Claude Sonnet 5 vs Grok 4.5: how they compare on coding

Grok 4.5 and Claude Sonnet 5 can both handle the tasks that make up most day-to-day coding work, but they differ on speed, cost, and how reliably the output actually works once it's rendered.

To help you pinpoint the better model for your coding tasks, we'll review the models and then compare them through our own experiment.

Overview on Claude Sonnet 5 and Grok 4.5

Claude Sonnet 5 is Anthropic's proprietary workhorse model and was released at the end of June, 2026.

It pairs a 1,000,000-token context window with strong coding and agentic performance. And it's priced at $2 per million input tokens and $10 per million output under Anthropic's introductory pricing (through August 31, 2026; standard pricing is $3/$15).

Grok 4.5 is xAI's current mainline model and was launched on July 8th, 2026.

It's a proprietary, reasoning-enabled model with a 500,000-token context window, and it's priced at $2 per million input tokens and $6 per million output, making it the cheaper of the two on a per-token basis.

Related: How Claude Sonnet 5 compares to GPT-5.6 Terra

Grok 4.5 vs Sonnet 5 (based on our research)

Artificial Analysis hasn't published a Coding Agent Index score for Claude Sonnet 5 yet, so there's no clean third-party head-to-head to point at.

Rather than lean on a one-sided benchmark, we ran our own build test:

1. We wrote one identical prompt for both models: "Build the marketing homepage for a fictional company, Cadence, a revenue-forecasting platform. It should be a single self-contained HTML file with a dynamic hero section, a nav bar, features, social proof, a pricing or CTA section, and a footer."

2. We routed that same prompt to each model through Merge Gateway at high reasoning effort, one generation each, and recorded the input tokens, output tokens, total response time, and estimated cost Gateway reported.

3. Then we rendered both results and looked at how the sites actually turned out.

On the numbers, Grok 4.5 completely outperformed Sonnet. It finished in 60.0 seconds to Sonnet 5's 115.9, used far fewer output tokens (10,418 vs 15,271), and cost less than half as much to generate the same page ($0.0633 vs $0.1532). Sonnet 5 did use fewer input tokens (259 vs 376), a minor exception to an otherwise one-sided result.

Here's Claude Sonnet 5's hero:

And Grok 4.5's:

Both models landed on a strikingly similar visual system for Cadence: a dark navy canvas, a moving constellation of connected dots in the background, and a purple-to-teal gradient on the word "confidence" in the headline. That's a coincidence of taste rather than evidence either model saw the other's output, but it made the real differences easier to spot.

Copy, visual design, page layout, and mobile responsiveness are effectively a tie: both wrote specific copy grounded in the revenue-forecasting premise instead of generic filler, landed on the same visual system, shipped a full page from hero through footer, and adapted cleanly to a 390px mobile viewport.

But they differ in two areas.

1. Sonnet 5 shipped a fuller main nav (with a Resources tab and separate Sign in and Start free trial actions) against Grok 4.5's leaner three links and single CTA.

2. Grok 4.5's animated stat row (98.4% forecast accuracy, $2.1B+ revenue modeled, 4 hrs saved per week) rendered cleanly every time, while Sonnet 5's centerpiece dashboard mockup, a canvas-drawn line chart meant to animate in on scroll, never actually paints, leaving an empty box under the hero.

Grok 4.5 won on every quantitative measure we captured. Sonnet 5 kept pace on copy, layout, and responsiveness, and shipped a fuller nav, but the empty mockup panel is a crucial miss. As a whole, Grok performed much better.

Related: How Kimi K2.6 compares to Claude Sonnet 4.6

Final thoughts

Sonnet 5's fuller navigation and matched depth on copy and layout mean it's still very much in play, especially for teams already leaning on Anthropic's broader agentic tooling. But on this test, Grok 4.5 was faster, cheaper, and the only one of the two that rendered its hero correctly on the first try.

To reap the benefits of each model (and any other), you can use Merge Gateway to route each request to the model that best fits your requirements.

• Reach every major model, including Claude Sonnet 5 and Grok 4.5, through one API and one integration

• Use Build Your Own Router (BYOR) to route on your own benchmark or eval scores, not just cost or latency

‍

• Set budgets, spend limits, and per-project cost visibility so a high-volume workload can't quietly blow past plan

• Get per-request logging and tracing across every model and provider

• Fall back automatically when a provider errors or rate-limits, so a single outage doesn't take your feature down

{{this-blog-only-cta}}

Claude Sonnet 5 vs Grok 4.5 FAQ

In case you have any more questions on either model, we've addressed several more below.

What is the context window for Claude Sonnet 5 and Grok 4.5?

Claude Sonnet 5 has a 1,000,000-token context window with a 128,000-token maximum output (300,000 on the Message Batches API), per Anthropic's model documentation, while Grok 4.5 has a 500,000-token context window, per xAI's model documentation.

This means Sonnet 5's window is double Grok 4.5's. This matters most when a task requires reasoning over a very large codebase or a long spec in a single request. Grok 4.5's smaller window is still large enough to hold a substantial codebase or a long multi-file diff in one pass for most day-to-day coding tasks.

What other models should I consider besides Claude Sonnet 5 and Grok 4.5?

A few others are worth evaluating depending on your priorities:

• ‍Claude Opus 4.8: ideal for the hardest agentic work, like large multi-file refactors and long autonomous runs

• GPT-5.5: OpenAI's frontier reasoning model is a strong pick when you want a benchmarked, third-party-verified Coding Agent Index score to point to

• Gemini 3 Pro: the long-context pick; it's best when a task means reasoning over a whole repo or a long spec in one pass before editing

• DeepSeek V4 Pro: an open-weight model that competes hard on cost. This makes it a fit for high-volume or batch code generation where per-token price matters most

What are the most common coding use cases for Claude Sonnet 5 and Grok 4.5?

Claude Sonnet 5 fits agentic and quality-first work, like multi-step tool use, complex refactors and debugging, and long-context tasks where its larger context window and Anthropic's coding pedigree pay off.

Grok 4.5 fits speed- and cost-sensitive work, including interactive coding assistants where response time is felt, high-volume code generation, and one-shot builds like the site test above.