Claude Opus 5.5 vs GPT-6 Astra

Specs side by side

Price per token

Prices exclude taxes and are charged from your prepaid USD balance. Both models work through the same key, in the OpenAI-compatible /v1/chat/completions endpoint. Failed generations cost nothing.

Use Claude Opus 5.5 for Claude Code and long repository changes: on regular chat it costs half as much as GPT-6 Astra, and of the two only Opus works through /v1/messages. Use GPT-6 Astra for the hardest tasks in OpenAI-compatible tools, especially when you send the same long prefix again and again: its cached input is cheap enough that with that kind of traffic it can come out cheaper than Opus. Both have about 1M tokens of context and up to 128K output tokens, so price, caching and tooling decide.

Key differences

• Price. Claude Opus 5.5 costs $5.40 / $27.00 per 1M tokens, GPT-6 Astra costs $10.80 / $54.00 per 1M tokens. Astra is 2 times more on both input and output, so the 1,000-reply row in the table above is 2 times higher too.
• Caching. Astra has a separate cached-input rate on Jantaris, ten times lower than its own input and 5 times lower than Opus's regular input. Claude has no such line, so a repeated prefix is billed as input. With a long, stable prompt and short replies, Opus's lead shrinks and can even flip.
• Context. Astra: 1,050,000 tokens, Opus: 1,000,000. Both return up to 128K output tokens. No practical difference.
• Claude Code. Opus works on /v1/chat/completions and on /v1/messages, so it runs in Claude Code. Astra runs on the OpenAI-compatible endpoint: Cursor, Cline or n8n yes, Claude Code no.
• Open weights. Neither. Both are closed models available only through an API.
• Polish and other languages. I have not measured this pair on Polish text. At a 2x price gap, it is worth running a dozen of your own non-English texts through both and comparing the output and the usage field.
• Parameters and thinking. According to the OpenAI API changelog, Astra does not accept custom temperature or top_p values. Thinking cannot be switched off on Opus 5.5. On both, thinking tokens are billed as output.
• Position. OpenAI calls Astra its best model across the board. Anthropic puts Opus 5.5 at Fable 5.1 level on most work at a lower price.

When to pick Claude Opus 5.5

• Agent sessions in Claude Code that run for hours.
• Refactors and migrations that touch hundreds of files.
• Code already written for the Anthropic SDK: you change only the base URL and key.
• Requests with a short prompt and a long answer, where the output rate matters most.

When to pick GPT-6 Astra

• Research that pulls dozens of sources into one report.
• Analysis of the same large document set across many requests in a row, where cheap caching kicks in.
• Code built on the OpenAI SDK and tools such as Cursor or n8n.
• A final check on answers from cheaper models.

Both models sit behind one key and one balance that never expires, with no subscription. I give each of them its own API key with a monthly limit: once it is reached the API returns 403, so a looping agent cannot drain the balance. The cheaper pairing is in Claude Opus 5.5 vs GPT-6 Sol, and the whole GPT-6 family in GPT-6 API pricing.

FAQ

Claude Opus 5.5 or GPT-6 Astra for coding?

For work in Claude Code, Opus 5.5, because of the two only Opus works through /v1/messages. In Cursor or your own agent on the OpenAI SDK you can use either: run a dozen tasks from your repository through both and compare the changes and the cost. I have not tested this pair on my own code, so I will not name a winner.

How much more expensive is GPT-6 Astra than Opus 5.5?

2 times on every input and output token. The exception is cached input: Astra bills it for less than Opus bills regular input. Current rates: $5.40 / $27.00 per 1M tokens and $10.80 / $54.00 per 1M tokens.

Can I use GPT-6 Astra in Claude Code?

Not through Jantaris. Claude Code speaks the Anthropic Messages format, and that endpoint serves Claude models only. Use Astra in OpenAI-compatible tools such as Cursor, Cline or n8n.