Grok 4.5 vs GPT-5.5: The Price-Aggressive Challenger vs the Established Flagship (2026)

Grok 4.5 and GPT-5.5 are the two frontier models compared here. Grok 4.5 is SpaceXAI's price-aggressive new flagship, public since July 9, 2026, priced at $2 per million input tokens and $6 per million output tokens with a 500,000-token context window. GPT-5.5 is OpenAI's established flagship, active since April 2026, priced at $5 per million input tokens and $30 per million output tokens with a 1,050,000-token context window. Grok 4.5 costs less than half of GPT-5.5 per token and Artificial Analysis measures its cost per task near the bottom of the frontier tier at about $2.49. GPT-5.5 answers with independent proof Grok 4.5 does not yet have: an 82.6 percent SWE-bench Verified score on vals.ai, an LMArena Elo of 1481, a marginally higher Artificial Analysis Intelligence Index of 55 to 54, and more than double the context. Grok 4.5 is not available in the EU. Best for lowest price on non-EU work: Grok 4.5. Best for verified capability, long context, and EU deployment: GPT-5.5.

Quick Verdict

This is a split verdict: Grok 4.5 owns the token rate card, the independent cost per task, and its vendor-stated speed, while GPT-5.5 owns the independently verified benchmarks, the larger context window, and EU availability — and the EU AI Act settles the choice outright for a large group of readers. Grok 4.5 reached public availability on July 9, 2026, and we tested it through our own SpaceXAI API key; GPT-5.5 has been OpenAI's established flagship since April 2026, and we have run it in production across the same window, so this is a genuine side-by-side. We lean on attributed third-party numbers from Artificial Analysis, LMArena, and vals.ai wherever a benchmark tells the story better than a few days of hands-on can. Every figure below carries its source, and self-reported vendor numbers are labeled as such. Here is the short version.

• 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 GPT-5.5 — less than half on both sides, verified on SpaceXAI's documentation.
• Best for cost per task: Grok 4.5. Artificial Analysis measures it at about $2.49 to run its Intelligence Index, near the bottom of the frontier tier; it publishes no equivalent per-task figure for GPT-5.5 in our sources, so we lean on the verified rate card, where Grok 4.5's advantage is unambiguous.
• Best for verified coding: GPT-5.5. It posts 82.6 percent on the independently run SWE-bench Verified suite at vals.ai; Grok 4.5 has no independently verified SWE-bench Verified score yet because it is too new to appear on that leaderboard.
• Best on human-preference ranking: GPT-5.5. It holds an LMArena Elo of 1481, while Grok 4.5 is not yet ranked on LMArena as of this comparison.
• Best on aggregate intelligence, marginally: GPT-5.5. Artificial Analysis scores it 55 on the Intelligence Index against Grok 4.5's 54 — a single-point gap, far smaller than the price difference.
• Roughly tied on agentic coding: both. On the Artificial Analysis Coding Agent Index, Grok 4.5 scores 76 and GPT-5.5 lands near the same score, so the independent agentic-coding signal is effectively level.
• Best for long context: GPT-5.5, by more than double. Its 1,050,000-token window is roughly 2.1 times Grok 4.5's 500,000 tokens.
• 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 no independent tokens-per-second figure for either model, so we flag this as a vendor claim, not a benchmarked win.
• Only option for EU teams: GPT-5.5. Grok 4.5 is not available in the European Union under the AI Act, which makes GPT-5.5 the default of these two for anyone serving EU users regardless of price.

The honest caveats up front: Grok 4.5 is days old at the time of writing, so we treat our hands-on notes on it as first impressions, not a settled verdict, and we lean harder on GPT-5.5's longer track record only where that is fair. SpaceXAI has not submitted Grok 4.5 to the independently run SWE-bench Verified suite yet, so there is no third-party verified-coding number for it, and we will not paper over that gap with the self-reported figures floating around launch coverage. 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 GPT-5.5. 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.

Grok 4.5 vs GPT-5.5 — Overview

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-5.5 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, a claim we treat as vendor positioning. 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. You can read our full Grok 4.5 review for the standalone breakdown.

What Is GPT-5.5?

