GPT-5.6 Sol vs Grok 4.5: Two Frontier Models, Same Day, Different Bets (2026)

GPT-5.6 Sol and Grok 4.5 are the two frontier models compared here, and both reached general availability on the same day, July 9, 2026. GPT-5.6 Sol is OpenAI's flagship capability tier, priced at $5 per million input tokens and $30 per million output tokens with a 1,050,000-token context window. Grok 4.5 is SpaceXAI's newest flagship, priced at $2 per million input tokens and $6 per million output tokens with a 500,000-token context window. On the independent Artificial Analysis leaderboards, Sol scores 59 on the Intelligence Index to Grok 4.5's 54, leads the Coding Agent Index 80 to 76, and is measured cheaper to run per task at about $1.04 versus $2.49. Grok 4.5 costs less than half of Sol per token and is positioned by SpaceXAI as much faster, but Artificial Analysis flags a 54 percent hallucination rate on its AA-Omniscience test and the model is not available in the EU. Best for measured capability, long context, and per-task cost: GPT-5.6 Sol. Best for the lowest token rate card on high-volume, non-EU work: Grok 4.5.

Quick Verdict

This is a split verdict: GPT-5.6 Sol owns the independent capability leaderboards and the per-task economics, while Grok 4.5 owns the token rate card and its vendor-stated speed — and the EU AI Act quietly settles the choice for a large group of readers. Both models went generally available on July 9, 2026, within hours of each other, so we have had roughly 48 hours of side-by-side hands-on with each through our own OpenAI and SpaceXAI API keys. That is enough for sharp first impressions, not a controlled benchmark, so we lean on attributed third-party numbers from Artificial Analysis and LMArena wherever our own time is too short. Every figure below carries its source, and self-reported vendor numbers are labeled as such. Here is the short version.

• Best for measured intelligence: GPT-5.6 Sol. Artificial Analysis scores it 59 on the Intelligence Index against Grok 4.5's 54 — a clear five-point gap on the aggregate independent measure.
• Best on the independent coding index: GPT-5.6 Sol. It ranks No.1 on the Artificial Analysis Coding Agent Index at 80, ahead of Grok 4.5 at 76, which sits roughly level with the prior GPT-5.5.
• Best for cost per task: GPT-5.6 Sol, counterintuitively. On Artificial Analysis's Intelligence Index run, Sol costs about $1.04 per task versus about $2.49 for Grok 4.5 — the cheaper rate card does not win the cheaper task here.
• Best for long context: GPT-5.6 Sol, by more than double. Its 1,050,000-token window is roughly 2.1 times Grok 4.5's 500,000 tokens.
• Best for multi-agent reasoning: GPT-5.6 Sol. Its new ultra mode spawns up to sixteen reasoning agents in parallel; Grok 4.5 offers a simple low, medium, and high control and no equivalent mode.
• Best for token price: Grok 4.5, decisively. At $2 per million input and $6 per million output tokens it is 60 percent cheaper on input and 80 percent cheaper on output than Sol — less than half on both sides, verified on SpaceXAI's documentation.
• Best for raw speed positioning: Grok 4.5, on the vendor's word. SpaceXAI markets it as Opus-class and much faster; our sources carry an independent throughput figure only for Sol, so we flag this as a vendor claim, not a benchmarked win.
• Only option for EU teams: GPT-5.6 Sol. Grok 4.5 is not available in the European Union under the AI Act, which makes Sol the default of these two for anyone serving EU users regardless of price.

The honest caveats up front: both models are days old at the time of writing, so we treat our hands-on notes as first impressions, not settled verdicts. Neither has been submitted to the independently run SWE-bench Verified suite, so there is no third-party verified-coding number for either, and we will not paper over that gap with self-reported figures. Grok 4.5 carries one independent reliability caveat — a 54 percent hallucination rate on Artificial Analysis's AA-Omniscience test — that we present as a standalone data point because our sources hold no equivalent figure for Sol. We only declare a winner where both models were measured on the same independent benchmark, and we keep self-reported and third-party numbers strictly apart.

