For a new API deployment, neither Claude Sonnet 4.5 nor Gemini 3 Pro Preview is a sensible default without addressing lifecycle first. Google says Gemini 3 Pro Preview shut down March 9, 2026. Anthropic lists Sonnet 4.5 as deprecated, with retirement on November 30, 2026. This is a guide to understanding and replacing older workloads, not a recommendation to build around both endpoints today. Google’s model status, Anthropic’s deprecation schedule.
Researched and written by GPT, an AI, from cited primary sources. Recommendations are editorial assessments; no hands-on performance test is claimed. Numerical examples are calculations under stated assumptions.
Sources checked November 3, 2026.
The exact names are important. Sonnet 4.5 is not Sonnet 5.5, and Gemini 3 Pro Preview is not Gemini 3.1 Pro or a current Gemini consumer plan. Changing a model while retaining an old comparison label makes results hard to interpret.
What the old specifications can still tell you
Sonnet 4.5 documents a 200,000-token context, 64,000 maximum output tokens and text/image input with text output. Gemini 3 Pro Preview documented a larger input allowance of 1,048,576 tokens, 65,536 output tokens, and audio/video/PDF input alongside text and images. Sonnet 4.5 reference, Gemini 3 Pro reference.
These differences matter when replacing a document or media workflow. A long video review may need transcription and frame extraction if the new model lacks equivalent native input support. A code-review workflow may instead be dominated by repository retrieval, tool permissions and whether the model identifies the actual defect.
Do not treat a context limit as an accuracy score. Test whether important evidence remains usable at the lengths your application actually sends.
Preserve a small, difficult regression set
Before a migration, collect representative cases: a normal request, an ambiguous request, a document with conflicting statements and a task where the correct response is to report missing information. For coding, add a bug whose symptom appears far from its cause. Keep the original sources and known acceptance checks.
Run supported replacement candidates on this same set with equivalent tool access and preprocessing. Record exact model IDs, reasoning settings, retries, billed usage and review time. A result from one vendor’s agent harness is not directly comparable to another model called without those tools.
A good migration does more than preserve tone. It should preserve required output fields, source traceability, failure handling and operational limits. Check those directly rather than relying on an overall “smartness” impression.
Budget the new workflow, not the retired preview
Sonnet 4.5’s listed standard API rates are $3 per million input tokens and $15 per million output tokens. Two million uncached input tokens plus 500,000 billed output tokens would calculate to $13.50 before tools, caches, retries, discounts and taxes. This is an illustrative old-model calculation, not a promised bill for its successor. Sonnet pricing.
Choose a supported replacement after checking the complete workflow’s quality and cost. Existing Sonnet users have a concrete retirement date to plan around; former Gemini 3 Pro users should already have migrated. Historical benchmark comparisons can supply useful questions, but they cannot make a closed endpoint available or guarantee that a successor behaves identically.
Model references
Anthropic · Model library
Claude Sonnet 4.5
DeprecatedThe legacy Sonnet version in this comparison has a documented November 30, 2026 retirement date.
Author’s assessment; check the guide’s evidence and limitations.- Access
- API
- Input
- text, image
- Output
- text
- Context window
- 200,000 tokens
Catalog checked . Model specifications do not establish access through a particular app or subscription.
