Model comparison
Claude Opus 5.5 vs Gemini 3.1 Pro
Anthropic against Google, compared on context, price, and verified benchmark results.
Catalog record checked September 26, 2026Individual provider fields may changeEvidence confidence: High — see receipts below
Anthropic
Claude Opus 5.5
Frontier
Gemini 3.1 Pro
Frontier
| Specification | Claude Opus 5.5 | Gemini 3.1 Pro |
|---|---|---|
| Provider | ||
| Provider | Anthropic | |
| Tier | ||
| Tier | Frontier | Frontier |
| Context window | ||
| Context window | 1M | Winner: 1.05M |
| Max output | ||
| Max output | Winner: 128K | 66K |
| Input / 1M tokens | ||
| Input / 1M tokens | $4 | Winner: $2 |
| Output / 1M tokens | ||
| Output / 1M tokens | $20 | Winner: $12 |
| Weights | ||
| Weights | Closed | Closed |
| Parameters | ||
| Parameters | Not disclosedUnverified | Not disclosedUnverified |
| Reasoning levels | ||
| Reasoning levels | adaptive | low, medium, high |
| Modalities | ||
| Modalities | text, image | text, image, video, audio, pdf |
| API model id | ||
| API model id | claude-opus-5-5 | gemini-3.1-pro-preview |
| Released | ||
| Released | September 22, 2026 | February 19, 2026 |
| Artificial Analysis Intelligence Index [max] (2026-09-26) | ||
| Artificial Analysis Intelligence Index [max] (2026-09-26) | 57.6 | Not verifiedUnverified |
| Artificial Analysis Intelligence Index (2026-09-26) | ||
| Artificial Analysis Intelligence Index (2026-09-26) | Not verifiedUnverified | 29.7 |
| Humanity's Last Exam [max] (2026-09-26) | ||
| Humanity's Last Exam [max] (2026-09-26) | 61.4 | Not verifiedUnverified |
| Humanity's Last Exam (2026-02) | ||
| Humanity's Last Exam (2026-02) | Not verifiedUnverified | 44.4 |
| Terminal-Bench 4.0 [max] (2026-09-26) | ||
| Terminal-Bench 4.0 [max] (2026-09-26) | 59.6 | Not verifiedUnverified |
| Terminal-Bench 4.0 [xhigh] (2026-09-22) | ||
| Terminal-Bench 4.0 [xhigh] (2026-09-22) | 66.4 | Not verifiedUnverified |
| SWE-bench Verified (2026-02) | ||
| SWE-bench Verified (2026-02) | Not verifiedUnverified | 80.6 |
| GPQA Diamond (2026-02) | ||
| GPQA Diamond (2026-02) | Not verifiedUnverified | 94.3 |
| Terminal-Bench 2.1 (2026-07) | ||
| Terminal-Bench 2.1 (2026-07) | Not verifiedUnverified | 73.8 |
Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.
Benchmark receipts
Where each score comes from, and how far it can be compared across models.
- 2026-09-26Artificial Analysis Terminal-Bench 4.0 (independent AA run, part of Intelligence Index v4.3.2)
Agentic terminal work: long multi-step tasks executed in a sandboxed shell environment.
Comparable with caveatNOT comparable with Terminal-Bench 2.x or 3.0 — 4.0 uses a new, non-overlapping task set. Within 4.0, scores from different harnesses (tbench.ai agent entries vs Artificial Analysis runs) are not interchangeable.
- 2026-09-26Artificial Analysis Humanity's Last Exam (independent, 2,158 text-only questions)
Frontier-knowledge ceiling: extremely hard multi-domain questions written to be near-impossible without deep expertise.
Comparable with caveatSubset/tool configurations (text-only vs with-tools) differ between vendors and materially change scores; must match configuration to compare.
- 2026-09-26Artificial Analysis
Composite index blending reasoning, knowledge, and coding evals into one 0–100 score.
Comparable with caveatOnly same-version scores are comparable. v4.3.2 was rebaselined (the top score fell from 66 on v4.1.1 to ~58), so v4.1.1 figures must not be compared with v4.3.2 figures — check measuredAt.
- 2026-09-22Anthropic — Claude Opus 5.5 announcement (vendor; conflicts with AA's independent 59.6 — harness difference preserved)
Agentic terminal work: long multi-step tasks executed in a sandboxed shell environment.
Comparable with caveatNOT comparable with Terminal-Bench 2.x or 3.0 — 4.0 uses a new, non-overlapping task set. Within 4.0, scores from different harnesses (tbench.ai agent entries vs Artificial Analysis runs) are not interchangeable.
- 2026-07Google DeepMind model evaluation report (vendor, Terminus-2; own Feb report separately reported TB 2.0 = 68.5 — versions preserved)
Agentic terminal work: multi-step tasks executed in a sandboxed shell environment.
