Gemini 4 Argon vs GPT-6 Astra vs Claude Opus 5.5: Prices, Limits & Access

Last updated: October 2, 2026

Gemini 4 vs GPT-6 is a comparison between one announced model and one live model. GPT-6 Astra from OpenAI and Claude Opus 5.5 from Anthropic are available today in an application programming interface (API) and in paid chat plans. Gemini 4 Argon from Google is limited to cyber defenders in the Fairwind Program, with no public date.

This page compares the 3 models on documented information only: access, price, context and output limits, tools, input types, reasoning modes, speed tiers, cloud availability and vendor benchmark figures. No model was tested for this article. Sources are OpenAI's GPT-6 Astra model page, the OpenAI pricing page, Anthropic's Claude Opus 5.5 page and Google's Gemini 4 Argon announcement.

Which of the 3 models can you use today?

Two of the 3 models are open to the public today: GPT-6 Astra and Claude Opus 5.5. Gemini 4 Argon is not.

Google names paid API customers and Google AI Ultra subscribers as the next groups for Argon and gives no date. The full access picture is in our Gemini 4 Argon guide.

How do the API prices compare?

Claude Opus 5.5 costs $4 input and $20 output per 1 million tokens, GPT-6 Astra costs $10 and $50, and Gemini 4 Argon has an announced introductory price of $2 and $10. Only the Astra and Opus 5.5 prices can be paid today.

A job with 1 million input tokens and 1 million output tokens costs $60 on GPT-6 Astra and $24 on Claude Opus 5.5 at standard rates. The same job would cost $12 on Gemini 4 Argon at the introductory price and $24 at the standard price, once Google opens the API.

There are 3 pricing rules that change the comparison.

• Long prompts cost more on Astra. Requests above 272,000 input tokens pay double for input and 1.5 times for output. Anthropic bills the full 1 million token window of Opus 5.5 at the standard rate.
• Cache writes cost 1.25 times the input price on both live models. OpenAI charges $12.50 per 1 million tokens on Astra, and Anthropic charges $5 on Opus 5.5, or $8 for a 1-hour cache.
• Argon's standard price matches Opus 5.5. Google has not published the date on which the introductory price ends.

Token counts differ between vendors, so an equal price per token does not mean an equal price per task.

How do the context window and output limits compare?

GPT-6 Astra and Claude Opus 5.5 both accept about 1 million tokens of context and return up to 128,000 tokens. Gemini 4 Argon has the largest announced output limit, 1 million tokens, and no published input limit.

GPT-6 Astra splits the context window into 922,000 input tokens and 128,000 output tokens. Claude Opus 5.5 raises the output limit to 300,000 tokens on the Message Batches API with a beta header.

How do input types and tool use compare?

GPT-6 Astra and Claude Opus 5.5 both take text and images as input and return text. Neither model page lists audio or video input. Google's announcement highlights video analysis for Gemini 4 Argon, with a reported 91.7% on the long video benchmark LVBench, and does not publish a full list of input types.

Tool support is documented for 2 of the 3 models.

• GPT-6 Astra supports 10 built-in tools: web search, file search, image generation, code interpreter, hosted shell, apply patch, skills, computer use, Model Context Protocol (MCP) and tool search.
• Claude Opus 5.5 works with 11 Anthropic-provided tools: web search, web fetch, code execution, advisor, tool search, MCP connector, memory, bash, text editor, computer use and browser use.
• Gemini 4 Argon has no published tool list. Google describes agentic coding and autonomous vulnerability patching and names no API tools.

One migration point for Opus 5.5: forced tool use returns an error, per Anthropic's model page.

How do the reasoning modes compare?

GPT-6 Astra and Claude Opus 5.5 use the same 5 effort levels: low, medium, high, xhigh and max. Opus 5.5 defaults to medium, and adaptive thinking on Opus 5.5 is always on. OpenAI's Astra model page lists the 5 levels and names no default. Google has not published thinking levels for Gemini 4 Argon and describes the model as built for "deep reasoning across complex, long-horizon workflows."

Which model has the fastest speed tier?

GPT-6 Astra has the fastest documented speed tier, Ultrafast, at up to 6 times the token generation speed in the API. Speed is sold as a paid option on both live models.

Each speed claim is the vendor's own figure, measured against that vendor's standard speed. OpenAI reports up to 8 times faster generation for Ultrafast inside Codex. Fast mode on Claude Opus 5.5 is a research preview on the Claude API only. Google has published no speed tier for Gemini 4 Argon.

Where is each API available?

Claude Opus 5.5 and GPT-6 Astra are both sold outside their makers' own APIs.

