Claude Sonnet 5 vs GPT-6 Sol

What each one accepts

Token prices

Charged from a prepaid USD balance, no taxes added. One key runs both, through /v1/chat/completions in the OpenAI format. A failed generation is $0.

Both sit in the middle of their families, and GPT-6 Sol has the lower rate per token. I pick Sonnet 5 for work inside Claude Code or on the Anthropic SDK, where an agent should plan and use tools by itself. Sol fits apps already built on the OpenAI SDK and workloads that resend the same long prefix, thanks to its low cached input rate.

When to pick Claude Sonnet 5

• You code daily in Claude Code, Cursor or Cline and need tests, fixes and new features.
• An agent chains many tool and API calls. Anthropic describes Sonnet 5 as its most agentic Sonnet to date.
• You are chasing a bug through legacy code that nobody wants to touch.
• You draft reports, emails and docs in bulk.

When to pick GPT-6 Sol

• Your app speaks the OpenAI format and you would rather not change the request shape.
• Users ask follow-up questions about the same contract or report, so the long text repeats.
• Traffic is large enough that a lower rate is real money every month.
• You are moving code off GPT-5.6 Sol and only want to change the model field.

Differences you will notice

• Rates. Claude Sonnet 5 is billed at $3.24 / $16.20 per 1M tokens and GPT-6 Sol at $2.16 / $10.80 per 1M tokens. Sonnet is higher on input and output, and the 1,000-reply row in the table above puts a number on it.
• Cache. Sol reads cached input at a small fraction of its input rate. See the cached input row in the table for both models; with a long system prompt or a document read many times, that row matters most.
• Endpoints. Sonnet answers on /v1/chat/completions and /v1/messages, so Claude Code can use it. Sol is reachable only through the OpenAI-compatible endpoint.
• Request fields. Sonnet 5 rejects non-default temperature, top_p and top_k with a 400 and thinks adaptively by default. Clean those fields out of older code.
• Token counting. Anthropic says Sonnet 5 counts the same text as about 30% more tokens than Sonnet 4.6, so compare full requests from usage.
• Background. Sonnet 5 shipped in June 2026, placed by Anthropic near Opus 4.8. Sol arrived in September 2026 as OpenAI's model for hard tasks under the flagship Astra. Limits match closely: 1,000,000 tokens for Sonnet, 1,050,000 for Sol, 128K output for both.

How to decide

• You work in the terminal with Claude Code - Sonnet, because Claude Code here connects to Claude models only. My setup is in Claude Code cost: pay per token.
• You build your own app - run 20 to 50 real examples through both. Code for switching models is in One LLM API in Python and Node.
• Budget comes first - Sol.

Questions

Is one of them clearly the better coder?

I have not run this pair on my own code, so I will not say. Anthropic puts Sonnet 5 near Opus 4.8, and OpenAI aims Sol at hard tasks with many iterations. A short trial on your repository is the honest tiebreaker.

Should I look at Sonnet 5.5 instead?

It is worth a test. Claude Sonnet 5.5 came out on September 28 and costs $1.89 / $9.45 per 1M tokens. The live list of chat models is at GET /v1/models?category=chat.

What happens to my balance if a request fails?

A failed request costs nothing: the held amount returns to your balance in full. Both models draw from the same prepaid balance with no subscription.