Comparable with caveatNot comparable with Terminal-Bench 3.0 or 4.0 (different task sets) or v1; harness configuration (container, time limits) also shifts results.
- 2026-02Google DeepMind model evaluation report (vendor, no tools; 51.4 with search+code)
Real GitHub issue resolution: does the model's patch pass the hidden tests.
Comparable with caveatPost-audit vendor claims and pre-audit scores sit on different task trust levels; scaffolding (agent harness, compute budget) also dominates results. Never aggregate across scaffolds.
Pricing tiers
Claude Opus 5.5: $4/$20 per MTok, no long-context surcharge. Cache reads $0.20; 5-minute cache writes $5, 1-hour writes $8. Batch $2/$10; Fast mode $8/$40. Batches API allows 300K output with the output-300k-2026-03-24 beta header. Knowledge cutoff Jun 2026; retirement not before 2027-09-22.
Gemini 3.1 Pro: $2/$12 per MTok (≤200K); $4/$18 (>200K). Still 'Preview' as of 2026-09-26; no Gemini 3.5 Pro or Gemini 4 release yet.
Claude Opus 5.5
Claude Opus 5.5 is Anthropic's default model for agentic coding and knowledge work — Anthropic says it performs near Fable 5.1 on most work at about 40% lower running cost than Opus 5, and it leads the Artificial Analysis Intelligence Index v4.3.2.
Best for
- Complex agentic coding
- Enterprise knowledge work
- Default frontier model
Watch out
Breaking changes from Opus 5: adaptive thinking cannot be disabled (effort runs low to max, default medium) and forced tool use returns an error. Verbose at max effort, so cap output on cost-sensitive routes.
Gemini 3.1 Pro
Gemini 3.1 Pro is Google's only Pro model (still in Preview), with a 1M-token context and strong multimodal reasoning.
Best for
- Very long documents
- Multimodal reasoning
- Frontier knowledge work
Watch out
Still in Preview; Google says Gemini 4 is in post-training but unreleased as of 2026-09-26, and newer Flash models outscore it on the Artificial Analysis index.
When the cheaper one wins
Gemini 3.1 Pro is cheaper on output at $12 per million tokens against $20 for Claude Opus 5.5 — about 1.7×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.
Run the model pickerEvidence confidence: High
How strong and complete the evidence behind this comparison is — not a prediction of which model is better.
- Pricing verified on both sides — Input and output rates are verified for both models.
- 4/5 core specs verified on both sides — Not published for at least one side: parameter count.
- 2 shared named benchmarks with differing scores — Measured on: Artificial Analysis Intelligence Index, Humanity's Last Exam.
- Verified within the last 90 days — Newest catalog check was 2 days ago.
- Both models carry source citations — Each side has at least two catalog sources on record.
Source receipts
Each catalog figure was checked against the provider or an independent second source on the date shown.
- Claude Opus 5.5: Anthropic — Claude Opus 5.5 (accessed 2026-09-26)
- Claude Opus 5.5: Anthropic docs — Opus 5.5 overview (1M context, 128K output) (accessed 2026-09-26)
- Claude Opus 5.5: Anthropic pricing (claude-opus-5-5 $4/$20, cache reads $0.20) (accessed 2026-09-26)
- Claude Opus 5.5: Artificial Analysis — Intelligence Index v4.3.2 (Opus 5.5 #1) (accessed 2026-09-26)
- Gemini 3.1 Pro: Google Cloud — Gemini 3.1 Pro (accessed 2026-08-29)
- Gemini 3.1 Pro: TechCrunch — Gemini 3.1 Pro (accessed 2026-08-29)
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Diving deeper on one model? Claude Opus 5.5 · Gemini 3.1 Pro
Common questions
Claude Opus 5.5 vs Gemini 3.1 Pro
Answered from the verified figures on this page rather than general guidance.
Is Claude Opus 5.5 or Gemini 3.1 Pro cheaper for input?
Is Claude Opus 5.5 or Gemini 3.1 Pro cheaper for output?
Which has the larger context window, Claude Opus 5.5 or Gemini 3.1 Pro?
Do Claude Opus 5.5 and Gemini 3.1 Pro support the same reasoning levels?
Should I use Claude Opus 5.5 or Gemini 3.1 Pro?
Next step
Choosing between them
The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.
- Input price: Gemini 3.1 Pro costs $2 per 1M tokens versus $4 for Claude Opus 5.5 — a 2x difference at the headline tier.
- Context: Gemini 3.1 Pro takes 1.05M against 1M for Claude Opus 5.5 — only decisive if your prompts approach the smaller window.
- Measured capability: Claude Opus 5.5 leads Artificial Analysis Intelligence Index 57.6 to 29.7 (measured 2026-09-26).
Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.