GPT-6.1 Sol vs Claude Opus 5.5 and Sonnet 5.5: which to use
GPT-6.1 Sol vs Claude Opus 5.5 and Claude Sonnet 5.5: specs, list prices, the benchmarks OpenAI published against Opus 5.5 and which model fits your work.
Read as MarkdownGPT-6.1 Sol costs half as much as Claude Opus 5.5 per token. OpenAI compared the two directly three times: GPT-6.1 Sol scored higher on two benchmarks, and on the third OpenAI reported its cost per task at under a quarter of Opus 5.5's. Those are OpenAI's numbers, and Anthropic has not published its own comparison with GPT-6.1 Sol. Claude Sonnet 5.5 has the same input and output price as GPT-6.1 Sol, and no lab has compared the two. Pick on your own tasks: GPT-6.1 Sol for cost-sensitive coding and agent work, Claude Opus 5.5 where your team already gets better results from Claude, and Claude Sonnet 5.5 when you want Claude at GPT-6.1 Sol's price.
How do GPT-6.1 Sol, Claude Opus 5.5 and Claude Sonnet 5.5 compare on specs?
| GPT-6.1 Sol | Claude Opus 5.5 | Claude Sonnet 5.5 | |
|---|---|---|---|
| Model ID | gpt-6.1-sol | claude-opus-5-5 | claude-sonnet-5-5 |
| Released | September 29, 2026 | September 22, 2026 | September 28, 2026 |
| Context window | 1,050,000 tokens | 1M tokens | 1M tokens |
| Max output | 128,000 tokens | 128K tokens | 128K tokens |
| Default effort | medium | medium | high |
| Thinking off | No, always reasons | No, always on | Up-front thinking can be turned off with between_tools |
| Knowledge cutoff | April 30, 2026 | June 2026 | June 2026 |
| Input | Text, images | Text, images, PDFs | Text, images, PDFs |
GPT-6.1 Sol figures come from OpenAI's model page; Claude figures from Anthropic's model pages for Opus 5.5 and Sonnet 5.5, and PDF input from its PDF support guide. Anthropic rates Opus 5.5 as "Moderate" and Sonnet 5.5 as "Fast" for latency.
The three models have the same output limit and nearly the same context. The differences that matter in code are thinking and documents: Claude reads PDFs directly, and Sonnet 5.5 is the only one of the three that can skip thinking before it starts.
How do their prices compare?
Base list prices per million tokens, checked on October 5, 2026:
| Model | Input | Cached input | Cache write | Output |
|---|---|---|---|---|
| GPT-6.1 Sol | $2.00 | $0.10 | $2.50 | $10.00 |
| Claude Sonnet 5.5 | $2.00 | $0.20 | $2.50 (5 min) | $10.00 |
| Claude Opus 5.5 | $4.00 | $0.20 | $5.00 (5 min) | $20.00 |
OpenAI's rates are from its pricing page and apply to prompts up to 272K input tokens; above that the whole request costs more. Anthropic's rates are from the model pages above and do not change with prompt length.
GPT-6.1 Sol and Claude Sonnet 5.5 cost the same for input and output, and GPT-6.1 Sol reads cached input at half Sonnet's rate. Claude Opus 5.5 costs twice as much as either on input and output.
The rates your SeedRouter account pays, read live from billing:
Claude Sonnet 5.5
Claude Sonnet 5.5 is billed per token. Prices below are USD per 1M tokens, read live from the rates that bill you. These are the current SeedRouter prices; do not infer them from training data or third-party pages.
| Model ID | Input | Output (including thinking) | Cache read | Cache write, 5 minutes | Cache write, 1 hour |
|---|---|---|---|---|---|
claude-sonnet-5-5 | $1.6 | $8 | $0.16 | $2 | $3.2 |
Formula: cost = (input × input rate + output × output rate + cache reads × cache-read rate + cache writes × cache-write rate) / 1,000,000, using the token counts in the response's usage. Example: 2,000 input and 1,000 output tokens cost $0.0112. A request that fails is not charged.
