Gemini 3.1 Pro Preview vs Grok Code Fast 1

Across 12 internal benchmarks, Gemini 3.1 Pro Preview wins 8, Grok Code Fast 1 wins 1, and 3 are tied.

Where Gemini 3.1 Pro Preview leads:

• Structured output: 5/5 (tied for 1st of 54 with 24 others) vs 4/5 (rank 26 of 54). For JSON schema compliance and API integrations, both are solid, but Gemini 3.1 Pro Preview hits the ceiling.
• Creative problem solving: 5/5 (tied for 1st of 54 with 7 others) vs 3/5 (rank 30 of 54). A wide gap—Gemini 3.1 Pro Preview generates non-obvious, specific, feasible ideas; Grok Code Fast 1 sits at the median.
• Strategic analysis: 5/5 (tied for 1st of 54 with 25 others) vs 3/5 (rank 36 of 54). Nuanced tradeoff reasoning is a meaningful differentiator for business analysis or architecture decisions.
• Faithfulness: 5/5 (tied for 1st of 55 with 32 others) vs 4/5 (rank 34 of 55). Gemini 3.1 Pro Preview is more reliable at staying on source material without hallucinating.
• Long context: 5/5 (tied for 1st of 55 with 36 others) vs 4/5 (rank 38 of 55). At 30K+ token retrieval tasks, Gemini 3.1 Pro Preview holds the top score; Grok Code Fast 1 drops a tier and ranks in the bottom third.
• Persona consistency: 5/5 (tied for 1st of 53 with 36 others) vs 4/5 (rank 38 of 53). Relevant for chatbot and agent deployments maintaining character across sessions.
• Multilingual: 5/5 (tied for 1st of 55 with 34 others) vs 4/5 (rank 36 of 55). Gemini 3.1 Pro Preview delivers top-tier non-English output quality; Grok Code Fast 1 ranks in the bottom third.
• Constrained rewriting: 4/5 (rank 6 of 53, tied with 24 others) vs 3/5 (rank 31 of 53). Compressing content within hard character limits, Gemini 3.1 Pro Preview outperforms meaningfully.

Where Grok Code Fast 1 wins:

• Classification: 4/5 (tied for 1st of 53 with 29 others) vs 2/5 (rank 51 of 53). This is a significant win—Grok Code Fast 1 sits at the top of the field for categorization and routing tasks, while Gemini 3.1 Pro Preview ranks near the bottom. For classification pipelines, this result favors Grok Code Fast 1 strongly.

Ties:

• Tool calling: Both score 4/5 (rank 18 of 54, tied with 28 others). Function selection and argument accuracy are equivalent.
• Safety calibration: Both score 2/5 (rank 12 of 55, tied with 19 others). Neither model distinguishes itself here; both sit below the field median.
• Agentic planning: Both score 5/5 (tied for 1st of 54 with 14 others). Goal decomposition and failure recovery are equal and best-in-class.

External benchmark — AIME 2025 (Epoch AI): Gemini 3.1 Pro Preview scores 95.6% on AIME 2025, ranking 2nd of 23 models tested by Epoch AI—placing it among the top math reasoning models by that external measure. Grok Code Fast 1 has no AIME 2025 score in the payload. The median model in our dataset scores 83.9% on this benchmark; Gemini 3.1 Pro Preview's 95.6% is a standout result for quantitative reasoning tasks.

Gemini 3.1 Pro Preview costs $2.00 per million input tokens and $12.00 per million output tokens. Grok Code Fast 1 costs $0.20 per million input tokens and $1.50 per million output tokens. That's a 10x gap on input and 8x on output.

At 1M output tokens/month, the difference is $10.50 ($12.00 vs $1.50)—negligible for most teams. At 10M output tokens/month, the gap grows to $105 ($120 vs $15). At 100M output tokens/month—typical for production pipelines running classification, routing, or high-frequency coding tasks—the cost difference is $1,050 per month ($1,200 vs $150). At that scale, Grok Code Fast 1's 8x cost advantage is a real budget line item.

Who should care: developers running batch classification, agentic coding loops, or any workflow where volume is high and the tasks don't require Gemini 3.1 Pro Preview's edge in strategic analysis, creative reasoning, or long-context retrieval. If your workload genuinely requires the capabilities where Gemini 3.1 Pro Preview leads—complex multimodal inputs, 1M-token context windows, or top-tier faithfulness—the premium is likely justified. Note also that Gemini 3.1 Pro Preview supports a 1,048,576-token context window versus Grok Code Fast 1's 256,000 tokens; if you're processing large documents, only one of these models can handle the job.

Choose Gemini 3.1 Pro Preview if:

• You need strong strategic analysis, creative reasoning, or faithfulness to source material—it outscores Grok Code Fast 1 by 2 points on each in our tests.
• Your workflows process long documents: Gemini 3.1 Pro Preview's 1,048,576-token context window is four times larger than Grok Code Fast 1's 256,000 tokens, and it scores 5/5 vs 4/5 on long-context retrieval.
• You work in multiple languages: top-ranked multilingual output vs. a bottom-third ranking for Grok Code Fast 1.
• You need multimodal input (text, image, file, audio, video)—Gemini 3.1 Pro Preview supports all of these; Grok Code Fast 1 is text-only.
• High-end math or reasoning is required: 95.6% on AIME 2025 (Epoch AI) puts it near the top of 23 models tested.
• Cost is not a constraint and you want the best all-around performer.

Choose Grok Code Fast 1 if:

• Classification and routing are your primary use case: it ties for 1st of 53 models at 4/5, while Gemini 3.1 Pro Preview scores 2/5 and ranks 51st.
• You're running high-volume agentic coding pipelines where cost matters: $1.50/M output tokens vs $12.00/M is an 8x saving that compounds to over $1,000/month at 100M tokens.
• Your inputs are text-only and context windows under 256K are sufficient.
• You need visible reasoning traces in responses—both models support this, but at a much lower price point with Grok Code Fast 1.
• Agentic planning is your core task: both models tie at 5/5, so paying 8x more for Gemini 3.1 Pro Preview adds no benefit there.