Claude Sonnet 5 vs Grok 4.3

Pricing math on a real workload

For a 10M input / 2M output token job, Sonnet 5 costs $40.00 and Grok 4.3 costs $17.50 at provider list prices — a 2.3x gap. On OpenKey, both carry the flat 3% fee: Sonnet 5's input goes from $2.00 to $2.06/M and completion from $10.00 to $10.30/M; Grok 4.3's input goes from $1.25 to $1.2875/M and completion from $2.50 to $2.575/M. The input price ratio between the two is 1.6x in Sonnet 5's favor for cost, meaning Grok 4.3 is the default choice unless you have a specific reason to pay more. Both run through the same OpenKey key with that same 3% fee, so switching between them mid-project is a one-line change, not a new integration.

Coding and agentic performance

Sonnet 5 posts a 71.5 coding index and 46.7 agentic index on artificial_analysis, well ahead of Grok 4.3's 42.2 coding index and 24.1 agentic index. That's the clearest signal in this comparison: for code generation, debugging, and multi-step agent tasks judged by intelligence-adjacent benchmarks, Sonnet 5 is the stronger model by a wide margin. Grok 4.3 does have its own benchmark trail — Design Arena results across 20 categories spanning the agents arena (agentic slides, fullstack, webapps, mobile apps, game dev) and the models arena (code categories, dataviz, UI components, website generation). Its highest Design Arena elo is 1250 in uicomponent and 1244 in website, with win rates in the 44-50% range across most model-arena categories — useful signal for web-generation-style tasks, but it doesn't close the coding-index gap against Sonnet 5.

Context and long documents

Both models carry a 1,000,000 token context window — the context ratio between them is 1.0, so there's no long-document advantage either way. The difference is output ceiling: Sonnet 5 caps completions at 128,000 tokens, while Grok 4.3 has no published max_completion_tokens limit in this data. If your workload needs very long generated output rather than long input, that's worth testing directly rather than assuming from context length alone.

Reasoning controls and parameters

Sonnet 5 supports five reasoning effort levels (low, medium, high, xhigh, max) with medium as default, plus verbosity control and structured outputs. Grok 4.3 supports four levels (none, low, medium, high) with reasoning enabled by default at low effort, and adds classic sampling controls — frequency_penalty, presence_penalty, logprobs, seed, temperature, top_p — that Sonnet 5's parameter list doesn't include. If you need fine-grained sampling control or logprob access for evaluation pipelines, Grok 4.3's parameter surface is the more complete one.

Questions

Which model is cheaper for a typical workload?

Grok 4.3, by a wide margin. On a 10M input / 2M output token job, Grok 4.3 costs $17.50 at provider pricing versus $40.00 for Sonnet 5 — roughly 2.3x cheaper. The gap comes from both input ($1.25 vs $2.00/M) and completion ($2.50 vs $10.00/M) pricing.

Which model is better at coding?

Claude Sonnet 5, based on artificial_analysis benchmarks: a 71.5 coding index versus Grok 4.3's 42.2. Sonnet 5 also leads on agentic index, 46.7 versus 24.1, so for multi-step coding agents the gap holds up.

Does Grok 4.3 have any published benchmark data Sonnet 5 lacks?

Yes. Grok 4.3 has Design Arena results across 20 categories in the agents and models arenas, with elo scores ranging from 1033 (agenticgamedev) to 1250 (uicomponent). Sonnet 5's benchmark record in this data has no Design Arena entries.

Do both models support the same context length?

Yes, both have a 1,000,000 token context window — a context ratio of exactly 1.0. The difference is on output: Sonnet 5 caps completions at 128,000 tokens, while Grok 4.3 has no published max_completion_tokens value in this data.