GPT-5.5 is OpenAI's established flagship, generally available since April 2026 and still active — GPT-5.5 was not deprecated by later releases, and it remains OpenAI's mainstream frontier model at the time of writing. Per OpenAI's documentation, it is the first fully retrained base model since GPT-4.5, runs a 1,050,000-token context window with a December 1, 2025 knowledge cutoff, and takes text and image inputs to text output. It exposes a five-level reasoning-effort scale — none, low, medium, high, and xhigh — which was the most granular reasoning control of any frontier model at its launch, and it ships a complete native agentic tool stack: function calling, structured outputs, web search, file search, code interpreter, computer use, and MCP client support, with Codex available across ChatGPT plans. API pricing is $5 per million input tokens and $30 per million output tokens, with cached input at $0.50 per million and a Batch mode at half price, all verified on OpenAI's pricing documentation. On independent leaderboards it posts an 82.6 percent SWE-bench Verified score on vals.ai and an LMArena Elo of 1481. Our full GPT-5.5 review covers the tier in depth.

How We Compared Them — and What We Did Not Do

Method transparency matters here, because one model is days old and the other has months of track record, 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. Grok 4.5's $2 input and $6 output per million tokens is confirmed against SpaceXAI's model documentation; GPT-5.5's $5 input and $30 output per million is confirmed against OpenAI's pricing 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), LMArena (Elo), and vals.ai (SWE-bench Verified). 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 both SWE-bench Verified and LMArena — we say so and do not substitute a self-reported number.
• Self-reported figures: SpaceXAI's Opus-class and much-faster positioning for Grok 4.5 is labeled as vendor-reported and not treated as head-to-head evidence. Grok 4.5's only independent coding credit in our sources is its Artificial Analysis Coding Agent Index score of 76. Our GPT-5.5 vs Grok 4.3 comparison covers the previous round of this same rivalry for context.
• Hands-on: we tested Grok 4.5 through our own SpaceXAI API key since its July 9 general availability, roughly a few days of side-by-side, and we have run GPT-5.5 in production since its April release. We scope every Grok 4.5 observation as a first impression, and we weight the attributed benchmarks above short hands-on time for both.
• Disclosure: we have no affiliate relationship with SpaceXAI or OpenAI. 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, LMArena, and vals.ai.

Synthesis: 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, plus a cost per task near the bottom of the frontier tier at about $2.49. The verified capability signals tilt to GPT-5.5 — it is the only one of the two with an independent SWE-bench Verified score (82.6 percent) and an LMArena ranking (1481), it edges the Intelligence Index 55 to 54, and it carries more than double the context. Agentic coding is a genuine tie on the shared Artificial Analysis Coding Agent Index near 76. Two structural facts sit outside the benchmark table and can decide the whole thing on their own: GPT-5.5'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 the cheapest rate card and vendor-stated speed against independently verified capability, reach, and maturity — and which of those you value decides the matchup.

Pricing — Grok 4.5 vs GPT-5.5 in 2026

Pricing is the sharpest contrast in this comparison, and unlike some frontier matchups it is not reversed by the cost-per-task data — here the cheaper rate card and the cheaper measured task point the same way. Both rate cards below come straight from SpaceXAI's and OpenAI's own documentation, and our pricing explainer covers how these translate into real spend.

Grok 4.5 Pricing

GPT-5.5 Pricing

Pricing verdict: Grok 4.5 wins the rate card decisively, and it wins cost per task on the one independent measurement we have. 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 GPT-5.5 ($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 GPT-5.5's $30. On cost per task, Artificial Analysis measures Grok 4.5 at about $2.49 to run its Intelligence Index, near the bottom of the frontier tier; it does not publish an equivalent per-task figure for GPT-5.5 in our sources, so we do not invent one, but nothing in the data reverses the rate-card advantage the way a token-efficient rival sometimes can. Both models discount cached input to the same $0.50 per million, so long-running agents with stable system prompts see the same read-side savings on each. If cost is your deciding factor and you are outside the EU, Grok 4.5 is the cheaper model to run on essentially every read of the numbers.

Hands-On Notes — Grok 4.5 New, GPT-5.5 Proven

We owe you precision about what this section is and is not. Grok 4.5 went public on July 9, 2026, and we had it running through our own SpaceXAI API key within hours, which gives us a few days of direct use at the time of writing — sharp first impressions, nowhere near a controlled benchmark. GPT-5.5 we have run in production since its April 2026 release, so our read on it is deeper. Take every Grok 4.5 observation as scoped and provisional, and weight the attributed benchmarks above our hands-on time for both.

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. It returned valid, schema-adherent JSON on every structured-output run in our testing, and its OpenAI-compatible API meant most of our existing SDK code ran with only a base-URL and model-name change. For workloads that are wide rather than deep, that combination of low price and apparent speed is its strongest hand.