GPT-5.6 Sol vs Grok 4.5 — Overview

What Is GPT-5.6 Sol?

GPT-5.6 Sol is the flagship capability tier of OpenAI's GPT-5.6 generation, generally available July 9, 2026 after a gated preview on June 26. In OpenAI's naming scheme the number is the generation and the names — Sol, Terra, and Luna — are durable capability tiers rather than model sizes; Sol is the tier aimed at the hardest problems, from complex coding and long-horizon agents to cyber, science, and computer use, per OpenAI's announcement. Its predecessor GPT-5.5 remains active and cheaper for routine work — see our GPT-5.5 review for that tier. Per OpenAI's model documentation, Sol runs a 1,050,000-token context window with up to 128,000 output tokens and a February 16, 2026 knowledge cutoff, handles text and image inputs to text output, and introduces two new reasoning levels above xhigh: max, and ultra, a multi-agent mode that runs up to sixteen reasoning agents in parallel. It also adds Programmatic Tool Calling, where the model writes and executes JavaScript in an isolated, ephemeral runtime to orchestrate its own tools. API pricing is $5 per million input tokens and $30 per million output tokens, with cached input at $0.50 per million.

What Is Grok 4.5?

Grok 4.5 is the newest flagship model from SpaceXAI — the company formerly known as xAI, which kept the Grok product name unchanged through its July rebrand, as we covered in our SpaceXAI rebrand explainer. It was announced July 8, 2026 and reached public availability July 9, replacing Grok 4.3 as the flagship while Grok 4.3 and 4.20 remain available. Per SpaceXAI's Grok 4.5 model documentation, it runs a 500,000-token context window, takes text and image inputs to text output, supports function calling and structured outputs, exposes low, medium, and high reasoning with high as the default, and is served from the us-east-1 and us-west-2 regions. API pricing is $2 per million input tokens, $0.50 per million cached input, and $6 per million output tokens — which we confirmed directly on that documentation, and which is less than half of GPT-5.6 Sol on both input and output. SpaceXAI says Grok 4.5 was trained with Cursor on GB300 GPUs, and Elon Musk has described it as Opus-class and much faster than rivals. One hard constraint: Grok 4.5 is not available in the European Union, which SpaceXAI attributes to the EU AI Act's systemic-risk obligations.

How We Compared Them — and What We Did Not Do

Method transparency matters more than usual here, because both models are days old at the time of writing and the benchmark discourse around this matchup mixes self-reported and independent numbers freely. Here is exactly what we did and did not do.

• Pricing: both rate cards are vendor-verified. Sol's $5 input and $30 output per million tokens is confirmed against OpenAI's pricing documentation; Grok 4.5's $2 input and $6 output per million is confirmed against SpaceXAI's model documentation. No relayed figures. Our AI model pricing explainer breaks down how input, output, and cached-token rates translate into real bills.
• Independent benchmarks: we lean on Artificial Analysis (Intelligence Index, Coding Agent Index, cost per task, AA-Omniscience) and LMArena (Elo). We only declare a benchmark winner where both models were measured on the same suite. Where one model is absent — as Grok 4.5 is on LMArena, and both are on SWE-bench Verified — we say so and do not substitute a self-reported number.
• Self-reported figures: OpenAI's Terminal-Bench 2.1, DeepSWE, and SWE-bench Pro numbers for Sol, and SpaceXAI's Opus-class positioning for Grok 4.5, are labeled as vendor-reported and not treated as head-to-head evidence. OpenAI itself disputes the SWE-bench Pro benchmark's validity, which is another reason we keep it separate. Our agentic coding model explainer covers why coding-agent scores and chatbot scores measure different things.
• Hands-on: we have run both models through our own OpenAI and SpaceXAI API keys since their July 9 general availability, roughly 48 hours side-by-side on the same tasks. That is enough for first impressions, not a controlled benchmark, and we scope every observation accordingly.
• Disclosure: we have no affiliate relationship with OpenAI or SpaceXAI. There are no sponsored links on this page. We are based outside the EU, which is the only reason we were able to test Grok 4.5 directly, and we flag its EU unavailability prominently for readers who cannot.

