Claude Sonnet 5 vs GPT-5.6 Terra: which is cheaper for your workload
These two sit in the same price bracket and are the default mid-tier choice for most production agents. The interesting part is not the headline input rate — it is how differently they price output, because output is where agent workloads spend most of their money.
Claude Sonnet 5 vs GPT-5.6 Terra: the numbers side by side
| Claude Sonnet 5 | GPT-5.6 Terra | |
|---|---|---|
| Gateway rate — input | $1 | $1 |
| Gateway rate — output | $5 | $6 |
| Official list — input | $2 | $2 |
| Official list — output | $10 | $12 |
| Blended at 1/3 output | $2.33 | $2.67 |
| Output : input price ratio | 5.0× | 6.0× |
USD per 1M tokens. Gateway rates checked 2026-09-16; official list prices as published by each vendor. Gateway rates move with upstream promotions — re-check before committing a budget.
What each costs per month
| Monthly tokens | Claude Sonnet 5 | GPT-5.6 Terra | Cheaper |
|---|---|---|---|
| 10M | $23.33 | $26.67 | Claude Sonnet 5 — 13% less |
| 100M | $233 | $267 | Claude Sonnet 5 — 13% less |
| 1000M | $2,333 | $2,667 | Claude Sonnet 5 — 13% less |
Assumes 1/3 of tokens are output and 2/3 input — roughly a chat or coding-agent mix. At a 100M tokens/month workload the gap is $33.33 a month, or $400 a year. Change the split in the calculator — output-heavy workloads widen the gap.
How much tokens each budget buys
| Budget | Claude Sonnet 5 | GPT-5.6 Terra | Extra tokens |
|---|---|---|---|
| $100 | 43M | 37M | Claude Sonnet 5 — 5M more |
| $1,000 | 429M | 375M | Claude Sonnet 5 — 54M more |
Tokens purchasable at the blended rate above. Output tokens cost more than input, so reading these figures as "all input" would overstate them.
Which one to pick
Both models land within a few cents of each other on blended cost, so the decision should not be made on price alone. Two questions settle it faster:
- Is your workload output-heavy? Long generations — multi-file code edits, long reports, chain-of-thought reasoning returned to you — amplify whichever model prices output higher. Check the output:input ratio row in the table above; the model with the lower ratio is the safer default for those workloads.
- Are you standardising on one vendor's tooling? If your team already runs Claude Code or the Anthropic SDK, the integration cost of switching is zero and the price difference is unlikely to justify moving. If you are greenfield, run your real token split through the calculator before choosing.
Do not pick on published list prices. Both models are discounted against list here, and the discounts are not identical, so the official-price ranking and the gateway-price ranking can differ. The table above shows both.
Switching between them
Both models are called through the same endpoint, so this is a model-ID change, not a migration. Setup references: OpenAI & Anthropic SDK · Claude Code · Cursor · reducing API cost.
Related comparisons: Opus 5 vs GPT-5.6 Sol · Claude vs Gemini · Three ways to pay for Claude
FAQ
Is Claude Sonnet 5 or GPT-5.6 Terra cheaper?
At current gateway rates Claude Sonnet 5 is cheaper for a mixed workload — $2.33 versus $2.67 per 1M tokens blended at one third output. The answer depends on your input/output split: output tokens are priced several times higher than input on both models (5x and 6x respectively), so an output-heavy workload widens the gap.
How much does Claude Sonnet 5 cost per month?
At $2.33 per 1M blended tokens: about $23.33 for 10M tokens a month, $233 for 100M, and $2,333 for 1B. That is pure token spend — there is no subscription on either model.
How much does GPT-5.6 Terra cost per month?
At $2.67 per 1M blended tokens: about $26.67 for 10M tokens a month, $267 for 100M, and $2,667 for 1B.
Can I switch between them without rewriting my code?
Both are reached through the same gateway endpoint, so switching is a model-ID change in the request rather than a new integration. See the SDK guide for the one-line change, or the Claude Code setup if you are switching inside a coding agent.
Can I use both models in the same application?
Yes, and it is often the right answer. Route mechanical work to the cheaper of the two and keep the other for tasks where the difference matters to you. Both are reached through the same endpoint with the same key, so a fallback is a model-ID change rather than a second vendor relationship.