Where GPT-5.5 held the edge: the hardest single problems, long inputs, and predictability. 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, and on deep multi-file reasoning we leaned on the model that carries an independent SWE-bench Verified number rather than the one that does not yet. Its five-level reasoning control gave us finer knobs than Grok 4.5's low, medium, and high, and months of production use mean we know its failure modes. That maturity is not a benchmark line, but it is real, and it is exactly what a brand-new model cannot offer yet.

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 a few days 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: Grok 4.5's latency under controlled conditions, its per-task token economics across a real workload mix, and whether its early behavior holds up over weeks. We will update this comparison as our Grok 4.5 time accumulates and as more independent harnesses — including SWE-bench Verified and LMArena — publish results for it.

Winner per Category

Best for Token Price and Cost per Task: Grok 4.5

This one is not close on the rate card. Grok 4.5 costs $2 per million input tokens against GPT-5.5'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. Unlike matchups where a token-efficient rival flips the cost story on a per-task basis, the independent cost-per-task data here reinforces Grok 4.5's lead: Artificial Analysis measures it at about $2.49 to run its Intelligence Index, near the bottom of the frontier tier. If price is your deciding factor and your work does not touch the EU, Grok 4.5 wins this category outright.

Best for Verified Coding: GPT-5.5

On independently verified coding, GPT-5.5 has a number and Grok 4.5 does not yet. GPT-5.5 posts 82.6 percent on the independently run SWE-bench Verified suite at vals.ai, where Claude Opus 4.8 sits at 88.6 percent and Claude Fable 5 leads at 95 percent. Grok 4.5 is too new to appear on that leaderboard, so it has no independently verified SWE-bench Verified score, and we will not substitute the self-reported Opus-class framing for one. The one independent coding chart where both do appear — the Artificial Analysis Coding Agent Index — has them roughly level near 76, so agentic coding is a tie while verified coding currently favors GPT-5.5 on the strength of a third-party number Grok 4.5 has not yet earned.

Best on Independent Rankings: GPT-5.5

Beyond coding, GPT-5.5 leads the two independent rankings that cover it and not Grok 4.5. It holds an LMArena Elo of 1481 on the human-preference leaderboard, where Grok 4.5 is not yet ranked, and it edges the Artificial Analysis Intelligence Index 55 to 54 — a single point, which we are careful not to oversell. Artificial Analysis placed Grok 4.5 at No.4 in the flagship field at its July 8 publication, behind Claude Fable 5, GPT-5.5, and Claude Opus 4.8. The Intelligence Index gap is marginal; the meaningful separation is that GPT-5.5 has independent human-preference and verified-coding rankings on the board while Grok 4.5's are still pending.

Best for Long Context and Maturity: GPT-5.5

GPT-5.5 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, GPT-5.5 fits jobs in one context that Grok 4.5 must split. It also brings a fuller native agentic tool stack — web search, file search, code interpreter, computer use, and MCP, with Codex across ChatGPT plans — and months of production maturity, against a model that is days old. For long-context pipelines, deep tool use, and teams that value a known, stable model, GPT-5.5 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 no independent tokens-per-second figure for either model, 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 GPT-5.5 is the only option of the two.

Best for the Independent Reliability Signal: GPT-5.5, 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 GPT-5.5 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

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 GPT-5.5's $5 and $30 — 60 percent and 80 percent cheaper, verified on SpaceXAI's docs.
• Low cost per task. About $2.49 to run the Artificial Analysis Intelligence Index, near the bottom of the frontier tier — the rate-card advantage is not reversed on a per-task basis here.
• Positioned as much faster. SpaceXAI calls it Opus-class and much faster; speed is its headline selling point for latency-sensitive work, though we treat it as a vendor claim.
• Roughly level on agentic coding. A 76 on the independent Artificial Analysis Coding Agent Index, effectively tied with GPT-5.5, and trained with Cursor on GB300 GPUs.
• OpenAI-compatible API and reliable structured outputs. Most existing SDK code runs with a base-URL and model-name change, and it returned valid JSON on every run in our testing.

Where Grok 4.5 falls short

• No independently verified SWE-bench Verified score. Too new to appear on vals.ai, so it has no third-party verified-coding number, while GPT-5.5 posts 82.6 percent.
• Absent from LMArena. Not yet ranked on the human-preference leaderboard, where GPT-5.5 holds an Elo of 1481.
• 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 GPT-5.5's 1,050,000, which forces chunking on the largest inputs.
• Not available in the EU, and days old. The EU AI Act restriction rules it out entirely for European teams, and its production behavior over weeks is unproven.

