Grok 4 Fast Reasoning vs o3 Deep Research
Grok 4 Fast Reasoning (2025) and o3 Deep Research (2025) are frontier-tier reasoning models from xAI and OpenAI. Grok 4 Fast Reasoning ships a 2m-token context window, while o3 Deep Research ships a 200k-token context window. On pricing, Grok 4 Fast Reasoning costs $1.25/1M input tokens versus $10/1M for the alternative. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Grok 4 Fast Reasoning is ~700% cheaper at $1.25/1M; pay for o3 Deep Research only for vision-heavy evaluation.
Decision scorecard
Local evidence first| Signal | Grok 4 Fast Reasoning | o3 Deep Research |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and long-context analysis | reasoning-heavy apps, multimodal apps, and tool-calling agents |
| Decision fit | Long context and Vision | RAG, Agents, and Long context |
| Context window | 2m | 200k |
| Cheapest output | $2.50/1M tokens | $40/1M tokens |
| Provider routes | 2 tracked | 1 tracked |
| Shared benchmarks | 0 shared | 0 shared |
Decision tradeoffs
- Grok 4 Fast Reasoning has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Grok 4 Fast Reasoning has the lower cheapest tracked output price at $2.50/1M tokens.
- Grok 4 Fast Reasoning has broader tracked provider coverage for fallback and procurement flexibility.
- Local decision data tags Grok 4 Fast Reasoning for Long context and Vision.
- o3 Deep Research uniquely exposes Function calling, Tool use, and Structured outputs in local model data.
- Local decision data tags o3 Deep Research for RAG, Agents, and Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Grok 4 Fast Reasoning
$1,625
Cheapest tracked route/tier: xAI Console
o3 Deep Research
$18,000
Cheapest tracked route/tier: Vercel AI Gateway
Estimated monthly gap: $16,375. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for Grok 4 Fast Reasoning and o3 Deep Research; plan for SDK, billing, or endpoint changes.
- o3 Deep Research is $37.50/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- o3 Deep Research adds Function calling, Tool use, and Structured outputs in local capability data.
- No overlapping tracked provider route is sourced for o3 Deep Research and Grok 4 Fast Reasoning; plan for SDK, billing, or endpoint changes.
- Grok 4 Fast Reasoning is $37.50/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Function calling, Tool use, and Structured outputs before moving production traffic.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-09-01 | 2025-10-10 |
| Context window | 2m | 200k |
| Parameters | — | — |
| Architecture | Decoder Only | Decoder Only |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Commercial use | Commercial use: conditional | Commercial use: conditional |
| Knowledge cutoff | - | 2024-06 |
Pricing and availability
| Pricing attribute | Grok 4 Fast Reasoning | o3 Deep Research |
|---|---|---|
| Input price | $1.25/1M tokens | $10/1M tokens |
| Output price | $2.50/1M tokens | $40/1M tokens |
| Providers |
Capabilities
| Capability | Grok 4 Fast Reasoning | o3 Deep Research |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | Yes | Yes |
| Function calling | No | Yes |
| Tool use | No | Yes |
| Structured outputs | No | Yes |
| Code execution | No | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
No shared benchmark scores are currently available for this pair.
Deep dive
The capability footprint differs most on function calling: o3 Deep Research, tool use: o3 Deep Research, and structured outputs: o3 Deep Research. Both models share vision, multimodal input, and reasoning mode, 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, Grok 4 Fast Reasoning lists $1.25/1M input and $2.50/1M output tokens on the cheapest tracked provider, while o3 Deep Research lists $10/1M input and $40/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Grok 4 Fast Reasoning lower by about $17.38 per million blended tokens. Availability is 2 providers versus 1, so concentration risk also matters.
Choose Grok 4 Fast Reasoning when long-context analysis, larger context windows, and lower input-token cost are central to the workload. Choose o3 Deep Research 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.
FAQ
Which has a larger context window, Grok 4 Fast Reasoning or o3 Deep Research?
Grok 4 Fast Reasoning supports 2m tokens, while o3 Deep Research supports 200k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, Grok 4 Fast Reasoning or o3 Deep Research?
Grok 4 Fast Reasoning is cheaper on tracked token pricing. Grok 4 Fast Reasoning costs $1.25/1M input and $2.50/1M output tokens. o3 Deep Research costs $10/1M input and $40/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Grok 4 Fast Reasoning or o3 Deep Research open source?
Grok 4 Fast Reasoning is listed under Proprietary. o3 Deep Research is listed under Proprietary. 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, Grok 4 Fast Reasoning or o3 Deep Research?
Both Grok 4 Fast Reasoning and o3 Deep Research expose vision. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Which is better for multimodal input, Grok 4 Fast Reasoning or o3 Deep Research?
Both Grok 4 Fast Reasoning and o3 Deep Research 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 Grok 4 Fast Reasoning and o3 Deep Research?
Grok 4 Fast Reasoning is available on Microsoft Foundry and xAI Console. o3 Deep Research is available on Vercel AI Gateway. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-06-15. Data sourced from public model cards and provider documentation.