Gemini 4 Argon vs GPT-6 Astra vs Claude Opus 5.5 Compared

Short answer: all three flagship models now sit at or near a 1-million-token context window, but they are priced, rationed and positioned very differently. Google's Gemini 4 Argon is the cheapest of the three during its introductory pricing window and leads on enterprise knowledge-work benchmarks in Google's own testing, but it is still rolling out in stages rather than open to everyone. OpenAI's GPT-6 Astra is the most expensive per token by a wide margin and carries a long-context surcharge above 272K tokens. Anthropic's Claude Opus 5.5 sits in the middle on price, is already live everywhere Claude ships, and leads the field on agentic coding in both Google's and Anthropic's own published benchmark tables. None of the three companies has published a single shared benchmark suite, so every number below is sourced to the specific vendor page that stated it.

What each model actually is

Gemini 4 Argon is Google DeepMind's newest frontier model, announced September 30, 2026. Google's own announcement describes it as built for "complex, long-horizon work," naming real-world software engineering, enterprise knowledge work such as legal and finance, cybersecurity defense and creative writing as its target use cases. Unusually for a flagship launch, Google is not opening it to everyone at once: the model first rolled out to a limited group of trusted cyber defenders through Google's Fairwind Program, with Google saying broader access would follow "starting with paid API customers and Google AI Ultra subscribers." Google Cloud's own documentation lists a general-availability date of October 13, 2026, and our rollout coverage from this morning has the details on what changed in the consumer Gemini app.

GPT-6 Astra is OpenAI's current flagship, reachable in the API under the model ID gpt-6-astra. OpenAI's own developer documentation lists a reliable knowledge cutoff of April 30, 2026 and supports it on the Chat Completions, Responses and Batch endpoints only — notably, OpenAI's docs show it does not support the Realtime, Assistants, fine-tuning, embeddings, image, video, audio or moderation endpoints, which is a real limitation if you're building a multimodal product around it. OpenAI's own announcement and safety pages were returning a bot-verification wall at the time of writing, so we could not independently confirm OpenAI's own marketing language or safety-level claims about Astra directly from openai.com; everything stated here about Astra comes from OpenAI's developer documentation at developers.openai.com, which loaded normally, plus Astra's scores as reported inside Google's and Anthropic's own published comparison tables.

Claude Opus 5.5 is Anthropic's Opus-tier model, released September 22, 2026, and billed by Anthropic as "the first model in our new Claude 5.5 family." Anthropic's own announcement says it performs close to Claude Fable 5.1 (Anthropic's larger model) on most work while costing roughly 40% less to run than its predecessor, Claude Opus 5. It's already available across Anthropic's full distribution: the Claude API, Amazon Bedrock, Google Cloud Vertex AI and Microsoft Foundry.

Pricing and specs, side by side

The table below pulls every number directly from each company's own developer documentation or announcement page — nothing here is a third-party aggregator's estimate.

Context windows: 1M tokens, three different ways

All three vendors now advertise roughly a million-token context window, but they count it differently. Google's own developer page for Argon describes the 1,048,576-token limit as a single pool shared between input and output — so a very long input leaves less room for the model's reply. OpenAI's developer documentation splits GPT-6 Astra's 1,050,000-token window into a 922,000-token maximum input plus a separate 128,000-token maximum output. Anthropic's platform documentation lists Claude Opus 5.5's window as a flat 1,000,000 tokens for context with a separate 128,000-token output ceiling (extendable to 300,000 tokens on the Batch API under a beta header). In practice, that means Astra and Opus 5.5 behave more predictably on long-input, long-output jobs, while Argon's combined pool can get squeezed if you feed it near its full input capacity and still expect a long answer.

Benchmarks: what each vendor actually published

This is the part most comparison posts get wrong by borrowing numbers from random blogs. Here, every score is one that a vendor published on its own site, and we say whose table it came from. Google's own Gemini 4 Argon model card on deepmind.google includes a comparison table against GPT-6 Astra, Claude Opus 5.5 and Claude Fable 5.1. Anthropic's own Claude Opus 5.5 announcement includes a similar table against GPT-6 Astra and GPT-5.6 Sol. We could not load OpenAI's own benchmark page directly (see above), so Astra's numbers below are only the ones that appear inside Google's and Anthropic's own published tables, which both companies presumably sourced from OpenAI's reporting or ran themselves — treat the Astra column as secondhand within an otherwise primary-sourced comparison.

Reading across both companies' own tables, a pattern holds up: Gemini 4 Argon leads decisively on enterprise knowledge-work tasks — financial agent work, legal agent work, and general business automation — while Claude Opus 5.5 leads on terminal-based agentic coding and on Anthropic's tool-using reasoning benchmark. GPT-6 Astra doesn't top either vendor's table on the rows shown here, though it's worth repeating that we're relying on competitors' tables for Astra's numbers because OpenAI's own benchmark pages weren't reachable at the time of writing. If OpenAI publishes a verifiable, independently-reachable benchmark page later, those figures may look different, and we'll update this piece.