GPT-5.5 Pros and Cons

What we like about GPT-5.5

• Independently verified coding score. 82.6 percent on SWE-bench Verified at vals.ai — a third-party number Grok 4.5 does not yet have.
• Ranked on human preference. An LMArena Elo of 1481, plus a marginally higher Artificial Analysis Intelligence Index of 55 to 54.
• More than double the context window. 1,050,000 tokens against 500,000, enough to hold whole repositories and long histories in one pass.
• Mature, full agentic stack. Web search, file search, code interpreter, computer use, and MCP, with Codex across plans and five-level reasoning control.
• Available in the EU and battle-tested. The only one of these two a European team can deploy, and in production since April 2026.

Where GPT-5.5 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.
• More expensive to run on the cost-per-task read. Grok 4.5's measured $2.49 and far cheaper rate card put GPT-5.5 on the costlier side of this matchup.
• Only a marginal intelligence edge. A single Artificial Analysis Intelligence Index point over Grok 4.5, far smaller than the price gap.
• Tied, not ahead, on agentic coding. The Artificial Analysis Coding Agent Index has it roughly level with Grok 4.5 near 76.
• Not the newest architecture. Grok 4.5 is the fresher release, and later OpenAI tiers now sit above GPT-5.5 on the very top of the capability charts.

When to Pick Grok 4.5 vs GPT-5.5

Pick Grok 4.5 if...

• Token price is the deciding factor — $2 input and $6 output per million is less than half of GPT-5.5 on both sides.
• Your workload is high-volume and cost-sensitive, where the cheap rate card and low cost per task matter more than a one-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.
• Agentic coding is your main use and the independent Coding Agent Index tie near 76 is good enough at a much lower price.

Pick GPT-5.5 if...

• You want independently verified capability — an 82.6 percent SWE-bench Verified score and an LMArena Elo of 1481 that Grok 4.5 does not yet have.
• 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.
• You serve or process data in the EU — Grok 4.5 is not available there, so GPT-5.5 is the only option of the two.
• You value a mature, battle-tested model with a full native agentic tool stack and Codex over a days-old release.
• Knowledge-intensive reliability matters and you would rather not deploy against Grok 4.5's published 54 percent hallucination caveat without heavy retrieval.

Frequently Asked Questions

Is Grok 4.5 or GPT-5.5 better in 2026?

It depends on whether you weigh price or independent proof, and we will not fake a single overall winner. Grok 4.5 wins the rate card decisively — $2 per million input tokens and $6 per million output against GPT-5.5's $5 and $30, less than half on both sides — and Artificial Analysis measures its cost per task near the bottom of the frontier tier at about $2.49. GPT-5.5 wins on verified capability: an independent SWE-bench Verified score of 82.6 percent on vals.ai that Grok 4.5 does not yet have, an LMArena Elo of 1481, a marginally higher Artificial Analysis Intelligence Index of 55 to 54, and more than double the context window. Best for cost and speed on non-EU work: Grok 4.5. Best for verified capability, long context, and EU deployment: GPT-5.5.

How much do Grok 4.5 and GPT-5.5 cost?

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. GPT-5.5 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. 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 GPT-5.5 on both sides. That headline gap is large and real, and here it is reinforced rather than reversed by an independent cost-per-task figure that also favors Grok 4.5.

Is Grok 4.5 really cheaper than GPT-5.5?

Yes, on both the rate card and the one independent cost figure we have. Grok 4.5's $2 input and $6 output per million tokens is less than half of GPT-5.5's $5 and $30. Artificial Analysis also publishes the cost to run its Intelligence Index evaluation and lists Grok 4.5 at about $2.49 per task, near the bottom of the frontier tier; it does not publish an equivalent per-task figure for GPT-5.5 in our sources, so we lean on the verified rate card, where Grok 4.5's advantage is unambiguous. Cost per task always depends on how many tokens a model burns to finish the work, so for token-heavy reasoning test on your own prompts, but the direction here is clear: Grok 4.5 is the cheaper model to run.

Which is better for coding: Grok 4.5 or GPT-5.5?

It splits by which coding signal you trust. On the one independent leaderboard where both are measured — the Artificial Analysis Coding Agent Index — they are roughly level, with Grok 4.5 at 76 and GPT-5.5 near the same score. On the independently run SWE-bench Verified suite, GPT-5.5 posts 82.6 percent on vals.ai, while Grok 4.5 has no independently verified SWE-bench Verified score yet because it is too new to appear on that leaderboard. SpaceXAI notes Grok 4.5 was trained with Cursor and calls it Opus-class, but that is a vendor claim, not an independent coding number. So agentic coding is a genuine tie on the shared index, while verified coding currently favors GPT-5.5 on the strength of a third-party number Grok 4.5 does not yet have.

