Short answer: For terminal-heavy, agentic coding, Claude Opus 5.5 is a reasonable first model to evaluate: Google’s published benchmark table gives it higher scores than Gemini 4 Argon on Terminal-Bench 4.0 and FrontierSWE 2. If API token cost is your main constraint, Gemini 4 Argon is cheaper than Opus 5.5 through November 30, 2026. Its introductory rates match Claude Sonnet 5.5’s listed rates, however, and benchmark results do not establish a universal coding winner. (Google’s benchmark table)
A June 2026 comparison of older models—Claude Opus 4.8 and Gemini 3.1 Pro—offers some task-specific examples, but it does not establish how Opus 5.5 or Argon will perform on your codebase. (Index.dev’s comparison)
What the current API comparison can—and can’t—tell you
As of November 8, 2026, the compared API models are Claude Opus 5.5, Claude Sonnet 5.5, and Gemini 4 Argon. Anthropic describes Opus as suited to long-running agentic coding and Sonnet as a balance of speed and intelligence; Google describes Argon as a model for complex software engineering and multi-step agents. These are provider descriptions, not independent performance findings. (Anthropic: Opus 5.5; Anthropic: Sonnet 5.5; Google: Gemini 4 Argon)
What task comparisons suggest
Google’s published evaluation table reports Claude Opus 5.5 at 59.6% versus Gemini 4 Argon at 57.1% on Terminal-Bench 4.0, and 62.3% versus 55.0% on FrontierSWE 2. Those results favor Opus on these two agentic coding evaluations. They are vendor-published benchmark results; the available comparison does not establish that the scores generalize to your repository or workflow. (Google’s benchmark table)
Index.dev’s June 2026 comparison reports that both older models fixed a BMI formula bug. In a Markdown-converter task whose prompt prohibited external libraries, Index.dev says Gemini used Tailwind despite the restriction, while Claude complied. These are reported outcomes from particular prompts—not results for Opus 5.5 or Argon, and not proof of a general quality or compliance advantage. (Index.dev’s comparison)
The practical takeaway is task-specific: the published benchmark rows give Opus a lead on two agentic coding evaluations, while the older task report suggests testing debugging explanations and strict dependency constraints in your own workflow. The evidence does not justify a blanket claim that either model writes better code in every situation.
Which should you try for your coding workload?
| Your priority | Sensible first comparison | What the evidence says—and its limit |
|---|---|---|
| Terminal-based, agentic coding | Claude Opus 5.5 vs Gemini 4 Argon | Google’s published table favors Opus on Terminal-Bench 4.0 and FrontierSWE 2. Treat that as a starting signal, not a guaranteed result on your repository. |
| Lowest listed API token rates through Nov. 30, 2026 | Gemini 4 Argon vs Claude Sonnet 5.5 | Both are listed at $2 per 1M input tokens and $10 per 1M output tokens during Argon’s introductory period. Matching rates do not establish matching output quality. |
| Lowest listed rates from Dec. 1, 2026 | Claude Sonnet 5.5, if it meets your needs | Argon is scheduled to move to $4/$20 per 1M input/output tokens, matching Opus 5.5’s listed rates; Sonnet remains listed at $2/$10. Recheck rates when budgeting. |
| Strict requirements or dependency limits | Test the exact constraint on both models | The historical Index.dev report describes one no-library task where Gemini used Tailwind and Claude did not. It is a reason to test your own constraints, not a current-model guarantee. |
| Very long generated output | Compare documented output limits for your API request mode | Argon’s model documentation gives a 65,536-token default synchronous output limit and describes long decode up to the shared input/output window. Anthropic lists a 128K-token maximum output for Opus and Sonnet. Confirm the limits for the request mode you will use. |
For a small evaluation, give both models the same representative repository task, prompt, and acceptance tests. Record test results, review or correction effort, latency, and billed usage. That will tell you more about your workload than token rates alone; it is an evaluation method, not a prediction of which model will win.
