5 Flash uniquely exposes Reasoning in local model data.
- Local decision data tags Step 3.5 Flash for Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
GPT-4o (11-20)
Unavailable
No complete token price in local provider data
Step 3.5 Flash
$155
Cheapest tracked route/tier: OpenRouter
Cost delta unavailable until both models have sourced input and output token prices.
Switch friction
- No overlapping tracked provider route is sourced for GPT-4o (11-20) and Step 3.5 Flash; plan for SDK, billing, or endpoint changes.
- Check replacement coverage for Vision and Code execution before moving production traffic.
- Step 3.5 Flash adds Reasoning in local capability data.
- No overlapping tracked provider route is sourced for Step 3.5 Flash and GPT-4o (11-20); plan for SDK, billing, or endpoint changes.
- Check replacement coverage for Reasoning before moving production traffic.
- GPT-4o (11-20) adds Vision and Code execution in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2024-11-20 | 2026-01-29 |
| Context window | 128k | 256k |
| Parameters | 1.76T (8x222B MoE)* | 196B (11B active) |
| Architecture | mixture of experts | mixture of experts |
| License | Proprietary | Open Source |
| Knowledge cutoff | 2023-10 | - |
Pricing and availability
| Pricing attribute | GPT-4o (11-20) | Step 3.5 Flash |
|---|---|---|
| Input price | - | $0.10/1M tokens |
| Output price | - | $0.30/1M tokens |
| Providers | - |
Capabilities
| Capability | GPT-4o (11-20) | Step 3.5 Flash |
|---|---|---|
| Vision | Yes | No |
| Multimodal | No | No |
| Reasoning | No | Yes |
| Function calling | No | No |
| Tool use | No | No |
| Structured outputs | No | No |
| Code execution | Yes | 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: GPT-4o (11-20), reasoning mode: Step 3.5 Flash, and code execution: GPT-4o (11-20). 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: GPT-4o (11-20) has no token price sourced yet and Step 3.5 Flash has $0.10/1M input tokens. Provider availability is 0 tracked routes versus 1. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose GPT-4o (11-20) when coding workflow support are central to the workload. Choose Step 3.5 Flash 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. It also helps separate model capability from provider packaging, which can change cost and latency. For teams standardizing a stack, that distinction is often the difference between a benchmark win and a reliable deployment.
FAQ
Which has a larger context window, GPT-4o (11-20) or Step 3.5 Flash?
Step 3.5 Flash supports 256k tokens, while GPT-4o (11-20) supports 128k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Is GPT-4o (11-20) or Step 3.5 Flash open source?
GPT-4o (11-20) is listed under Proprietary. Step 3.5 Flash is listed under Open Source. 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-4o (11-20) or Step 3.5 Flash?
GPT-4o (11-20) 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 reasoning mode, GPT-4o (11-20) or Step 3.5 Flash?
Step 3.5 Flash 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 code execution, GPT-4o (11-20) or Step 3.5 Flash?
GPT-4o (11-20) has the clearer documented code execution signal in this comparison. If code execution is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run GPT-4o (11-20) and Step 3.5 Flash?
GPT-4o (11-20) is available on the tracked providers still being sourced. Step 3.5 Flash is available on OpenRouter. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-05-29. Data sourced from public model cards and provider documentation.