Claude Opus 5.5 vs GPT-6 Astra: Frontier Intelligence Compared

Astra costs 2.5 times as much per token, and more above 272K

Prices are per million tokens on each vendor's standard API. The gap is widest on cache reads, five times, and on long prompts, where Astra doubles its input and cache rates and raises output by half for the full request. Meta's Muse Wonder, on its Model API, lists the same $4 input, $20 output and $0.20 cache-read rates as Opus 5.5 (Muse Wonder vs Muse Spark).

Both models write up to 128K output tokens. Opus 5.5's context window is 1M tokens and Astra's is 1,050,000. OpenAI also sells an Ultrafast tier for Astra at six times standard ($60 and $300). Opus 5.5's Fast mode runs on Anthropic's API and also on Claude Models on Google Cloud (Anthropic managed) and Microsoft Foundry on Azure.

Three illustrative requests show how the gap moves. The sizes are examples, not vendor figures, and each vendor counts tokens with its own tokenizer, so the same text does not come to exactly the same count on both.

Astra costs 2.5 times as much on a plain request, about three times with a warm cache and nearly five times past 272K. The cached row leaves out the one-time cache write. On Opus 5.5 the output count includes its thinking, which Anthropic bills as output.

Anthropic's table: Opus 5.5 ahead on four of six rows

These scores come from the benchmark table in Anthropic's Opus 5.5 announcement, so they are one vendor's comparison. Anthropic ran Opus 5.5 at max effort except on Terminal-Bench 4.0 (xhigh), and notes that Astra's Terminal-Bench 4.0 result was "at high effort, as reported by OpenAI", so that row compares different settings. Google's own table for Gemini 4 Argon also includes Opus 5.5; Gemini 4 Argon vs Claude Opus 5.5 covers where Google puts each model ahead, and Gemini 4 Argon vs GPT-6 Astra does the same for Astra.

FrontierCode is close to level. The clear Opus 5.5 leads are Terminal-Bench 4.0, GDPval-AA and HLE with tools; Astra's clear lead is Terminal-Bench-Science, where OpenAI's later GPT-6.1 Sol post and Google's Argon card both give Astra 68.1% rather than the 64.6% above. The table has no Astra scores for CursorBench, OSWorld or Chartography. OpenAI describes Astra as "our most capable model for the most demanding work".

Opus 5.5 always thinks; effort is its control

On Opus 5.5, "Adaptive thinking is always on and can't be turned off", so effort is the setting that matters: low, medium, high, xhigh or max, with medium as the default on the API and in Claude Code. Anthropic calls effort "a behavioral signal, not a strict token budget", and the thinking tokens count as output on the bill and toward max_tokens. Astra's model page lists low, medium, high, xhigh and max reasoning effort, and OpenAI's latest-model guide says Astra does not support none. Effort names are each vendor's own and do not map one to one, so compare the two at the settings you would actually run.

In the apps: Claude Pro or Max for Opus, ChatGPT Plus for Astra

• Claude: Opus is on Pro ($20 a month, or $17 a month billed annually), Max ($100 a month, five times Pro's usage every five hours and every week), Ultra ($200 a month, ten times Pro's weekly usage and no five-hour limit once the account is verified), Team and Enterprise, but not Free. Claude Code uses Opus 5.5 by default on those plans. Outside a verified Ultra account, usage resets on a rolling five-hour window with weekly limits on top, and Anthropic raised five-hour limits on Pro, Max and Team when Opus 5.5 launched.
• ChatGPT: Astra is in Plus ($20 a month, monthly only) and not in Go ($8). In Codex, OpenAI estimates 5 to 45 local Astra messages per five hours on Plus, against 15 to 160 for GPT-6.1 Sol, so Astra uses up a Plus allowance fastest. Pro ($100, $200 or $500 a month) currently has no five-hour Codex limit.

Neither entry plan includes API use: Claude Pro "does not include API usage through the Claude Console", and OpenAI bills API tokens separately from subscription usage. Claude Max adds $100 of monthly API credits and Ultra $200.

If Astra's price is the obstacle, OpenAI positions GPT-6.1 Sol ($2 and $10) as "near-Astra performance at a lower cost"; see GPT-6.1 Sol vs GPT-6 Sol. On the Claude side, Sonnet 5.5 costs the same $2 and $10; see Claude Sonnet 5.5 vs Opus 5.5. The Claude Code and Codex profiles cover the coding agents these models run in.