Claude Sonnet 5.5 vs Gemini 3.8 Flash: 2026 comparison

Claude Sonnet 5.5 and Gemini 3.8 Flash in brief

Claude Sonnet 5.5 and Gemini 3.8 Flash both handle long inputs, support reasoning and can call tools. Text, images and files are common to both, while Gemini additionally accepts audio and video. Claude allows longer outputs and leads on several shared evaluations. Gemini has lower token prices and a higher SimpleQA result. Your choice therefore turns on the material you need to process, the length of the responses you expect and how strongly usage costs affect your project.

Claude Sonnet 5.5 : Claude Sonnet 5.5 (Anthropic): $2 / $10 per million tokens, 1M context, benchmarks, verdict and alternatives. Checked October 25, 2026.

Gemini 3.8 Flash : Gemini 3.8 Flash (Google): $0.83 / $4.13 per million tokens, 1M context, benchmarks, verdict and alternatives. Checked October 25, 2026.

They are often weighed against each other by people who hesitate. This page lines up their features point by point (11 criteria), with no partnership with either publisher.

Comparison table

Criterion by criterion

For each criterion: why it matters, each one's value and who has the edge. A criterion without data on both sides is not decided.

Capabilities (Epoch AI index)

Epoch AI's capabilities index rolls many benchmarks into one number: the higher, the better the model does on hard tasks. Claude Sonnet 5.5 : 166.2. Gemini 3.8 Flash : 157.4. Edge: Claude Sonnet 5.5.

Shared benchmarks

On the benchmarks both models took, we count each one's wins. Claude Sonnet 5.5 : 3 of 4. Gemini 3.8 Flash : 1 of 4. Edge: Claude Sonnet 5.5.

Input price

The price of tokens sent to the model weighs heavily as soon as you send long documents or chat history. Claude Sonnet 5.5 : $2 / M tokens. Gemini 3.8 Flash : $0.83 / M tokens. Edge: Gemini 3.8 Flash.

Output price

Generated tokens usually cost several times more; they dominate the bill for writing and code. Claude Sonnet 5.5 : $10 / M tokens. Gemini 3.8 Flash : $4.13 / M tokens. Edge: Gemini 3.8 Flash.

Cost of a typical task

For a request of 2,000 input and 500 output tokens, repeated 30,000 times a month (1,000 a day). Claude Sonnet 5.5 : $270 per month. Gemini 3.8 Flash : $111 per month. Edge: Gemini 3.8 Flash.

Context window

The context window sets how much text the model reads at once: useful for long documents and agents. Claude Sonnet 5.5 : 1M tokens. Gemini 3.8 Flash : 1M tokens. Edge: Gemini 3.8 Flash.

Max output

The maximum answer length matters to generate long code files or reports. Claude Sonnet 5.5 : 128K tokens. Gemini 3.8 Flash : 65.5K tokens. Edge: Claude Sonnet 5.5.

Accepted inputs

Text, images, files, audio: the more formats accepted, the more cases covered without extra tools. Claude Sonnet 5.5 : 3. Gemini 3.8 Flash : 5. Edge: Gemini 3.8 Flash.

Tool calling

Essential for an agent: the model can call functions, APIs or MCP servers. Claude Sonnet 5.5 : yes. Gemini 3.8 Flash : yes. A tie on this point.

Open weights

Downloadable weights let you run the model yourself, without sending data to a provider. Claude Sonnet 5.5 : no. Gemini 3.8 Flash : no. A tie on this point.

Release date

A newer model often has fresher data and better training techniques. Claude Sonnet 5.5 : September 28, 2026. Gemini 3.8 Flash : September 2, 2026. Edge: Claude Sonnet 5.5.

In charts

Our analysis

Anthropic released Claude Sonnet 5.5 on September 28, 2026, while Google released Gemini 3.8 Flash on September 2, 2026. Both publishers are based in the United States. Their declared capabilities suggest different practical audiences. Claude may appeal to teams producing long responses and working on tasks related to the supplied mathematical evaluations. Gemini may fit projects that need audio or video inputs alongside lower token spending. Both support reasoning and tool calls, so neither has an exclusive claim to those functions. The records do not report response speed or application reliability, and the product names should not be treated as evidence for either.

Claude has an Epoch capability index of 166.18, compared with Gemini's 157.44. Their GPQA results are close, at 95.6% and 95.4%. Claude scores 88.8% on FrontierMath and 100% on AIME, against Gemini's 68.4% and 98.9%. Gemini leads on SimpleQA with 69.7%, compared with 46.5% for Claude. Only Gemini has ARC1 and ARC2 figures in the supplied data. Claude costs $2 per million input tokens and $10 per million output tokens. Gemini costs $0.825 and $4.125, respectively. These figures support a workload-specific comparison, since the benchmark pattern and token bill may point toward different choices.

