Claude Sonnet 5 vs GPT-5.6 Sol: API Cost Compared
The verdict, in numbers: On our reference 200-step agent workload, Claude Sonnet 5 bills $2.69 against $5.38 for GPT-5.6 Sol — 2.0x apart. List rates alone would not have told you that.
This page compares list rates and workload cost only. It does not tell you which model is better — capability belongs to your own evaluation. What it does give you is the half of the decision that can be verified: what each provider will actually charge, read from their own documentation on September 18, 2026.
Rate cards side by side
| Item | Claude Sonnet 5 | GPT-5.6 Sol |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Input / 1M | $2.00 | $4.00 |
| Output / 1M | $10.00 | $20.00 |
| Cache read / 1M | $0.20 | $0.40 |
| Context window | 1M | 1.05M |
Sources: Anthropic pricing ↗ and OpenAI pricing ↗, both checked September 18, 2026.
The same 200-step agent task, priced twice
One coding-agent task: 200 steps, a stable 40,000-token prefix written to cache on step 1 and re-read on the remaining 199, 500 output tokens per step. Cache-write billing follows each provider’s own rules (cache writes bill at 1.25x the input rate; cache writes bill at 1.25x the uncached input rate).
| Component | Claude Sonnet 5 | GPT-5.6 Sol |
|---|---|---|
| Cache write (once) | $0.10 | $0.20 |
| Cache reads (199 × 40K) | $1.59 | $3.18 |
| Output (200 × 500) | $1.00 | $2.00 |
| Total per task | $2.69 | $5.38 |
A heavy month on each
50M fresh input, 150M cached input, 10M output tokens in a month:
| Component | Claude Sonnet 5 | GPT-5.6 Sol |
|---|---|---|
| Fresh input (50M) | $100.00 | $200.00 |
| Cached input (150M) | $30.00 | $60.00 |
| Output (10M) | $100.00 | $200.00 |
| Monthly total | $230.00 | $460.00 |
What this comparison does and does not say
Claude Sonnet 5: Fast agentic coding with a 1M context window; the default choice for most production work.
GPT-5.6 Sol: Frontier model for complex professional work, coding, research, and tool use.
Cost is the verifiable half of the decision; quality is the half only your workload can answer. Run both candidates on a representative evaluation set and measure cost per accepted task — the cost planning guide walks through that method, and the calculator lets you re-price this exact comparison with your own token mix.
Frequently asked questions
Is Claude Sonnet 5 cheaper than GPT-5.6 Sol?
On list rates, Claude Sonnet 5 costs $2.00/$10.00 per 1M input/output tokens versus $4.00/$20.00 for GPT-5.6 Sol. On a 200-step agent workload (40K cached prefix, 500 output tokens per step), Claude Sonnet 5 totals $2.69 versus $5.38 for GPT-5.6 Sol. Prices verified September 18, 2026.
Claude Sonnet 5 vs GPT-5.6 Sol: which has the longer context window?
Claude Sonnet 5 offers 1M tokens; GPT-5.6 Sol offers 1.05M tokens, per provider documentation checked September 18, 2026.
Where do these Claude Sonnet 5 and GPT-5.6 Sol prices come from?
Both rate cards were read from the providers' own pricing pages on September 18, 2026: https://platform.claude.com/docs/en/about-claude/pricing and https://developers.openai.com/api/docs/models/gpt-5.6-sol.