Gemini 3 Flash Preview vs Grok 4.20

Across our 12-test internal suite, Gemini 3 Flash Preview wins 2 benchmarks outright and ties Grok 4.20 on the remaining 10. Grok 4.20 wins none.

Where Gemini 3 Flash Preview wins:

• Agentic planning (5 vs 4): Gemini 3 Flash Preview scores 5/5, tied for 1st with 14 other models out of 54 tested. Grok 4.20 scores 4/5, ranking 16th of 54. This is a meaningful gap for developers building autonomous agents — agentic planning covers goal decomposition and failure recovery, both critical for multi-step workflows.
• Creative problem solving (5 vs 4): Gemini 3 Flash Preview scores 5/5, tied for 1st with 7 other models out of 54 — a tighter top cluster, making this score more distinguishing. Grok 4.20 scores 4/5, ranking 9th of 54. For tasks requiring non-obvious, feasible ideas, Gemini 3 Flash Preview has a measurable edge in our testing.

Where they tie (both at the top or equivalent tier):

• Tool calling (5/5 each): Both tied for 1st with 16 others out of 54. Reliable function selection and argument accuracy for API-integrated applications.
• Structured output (5/5 each): Both tied for 1st with 24 others out of 54. JSON schema compliance is solid from either model.
• Strategic analysis (5/5 each): Both tied for 1st with 25 others out of 54. Nuanced tradeoff reasoning is equally strong.
• Long context (5/5 each): Both tied for 1st with 36 others out of 55. Retrieval accuracy at 30K+ tokens is equivalent — though Grok 4.20's 2M context window means it can process longer documents even if per-task accuracy is the same.
• Faithfulness (5/5 each): Both tied for 1st with 32 others out of 55. Neither hallucinates from source material in our testing.
• Multilingual (5/5 each): Both tied for 1st with 34 others out of 55.
• Persona consistency (5/5 each): Both tied for 1st with 36 others out of 53.
• Classification (4/5 each): Both tied for 1st with 29 others out of 53.
• Constrained rewriting (4/5 each): Both rank 6th of 53, sharing the score with 25 models.
• Safety calibration (1/5 each): Both rank 32nd of 55, sharing the score with 24 models. This is below the 25th percentile (p25 = 1) for the field, indicating that refusing harmful requests while permitting legitimate ones is a weak point for both models.

External benchmarks (Epoch AI): Gemini 3 Flash Preview scores 75.4% on SWE-bench Verified (real GitHub issue resolution), ranking 3rd of 12 models with that data — above the p75 of 75.25% across models tested. It also scores 92.8% on AIME 2025 (math olympiad), ranking 5th of 23 models, well above the p50 of 83.9%. These place Gemini 3 Flash Preview among the stronger performers on third-party coding and math benchmarks. Grok 4.20 does not have SWE-bench Verified or AIME 2025 scores in our data, so a direct external comparison is not available.

Gemini 3 Flash Preview is priced at $0.50 input / $3.00 output per million tokens. Grok 4.20 is priced at $2.00 input / $6.00 output per million tokens — 4× more expensive on input and 2× on output.

At 1M output tokens/month: Gemini 3 Flash Preview costs $3, Grok 4.20 costs $6 — a $3 difference that matters little at this scale.

At 10M output tokens/month: $30 vs $60 — a $30/month gap. Still modest, but the performance case for paying more is thin given the benchmark data.

At 100M output tokens/month: $300 vs $600 — a $300/month difference. At this volume, the cost gap becomes a meaningful budget line item, and Gemini 3 Flash Preview's equal or superior benchmark scores make it hard to justify the Grok 4.20 premium.

The input cost gap is even sharper at scale: 100M input tokens costs $50 with Gemini 3 Flash Preview vs $200 with Grok 4.20 — a $150/month difference on input alone. Teams running high-context, retrieval-heavy pipelines will feel this most acutely. The only scenario where Grok 4.20's premium is clearly justified is workloads that require prompts exceeding 1M tokens, where its 2M context window is a hard requirement Gemini 3 Flash Preview cannot meet.

Choose Gemini 3 Flash Preview if:

• You're building agentic workflows or autonomous pipelines — it scores 5/5 on agentic planning vs Grok 4.20's 4/5 in our testing.
• Cost efficiency matters at any meaningful scale — it's 4× cheaper on input and 2× cheaper on output.
• You need strong coding or math performance — it scores 75.4% on SWE-bench Verified and 92.8% on AIME 2025 (Epoch AI), placing it 3rd and 5th respectively in those external rankings.
• You want multimodal input support including audio and video — Gemini 3 Flash Preview accepts text, image, file, audio, and video inputs.
• Your context needs fit within 1M tokens — the vast majority of use cases do.

Choose Grok 4.20 if:

• Your specific workload requires processing inputs longer than 1M tokens — its 2M context window is a hard capability that Gemini 3 Flash Preview cannot match.
• You need logprobs or top_logprobs parameter support for probability-based downstream processing — Grok 4.20 supports these; Gemini 3 Flash Preview does not.
• Your inputs are primarily text, images, and files (no audio/video) and the extended context window is the deciding factor.

The cost and benchmark case both point toward Gemini 3 Flash Preview for most teams. Grok 4.20 commands a premium that the benchmark data, in our testing, does not justify unless the 2M context window or logprobs support are hard requirements.