Both models have closed weights, and neither record specifies a license. The available information does not explain content retention, possible training use of submitted material or processing locations. The publishers' shared country does not settle those questions. Gemini lists text, images, video, files and audio as supported inputs. Claude lists text, images and files. Gemini's additional input categories may matter if you work directly with multimedia content, but the records do not detail supported formats or media-specific limits. Input breadth also says nothing about confidentiality safeguards. Those handling conditions need separate examination before these specifications can support a decision involving sensitive content.

Claude offers a context window of 1,000,000 tokens and a maximum output of 128,000 tokens. Gemini provides 1,048,576 tokens of context and a maximum output of 65,536 tokens. Gemini therefore has somewhat more input room, while Claude permits longer generated responses. Both support tool calls, but no connectors or execution arrangements are described. There are also no latency figures to establish how either would feel in an interactive workflow. For everyday integration, the concrete questions are whether you need audio or video, whether the output ceiling fits your responses and how much repeated use would cost at the published token rates.

Depending on your situation

The right choice depends on use. For a few common situations, here are the criteria that matter and who wins (Claude Sonnet 5.5 value / Gemini 3.8 Flash value).

High request volume

Here, Gemini 3.8 Flash has the edge: it wins 3 of the 3 criteria that matter in this situation, namely cost of a typical task ($270 per month / $111 per month), input price ($2 / M tokens / $0.83 / M tokens), and output price ($10 / M tokens / $4.13 / M tokens).

Hard tasks (reasoning, code)

Here, Claude Sonnet 5.5 has the edge: it wins 3 of the 3 criteria that matter in this situation, namely capabilities (epoch ai index) (166.2 / 157.4), shared benchmarks (3 of 4 / 1 of 4), and max output (128K tokens / 65.5K tokens).

Agents and long documents

Here, Gemini 3.8 Flash has the edge: it wins 2 of the 3 criteria that matter in this situation, namely tool calling (yes / yes), context window (1M tokens / 1M tokens), and accepted inputs (3 / 5).

Maximum privacy

Neither stands out on the criteria for this situation (open weights (no / no)): decide with a trial.

Which one to choose?

Choose Claude Sonnet 5.5 if…

• you value capabilities (epoch ai index) (166.2)
• you value shared benchmarks (3 of 4)
• you value max output (128K tokens)
• you value release date (September 28, 2026)

Claude Sonnet 5.5 is a logical choice when long outputs matter and the FrontierMath or AIME results are relevant to your work. It also has a small numerical lead on GPQA. This makes it worth considering for text, image and file workflows where the larger output allowance can justify accepting the higher published token prices.

Choose Gemini 3.8 Flash if…

• you value input price ($0.83 / M tokens)
• you value output price ($4.13 / M tokens)
• you value cost of a typical task ($111 per month)
• you value context window (1M tokens)
• you value accepted inputs (5)

Gemini 3.8 Flash fits projects that need audio or video inputs, or where token costs strongly influence the decision. Its SimpleQA result is also higher than Claude's in the supplied evaluations. You should check that its smaller output ceiling meets your requirements, especially if your application is expected to produce particularly long responses in one generation.

Strengths and limits of each

Claude Sonnet 5.5

• + Among the top 20% of models according to Epoch AI (ECI 166.2).
• + Very large context (1M tokens): long documents or a whole codebase fit in one request.
• + Agent-ready: tool calling and structured JSON output.
• − Expensive: costlier than 84 % of paid models.

Gemini 3.8 Flash

• + Among the top 20% of models according to Epoch AI (ECI 157.4).
• + Very large context (1M tokens): long documents or a whole codebase fit in one request.
• + Agent-ready: tool calling and structured JSON output.

The best test is still yours: take three real tasks from your day and give them to both for a week. The price calculator works out the gap on your own volume.

What about the others?

If neither suits you, look at Claude Opus 5.5, GPT-6 Astra, GPT-6.1 Sol, Claude Fable 5.1, Gemini 4 Argon, and Claude Opus 5.

Conclusion

Claude's clearest advantages are longer outputs and stronger FrontierMath and AIME results. Gemini combines broader input support, lower token prices and a higher SimpleQA score. Those strengths serve different requirements, so start with your own content and tasks. Representative testing can show whether a benchmark advantage matters enough to justify the cost. The supplied information does not establish a winner on response speed or privacy conditions.