Short answer: There is no evidence here to declare a universal quality winner. This comparison uses Claude Opus 5.5 through the Anthropic API and Gemini 3.1 Pro Preview through the Gemini Developer API. Gemini is a candidate when your workload needs video or audio input. Both models have documented PDF support and tool/function calling, so those needs alone do not establish a reason to choose one over the other. Claude’s official materials describe it for long-running coding and knowledge work; treat that as positioning, not proof of better results on your tasks. (Claude Opus 5.5 model documentation)
For a production decision, confirm each model’s current status, API channel, region, terms, and prices, then test both against representative tasks. Gemini 3.1 Pro is labeled Preview in the selected API documentation, so assess that status against your deployment requirements before committing. (Gemini 3.1 Pro Preview model documentation)
Models and API channels compared
This is a comparison of two specific model/channel pairings—not every Claude and Gemini model. Model status, pricing, and availability can change; verify them before making a production decision.
| Claude | Gemini | |
|---|---|---|
| Model | Claude Opus 5.5 | Gemini 3.1 Pro Preview |
| API channel | Anthropic Claude API | Gemini Developer API |
| Model ID | claude-opus-5-5 |
gemini-3.1-pro-preview |
| Status in cited documentation | Active | Preview |
Anthropic lists the Claude API model ID and describes Claude Opus 5.5 for long-running agentic coding and knowledge work. Google’s model documentation identifies Gemini 3.1 Pro Preview by its model ID. This comparison does not assume that similarly named models on Vertex AI or another hosted service have identical access, terms, or billing. (Claude Opus 5.5 model documentation)
Which model fits your workload?
| Workload or requirement | What the documentation supports | Decision takeaway |
|---|---|---|
| Long-running coding, refactoring, complex systems work | Anthropic describes Claude Opus 5.5 for long-running agentic coding and knowledge work. | It is a reasonable candidate to test for those tasks, not a verified head-to-head winner. (Claude Opus 5.5 model documentation) |
| PDF input | Both have documented PDF support. Anthropic says all active Claude models support PDF processing; Google lists PDF among Gemini 3.1 Pro Preview’s inputs. | PDF support alone does not distinguish the two. Check each API’s document limits and test your actual files. (Claude PDF support documentation) |
| Function calling or custom tools | Anthropic documents tool use for Claude and gives an example using claude-opus-5-5. Google documents function calling for the Gemini API and describes Gemini 3.1 Pro Preview as optimized for precise tool use. |
Both are candidates for tool-using applications. Verify the exact feature, interaction pattern, and constraints your application requires. (Claude tool-use documentation) |
| Video or audio input | Google lists video and audio input for Gemini 3.1 Pro Preview. Anthropic lists text and image input for Claude Opus 5.5. | If the model itself must ingest video or audio, Gemini has a documented modality difference in these materials. Confirm supported formats and limits for your use case. (Gemini 3.1 Pro Preview model documentation) |
| Web search or grounding | Anthropic documents a web search tool for Claude. Google documents Google Search grounding for the Gemini API. The available documentation does not establish all model-specific compatibility, restrictions, or charges for this exact pair. | Both providers document search-related tools; check compatibility, terms, and pricing for the selected model and API channel before relying on either. (Claude tool-use documentation) |
| A deployment that cannot accept preview status | Google labels Gemini 3.1 Pro Preview as Preview. | Review preview terms and change-management requirements before selecting it. Preview status alone does not establish whether your particular production use is permitted. (Gemini 3.1 Pro Preview model documentation) |
These are documented capability differences and provider descriptions—not claims that one model writes better, codes more accurately, or reasons more reliably. The supplied third-party comparisons do not provide enough reproducible evidence to establish a general quality winner. When quality matters, evaluate both on the same realistic tasks and criteria rather than treating a publisher’s category winner as a guarantee.
Production API fit: check channel and region
The comparison above uses the first-party Anthropic API and Gemini Developer API, not Vertex AI. Before committing, confirm that the exact model is available through your intended channel and region, and review rate limits, model status, and applicable terms. Availability or pricing for one provider’s API should not be assumed to apply to its other hosting channels.
Anthropic lists Claude Opus 5.5 with a 1-million-token context window, a 128,000-token maximum output, and text-and-image input. Google lists Gemini 3.1 Pro Preview with a 1,048,576-token input limit, a 65,536-token output limit, text output, and text, image, video, audio, and PDF inputs. A maximum context window does not guarantee that a request of that size will be practical or cost-effective. (Claude Opus 5.5 model documentation)
Google describes its paid Gemini API tier as intended for production applications with higher volumes and advanced features, including higher rate limits and batch access. Check the current account tier and data-use terms for your project before sending production data. (Gemini Developer API pricing)
API pricing: compare verified rates, not impressions
Anthropic’s pricing documentation lists Claude Opus 5.5 at $4 per million input tokens and $20 per million output tokens for the Claude API. It separately lists prompt-caching prices and a 50% discount for the Message Batches API. Those rates are not a quote for other hosting channels. (Anthropic API pricing)
A like-for-like Gemini cost comparison is not established here. Google’s pricing documentation says its billing counts every token processed, including thinking tokens and internal tool-system tokens, but the available official evidence here does not establish the applicable Gemini 3.1 Pro Preview rate row or any prompt-length tier. Confirm the current input and output prices and billing conditions in Google’s pricing documentation before budgeting. Without those details, do not infer that Gemini is cheaper or treat a Gemini cost estimate as confirmed. (Gemini Developer API pricing)
Once both current rates and billing conditions are confirmed, use the same assumed billable input and output tokens for each model, and include tool, grounding, caching, or batch charges only when their current terms apply. A basic token-charge estimate is:
(input tokens ÷ 1,000,000 × input price) + (output tokens ÷ 1,000,000 × output price)
That estimates token charges, not cost per successful task. Retries, output length, tool usage, and the quality of the accepted result can change total cost. Do not treat a consumer subscription as an API price.
How to make the final choice
- Lock the model and channel. Confirm the exact model IDs and that both are currently available through the API channel and region you intend to use.
- Apply must-have filters. If your application needs video or audio input, Gemini’s documented modality list is a reason to evaluate it. PDF input and function calling are documented for both, so compare their behavior and constraints rather than assuming one is missing a feature.
- Confirm pricing before comparing cost. Use current official rates for the selected APIs and the same representative input/output mix. Until Gemini’s model-specific pricing and billing conditions are confirmed, treat its cost—and any price-based winner—as unknown.
- Run a representative side-by-side test. Use the same realistic tasks for both. Score correctness, format compliance, tool use, failure and retry rate, latency, and cost per accepted result; repeat enough times to assess variation.
- Choose on measured fit. If neither meets your quality or operational requirements, evaluate another model or API channel rather than forcing a winner from this comparison.
Bottom line: Evaluate Gemini 3.1 Pro Preview when its documented video or audio inputs fit the job and preview status is acceptable. Evaluate Claude Opus 5.5 when its documented long-running coding and knowledge-work focus matches the task. For PDFs and function calling, the cited materials support both; test the exact workflow. No API cost winner is established here until Gemini’s current model-specific pricing and billing conditions are confirmed.
Sources
Claude Opus 5.5 — Claude Platform Docs
Pricing — Claude Platform Docs
PDF support — Claude Platform Docs
Tool use with Claude — Claude Platform Docs
Gemini 3.1 Pro Preview — Gemini API