GPT-6 Astra vs Claude Opus 5.5: cost, coding and usage limits

Which is cheaper, GPT-6 Astra or Claude Opus 5.5?

Opus 5.5, by a wide margin. Astra costs 2.5x as much for input and output, and 5x as much for cached input. Our sample month of 30M input and 6M output tokens comes to $600 on Astra and $240 on Opus.

Coding agents reread the same files all day, so caching matters more than the headline rate. A busy coding day of 4M fresh input, 16M cached input and 1M output tokens costs about $106 on Astra and $39.20 on Opus. That's our estimate at list price, with cache write fees left out.

Costs that aren't in the headline price

• Long prompts: Astra's price goes up for prompts over 272K tokens: $20 input and $75 output per 1M. Anthropic's pricing page lists one Opus 5.5 rate with no long-prompt tier, so a single 400K-token prompt costs $8 in input on Astra and $1.60 on Opus.
• Cache writes: OpenAI charges $12.50 per 1M tokens to write Astra's 30-minute cache and $25 for the 12-hour cache. Anthropic charges $5 per 1M for Opus 5.5's 5-minute cache.
• Batch: both providers halve the price for batch jobs. Astra drops to $5 input and $25 output.
• Fast mode: Astra's Fast rate is $20 input and $100 output, double the standard price. Anthropic's fast mode for Opus 5.5 is also 2x standard pricing, for "up to 2.5x faster speeds".
• US-only inference: Anthropic charges 1.1x for input and output tokens if your workload has to run in the US.

From OpenAI's API pricing page and Anthropic's pricing page, read Oct 24, 2026.

Is GPT-6 Astra or Claude Opus 5.5 better for coding?

On the leaderboards, Opus 5.5. In our LMArena data it ranks above Astra on every board where both appear: coding, chat, creative writing, roleplay, reasoning and math, vision and agent tasks. Bold marks the higher rank. Ranks count only the models in our API price table.

From the LMArena (CC BY 4.0) leaderboard dataset, using each model's best listed reasoning setting. Updated with our data on 2026-10-24.

Each vendor pitches its model a little differently. Anthropic calls Opus 5.5 its "Daily driver for agentic coding and enterprise work" on its pricing page. OpenAI's model guide says "Astra, for the hardest end-to-end work", and adds that GPT-6.1 Sol "offers near-Astra performance at a lower cost than Astra." Leaderboards measure people's votes on short tasks, so a long agent run in your own repo is still the real test.

GPT-6 Astra vs Opus 5.5 usage limits on $20 plans

You don't need the API to use either. ChatGPT lists GPT-6 Astra on Plus, Pro 100, Pro 200 and Pro 500, and Claude includes Opus on Pro, Max 5x and Max 20x (not Free), per the Claude plans page.

• Codex on ChatGPT Plus ($20): OpenAI estimates 5 to 45 local Astra messages per 5 hours, and weekly limits may also apply. That's far fewer than the 15 to 160 it estimates for GPT-6.1 Sol. Pro plans currently have no 5-hour limit. Fast mode uses your included usage 2.5x faster, per the Codex pricing page.
• Claude Code on Claude Pro ($20): Anthropic publishes no message count. Pro gets at least 5x Free usage per 5-hour session plus a weekly limit, shared between chat and Claude Code, and how far it goes "depends on the length and complexity of your conversations, the model you choose, and the features you use."
• Both in one plan: GitHub Copilot lists Astra and Opus 5.5 on Pro+ ($39) and Max ($100), billed from monthly AI Credits.

Because Anthropic gives no number, nobody can say which $20 plan buys more frontier-model work. What we can say: Astra is OpenAI's most expensive model, and OpenAI's own Plus estimate for it is small. For the current windows see when Codex resets and when Claude resets, and the Claude Code weekly limit explainer.

GPT-6 Astra or Claude Opus 5.5: which should you pick?

• Paying per token: Opus 5.5. It costs less on every line of the price list and ranks higher in our LMArena data.
• Long prompts over 272K tokens: Opus 5.5, since Astra's price goes up past that point and Opus has one rate.
• Already on ChatGPT Plus or Pro: try Astra for the hardest jobs, but expect it to eat your Codex window. OpenAI points most work to GPT-6.1 Sol, which we compare in GPT-6 Astra vs GPT-6.1 Sol.
• Want both: GitHub Copilot's higher plans carry both models, or run them side by side on the API.

To weigh other models too, open the model compare builder with these two loaded, or check GPT-6.1 Sol vs Claude Opus 5.5 and GPT-6 Astra vs Claude Fable 5.1. To see whether a plan or the API is cheaper for your usage, try the plan vs API calculator.