Comparison · Chat & code
Claude Opus 5.5 vs GPT-6 Sol
Claude Opus 5.5 vs GPT-6 Sol for code, agents and long documents. Rates, cached input, Claude Code support and when the pricier Opus is worth it.
What each one accepts
| Claude Opus 5.5 | GPT-6 Sol | |
|---|---|---|
| Vendor | Anthropic | OpenAI |
| Type | Chat & code | Chat & code |
| Released | 2026-09 | 2026-09 |
| Context window | 1,000,000 tokens | 1,050,000 tokens |
| Max output | 128,000 tokens | 128,000 tokens |
| Endpoints | /v1/chat/completions · /v1/messages | /v1/chat/completions |
Token prices
| Claude Opus 5.5 | GPT-6 Sol | |
|---|---|---|
| Input / 1M tokens | $3.78 | $2.16 |
| Output / 1M tokens | $18.90 | $10.80 |
| Input from cache / 1M | $0.189 | $0.216 |
| 1,000 replies, 1,500 in / 400 out | $13.23 | $7.56 |
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.
GPT-6 Sol is the cheaper of the two per token, so it makes a sensible default for code, agents and document work when every request is on your budget. Claude Opus 5.5 is worth its higher rate in long Claude Code sessions and wide repository changes, where one avoided error saves more than the extra tokens cost. Limits are nearly identical, so price, tooling and your own trials settle it.
When to pick Claude Opus 5.5
- An agent works in Claude Code for hours. The setup is in Claude Code with a custom base URL.
- A refactor touches hundreds of files and has to stay consistent.
- Technical texts must follow a house style guide closely.
- Your code is written against the Anthropic SDK and you want to keep it.
When to pick GPT-6 Sol
- You need a default model for internal tools, code and tool-calling agents, and you pay for every retry.
- Long contracts or reports come back in many follow-up requests with the same prefix.
- Your app runs on the OpenAI SDK, for example an upgrade from GPT-5.6 Sol where only
modelchanges. - Volume is high and the rate gap would add up quickly.
Differences you will notice
- Rates. Claude Opus 5.5 is billed at $3.78 / $18.90 per 1M tokens and GPT-6 Sol at $2.16 / $10.80 per 1M tokens. Opus costs more on input and output, and the cost of 1,000 replies in the table above shows by how much.
- Repeated prefixes. Sol's cached input rate is a tenth of its regular input. Check the cached input row for both models if you resend a long system prompt.
- Where they run. Opus works on
/v1/chat/completionsand the Anthropic-style/v1/messages, so it fits Claude Code. Sol works on the OpenAI-compatible endpoint only, which covers Cursor, Cline and n8n but not Claude Code. - Reasoning. Both think before answering, and thinking is billed as output. On Opus 5.5 it cannot be disabled, so a short reply to a hard prompt may cost more than its length suggests.
- Family role. Anthropic puts Opus 5.5 at Fable 5.1 level on most work. OpenAI places Sol under the flagship Astra, for hard tasks you iterate on many times.
How to decide
- Default to Sol and send to Opus only the task types where Sol fails on your examples.
- If the work happens in Claude Code, Opus is the one that connects.
- Run a dozen tasks from your own repository through both before you commit.
Rates for each family are in Claude Opus 5.5 API pricing and GPT-6 API pricing.
Questions
Which window is larger?
On paper Sol, with 1,050,000 tokens against 1,000,000 for Opus. In practice that is no difference. Both write up to 128K tokens per reply.
Is GPT-6.1 Sol available?
OpenAI released GPT-6.1 Sol on September 29 as an update at the same base price. The catalog currently serves gpt-6-sol, and GET /v1/models?category=chat shows the live list.
Can one app call both models?
Yes. Both take the OpenAI request format on /v1/chat/completions, so one client and one key can route each task to whichever model fits.