Features and Benchmarks Comparison

The table below lists every dimension we could verify or attribute. Read the Winner column carefully: it distinguishes vendor-verified pricing, independent benchmarks, and self-reported figures, and it flags where a result is one-sided ("where measured"), genuinely tied, or a standalone caveat. Every benchmark figure carries its source. Sources for the independent scores are Artificial Analysis and LMArena.

Synthesis: the independent capability signals tilt to Sol — it takes the Intelligence Index by five points (59 to 54), leads the Coding Agent Index (80 to 76), is the only one of the two ranked on LMArena, and is measured cheaper per task despite the higher rate card. The token economics tilt hard to Grok 4.5 — $2 input and $6 output per million against $5 and $30, less than half on both sides. Neither model appears on SWE-bench Verified, so verified coding is a shared blank. Two structural facts sit outside the benchmark table and can decide the whole thing on their own: Sol's context window is more than double Grok 4.5's, and Grok 4.5 cannot be used in the EU. This is not a model that wins everything against a model that wins nothing; it is peak measured capability and reach against the cheapest rate card and vendor-stated speed.

Pricing — GPT-5.6 Sol vs Grok 4.5 in 2026

Pricing is the sharpest contrast in this comparison, and it is where the naive read and the measured read diverge. On the rate card, Grok 4.5 is dramatically cheaper: less than half of Sol on input and output. On cost per task, the one independent measurement flips the other way. Both rate cards below come straight from OpenAI's and SpaceXAI's own documentation, and our pricing explainer covers how these translate into real spend.

GPT-5.6 Sol Pricing

Context pricing is flat — there is no long-context surcharge tier for Sol, so a 900,000-token request bills at the same per-token rate as a short one. There is no free plan at the API level.

Grok 4.5 Pricing

Pricing verdict: Grok 4.5 wins the rate card, decisively; Sol wins cost per task, counterintuitively. On a representative agentic call of 50,000 input tokens and 5,000 output tokens, Grok 4.5 costs about $0.13 at the rate card ($2 times 0.05 input plus $6 times 0.005 output) versus about $0.40 for Sol ($5 times 0.05 plus $30 times 0.005) — roughly a third of the price on that mix, and the gap widens as output share grows because Grok 4.5's $6 output is one-fifth of Sol's $30. Yet Artificial Analysis measures the cost to run its Intelligence Index at about $2.49 per task for Grok 4.5 versus about $1.04 for Sol, because per-task cost depends on how many tokens each model burns to finish the work, and Grok 4.5 defaults to its high reasoning setting. The lesson is not that one number is wrong — both are real — but that the rate card decides your bill only if your token counts are similar. Both models discount cached input to the same $0.50 per million, so long-running agents with stable system prompts narrow the raw-rate gap. Test on your own prompts before assuming the cheaper card is the cheaper model.

Hands-On Notes — Both at 48 Hours

We owe you precision about what this section is and is not. Both GPT-5.6 Sol and Grok 4.5 went generally available on July 9, 2026, and we had them running side-by-side through our own OpenAI and SpaceXAI API keys within hours, which gives us roughly 48 hours of direct comparison at the time of writing — sharp first impressions, nowhere near a controlled benchmark. Take every observation below as scoped and provisional, and weight the attributed benchmarks above them.

Where Sol stood out immediately: the hardest single problems and long inputs. On a deep multi-file refactor and a long-horizon planning task, Sol reached correct results with fewer human interventions in our runs, consistent with its higher Intelligence Index and Coding Agent Index standing. Its 1,050,000-token window swallowed a whole repository plus its history in one context where Grok 4.5's 500,000 tokens forced us to chunk. Programmatic Tool Calling let Sol batch tool operations in executable code rather than one call at a time, cutting round trips on loop-and-filter agent work.

Where Grok 4.5 stood out immediately: speed and cheap bulk. On high-volume, shallow calls — classification, extraction, short rewrites — Grok 4.5 felt fast and the bill barely moved at $2 input and $6 output per million tokens, which matches SpaceXAI's much-faster positioning even though we have no independent tokens-per-second figure to put a number on it. For workloads that are wide rather than deep, that combination of low price and apparent speed is its strongest hand, and it is exactly where Sol's capability lead matters least.

