Gemini 2.5 Pro vs Gemini 3.1 Pro
| Spec | Gemini 2.5 Pro | Gemini 3.1 Pro |
|---|---|---|
| Provider | ||
| Input price (per 1M) | $1.25 | $2.00 |
| Output price (per 1M) | $10.00 | $12.00 |
| Context window | 2,000,000 | 1,000,000 |
| Tokenizer accuracy | exact (uses official tokenizer) | exact (uses official tokenizer) |
Cost per 1,000 calls across common workloads
| Workload | Gemini 2.5 Pro | Gemini 3.1 Pro | Winner |
|---|---|---|---|
| Short chat (200 in / 100 out) |
$1,250.00 | $1,600.00 | Gemini 2.5 Pro 22% cheaper |
| Medium chat (1,000 in / 500 out) |
$6,250.00 | $8,000.00 | Gemini 2.5 Pro 22% cheaper |
| Heavy generation (1,000 in / 2,000 out) |
$21,250.00 | $26,000.00 | Gemini 2.5 Pro 18% cheaper |
| Long context (8,000 in / 500 out) |
$15,000.00 | $22,000.00 | Gemini 2.5 Pro 32% cheaper |
| Code review (3,000 in / 600 out) |
$9,750.00 | $13,200.00 | Gemini 2.5 Pro 26% cheaper |
Costs are per 1,000 API calls. Multiply by 1,000 for per-million-calls.
Verdict
Gemini 3.1 Pro is a meaningful upgrade for reasoning and tool-use, but 2.5 Pro is still the value pick for most workloads. If you're using Gemini Pro for retrieval-augmented generation, document analysis, or vision tasks, 2.5 Pro's output is rarely the bottleneck, and the price gap matters at scale.
If you're using Pro for hard reasoning, code generation, or agent workflows, the upgrade to 3.1 pays back.
Cost example
For a 1,000-token prompt with a 200-token reply:
Gemini 2.5 Pro: 1000 × $1.25/M + 200 × $5/M = $0.00225 per call
Gemini 3.1 Pro: 1000 × $1.25/M + 200 × $10/M = $0.00325 per call3.1 Pro costs ~44% more per call at this prompt/output ratio. The gap is in the output price; input pricing is identical.
For output-heavy workloads (4k+ token responses), the gap widens proportionally.
Context windows
- Gemini 2.5 Pro: 2,000,000 tokens
- Gemini 3.1 Pro: 2,000,000 tokens
Identical 2M-token windows. Both can hold entire codebases, multi-volume books, or hundreds of pages of documents in a single call.
Capability differences
Where 3.1 Pro leads:
- Reasoning benchmarks (MMLU, GPQA), meaningful gain over 2.5
- Code generation on novel problems
- Tool use reliability for agent workflows
- Multimodal reasoning quality on dense documents
- Lower hallucination rate on long-context tasks
Where 2.5 Pro is competitive:
- Standard summarization and Q&A workloads (no measurable difference)
- Vision tasks at typical resolutions (both at 258 tokens per image, similar quality)
- High-volume classification (both at ~95%+ accuracy on most benchmarks)
- Anything where 2.5's output is already "good enough"
The 2.5 → 3.1 gap is real but narrower than the marketing suggests. Run A/B tests on your specific workload before paying 44% more.
Vision and multimodal
Both models share Google's same multimodal architecture:
- ~258 tokens per image at standard resolutions
- ~258 tokens per second of audio
- Video handled as frame samples + audio track
For high-volume vision workloads, the cost advantage of 2.5 Pro compounds: at 100k images/month with 1k-token text prompts and 500-token outputs, 2.5 Pro saves roughly $250/month vs 3.1 Pro for the same task.
Migration considerations
If you're currently on 2.5 Pro:
- Don't blindly upgrade. Test 3.1 on a representative sample of your workload.
- Watch output token consumption. 3.1 occasionally produces longer responses than 2.5 for the same prompt; this widens the cost gap further.
- Update prompt templates. 3.1 responds slightly differently to system prompts; minor tuning often improves output quality.
If you're new and choosing:
- Default to 2.5 Pro unless you've identified a specific reasoning task where 3.1 wins.
- 2.5 Pro is also more battle-tested across third-party tools and frameworks.
When to choose each
Use Gemini 2.5 Pro when:
- Your workload is RAG, summarization, or document Q&A
- You're processing images at scale
- Cost matters at the per-call level
- Output quality on your workload is already acceptable
Use Gemini 3.1 Pro when:
- You're running agent workflows with tool use
- Your tasks are reasoning-heavy (code, math, scientific analysis)
- You've A/B tested and 3.1 outputs are meaningfully better
- The 44% cost premium fits your budget
Count tokens on Gemini 2.5 Pro → · Count tokens on Gemini 3.1 Pro →