Claude Sonnet 5 vs GPT-6 Sol

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.

Claude Sonnet 5 and GPT-6 Sol are two mid-priced models with a small gap between them: Sonnet costs about 25% more per token. Pick Sonnet 5 when you work in Claude Code or on the Anthropic SDK and want an agent that plans and uses tools on its own. Pick GPT-6 Sol when your app is built on the OpenAI SDK or sends the same long prefix over and over, because Sol has a separate, low cached-input rate.

Key differences

• Price. Claude Sonnet 5 costs $3.24 / $16.20 per 1M tokens, GPT-6 Sol costs $2.16 / $10.80 per 1M tokens. Sonnet is about 1.25 times more on both input and output.
• Caching. Sol's cached-input rate on Jantaris is ten times lower than its input rate. Claude has no separate line, so a repeated prefix is billed as input. With a long system prompt or a document read many times, the gap grows well past 25%.
• Endpoints. Sonnet works on /v1/chat/completions and /v1/messages, so it also runs in Claude Code. Sol works only on the OpenAI-compatible endpoint.
• Parameters. Sonnet 5 rejects non-default temperature, top_p and top_k with a 400 error, and adaptive thinking is on by default. Strip those fields when porting older code.
• Tokenizer. Anthropic says Sonnet 5 counts the same text as about 30% more tokens than Sonnet 4.6. Compare the cost of whole requests from the usage field, not just the rate.
• Release and positioning. Sonnet 5 came out in June 2026, and Anthropic places it close to Opus 4.8 at a lower price. Sol is from September 2026, OpenAI's model for hard tasks below the flagship Astra.
• Limits. Nearly identical: 1,000,000 tokens of context (Sonnet) and 1,050,000 (Sol), up to 128K output tokens in both.

When to pick Claude Sonnet 5

• Day-to-day coding in Claude Code, Cursor or Cline: tests, fixes, new features.
• Agents that call tools and APIs over many steps. Anthropic calls Sonnet 5 its most agentic Sonnet so far.
• Debugging messy legacy code down to the root cause.
• Reports, emails and documentation at volume.

When to pick GPT-6 Sol

• An app on the OpenAI SDK where you do not want to change the request format.
• Contracts and reports where the same long text comes back in follow-up questions.
• High traffic, where a 25% rate difference is real money.
• Code written for GPT-5.6 Sol that you move to the new generation by changing the model field.

If you code in the terminal, I would stay with Sonnet, because Claude Code on Jantaris works only with Claude models (setup: Claude Code cost: pay per token). For your own app, run 20 to 50 real examples through both; the code for that is in One LLM API in Python and Node.

FAQ

Claude Sonnet 5 or GPT-6 Sol: which is cheaper?

GPT-6 Sol, by about 20% on every token (Sonnet is 1.25 times the price). With a repeated prefix Sol's lead grows thanks to its cached-input rate. Currently: $3.24 / $16.20 per 1M tokens and $2.16 / $10.80 per 1M tokens.

Which one codes better?

I have not tested this pair on my own code, so I will not name a winner. Anthropic places Sonnet 5 close to Opus 4.8, and OpenAI positions Sol for hard tasks with many iterations. A test on your own repository settles it.

Why does Sonnet 5 return a 400 error for temperature?

Anthropic changed this in Sonnet 5: non-default temperature, top_p and top_k values are rejected. Remove those parameters from the request.

Is Sonnet 5.5 available on Jantaris?

Anthropic released Sonnet 5.5 on September 28 at the same price as Sonnet 5. The Jantaris catalog serves claude-sonnet-5 for now. The live list is at GET /v1/models?category=chat.

Can I use both from one account?

Yes. One key and one prepaid USD balance cover both models, with no subscription. Failed requests are not charged.