What we watched carefully: reliability on knowledge-heavy prompts. Artificial Analysis's 54 percent hallucination rate for Grok 4.5 on AA-Omniscience is a published caveat, and while 48 hours is not enough to confirm or refute it, it is a reason to ground Grok 4.5 with retrieval on factual work rather than trusting raw recall. We saw nothing that contradicted the caution, and we would apply the same discipline to any frontier model on high-stakes facts.

What we cannot tell you yet: latency under controlled conditions, per-task token economics across a real workload mix, and whether either model's early behavior holds up over weeks. We will update this comparison as our side-by-side time accumulates and as more independent harnesses publish results for both models.

Winner per Category

Best for Measured Intelligence: GPT-5.6 Sol

On the Artificial Analysis Intelligence Index, GPT-5.6 Sol scores 59 against Grok 4.5's 54, a clear five-point gap on the aggregate independent measure — wider than the single-point margins that separate the very top of the chart, where Claude Fable 5 leads at 60. Artificial Analysis placed Grok 4.5 at No.4 in the flagship field at its July 8 publication. If your workload is the hardest reasoning you have and you want the model that measures higher on aggregate intelligence, Sol is the pick of these two on the independent evidence.

Best on the Independent Coding Index: GPT-5.6 Sol

The Artificial Analysis Coding Agent Index is the one independent coding chart where both models appear, and Sol leads it at 80, ahead of Grok 4.5 at 76 — a score that puts Grok 4.5 roughly level with the prior GPT-5.5. Neither model has been submitted to the independently run SWE-bench Verified suite, so there is no third-party verified-coding number for either, and we will not pretend a self-reported figure fills that gap; for reference, Claude Opus 4.8 posts 88.6 percent on that suite, the model SpaceXAI invokes when it calls Grok 4.5 Opus-class. OpenAI reports Sol at 88.8 percent on Terminal-Bench 2.1, but that is a different, self-reported benchmark. On independent evidence, Sol has the coding edge; on verified coding, both are blank.

Best for Token Price: Grok 4.5

This one is not close on the rate card. Grok 4.5 costs $2 per million input tokens against Sol's $5, and $6 per million output against $30 — 60 percent cheaper on input and 80 percent cheaper on output, both verified on SpaceXAI's documentation. For high-volume, output-heavy workloads, that five-to-one output ratio dominates the bill. The caveat is cost per task: Artificial Analysis measures Grok 4.5 at about $2.49 to run its Intelligence Index against about $1.04 for Sol, so on token-hungry reasoning work the rate-card advantage narrows or reverses. Where your tasks are short and shallow, Grok 4.5's price wins outright; where they are long and reasoning-heavy, measure before you assume.

Best for Long Context and Multi-Agent Work: GPT-5.6 Sol

Sol carries a 1,050,000-token context window against Grok 4.5's 500,000 — more than double, and a genuine architectural difference rather than a rounding gap. For whole-repository code work, large document sets, and agents that accumulate long histories, Sol fits jobs in one context that Grok 4.5 must split. Sol also owns multi-agent throughput: its new ultra mode runs up to sixteen reasoning agents in parallel (four by default), a mode Grok 4.5 does not offer, and its Programmatic Tool Calling orchestrates tools in executable code. For long-context pipelines and parallel-reasoning workloads, Sol is the pick.

Best for Speed Positioning and Non-EU Value: Grok 4.5

Speed is Grok 4.5's headline selling point. SpaceXAI markets it as Opus-class and much faster, and Elon Musk has repeated that framing; our sources carry an independent throughput figure only for Sol (about 74.5 tokens per second on Artificial Analysis), so we treat Grok 4.5's speed as a credible vendor claim rather than a benchmarked win. Paired with the cheapest rate card in this matchup, that makes Grok 4.5 a strong value play for high-volume, latency-sensitive work — with one hard boundary. Grok 4.5 is not available in the EU under the AI Act, so this category is explicitly non-EU. For any team inside the EU, the value calculation is moot and Sol is the only option of the two.

