Short answer (status as of November 9, 2026): This is no longer a like-for-like choice for a new integration through the providers’ native APIs. Anthropic lists Claude Opus 4.5 as active (legacy) and says it remains available, with retirement no sooner than November 24, 2026. Google says the Gemini 3 Pro Preview endpoint on the Gemini API shut down on March 9, 2026. Anthropic recommends considering migration to Opus 5.5. Lifecycle dates may differ on partner-operated platforms, so check the documentation for the specific route you use. (Anthropic model reference; Google model reference; Anthropic lifecycle guidance)
For historical comparison, launch-era coverage suggested different strengths: Opus 4.5 scored higher on some reported coding benchmarks, while Gemini 3 Pro scored higher on a reported reasoning benchmark and supported a larger input limit and more input types. These results and specifications describe the older models; they are not a current model-selection recommendation.
Quick comparison
| Decision factor | Claude Opus 4.5 | Gemini 3 Pro Preview |
|---|---|---|
| Native API status | Listed as active (legacy) on Anthropic’s platform; retirement no sooner than November 24, 2026 | Gemini API endpoint shut down March 9, 2026 |
| API model ID | claude-opus-4-5-20251101 |
gemini-3-pro-preview |
| Context and output | 200,000-token context window; 64,000 maximum output tokens | 1,048,576-token input limit; 65,536-token output limit |
| Documented inputs and outputs | Text and images in; text out | Text, images, video, audio, and PDF in; text out |
| Listed API price | $5 per million input tokens; $25 per million output tokens | Historical launch price: $2 per million input tokens and $12 per million output tokens for prompts up to 200,000 tokens; not a current price for the shut-down endpoint |
Anthropic’s model reference gives Opus 4.5’s ID, limits, input/output types, pricing, and lifecycle status. Google’s model reference gives Gemini 3 Pro Preview’s ID, limits, and supported data types, alongside its shutdown notice. (Anthropic model reference; Google model reference)
Request-sizing note: A context window is not an input-only allowance. Anthropic explains that the context window includes the material the model references and the response it generates; with thinking enabled, thinking tokens count too. So Opus’s 64,000-token maximum output is not extra capacity on top of its 200,000-token context window. Google lists Gemini’s input and output limits separately; do not treat those two figures as one shared limit. (Anthropic context-window documentation; Google model reference)
What the historical comparison suggests
Coding and agent workflows: reported benchmark edge for Opus 4.5
TheToolNerd’s November 27, 2025 comparison reported 80.9% for Opus 4.5 versus 76.2% for Gemini 3 Pro on SWE-bench Verified, and 59.3% versus 54.2% on Terminal-Bench 2.0. These are secondary-source, launch-era figures—not an independently verified or controlled head-to-head test. Benchmark setup, model configuration, and evaluation date matter, and benchmark scores do not establish which model will work better on your codebase. (TheToolNerd comparison)
Use those results only as a reason to evaluate coding and tool-driven tasks—not as a substitute for evaluating them. Measure whether a model meets your requirements, passes your tests, and completes your agent workflow successfully.
Large and multimodal inputs: Gemini’s documented specifications
The Gemini 3 Pro Preview API reference lists a 1,048,576-token input limit and text, image, video, audio, and PDF inputs. Anthropic lists Opus 4.5 with a 200,000-token context window and text and image inputs. Those specifications could have made Gemini a better fit on paper for certain large-document or mixed-media workflows while the endpoint was available. They do not make the shut-down Gemini API endpoint an option for a new integration. (Google model reference; Anthropic model reference)
Reasoning scores were task-specific
Google reported 91.9% on GPQA Diamond for Gemini 3 at launch. TheToolNerd’s November 2025 comparison also reported Gemini at 91.9% and Opus 4.5 at 87.0% on that benchmark, while reporting Opus ahead on the coding benchmarks it listed. These are benchmark-specific, launch-era claims; they do not establish a general reasoning winner or predict performance on your production prompts. (Google Gemini 3 announcement; TheToolNerd comparison)
API pricing: historical rates are not a current matchup
Anthropic lists Opus 4.5 at $5 per million input tokens and $25 per million output tokens. Its model reference also labels Opus 4.5 legacy and recommends considering migration to Opus 5.5. (Anthropic model reference)
Google’s developer announcement listed Gemini 3 Pro Preview at $2 per million input tokens and $12 per million output tokens for prompts of 200,000 tokens or less. That is a historical launch price, not an available price for the Gemini API endpoint that shut down. (Google Gemini developer announcement; Google model reference)
Per-token prices do not determine total task cost. For a production comparison, account for input and output usage, retries, tool calls, and the work needed to review or repair responses. Do not compare Gemini’s historical launch price with Opus 4.5’s listed price as though they were current competing offers.
Which should you choose?
- Maintaining an Opus 4.5 integration on Anthropic’s platform? The model reference lists it as active (legacy) and says retirement will be no sooner than November 24, 2026—not that it is already retired. Anthropic recommends considering migration to Opus 5.5. Test the replacement on your own prompts, tools, and acceptance checks. For Amazon Bedrock and Google-managed Claude routes, check that provider’s lifecycle schedule; Anthropic says partner-operated platforms can set different dates. (Anthropic model reference; Anthropic lifecycle guidance)
- Building a new integration through the Gemini API that expected Gemini 3 Pro Preview? That endpoint shut down on March 9, 2026. Select a currently available model and verify its ID, limits, pricing, and lifecycle in the documentation for your intended Google API or cloud route. The shutdown statement here is specific to the Gemini API endpoint; check any other provider route separately. (Google model reference)
- Comparing models for coding, reasoning, or multimodal work now? Don’t carry the 2025 comparison forward as if it tested current model versions. Use currently documented candidates and compare them against your actual workload.
A practical evaluation checklist
Before selecting a current replacement, test candidates on a small, representative set of real tasks:
- Use the same inputs, task instructions, tools, and acceptance criteria.
- Score successful completion, correctness, and valid tool calls—not just response quality at a glance.
- Record latency, retries, input/output tokens, and cost per accepted result.
- Test the context sizes and modalities your application actually needs.
- Confirm model IDs, limits, prices, and retirement conditions for your chosen API platform.
Bottom line: Opus 4.5 remains listed as active (legacy) on Anthropic’s platform as of November 9, 2026, with retirement no sooner than November 24, 2026. Gemini 3 Pro Preview’s Gemini API endpoint has shut down. The historical comparison can inform evaluation criteria, but a production decision should use current models, platform-specific lifecycle documentation, and workload-specific testing. (Anthropic model reference; Google model reference)
Sources
Claude Opus 4.5 — Claude Platform Docs
Model deprecations — Claude Platform Docs
Context windows — Claude Platform Docs
Gemini 3 Pro Preview — Gemini API model reference
Gemini 3 for developers: New reasoning, agentic capabilities
Gemini 3: Introducing the latest Gemini AI model from Google
Claude Opus 4.5 vs Gemini 3, Nano Banana Pro and Google Antigravity IDE: Nov 2025 Mega Review