Claude Sonnet 5 vs GPT-5.2 Pro
Claude Sonnet 5 (Anthropic, released 2026-06-30) and GPT-5.2 Pro (OpenAI, released 2025-12-10) both handle text, image, and file input with text-only output, and both support tool calling and structured outputs. The gap that matters is price and context: Sonnet 5 runs a 1M-token context window against GPT-5.2 Pro's 400K, and its provider pricing is a fraction of GPT-5.2 Pro's per-token cost. Both are available on OpenKey with one API key and a flat 3% fee on provider list price.
Spec vs spec
| Spec | Claude Sonnet 5 | GPT-5.2 Pro |
|---|---|---|
| Context window | 1M | 400K |
| Max output | 128K | 128K |
| Input modalities | text, image, file | image, text, file |
| Output modalities | text | text |
| Released | Jun 30, 2026 | Dec 10, 2025 |
| Reasoning | optional | always on |
Pricing
Per 1M tokens. Provider price plus the flat 3% fee — the sum is what you pay.
anthropic/claude-sonnet-5
Input · 1M tokens
$2.00 + 3%$2.06
Output · 1M tokens
$10.00 + 3%$10.30
Cache read · 1M tokens
$0.200 + 3%$0.206
Cache write · 1M tokens
$2.50 + 3%$2.58
FEE — FLAT, EVERY MODEL3%
openai/gpt-5.2-pro
Input · 1M tokens
$21.00 + 3%$21.63
Output · 1M tokens
$168.00 + 3%$173.04
FEE — FLAT, EVERY MODEL3%
One workload, priced on both
10M input + 2M output tokens at each model's price, flat 3% fee included.
anthropic/claude-sonnet-5Cheaper
$41.20
$40.00 provider + 3%
openai/gpt-5.2-pro
$562.38
$546.00 provider + 3%
Pricing math
Provider list price: Claude Sonnet 5 is $2.00/M input and $10.00/M output. GPT-5.2 Pro is $21.00/M input and $168.00/M output — roughly 10x the input cost (input_price_ratio: 0.1) and far more on output.
On OpenKey, add the flat 3% fee: Sonnet 5 becomes $2.06/M input ($2.00 x 1.03) and $10.30/M output ($10.00 x 1.03). GPT-5.2 Pro becomes $21.63/M input ($21.00 x 1.03) and $173.04/M output ($168.00 x 1.03).
Run the numbers on a real workload — 10M input tokens plus 2M output tokens — and Sonnet 5 costs $40.00 total while GPT-5.2 Pro costs $546.00. That's not a rounding difference; it's over 13x. Sonnet 5 also supports cache reads at $0.20/M and cache writes at $2.50/M (provider pricing), which GPT-5.2 Pro doesn't list at all — another lever for cutting cost on repeated-context workloads.
Context and long-document work
Sonnet 5 handles up to 1,000,000 tokens of context; GPT-5.2 Pro caps at 400,000 — a 2.5x gap (context_ratio: 2.5). If you're feeding in large codebases, long transcripts, or multi-document research bundles, Sonnet 5 has more headroom before you need chunking or retrieval tricks. Both models cap max completion output at 128,000 tokens, so output length isn't a differentiator here — only what you can feed in.
Reasoning and coding signals
Sonnet 5 supports adaptive reasoning with five effort levels (low, medium, high, xhigh, max) and defaults to medium — reasoning is optional, so you can turn it off for latency-sensitive calls. GPT-5.2 Pro's reasoning is mandatory, with three effort levels (medium, high, xhigh) and no way to disable it.
On the artificial_analysis benchmarks, Sonnet 5 posts a 71.5 coding index, a 53.4 intelligence index, and a 46.7 agentic index. No artificial_analysis or design_arena scores are available for GPT-5.2 Pro in this dataset, so a direct benchmark comparison isn't possible — go by the pricing and context deltas instead.
When to pick each
Pick Sonnet 5 by default: it's cheaper on every pricing dimension, has more context, and gives you control over reasoning effort (including turning it off). Pick GPT-5.2 Pro only if you've already validated it beats Sonnet 5 on your specific task and the 13x cost premium at the 10M/2M workload size is acceptable for your budget — mandatory high-effort reasoning also means you can't dial it back for cheap, fast calls.
Which model for which job
| Use case | Pick | Why |
|---|---|---|
| High-volume API workloads | Claude Sonnet 5 | $40.00 vs $546.00 on a 10M-input/2M-output workload |
| Long-document or large-codebase analysis | Claude Sonnet 5 | 1M-token context vs 400K, a 2.5x gap |
| Latency-sensitive, low-reasoning calls | Claude Sonnet 5 | Reasoning is optional (default effort: medium) vs GPT-5.2 Pro's mandatory reasoning |
| Coding tasks where index matters | Claude Sonnet 5 | 71.5 coding index on artificial_analysis (no comparable score exists for GPT-5.2 Pro) |
| Repeated-context prompts (caching) | Claude Sonnet 5 | Provider cache pricing at $0.20/M read and $2.50/M write; GPT-5.2 Pro lists none |
Questions
- How much cheaper is Claude Sonnet 5 than GPT-5.2 Pro?
- On provider list pricing, Sonnet 5 input tokens cost $2.00/M versus GPT-5.2 Pro's $21.00/M — a 10x ratio. On a 10M-input/2M-output workload, total cost is $40.00 for Sonnet 5 versus $546.00 for GPT-5.2 Pro, over 13x more.
- Which model has a bigger context window?
- Claude Sonnet 5 supports 1,000,000 tokens of context, GPT-5.2 Pro supports 400,000 — a 2.5x ratio. Both cap max completion output at 128,000 tokens, so the gap only affects how much you can feed in, not generate.
- Can I turn off reasoning to save cost or latency?
- Yes on Sonnet 5 — reasoning is optional with five effort levels (low, medium, high, xhigh, max) defaulting to medium. On GPT-5.2 Pro reasoning is mandatory with only medium, high, and xhigh available — you can't disable it.
- Do both models run on OpenKey with the same billing?
- Yes — both are available through OpenKey with one API key, and OpenKey adds a flat 3% fee to provider list price. For Sonnet 5 that puts input at $2.06/M and output at $10.30/M; for GPT-5.2 Pro it's $21.63/M input and $173.04/M output.