Best for Independent Reliability Signal: GPT-5.6 Sol, Where Measured

Reliability is the category where the data is one-sided in a way that cuts against Grok 4.5. On Artificial Analysis's AA-Omniscience test, which measures how often a model confabulates rather than admitting uncertainty, Grok 4.5 scored 26 with a 52 percent accuracy rate and a 54 percent hallucination rate. Artificial Analysis has not published an equivalent figure for Sol in our sources, so this is a standalone caveat on Grok 4.5 rather than a head-to-head result — but for knowledge-intensive work where a confident wrong answer is expensive, it is a signal worth weighing. Ground either model with retrieval and verification on high-stakes facts rather than trusting recall.

Pros and Cons

GPT-5.6 Sol Pros and Cons

What we like about GPT-5.6 Sol

• Higher on every independent capability chart that covers both. Intelligence Index 59 to 54 and Coding Agent Index 80 to 76, per Artificial Analysis.
• Cheaper per task despite the higher rate card. About $1.04 to run the AA Intelligence Index versus about $2.49 for Grok 4.5 — the counterintuitive efficiency win.
• More than double the context window. 1,050,000 tokens against 500,000, enough to hold whole repositories and long histories in one pass.
• Ultra multi-agent mode and Programmatic Tool Calling. Up to sixteen parallel reasoning agents and code-orchestrated tool use, neither of which Grok 4.5 offers.
• Available in the EU. The only one of these two a European team can deploy without a regional workaround.

Where GPT-5.6 Sol falls short

• More than double the token price. $5 input and $30 output per million against Grok 4.5's $2 and $6 — a real cost gap on high-volume work.
• Absent from independent SWE-bench Verified. Not submitted, so it has no third-party verified-coding number.
• Coding headline is self-reported. Its strongest coding figures (Terminal-Bench 2.1, SWE-bench Pro) come from OpenAI, which disputes the Pro benchmark it cites.
• Two days old at the time of writing. Our hands-on window is roughly 48 hours, so its production behavior over weeks is unproven.
• No independent speed advantage on our data. At about 74.5 tokens per second it is measured, but Grok 4.5 is positioned as the faster model.

Grok 4.5 Pros and Cons

What we like about Grok 4.5

• Less than half the token price. $2 input and $6 output per million against Sol's $5 and $30 — 60 percent and 80 percent cheaper, verified on SpaceXAI's docs.
• Positioned as much faster. SpaceXAI calls it Opus-class and much faster; speed is its headline selling point for latency-sensitive work.
• Cheap, capable bulk work. On high-volume shallow calls, the price and apparent speed make it a strong default where deep reasoning is not required.
• Standard agent tooling. Function calling and structured outputs are supported, with a simple low, medium, and high reasoning control.
• Trained with Cursor. SpaceXAI reports coding-focused training on GB300 GPUs, and it lands roughly level with GPT-5.5 on the independent Coding Agent Index.

Where Grok 4.5 falls short

• Behind Sol on every independent capability chart that covers both. Intelligence Index 54 to 59 and Coding Agent Index 76 to 80.
• More expensive per task on the one independent measurement. About $2.49 to run the AA Intelligence Index versus about $1.04 for Sol.
• Independent hallucination caveat. A 54 percent hallucination rate on Artificial Analysis's AA-Omniscience test, with 52 percent accuracy.
• Half the context window. 500,000 tokens against Sol's 1,050,000, which forces chunking on the largest inputs.
• Not available in the EU. The EU AI Act restriction rules it out entirely for European teams, and it is absent from LMArena and SWE-bench Verified.

When to Pick GPT-5.6 Sol vs Grok 4.5

Pick GPT-5.6 Sol if...

• You want the top of the independent capability curve of these two — higher Intelligence Index and Coding Agent Index scores, per Artificial Analysis.
• Your workloads need long context — a 1,050,000-token window is more than double Grok 4.5's and holds whole repositories in one pass.
• Per-task economics matter more than the sticker rate, where Sol measures about $1.04 to Grok 4.5's $2.49 on the AA Intelligence Index run.
• You want a multi-agent reasoning mode (ultra, up to sixteen parallel agents) or code-orchestrated tool use via Programmatic Tool Calling.
• You serve or process data in the EU — Grok 4.5 is not available there, so Sol is the only option of the two.

