Grok Code Fast 1 vs Phi 3.5 MoE Instruct
Grok Code Fast 1 (2025) and Phi 3.5 MoE Instruct (2024) compare a coding-specialized model against a standalone API model. Grok Code Fast 1 ships a 262k-token context window, while Phi 3.5 MoE Instruct ships a 128k-token context window. On pricing, Grok Code Fast 1 costs $0.20/1M input tokens versus $0.50/1M for the alternative. This page treats the result as workflow and deployment fit, not a universal model winner.
Treat this as a product-type comparison: Grok Code Fast 1 is coding-specialized model, while Phi 3.5 MoE Instruct is standalone API model. Choose based on workflow fit before reading any benchmark or price row as decisive.
Decision scorecard
Local evidence first| Signal | Grok Code Fast 1 | Phi 3.5 MoE Instruct |
|---|---|---|
| Product type | Coding-specialized model | Standalone API model |
| Best for | custom coding agents, code generation, and tool loops | general production evaluation |
| Decision fit | Coding, RAG, and Agents | Long context |
| Context window | 262k | 128k |
| Cheapest output | $1.50/1M tokens | $0.50/1M tokens |
| Provider routes | 3 tracked | 1 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Grok Code Fast 1 has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Grok Code Fast 1 has broader tracked provider coverage for fallback and procurement flexibility.
- Grok Code Fast 1 uniquely exposes Function calling, Tool use, and Structured outputs in local model data.
- Local decision data tags Grok Code Fast 1 for Coding, RAG, and Agents.
- Phi 3.5 MoE Instruct has the lower cheapest tracked output price at $0.50/1M tokens.
- Local decision data tags Phi 3.5 MoE Instruct for Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Grok Code Fast 1
$535
Cheapest tracked route/tier: OpenRouter
Phi 3.5 MoE Instruct
$525
Cheapest tracked route/tier: Fireworks AI
Estimated monthly gap: $10.00. 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 Code Fast 1 and Phi 3.5 MoE Instruct; plan for SDK, billing, or endpoint changes.
- Phi 3.5 MoE Instruct is $1/1M 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.
- No overlapping tracked provider route is sourced for Phi 3.5 MoE Instruct and Grok Code Fast 1; plan for SDK, billing, or endpoint changes.
- Grok Code Fast 1 is $1/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Grok Code Fast 1 adds Function calling, Tool use, and Structured outputs in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-08-27 | 2024-08-20 |
| Context window | 262k | 128k |
| Parameters | 314B | 16x3.8B (42B, 6.6B active) |
| Architecture | mixture of experts | decoder only |
| License | Proprietary | MIT(OSI) |
| Openness | Proprietary | Open source |
| Commercial use | Commercial use with conditions | Commercial use allowed |
| Knowledge cutoff | - | 2023-10 |
Pricing and availability
| Pricing attribute | Grok Code Fast 1 | Phi 3.5 MoE Instruct |
|---|---|---|
| Input price | $0.20/1M tokens | $0.50/1M tokens |
| Output price | $1.50/1M tokens | $0.50/1M tokens |
| Providers |
Capabilities
| Capability | Grok Code Fast 1 | Phi 3.5 MoE Instruct |
|---|---|---|
| Vision | No | No |
| Multimodal | No | No |
| Reasoning | No | 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 function calling: Grok Code Fast 1, tool use: Grok Code Fast 1, and structured outputs: Grok Code Fast 1. 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.
For cost, Grok Code Fast 1 lists $0.20/1M input and $1.50/1M output tokens on the cheapest tracked provider, while Phi 3.5 MoE Instruct lists $0.50/1M input and $0.50/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Phi 3.5 MoE Instruct lower by about $0.09 per million blended tokens. Availability is 3 providers versus 1, so concentration risk also matters.
Choose Grok Code Fast 1 when coding workflow support, larger context windows, and lower input-token cost are central to the workload. Choose Phi 3.5 MoE Instruct when provider fit 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 Code Fast 1 or Phi 3.5 MoE Instruct?
Grok Code Fast 1 supports 262k tokens, while Phi 3.5 MoE Instruct supports 128k 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 Code Fast 1 or Phi 3.5 MoE Instruct?
Phi 3.5 MoE Instruct is cheaper on tracked token pricing. Grok Code Fast 1 costs $0.20/1M input and $1.50/1M output tokens. Phi 3.5 MoE Instruct costs $0.50/1M input and $0.50/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Grok Code Fast 1 or Phi 3.5 MoE Instruct open source?
Grok Code Fast 1 is listed under Proprietary. Phi 3.5 MoE Instruct is listed under MIT. 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 function calling, Grok Code Fast 1 or Phi 3.5 MoE Instruct?
Grok Code Fast 1 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 Code Fast 1 or Phi 3.5 MoE Instruct?
Grok Code Fast 1 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.
Where can I run Grok Code Fast 1 and Phi 3.5 MoE Instruct?
Grok Code Fast 1 is available on OpenRouter, Microsoft Foundry, and xAI Console. Phi 3.5 MoE Instruct is available on Fireworks AI. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-05-20. Data sourced from public model cards and provider documentation.