• Claude Opus 5.5 runs on the Claude API, Amazon Bedrock, Google Cloud, Microsoft Foundry and Claude Platform on AWS under the model ID claude-opus-5-5.
• GPT-6 Astra runs on the OpenAI API under the model ID gpt-6-astra, with Chat Completions, Responses and Batch endpoints. AWS announced general availability on Amazon Bedrock on September 8, 2026, and OpenAI's launch post lists Microsoft Azure.
• Gemini 4 Argon has no public API. The Gemini API models page and the Vertex AI model list show no Argon model ID.

Entry rate limits differ in how they are counted. OpenAI's Tier 1 allows 500 requests and 500,000 tokens per minute for Astra. Anthropic's Start tier allows 1,000 requests, 2,000,000 input tokens and 400,000 output tokens per minute for Opus 5.5.

What do the vendors report for coding and agent work?

No independent test has run all 3 models under one setup, so this page names no winner. The table lists vendor-published scores where the benchmark name matches.

Read the table with 4 limits in mind.

1. Google ran the DeepSWE v1.1 test for Argon, and OpenAI ran the test for Astra. Settings such as effort level and scaffolding are not shown to match.
2. Anthropic states that Zapier ran AutomationBench for Opus 5.5 and counted safeguard interventions as failures. Google and Anthropic name no AutomationBench version, and OpenAI names version 1.0.6 in a later post.
3. Anthropic's Terminal-Bench 4.0 figure for Astra is the number OpenAI reported.
4. OSWorld scores are left out. OpenAI reports 72.6% for Astra on OSWorld 2.0, and Anthropic reports 81.8% for Opus 5.5 on OSWorld 2.1, a different version.

How does the GPT-6.1 Astra cancellation change the comparison?

GPT-6 Astra stays OpenAI's top model, so the comparison with Gemini 4 Argon and Claude Opus 5.5 uses the model that launched in September 2026 and not a newer one. OpenAI cancelled GPT-6.1 Astra on September 28, 2026. The model "didn't quite meet the bar in terms of staying within scope and authorization", said Saachi Jain, OpenAI's head of safety systems, in a statement quoted by CNBC.

The cancellation has 2 effects on buyers.

• Price. Astra keeps its $10 and $50 price while Opus 5.5 and the announced Argon price sit far lower. OpenAI's cheaper answer is GPT-6.1 Sol at $2 and $10, which OpenAI reports as level with Astra on DeepSWE v1.1. Our GPT-6 Astra vs Sol vs Luna comparison covers the tiers.
• Lineup. Opus 5.5 is not Anthropic's most expensive model. Claude Fable 5.1 costs $10 and $50, the same as Astra.

Which model fits which job?

The right model depends on access, budget and the stack already in use.

• Choose GPT-6 Astra for work inside ChatGPT, Codex or the OpenAI API where response speed matters and the budget covers Ultrafast. The ChatGPT listing tracks plan prices.
• Choose Claude Opus 5.5 for long agentic coding and knowledge work at $4 and $20, with long prompts billed at the standard rate. The Claude listing tracks plan prices.
• Wait for Gemini 4 Argon when a single response needs more than 128,000 output tokens or the work runs on Google Cloud. No public customer can buy Argon today.

Frequently asked questions

Is Gemini 4 better than GPT-6?

No comparable evidence shows that Gemini 4 Argon is better than GPT-6 Astra. Google reports 77.9% on DeepSWE v1.1 for Argon and OpenAI reports 74.1% for Astra, and each vendor ran its own test. Public users cannot run Argon yet.

Is Gemini 4 Argon cheaper than GPT-6 Astra?

Yes, the announced Gemini 4 Argon price is lower. Argon is announced at $2 input and $10 output per 1 million tokens, rising to $4 and $20, compared with $10 and $50 for GPT-6 Astra. The Argon price is not payable until Google opens API access.

Which model has the largest context window?

GPT-6 Astra has the largest published context window, 1,050,000 tokens. Claude Opus 5.5 has a 1M token context window. Google has not published the input context size of Gemini 4 Argon and has announced a 1 million token output limit.

Is Claude Opus 5.5 available now?

Yes, Claude Opus 5.5 is available now. Anthropic released Claude Opus 5.5 on September 22, 2026, on the Claude API, Amazon Bedrock, Google Cloud and Microsoft Foundry, and in Claude for Pro, Max, Team and Enterprise users.

Did OpenAI release GPT-6.1 Astra?

No, OpenAI cancelled GPT-6.1 Astra on September 28, 2026. GPT-6 Astra remains OpenAI's top model, and GPT-6.1 Sol is the only 6.1 model.