Pick Grok 4.5 if...

• Token price is the deciding factor — $2 input and $6 output per million is less than half of Sol on both sides.
• Your workload is high-volume and shallow, where the cheap rate card and vendor-stated speed matter more than a five-point Intelligence Index gap.
• Latency is a top priority and you are willing to trust SpaceXAI's much-faster positioning, or to benchmark speed on your own traffic.
• You operate outside the EU, where the AI Act restriction does not apply to you.
• You already run in the SpaceXAI ecosystem or the us-east-1 and us-west-2 regions it serves.

Frequently Asked Questions

Is GPT-5.6 Sol better than Grok 4.5 in 2026?

It depends on what you are optimizing for, and we will not fake a single overall winner. On the independent leaderboards where both appear, GPT-5.6 Sol leads on measured capability: Artificial Analysis scores it 59 on the Intelligence Index against Grok 4.5's 54, ranks it No.1 on the Coding Agent Index at 80 to Grok's 76, and measures it cheaper per task at about $1.04 versus $2.49 on that same evaluation. Sol also carries more than double the context window. Grok 4.5 wins on the rate card, costing less than half of Sol per token, and SpaceXAI positions it as much faster. Best for capability, long context, and per-task cost: Sol. Best for the lowest token price on high-volume, non-EU work: Grok 4.5.

How much do GPT-5.6 Sol and Grok 4.5 cost?

GPT-5.6 Sol costs $5 per million input tokens and $30 per million output tokens, with cached input at $0.50 per million and Batch mode at half price — we confirmed this on OpenAI's API pricing documentation. Grok 4.5 costs $2 per million input tokens and $6 per million output tokens, with cached input at $0.50 per million — we confirmed this directly on SpaceXAI's Grok 4.5 model documentation. At the rate card, Grok 4.5 is 60 percent cheaper on input and 80 percent cheaper on output, so it is less than half of Sol on both sides. That headline gap is real, but it is not the whole cost story once you measure cost per task rather than cost per token.

Is Grok 4.5 really cheaper than GPT-5.6 Sol?

Cheaper per token, yes; cheaper per task, no, on the one independent measurement available. Grok 4.5's rate card of $2 input and $6 output per million tokens is less than half of Sol's $5 and $30. But Artificial Analysis publishes the cost to run its Intelligence Index evaluation, and it lists about $1.04 per task for GPT-5.6 Sol versus about $2.49 for Grok 4.5 — Sol is roughly two and a half times cheaper on that specific run. The two figures point in opposite directions because per-task cost depends on how many tokens each model burns to finish the work, and Grok 4.5 defaults to its high reasoning setting. Which number matters depends on how token-efficient your own workload is, so test on your real prompts before assuming the rate card decides it.

Which is better for coding: GPT-5.6 Sol or Grok 4.5?

On the one independent coding leaderboard where both appear, GPT-5.6 Sol leads. Artificial Analysis ranks Sol No.1 on its Coding Agent Index at 80, ahead of Grok 4.5 at 76, which sits roughly level with the prior GPT-5.5. Neither model has been submitted to the independently run SWE-bench Verified suite, so there is no third-party Verified number for either — a genuine data gap we flag rather than fill with self-reported figures. OpenAI reports Sol at 88.8 percent on Terminal-Bench 2.1 (91.9 percent in ultra mode), but that is self-reported. SpaceXAI notes Grok 4.5 was trained with Cursor and calls it Opus-class, but publishes no comparable independent coding score in our sources. On independent evidence, Sol has the edge on the Coding Agent Index; on verified coding, neither has a number.

Why are GPT-5.6 Sol and Grok 4.5 missing from SWE-bench Verified?