Pricing deep dive: who actually costs what

On raw per-token price, the order is consistent across every official page we fetched. Gemini 4 Argon is cheapest right now because of its introductory discount: $2 per million input tokens and $10 per million output tokens through November 30, 2026, after which Google's own pricing reverts to $4 and $20 — which lands it exactly level with Claude Opus 5.5's standard $4 input / $20 output pricing once the promotion ends. GPT-6 Astra is priced well above both, at $10 input and $50 output per million tokens on OpenAI's own developer pricing page, and that gap widens further on long prompts: anything over 272,000 input tokens bills the entire request at $20 input and $75 output, according to the same page.

Cache pricing also diverges. Google discounts cached input tokens by 95% off the standard input rate for Argon. OpenAI prices cached input for Astra at $1 per million tokens, 10% of the $10 standard rate. Anthropic prices Claude Opus 5.5 cache reads at a flat $0.20 per million tokens, with 5-minute cache writes at $5 and 1-hour cache writes at $8. If your workload leans heavily on repeated system prompts or long static context, Anthropic's and Google's cache discounts both beat OpenAI's on a like-for-like basis.

Availability: who can actually use these today

This is where the three diverge most. Claude Opus 5.5 is simply live: Anthropic's own announcement confirms it shipped September 22, 2026 across the Claude API, Amazon Bedrock, Google Cloud Vertex AI and Microsoft Foundry, with no waitlist described. GPT-6 Astra is reachable through OpenAI's standard API usage tiers (Build, Launch, Grow), per OpenAI's developer documentation, which implies normal self-serve access rather than an invite-only preview — though we could not confirm consumer ChatGPT availability directly from openai.com. Gemini 4 Argon is the odd one out: Google's own announcement describes a deliberately staged rollout, starting with vetted cyber-defense partners in its Fairwind Program and a voluntary pre-release review process with the U.S. government, before opening more broadly to paid API customers and Google AI Ultra subscribers. Google Cloud's documentation separately lists October 13, 2026 as a general-availability date for the Cloud-hosted version, so enterprise customers on Google Cloud may already have access even while the consumer rollout is still expanding.

Which model wins for which job

Based only on what each company has put on its own pages:

• Long, autonomous coding agents (terminal/IDE work): Claude Opus 5.5, per its Terminal-Bench 4.0 lead in both Google's and Anthropic's own tables (66.4% vs. the 50s–60s for the other two).
• Legal and financial analysis workflows: Gemini 4 Argon, which leads Harvey's Legal Agent Benchmark and Vals Finance Agent v2 by wide margins in Google's own model card.
• Tightest budget per token, right now: Gemini 4 Argon's introductory pricing, though that expires November 30, 2026, after which it ties Claude Opus 5.5's standard rate.
• Immediate, no-waitlist access across every major cloud: Claude Opus 5.5, which is already distributed on AWS, Google Cloud and Microsoft Foundry simultaneously.
• Cybersecurity defense use cases: a near-tie on the one shared benchmark we found — Argon and Astra both score 68.0% on CWE-bench v1 in Google's own table — so neither vendor's own numbers show a clear winner here.

If you're choosing an AI browser or agent layer to put on top of any of these models, it's also worth reading our head-to-head on the two leading AI browsers, and if you want to understand how Google expects agents built on Argon to talk to agents built on other platforms, our explainer on Google's agent interoperability standard covers the protocol Google is pushing industry-wide.

What none of the three vendors will confirm yet

A few things are genuinely unconfirmed, and we're flagging them rather than guessing. OpenAI has not published, on any page we could reach, a specific public release date, a consumer-tier rollout timeline, or an independently-verifiable benchmark page for GPT-6 Astra — its own index/announcement and safety-overview URLs returned a bot-verification wall rather than content when we tried to fetch them directly, so claims you may see elsewhere about Astra's safety classification or exact launch date should be treated as unconfirmed until OpenAI's own pages are reachable. Google has not published a context-window figure in its main announcement post (only in the separate developer docs), and has not given a firm date for when Gemini 4 Argon leaves its defender-only preview for general consumer access. Anthropic has not published a long-context pricing surcharge for Opus 5.5 the way OpenAI has for Astra, which may mean there isn't one, or may simply mean it hasn't been disclosed.

What next

If you need a decision today: pick Claude Opus 5.5 for coding-heavy agentic work you want running in production right now across any major cloud, pick Gemini 4 Argon if your workload is legal, financial or enterprise-document-heavy and you can tolerate a staged rollout, and hold off on GPT-6 Astra unless its $10/$50 pricing and endpoint limitations (no Realtime, no Assistants, no embeddings) specifically fit your use case. All three companies continue to publish new system cards, pricing updates and availability changes on a near-weekly cadence this quarter, so check each vendor's own pricing and model pages (linked below) before committing budget, and revisit this comparison once OpenAI's own Astra pages are reachable for direct verification.

Written byTheo Park

Theo Park runs the AI desk at Pandromeda. He follows model launches from the frontier labs and the open-weight community, tracks the assistants and developer tools built on them, and explains what each release changes on pricing, capability and safety. His reporting leans on primary sources: model cards, technical reports, API documentation and the companies' own announcements.

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