First Impressions of Sonic (the stealth xAi Grok coding model?) -
Update (August 26, 2025): Sonic has been confirmed as the new Grok Code model and is now officially available today! What was once a “stealth” model is now xAi’s publicly released coding assistant.
A new stealth model called Sonic has quietly appeared in places like Opencode and Cursor, and it’s rumored to be xAi’s Grok coding model. I spent a full day working with it inside Opencode, replacing my usual Claude Sonnet 4 workflow — and came away impressed. The short version? It feels like Sonnet, but turbocharged.
Getting Access
Sonic showed up in Opencode’s model selector — no special invite required. Selecting it as the active model made it fully functional, with no setup beyond choosing it in the dropdown. During this stealth period it’s free to use and offers a massive 256,000 token context window. I didn’t encounter any rate limits or throttling all day.
First Test
Instead of a contrived “hello world,” I dropped Sonic into my real workflow. Where I’d usually use Sonnet 4, I asked Sonic to help me build a new Training Center CRUD feature in a Ruby on Rails application.
It generated the models, migrations, controllers, and views exactly as expected — and most importantly, it did it fast. Text streamed out so quickly it was hard to keep up. Compared to Claude Code, I’d estimate 3x faster tokens per second, consistently.
That was my wow moment: speed without sacrificing accuracy. It nailed the Rails conventions and felt like a drop-in Sonnet replacement.
My Standard Benchmark
My go-to evaluation prompt for coding models is: “Tell me about this codebase and what the most complex parts are.” On my legacy Rails codebase, Sonic immediately identified the correct overloaded model as the main complexity hotspot, and even suggested ways to refactor it.
The result was near identical in quality to what I’d get from Sonnet or even Opus — but again, the response flew back near-instantly. For day-to-day comprehension and reasoning, Sonic seems to match the best while dramatically cutting wait time.
Comparison to Claude Sonnet
- Reasoning & Accuracy: Nearly identical to Sonnet. No hallucinations, no weird Rails missteps.
- Personality: Very similar, though Sonic felt a bit more positive and agreeable to suggestions.
- Speed: The standout. At least 3x faster than Claude Code/Sonnet, with the speed holding steady across short and long generations.
- Where Sonnet Might Still Win: Hard to say yet — I didn’t hit any reasoning failures, but Sonnet have a longer track record of reliability under heavy workloads.
Bottom line: if you’re used to Sonnet, Sonic feels like the same experience at high speed.
Pricing and Availability
Right now Sonic is free to use in Opencode during its stealth rollout. No public pricing details are available yet, but if it undercuts Sonnet, it could be a winner.
I haven’t seen any rate limits or regional restrictions. Cursor users also report seeing Sonic available as a selectable model.
Initial Verdict
After a full day of work, I would — and did — ship production code with Sonic. It handled CRUD features, comprehension of a large legacy codebase, and various refactors without issue.
The real differentiator is speed. If Sonnet is your baseline, Sonic offers the same reasoning ability but with response times that feel instantaneous. Unless something changes in pricing or reliability, this could easily become my daily driver.
Quick Reference
- Access: Select “Sonic” in Opencode’s model selector (no invite required during stealth)
- Pricing: Free during stealth; official pricing TBD
- Best for: Day-to-day coding tasks, CRUD features, codebase comprehension, Rails development
- Avoid for: Nothing obvious yet — but keep human oversight on critical code
- API docs: Not yet public
- Hot take: As I posted on X, this feels like my Sonnet replacement should I be forced to not have Sonnet. @robzolkos