Grok 4.5 vs Claude Opus 4.8: cost-efficient coding vs consistency

xAI's Grok 4.5 made its name on being cheap and strong. Anthropic's Claude Opus 4.8 is a closed flagship with a track record on long autonomous runs. The question is how far the newcomer closes the gap.

The short version: Grok 4.5 to keep production coding cheap, Opus 4.8 when quality and consistency come first. 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 24, 2026 (Opus 4.8 rounded to the cent); the current figures are on the models page. Grok 4.5's rates double on prompts over 200K tokens.

On a task of 100,000 input tokens and 10,000 output tokens, that's about $0.29 on Grok 4.5 and $0.79 on Opus 4.8. Output is where they part: Opus 4.8 costs four times as much per output token, and long agent runs are output-heavy.

Where each is stronger

Grok 4.5 is built for coding first. Reviews of its autonomous software engineering put it level with OpenAI's best coding agent and close behind Anthropic's flagship. It was trained on real development sessions, and early users said it was fast, cheap, and found bugs other models had missed. It earns its place wherever cost has to stay down.

Claude Opus 4.8 is the strongest closed model of Anthropic's Opus 4 generation. It is at its best on long autonomous agent runs, planning, delegating and checking as it works through a large job. It is also known for clear writing and for following instructions closely.

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 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 half of Opus 4.8's.

Opus 4.8: it's expensive, and long runs multiply that. The per-token price is high, and a long agent run uses a lot of tokens. For everyday light work it's overkill; a smaller model usually does the job for much less.

Which to use where

• Grok 4.5: production coding where cost matters and "good and cheap" wins.
• Claude Opus 4.8: long autonomous agent runs and the hardest tasks, where quality and consistency come first.

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"}]}'

# Claude Opus 4.8: 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": "anthropic-claude-opus-4-8", "messages": [{"role": "user", "content": "Hello"}]}'

FAQ

Which is better for coding? Grok 4.5 gets close to flagship level and wins on cost. Opus 4.8 still leads on the hardest problems and on staying consistent over a long run. Choose by the work.

How big is the price gap? Grok 4.5 costs $2.20 in and $6.60 out per million tokens on FastMetal, against $5.28 and $26.38 for Opus 4.8. 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 cost-efficient coding, Claude Opus 4.8 for quality and consistency. The newcomer really does get close to the flagship, but trust in the vendor belongs in the decision alongside the benchmarks. Run both on your own tasks and let that decide.

Both models, with current prices, are in the model catalog. Grok 4.5 against OpenAI's flagship is in Grok 4.5 vs GPT-5.6 Sol.