Pick GPT-5.6 Sol for the highest reasoning ceiling, the best coding-benchmark scores, and the biggest context. Pick Grok 4.5 for agentic tool use, token efficiency, and a much lower bill. Both launched within a day of each other in July 2026, and they're genuinely built for different priorities — quality-at-any-cost versus results-per-dollar. Here's the full breakdown.
Quick verdict
GPT-5.6 Sol is OpenAI's top-end model for hard professional, coding, and research work, with class-leading coding benchmarks and a ~1M-token context. Grok 4.5 is xAI's efficiency play: the best agentic tool-use result on the board, resolving tasks in far fewer tokens, at roughly a third of GPT-5.6's per-token cost. Both are excellent — the right pick hinges on whether you optimize for peak capability or cost-efficient throughput.
Side by side
| Spec | Grok 4.5 | GPT-5.6 Sol |
|---|---|---|
| Maker | xAI | OpenAI |
| Released | July 8, 2026 | July 9, 2026 (GA) |
| Context window | 500K | ~1.05M (128K max output) |
| Standout strength | Agentic tool use, efficiency | Raw reasoning & coding |
| Coding benchmark | Top-tier, very token-efficient | Terminal-Bench 2.1: 88.8% (Ultra 91.9%) |
| API input / output | $2 / $6 per M | $5 / $30 per M |
| Image input | Yes | Yes |
Grok 4.5
Grok 4.5 ranks #4 of 168 on the Artificial Analysis Intelligence Index but posts the single best agentic tool-use result of any model tested — the capability that matters most for automation. Its defining trait is efficiency: xAI reports it resolving engineering tasks in about 15,954 output tokens versus roughly 67,020 for a max-effort Opus 4.8 run, about 4.2× fewer.
It has a 500K context, accepts image input, and lets you set reasoning effort to low, medium, or high. On the API it's $2/M input and $6/M output with an ~85% cache discount, plus up to $175/mo in free credits via xAI's data-sharing program. The one caveat is context: 500K is smaller than the 1M window on the older Grok 4.3, and much smaller than GPT-5.6's.
GPT-5.6 Sol
GPT-5.6 Sol is OpenAI's flagship for the hardest work — difficult professional tasks, deep coding, research, computer use, and tool-heavy pipelines. It reached general availability July 9, 2026, and leads on coding benchmarks: base Sol scored 88.8% on Terminal-Bench 2.1 and Sol Ultra hit 91.9%, edging Claude Mythos 5 and GPT-5.5.
Its ~1.05M-token context with 128K max output is the biggest here, ideal for enormous codebases and long research packets. The cost is real, though: $5/M input and $30/M output, with requests above 272K input tokens charged at a steeper $10/$45. It's the quality leader, priced like one.
Coding & agents
On pure coding-benchmark quality, GPT-5.6 Sol is ahead — its Terminal-Bench numbers are the best in this pair, and it tends to one-shot gnarly problems more reliably. If correctness on a single hard task is everything, it's the safer model.
For agent loops — repeated tool calls, multi-step tasks, long automation runs — Grok 4.5 flips the equation. Its best-in-class tool use plus ~4× token efficiency means it completes agentic work faster and far cheaper. In a workflow that calls the model hundreds of times, Grok 4.5's efficiency compounds into a large real-world cost and latency advantage even where GPT-5.6 edges it on a single-shot score.
Pricing
| Model | Input / M | Output / M | Consumer entry |
|---|---|---|---|
| Grok 4.5 | $2 | $6 | SuperGrok Lite $10/mo |
| GPT-5.6 Sol | $5 | $30 | ChatGPT Plus $20/mo |
Grok 4.5 is dramatically cheaper per token, and its token efficiency widens the gap further on real tasks. GPT-5.6 justifies its premium only when you need the top reasoning ceiling or the huge context. For the full plan breakdowns, see our Grok 4.5 pricing and GPT-5.6 pricing guides.
Which should you pick?
Choose GPT-5.6 Sol if you need the highest-quality answers on hard problems, the strongest coding benchmarks, or a context past 500K for massive documents and repos. Choose Grok 4.5 if you're building agents, running high-volume coding or automation, or simply want the best results-per-dollar — its efficiency makes it the value flagship of 2026.
Many teams end up using both: GPT-5.6 for the hardest calls, Grok 4.5 for the bulk of the loop. See how they stack against Claude and Gemini in our best AI chatbots roundup, or read the standalone Grok 4.5 review.
Frequently Asked Questions
Is Grok 4.5 or GPT-5.6 better?
GPT-5.6 Sol has the higher raw-reasoning ceiling and a larger 1M+ context, making it the pick for the hardest problems and biggest documents. Grok 4.5 wins on agentic tool use, token efficiency, and price, making it the better value for automation and coding at scale.
Which is cheaper, Grok 4.5 or GPT-5.6?
Grok 4.5 is much cheaper: $2/M input and $6/M output versus GPT-5.6 Sol's $5/M input and $30/M output. Grok 4.5 also finishes agentic tasks in far fewer tokens, widening the cost gap in its favor.
Which has the bigger context window?
GPT-5.6 Sol has a larger context at about 1.05M tokens with 128K max output, versus Grok 4.5's 500K. For very long documents or huge codebases, GPT-5.6 has the edge.
Which is better for coding?
GPT-5.6 Sol leads on coding benchmarks (88.8% on Terminal-Bench 2.1, 91.9% for Ultra). Grok 4.5 is close on quality and far more token-efficient, so it's often the better pick for coding inside agent loops and at scale.
Which is better for building AI agents?
Grok 4.5. It posts the best agentic tool-use result on the board and resolves tasks in roughly 4× fewer tokens, so agent workflows run faster and cheaper on it than on GPT-5.6.
Can I use both together?
Yes, and many teams do — routing the hardest, highest-stakes calls to GPT-5.6 and the bulk of high-volume agent or coding work to Grok 4.5 to balance quality against cost.