Claude Opus 5.5 vs GPT-6 Astra: Plan or API?

Update (9 Nov 2026): Claude Fable 5.2 and Mythos 5.2 are out - prices, access and benchmarks are in my Claude Fable 5.2 guide.

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Claude Opus 5.5 and GPT-6 Astra scored highest in my test across 10 languages, with 98.7% and 97.8% of the points. They are also the most expensive. I compared the official ways to access both models and used my logs from October 24, 2026, to work out which costs least for light, medium and heavy use.

Every way to access Opus 5.5

There is also prompt caching: cached input costs $0.20 per million tokens instead of $4. If you ask multiple questions about the same long instruction or document, input costs one-twentieth as much. See How much does Claude Opus 5.5 cost? for more pricing details.

Every way to access GPT-6 Astra

OpenAI also offers more expensive modes: Fast ($20 / $100) and Ultrafast ($60 / $300). In ChatGPT Pro 500, Ultrafast uses your allocation eight times faster than standard mode. If price matters, avoid both.

Cost across three usage profiles

Each profile covers 22 working days. The short-task and long-document figures (about 30,000 tokens) are medians from my test.

For Astra, even the heavy-use profile costs $89.52 via API, less than the $100 ChatGPT Pro plan, the only plan with Astra in chat. Using Flex for batch work brings that to about $45. For Opus, the break-even point is the medium profile: $24.09 via API versus $20 for Pro, assuming the Pro limits are enough for you.

Astra, heavy-use profile:
(100 x 0.0170 + 10 x 0.2368) x 22
= $89.52

What to watch out for

• Opus writes more. Its median response was 876 tokens for a short task, compared with 294 for Astra. Asking for a concise answer in the system prompt can lower your bill.
• Tokenizers differ. Opus counted the same document as 39,700 tokens, while Astra counted 23,500. On long texts, Opus loses its advantage from a lower rate.
• Conversation history. With the API, each turn resends the conversation history. Ten turns with history growing by 1,000 tokens each (an example calculation) cost about $0.40 on Opus and $0.70 on Astra.
• Agents. Claude Code and Codex use many times more tokens than a single question. A subscription usually works out cheaper here; see Claude Code without a subscription.

My recommendation

• For occasional difficult tasks, use the API for either model; expect a bill of a few dollars a month.
• For daily chat with a top model, choose Claude Pro: it includes Opus for $20, while Astra in chat requires a plan starting at $100.
• If you have a large budget for Claude API usage, consider Max 5x instead of topping up: the credits offset the plan price.
• For automation, use Batch or Flex to cut the price in half.

For a full comparison of plans and usage thresholds for seven models, see the subscription or API guide.

Frequently asked questions

What is the cheapest way to use GPT-6 Astra?

Use the API through Flex or Batch: $5 / $25 per million tokens, or about $0.0085 for a typical short task in my test. In ChatGPT, Astra is available only in Pro plans starting at $100.

What is the cheapest way to use Claude Opus 5.5?

For occasional use, the API costs about $0.019 for a typical task, or half that with Batch. For daily chat, Claude Pro costs $20, or $17 per month when billed annually.

Is OpenRouter cheaper?

No. On October 24, OpenRouter listed the same rates as the model providers for Opus 5.5 and GPT-6 Astra: $4 / $20 and $10 / $50.

Sources and date checked

• Claude: plans and API pricing - Opus 5.5, caching, Batch, Pro and Max (checked October 24, 2026)
• Claude Help: API credits for Max (checked October 24, 2026)
• OpenAI API pricing - Astra standard, Flex/Batch, Fast and Ultrafast (checked October 24, 2026)
• OpenAI Help: GPT-6 in ChatGPT - Astra availability by plan (checked October 24, 2026)
• OpenAI Help: Pro plans - Ultrafast 8x usage (checked October 24, 2026)
• OpenRouter: model and pricing list (checked October 24, 2026)
• Task costs: my test through OpenRouter on October 24, 2026, with 120 queries per model, calculated using standard pricing

// read moreGPT-6 Astra vs Claude Opus 5.5: 9 Tests, Results and CostsBenchmarksMuse Wonder vs Claude Opus 5.5, Fable 5.1 and GPT-6 Astra: BenchmarksBenchmarksClaude Opus 5.5 Pricing: How Much Does It Cost?Benchmarks

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