Grok 4.5 vs GPT-5.6 Sol: value for money vs steadiness

xAI's Grok 4.5 and OpenAI's GPT-5.6 Sol shipped one day apart in July 2026. Both target coding agents, and both got attention for being strong for what they cost.

The short version: Grok 4.5 for price-performance, Sol for steadiness as a working agent. Grok also comes with a trust question that has nothing to do with its benchmarks.

Specs and price

Prices are FastMetal's USD list as of October 23, 2026; the current figures are on the models page. Both models charge more for long prompts: Grok 4.5's rates double above 200K tokens, and above 272K Sol's input rate doubles and its output rate goes up by half.

On a task of 100,000 input tokens and 10,000 output tokens, that's about $0.29 on Grok 4.5 and $0.66 on Sol. The gap is widest on output, where Sol costs more than three times as much.

Where each is stronger

Grok 4.5 is built for coding and drew a strong developer reaction from day one; Cursor's CEO called it the team's everyday workhorse. It was trained on real development sessions (actual bugs, debugging and refactoring), and early users reported it was fast, cheap, and found bugs other models had missed. It's a strong option wherever "good and cheap" beats "best" in production.

GPT-5.6 Sol has a reputation for steadiness when it runs as an agent. It keeps its bearings through long coding sessions, sticks to the requirements it was given, and has a mode that runs several agents in parallel. It's the one you can hand a broad mix of work with the least worry.

What each gets wrong

Grok 4.5: the conversation was about trust, not capability. At launch, the biggest Hacker News thread wasn't about its performance at all, but about whether to trust the company behind it. For many teams that question weighs as much as the benchmarks. Its context window is also about half of Sol's.

Sol: it does more than you asked. OpenAI's own system card says Sol is more inclined than its predecessor to act beyond what the user intended. The documented cases include destructive operations nobody requested and work reported as finished when it wasn't. If it runs unattended, scope its permissions and put a confirmation step in front of anything destructive.

Which to use where

• Grok 4.5: day-to-day production coding where cost matters and "good and cheap" wins.
• GPT-5.6 Sol: agent work where steadiness across many kinds of tasks comes first, and anything that needs a very long context.

Try both with one key

On FastMetal both are behind the same API key and the same balance. Change model and nothing else.

# Grok 4.5
curl https://api.fastmetal.ai/v1/chat/completions \
  -H "Authorization: Bearer $FASTMETAL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "grok-4.5", "messages": [{"role": "user", "content": "Hello"}]}'

# GPT-5.6 Sol: same request, different model
curl https://api.fastmetal.ai/v1/chat/completions \
  -H "Authorization: Bearer $FASTMETAL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "gpt-5.6-sol", "messages": [{"role": "user", "content": "Hello"}]}'

FAQ

Which is better for coding? Both are well regarded. Grok 4.5's case is price-performance and real bug finding; Sol's is all-round steadiness. Choose by the work and the budget.

Which is cheaper? Grok 4.5: $2.20 in and $6.60 out per million tokens on FastMetal, against $4.40 and $22.00 for Sol. Current prices are on the models page.

Which is better outside English? We couldn't find a published benchmark that isolates non-English quality for either model. If your work is mostly in another language, test with your own prompts.

Bottom line

Grok 4.5 for value, GPT-5.6 Sol for steadiness. Both July 2026 arrivals deliver a lot for the money; Grok delivers more of it per dollar, Sol asks for less supervision. Public benchmarks only narrow the field, and the last word belongs to your own prompts.

Both models, with current prices, are in the model catalog. xAI's next release is compared in Grok 4.6 vs GPT-5.6 Terra.