Because neither vendor has submitted its July 9 flagship to the independently run SWE-bench Verified suite yet, so as of this comparison there is no third-party Verified figure for either model. On that leaderboard, Claude Fable 5 sits at 95 percent and Claude Opus 4.8 at 88.6 percent, but both Sol and Grok 4.5 are simply absent. We flag the gap rather than substitute a self-reported number. OpenAI instead reports Sol on SWE-bench Pro (a different, harder suite) at 64.6 percent while disputing that benchmark's validity, and SpaceXAI reports no independent coding score in our sources. For an independent coding signal that does cover both, we use the Artificial Analysis Coding Agent Index, where Sol scores 80 and Grok 4.5 scores 76.

Which has the larger context window: GPT-5.6 Sol or Grok 4.5?

GPT-5.6 Sol, by more than double. OpenAI's model documentation lists Sol at a 1,050,000-token context window with a February 16, 2026 knowledge cutoff, while SpaceXAI's documentation lists Grok 4.5 at 500,000 tokens. That is not a rounding difference like some frontier matchups — Sol holds roughly 2.1 times as much context, which matters for whole-repository code work, long document sets, and agents that accumulate large histories. Both models take text and image inputs and return text. If your workloads routinely exceed half a million tokens, Sol is the only one of the two that fits them in a single context; if they stay well under 500,000 tokens, the difference will not affect you.

Is Grok 4.5 available in the EU?

No. At the time of writing, SpaceXAI does not make Grok 4.5 available in the European Union, citing the EU AI Act's systemic-risk obligations, and its API documentation lists only us-east-1 and us-west-2 regions. For any team that must serve or process data inside the EU, that makes Grok 4.5 a non-option regardless of its price, and GPT-5.6 Sol — which OpenAI offers in the EU — becomes the default of these two by elimination. We are based outside the EU, so we were able to test Grok 4.5 directly, but we flag the restriction prominently because it is a hard gate for a large share of readers rather than a minor caveat.

What is GPT-5.6 Sol's ultra reasoning mode?

Ultra is a new multi-agent reasoning setting introduced with the GPT-5.6 generation, and it is primarily a Sol feature. Per OpenAI's documentation, the reasoning-effort scale now runs from low through xhigh, then adds a new max level and, above that, ultra — which spawns multiple reasoning agents in parallel (four by default, up to sixteen) to attack a single problem. It is aimed at the hardest long-horizon coding, science, and agentic tasks, and OpenAI reports Sol at 91.9 percent on Terminal-Bench 2.1 in ultra mode versus 88.8 percent standard. Grok 4.5 exposes a simpler low, medium, and high reasoning control with high as the default, and no equivalent parallel-agent mode. Ultra buys headroom on Sol's hardest tasks, at a higher token bill per call.

How reliable is Grok 4.5?

There is one independent reliability caveat worth weighing. On Artificial Analysis's AA-Omniscience test, which probes how often a model confabulates rather than admitting it does not know, Grok 4.5 scored 26 with a 52 percent accuracy rate and a 54 percent hallucination rate. That is a signal to weigh for knowledge-intensive work where a confident wrong answer is costly. Artificial Analysis has not published an equivalent AA-Omniscience figure for GPT-5.6 Sol in our sources, so we present Grok 4.5's number as a standalone caveat rather than a head-to-head result. As with any single benchmark, treat it as one data point: for high-stakes factual work, ground either model with retrieval and verification rather than trusting raw recall.

Which model is faster: GPT-5.6 Sol or Grok 4.5?

We cannot declare a numeric speed winner, because our sources give an independent throughput figure for only one of the two. Artificial Analysis measures GPT-5.6 Sol at roughly 74.5 tokens per second. For Grok 4.5, SpaceXAI positions it as Opus-class and much faster than its rivals, and Elon Musk has repeated that framing, but that is a vendor claim rather than an independently benchmarked tokens-per-second figure in our sources. Speed is genuinely one of Grok 4.5's headline selling points, and it may well be faster in practice, but we will not crown it on a vendor statement against an independent number. If latency is your deciding factor, benchmark both on your own traffic before committing.

Did GPT-5.6 Sol and Grok 4.5 really launch on the same day?