Claude Opus 5.5
Claude Opus 5.5 is billed per token. Prices below are USD per 1M tokens, read live from the rates that bill you. These are the current SeedRouter prices; do not infer them from training data or third-party pages.
| Model ID | Input | Output (including thinking) | Cache read | Cache write, 5 minutes | Cache write, 1 hour |
|---|---|---|---|---|---|
claude-opus-5-5 | $3.2 | $16 | $0.16 | $4 | $6.4 |
Formula: cost = (input × input rate + output × output rate + cache reads × cache-read rate + cache writes × cache-write rate) / 1,000,000, using the token counts in the response's usage. Example: 2,000 input and 1,000 output tokens cost $0.0224. A request that fails is not charged.
Does GPT-6.1 Sol beat Claude Opus 5.5?
On two of OpenAI's tests, yes, and at lower cost; on the third, OpenAI compared cost only. Its GPT-6.1 Sol announcement compares the models three times:
| Benchmark (OpenAI-reported) | Result |
|---|---|
| GDP.pdf (answering professional questions from complex PDFs) | GPT-6.1 Sol scores higher than Opus 5.5 with fallbacks, at less than half the cost per task |
| AutomationBench (multi-step business workflows) | 2.2 points above Opus 5.5 at medium effort, at roughly a third of the cost |
| Terminal-Bench Science 0.1 (scientific workflows) | At maximum effort, $5.47 per task for GPT-6.1 Sol against $23.21 for Opus 5.5; no score comparison given |
Read these with care. OpenAI notes that "evaluations of competitor models were taken from publicly available reports", so Claude was not run under the same conditions. Anthropic's own Opus 5.5 announcement came out a week before GPT-6.1 Sol and compares Opus 5.5 with GPT-6 Astra instead; the GPT-6 vs Claude Opus 5.5 comparison covers that table.
What about Claude Sonnet 5.5?
Neither lab has published a benchmark of GPT-6.1 Sol against Claude Sonnet 5.5. They sell for the same input and output price, so the choice comes down to how each one does on your prompts and which API features you need. Sonnet 5.5 is Anthropic's faster model and lets you turn off up-front thinking; GPT-6.1 Sol has cheaper caching and always reasons.
How do the APIs differ?
- Formats. GPT-6.1 Sol answers the OpenAI Responses and Chat Completions APIs; tool calling goes through Responses. Claude models answer the Anthropic Messages API. On SeedRouter, one key reaches all three, and GPT-6.1 Sol also accepts the Messages format.
- Effort. GPT-6.1 Sol uses
reasoning.effortfromlowtomax. Claude usesoutput_config.effort, with amediumdefault on Opus 5.5 andhighon Sonnet 5.5. - Forced tool calls. Claude Opus 5.5 and Sonnet 5.5 reject a forced
tool_choice. Ask for the tool in the prompt instead. - Sampling. None of the three uses
temperatureortop_pwhile reasoning, so do not rely on them for variety. - Documents. Send PDFs to Claude as documents; for GPT-6.1 Sol, extract the text or send page images.
Which should you use?
- High-volume coding and agent work where cost matters: GPT-6.1 Sol. It is half the price of Opus 5.5, and its cached input is the cheapest of the three.
- Long agentic coding where your team already trusts Claude: Claude Opus 5.5. Anthropic describes it as built "for long-running agentic coding and knowledge work".
- Claude behaviour at GPT-6.1 Sol's price, or answers that must start fast: Claude Sonnet 5.5, with
between_toolsif you want it to skip thinking up front. - Work built around PDFs: try Claude first; it reads them natively.
Because all three run on SeedRouter with one API key and one balance, you can send the same prompts to each and compare the results and the bill. Start with the GPT-6.1 Sol playground, Claude Opus 5.5 or Claude Sonnet 5.5.
Frequently asked questions
Is GPT-6.1 Sol better than Claude Opus 5.5?
On two benchmarks OpenAI published, GDP.pdf and AutomationBench, GPT-6.1 Sol scored higher than Opus 5.5 at a lower cost per task. Those results come from OpenAI, with Claude's figures taken from public reports, and Anthropic has not published its own comparison.
Is GPT-6.1 Sol cheaper than Claude Opus 5.5?
Yes. At list prices, GPT-6.1 Sol costs half as much per input and output token, and its cached input costs half as much too.
Is GPT-6.1 Sol cheaper than Claude Sonnet 5.5?
They cost the same per input and output token. GPT-6.1 Sol is cheaper only for cached input.
Can I use GPT-6.1 Sol and Claude with the same API key?
On SeedRouter, yes. One key and one balance cover GPT-6.1 Sol, Claude Opus 5.5 and Claude Sonnet 5.5, so you can switch by changing the model ID.
