Grok 4 Fast Reasoning vs Grok 4.20 Multi-Agent
Grok 4 Fast Reasoning (2025) and Grok 4.20 Multi-Agent (2026) are frontier-tier reasoning models from xAI. Grok 4 Fast Reasoning ships a not-yet-sourced context window, while Grok 4.20 Multi-Agent ships a 2M-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.
Grok 4.20 Multi-Agent is safer overall; choose Grok 4 Fast Reasoning when provider fit matters.
Decision scorecard
Local evidence first| Signal | Grok 4 Fast Reasoning | Grok 4.20 Multi-Agent |
|---|---|---|
| Decision fit | General | RAG, Agents, and Long context |
| Context window | — | 2M |
| Cheapest output | - | $2.5/1M tokens |
| Provider routes | 1 tracked | 2 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Use Grok 4 Fast Reasoning when your own prompt tests beat the comparison signals; the local data does not show a decisive standalone advantage yet.
- Grok 4.20 Multi-Agent has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Grok 4.20 Multi-Agent has broader tracked provider coverage for fallback and procurement flexibility.
- Grok 4.20 Multi-Agent uniquely exposes Function calling, Tool use, and Structured outputs in local model data.
- Local decision data tags Grok 4.20 Multi-Agent for RAG, Agents, and Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output prices on this page.
Grok 4 Fast Reasoning
Unavailable
No complete token price in local provider data
Grok 4.20 Multi-Agent
$1,625
Cheapest tracked route: xAI Console
Cost delta unavailable until both models have sourced input and output token prices.
Switch friction
- No overlapping tracked provider route is sourced for Grok 4 Fast Reasoning and Grok 4.20 Multi-Agent; plan for SDK, billing, or endpoint changes.
- Grok 4.20 Multi-Agent adds Function calling, Tool use, and Structured outputs in local capability data.
- No overlapping tracked provider route is sourced for Grok 4.20 Multi-Agent and Grok 4 Fast Reasoning; plan for SDK, billing, or endpoint changes.
- Check replacement coverage for Function calling, Tool use, and Structured outputs before moving production traffic.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-09-01 | 2026-01-01 |
| Context window | — | 2M |
| Parameters | — | — |
| Architecture | decoder only | - |
| License | Proprietary | Proprietary |
| Knowledge cutoff | - | - |
Pricing and availability
| Pricing attribute | Grok 4 Fast Reasoning | Grok 4.20 Multi-Agent |
|---|---|---|
| Input price | - | $1.25/1M tokens |
| Output price | - | $2.5/1M tokens |
| Providers |
Capabilities
| Capability | Grok 4 Fast Reasoning | Grok 4.20 Multi-Agent |
|---|---|---|
| Vision | No | No |
| Multimodal | No | No |
| Reasoning | Yes | Yes |
| Function calling | No | Yes |
| Tool use | No | Yes |
| Structured outputs | No | Yes |
| Code execution | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on function calling: Grok 4.20 Multi-Agent, tool use: Grok 4.20 Multi-Agent, and structured outputs: Grok 4.20 Multi-Agent. Both models share 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.
Pricing coverage is uneven: Grok 4 Fast Reasoning has no token price sourced yet and Grok 4.20 Multi-Agent has $1.25/1M input tokens. Provider availability is 1 tracked routes versus 2. Treat unknown pricing as an integration gap, then verify the route you will actually call before estimating production spend.
Choose Grok 4 Fast Reasoning when provider fit are central to the workload. Choose Grok 4.20 Multi-Agent when provider fit 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
Is Grok 4 Fast Reasoning or Grok 4.20 Multi-Agent open source?
Grok 4 Fast Reasoning is listed under Proprietary. Grok 4.20 Multi-Agent 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 reasoning mode, Grok 4 Fast Reasoning or Grok 4.20 Multi-Agent?
Both Grok 4 Fast Reasoning and Grok 4.20 Multi-Agent expose reasoning mode. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Which is better for function calling, Grok 4 Fast Reasoning or Grok 4.20 Multi-Agent?
Grok 4.20 Multi-Agent 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.
Which is better for tool use, Grok 4 Fast Reasoning or Grok 4.20 Multi-Agent?
Grok 4.20 Multi-Agent has the clearer documented tool use signal in this comparison. If tool use is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for structured outputs, Grok 4 Fast Reasoning or Grok 4.20 Multi-Agent?
Grok 4.20 Multi-Agent has the clearer documented structured outputs signal in this comparison. If structured outputs is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run Grok 4 Fast Reasoning and Grok 4.20 Multi-Agent?
Grok 4 Fast Reasoning is available on Microsoft Foundry. Grok 4.20 Multi-Agent is available on OpenRouter and xAI Console. 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.