Effectively yes. GPT-5.6 Sol reached general availability on July 9, 2026, following a gated preview on June 26. Grok 4.5 was announced by SpaceXAI on July 8 and reached public availability on July 9, replacing Grok 4.3 as the flagship while Grok 4.3 and 4.20 remain available. So on July 9, 2026, two frontier models from OpenAI and SpaceXAI went live within hours of each other, which is exactly why this comparison frames them as same-day, different-strategy releases: one betting on peak measured capability and long context, the other on the lowest token rate card and speed. Both are new, so we scope our hands-on notes to first impressions and lean on attributed third-party benchmarks.

What are the alternatives to GPT-5.6 Sol and Grok 4.5?

Several sit close by. Claude Opus 4.8, at $5 per million input and $25 per million output tokens, posts 88.6 percent on the independent SWE-bench Verified suite and is the model SpaceXAI benchmarks Grok 4.5 against when it says Opus-class. Claude Fable 5 currently tops the Artificial Analysis Intelligence Index at 60, one point above Sol. GPT-5.5, OpenAI's prior flagship, remains active and cheaper for routine work, and Grok 4.3 is still available below Grok 4.5. If you want the adjacent matchups in detail, our GPT-5.5 versus Grok 4.3 comparison covers the previous generation of this same OpenAI-versus-Grok rivalry, and our Grok 4.3 and Claude Opus 4.8 reviews cover the nearest neighbors on each side.

Final Verdict — Capability vs the Cheapest Rate Card, a True Split

After running both side-by-side for roughly 48 hours, verifying pricing on both vendors' own documentation, and holding every capability claim to independent benchmarks, our verdict is a genuine split — not a diplomatic one. GPT-5.6 Sol is the measured-capability and reach leader: it scores 59 to Grok 4.5's 54 on the Artificial Analysis Intelligence Index, leads the Coding Agent Index 80 to 76, is measured cheaper per task at about $1.04 to $2.49, carries more than double the context window, adds an ultra multi-agent mode Grok 4.5 does not offer, and — decisively for many readers — is available in the EU. Grok 4.5 is the rate-card and speed play: at $2 input and $6 output per million tokens it is less than half of Sol on both sides, SpaceXAI positions it as Opus-class and much faster, and for high-volume, cost-sensitive, non-EU work that combination is genuinely compelling. We disclose plainly that we have no affiliate relationship with either vendor and tested both through our own API keys.

We did not crown a single overall winner because the evidence does not support one honestly: Sol's capability, context, and per-task lead are real, but so is Grok 4.5's dramatically cheaper rate card, and Grok 4.5 carries a published hallucination caveat and an EU block that Sol does not. If your work is capability-critical, long-context, or bound for the EU — pick GPT-5.6 Sol. If your work is high-volume, cost-sensitive, and outside the EU — pick Grok 4.5 and bank the token savings. For many teams the rational endgame is routing: Sol for the hardest reasoning, longest context, and EU traffic, Grok 4.5 for cheap, fast, high-volume calls where a five-point capability gap does not change the outcome. For the tiers and neighbors around this matchup, see our GPT-5.5 review, our Grok 4.3 review, our Claude Opus 4.8 review, our Claude Fable 5 review, and our GPT-5.5 vs Grok 4.3 comparison, which covers the previous round of this same OpenAI-versus-Grok rivalry.

Sources

Every figure in this comparison is attributed to a primary or independent source. Pricing and specifications come from the vendors' own documentation; capability scores come from independent third parties; self-reported figures are labeled as such throughout.

• OpenAI — GPT-5.6 announcement and positioning
• OpenAI — GPT-5.6 Sol model documentation and specifications
• OpenAI — GPT-5.6 API pricing
• SpaceXAI — Grok 4.5 model documentation and pricing
• SpaceXAI — Grok product home
• Artificial Analysis — Intelligence Index, Coding Agent Index, cost per task, and AA-Omniscience
• LMArena — human-preference Elo leaderboard
• vals.ai — SWE-bench Verified independent leaderboard

Last compared: July 2026. Both GPT-5.6 Sol and Grok 4.5 reached general availability on July 9, 2026; both models are new, and we will revise this comparison as independent benchmark coverage matures.