Production API details that affect the decision
Use the documented API model ID and check the provider documentation for the request mode you plan to use. The following comparison summarizes the available model information; capability details that are not confirmed for both named Claude models are identified rather than assumed.
| API dimension | Claude Opus 5.5 / Sonnet 5.5 | Gemini 4 Argon |
|---|---|---|
| Model IDs | claude-opus-5-5 / claude-sonnet-5-5 |
gemini-4-argon |
| Context | 1M tokens for each model | 1,048,576-token unified input/output window; input and output share the limit |
| Maximum output | 128K tokens for each model | 65,536 tokens is the documented default synchronous limit; long decode is described as supporting up to 1,048,576 tokens minus input tokens. The specific streaming/non-streaming foreground split is not confirmed here. |
| Tool/function use | Tool use is documented generally; model-specific support or conditions for both named models are not confirmed here. | Function calling is listed as supported. |
| Structured output | Structured outputs are documented generally; model-specific support or conditions for both named models are not confirmed here. | Structured outputs are listed as supported. |
For Argon, the available model documentation supports a 65,536-token default synchronous output limit and describes a long-decode option that can extend output up to the shared input/output window. I could not establish the more specific streaming-versus-non-streaming foreground limits from the available documentation, so do not rely on a separate limit for each mode based on this comparison. For Claude, the model documentation lists a 128K maximum output, but the available excerpts do not confirm model-specific tool-use or structured-output conditions for both Opus 5.5 and Sonnet 5.5. Check the Claude tool-use and structured-output documentation before depending on those features.
Google describes Argon’s context as a shared input-and-output window. Its Google Cloud guide further says that output there includes thinking, function calls, and the final response; that is a Google Cloud guide, so do not assume its accounting guidance applies unchanged to Gemini Developer API billing. Check the applicable API documentation for your channel before estimating usage. (Gemini API model documentation; Google Cloud Argon guide)
API pricing: compare rates and dates
For the Google Gemini Developer API, Gemini 4 Argon is listed at an introductory $2 per 1 million input tokens and $10 per 1 million output tokens through November 30, 2026. Google says those rates become $4 input and $20 output per 1 million tokens on December 1, 2026. The model is not available on the Gemini API free tier. (Google’s Gemini API model update; Google AI Studio pricing)
Anthropic lists Claude Opus 5.5 at $4 per million input tokens and $20 per million output tokens, and Claude Sonnet 5.5 at $2 and $10, respectively. These are USD API rates, not subscription or CLI plan prices. (Anthropic API pricing)
| API model | Input, USD / 1M tokens | Output, USD / 1M tokens | Pricing note |
|---|---|---|---|
| Gemini 4 Argon | $2 through Nov. 30; $4 from Dec. 1, 2026 | $10 through Nov. 30; $20 from Dec. 1, 2026 | Introductory rate; unavailable on API free tier |
| Claude Opus 5.5 | $4 | $20 | Anthropic published API rate |
| Claude Sonnet 5.5 | $2 | $10 | Anthropic published API rate |
Worked example: At these listed rates, 1 million input tokens and 100,000 output tokens would cost about $3 for Argon at its introductory rate, $6 at its December rate, $6 for Opus, or $3 for Sonnet. This is token-rate arithmetic, not a full workload estimate; retries and other applicable charges can change the bill. Google’s Cloud Argon guide says its output accounting includes thinking and function-call tokens as well as the final response. Because that guidance is for Google Cloud, confirm applicable usage accounting for the Gemini Developer API separately. (Google Cloud Argon guide)
Bottom line
For terminal-heavy agentic coding, try Claude Opus 5.5 first if you want to follow the current benchmark signal: Google’s table gives it higher scores on Terminal-Bench 4.0 and FrontierSWE 2. For a budget-first API comparison, compare Gemini 4 Argon with Claude Sonnet 5.5 through November 30, 2026, when their listed rates match. From December 1, Argon’s listed rates match Opus 5.5’s instead. None of these price comparisons settles coding quality: choose based on your own task results, API requirements, and cost per successfully completed task.
Sources
Gemini — Google DeepMind (published benchmark table)
Claude Opus 5.5 — Claude Platform Docs
Claude Sonnet 5.5 — Claude Platform Docs
Pricing — Claude Platform Docs
Tool use with Claude — Claude Platform Docs
Structured outputs — Claude Platform Docs
What’s new in Gemini 4 Argon — Gemini API
Gemini Developer API pricing — Google AI Studio
Developer’s guide to Gemini 4 Argon — Google Cloud
Gemini vs Claude for Coding in 2026: Which AI Writes Better Code?