GPT-5.4 Pro vs Step 3.5 Flash
GPT-5.4 Pro (2026) and Step 3.5 Flash (2026) are frontier-tier reasoning models from OpenAI and StepFun. GPT-5.4 Pro ships a 1.05m-token context window, while Step 3.5 Flash ships a 256k-token context window. On pricing, GPT-5.4 Pro ranges from $30 to $60/1M input tokens by tier; Step 3.5 Flash costs $0.10/1M input tokens. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
GPT-5.4 Pro fits 4x more tokens; pick it for long-context work and Step 3.5 Flash for tighter calls.
Decision scorecard
Local evidence first| Signal | GPT-5.4 Pro | Step 3.5 Flash |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and tool-calling agents | reasoning-heavy apps |
| Decision fit | Coding, RAG, and Agents | Coding, Agents, and Long context |
| Context window | 1.05m | 256k |
| Cheapest output | $180/1M tokens | $0.30/1M tokens |
| Provider routes | 3 tracked | 1 tracked |
| Shared benchmarks | 0 shared | 0 shared |
Decision tradeoffs
- GPT-5.4 Pro has the larger context window for long prompts, retrieval packs, or transcript analysis.
- GPT-5.4 Pro has broader tracked provider coverage for fallback and route flexibility.
- GPT-5.4 Pro uniquely exposes Vision, Multimodal, and JSON / Tool use in local model data.
- Local decision data tags GPT-5.4 Pro for Coding, RAG, and Agents.
- Step 3.5 Flash has the lower cheapest tracked output price at $0.30/1M tokens.
- Local decision data tags Step 3.5 Flash 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.
GPT-5.4 Pro
$69,000
Cheapest tracked route/tier: OpenRouter
Step 3.5 Flash
$155
Cheapest tracked route/tier: OpenRouter
Estimated monthly gap: $68,845. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- Step 3.5 Flash is $180/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Vision, Multimodal, and JSON / Tool use before moving production traffic.
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- GPT-5.4 Pro is $180/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- GPT-5.4 Pro adds Vision, Multimodal, and JSON / Tool use in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-03-01 | 2026-01-29 |
| Context window | 1.05m | 256k |
| Parameters | — | 196B (11B active) |
| Architecture | Decoder Only | Mixture of Experts |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Weights | Not released | Not released |
| Code | Unknown | Unknown |
| Commercial use | Commercial use: conditional | Commercial use: conditional |
| Knowledge cutoff | 2025-08 | - |
Pricing and availability
| Pricing attribute | GPT-5.4 Pro | Step 3.5 Flash |
|---|---|---|
| Input price |
| $0.10/1M tokens |
| Output price |
| $0.30/1M tokens |
| Providers |
Capabilities
| Capability | GPT-5.4 Pro | Step 3.5 Flash |
|---|---|---|
| Vision | Yes | No |
| Multimodal | Yes | No |
| Reasoning | Yes | Yes |
| JSON / Tool use | Yes | No |
| Structured outputs | Yes | No |
| Code execution | Yes | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
No shared benchmark scores are currently available for this pair.
Continue comparing
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Last reviewed: 2026-06-29. Data sourced from public model cards and provider documentation.