Why isn't Grok 4.5 on the SWE-bench Verified leaderboard?

Because Grok 4.5 reached public availability only on July 9, 2026, and as of this comparison it does not have an independently verified SWE-bench Verified score on vals.ai. That is a data gap we flag rather than fill with a self-reported figure. On that same independently run suite, GPT-5.5 posts 82.6 percent, Claude Opus 4.8 posts 88.6 percent, and Claude Fable 5 leads at 95 percent, but Grok 4.5 is simply absent. For an independent coding signal that does cover Grok 4.5, we use the Artificial Analysis Coding Agent Index, where it scores 76, roughly level with GPT-5.5. We treat SpaceXAI's Opus-class positioning as a vendor claim and keep it separate from verified numbers.

Which has the larger context window: Grok 4.5 or GPT-5.5?

GPT-5.5, by more than double. OpenAI documents GPT-5.5 at a 1,050,000-token context window with a December 1, 2025 knowledge cutoff, while SpaceXAI's documentation lists Grok 4.5 at 500,000 tokens. That is not a rounding difference — GPT-5.5 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, GPT-5.5 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 and Grok 4.5's price advantage carries more weight.

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 the 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-5.5 — 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, and it can settle the entire decision before price or benchmarks enter the picture.

Is GPT-5.5 still worth it now that Grok 4.5 is cheaper?

For a large set of teams, yes. GPT-5.5 remains OpenAI's active, non-deprecated flagship, and it brings things Grok 4.5's lower price cannot yet buy: an independently verified SWE-bench Verified score of 82.6 percent on vals.ai, an LMArena Elo of 1481, more than double the context window, a mature native agentic tool stack with Codex, and EU availability. If your work is verification-critical, long-context, or bound for the EU, GPT-5.5's proof and reach outweigh Grok 4.5's rate card. If your work is high-volume, cost-sensitive, and outside the EU, Grok 4.5's price advantage is hard to argue with. This is exactly why the verdict is a split rather than a clean upgrade in either direction.

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-5.5 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: Grok 4.5 or GPT-5.5?

We cannot declare a numeric speed winner, because our sources give no independent tokens-per-second figure for either model in this matchup. SpaceXAI positions Grok 4.5 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 figure. Speed is genuinely one of Grok 4.5's headline selling points, and paired with its low price it may well be the faster and cheaper choice for high-volume work, but we will not crown it on a vendor statement alone. If latency is your deciding factor, benchmark both models on your own traffic before committing, because published rate cards and marketing claims do not measure real-world tail latency on your prompts.

Which has the higher Artificial Analysis Intelligence Index: Grok 4.5 or GPT-5.5?

GPT-5.5, but only just. Artificial Analysis scores GPT-5.5 at 55 on its Intelligence Index against Grok 4.5's 54, and it placed Grok 4.5 at No.4 in the flagship field at its July 8 publication, behind Claude Fable 5, GPT-5.5, and Claude Opus 4.8. A single point on an aggregate index is a marginal gap, not a decisive one, and it is far smaller than the price difference between the two models. On this measure alone, the two are effectively neighbors; the more meaningful capability separations in this matchup are the verified SWE-bench Verified score and the LMArena ranking that GPT-5.5 has and Grok 4.5 does not yet, plus the context window, rather than the one-point Intelligence Index margin.

What are the alternatives to Grok 4.5 and GPT-5.5?

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. On the cheaper end, DeepSeek V4 and Grok's own predecessor Grok 4.3 are worth weighing, and Gemini 3.1 Pro is another frontier option. 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 Claude Opus 4.8 versus GPT-5.5 comparison covers the verified-coding leader against this same GPT-5.5.

Final Verdict — The Cheapest Rate Card vs the Most Proven Flagship, a True Split

After testing Grok 4.5 through our own SpaceXAI API key since its July 9 launch, running GPT-5.5 in production since April, 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. Grok 4.5 is the rate-card and cost play: at $2 input and $6 output per million tokens it is less than half of GPT-5.5 on both sides, its cost per task sits near the bottom of the frontier tier at about $2.49, and SpaceXAI positions it as Opus-class and much faster; for high-volume, cost-sensitive, non-EU work that combination is genuinely compelling. GPT-5.5 is the independently proven, higher-reach flagship: it is the only one of the two with a verified SWE-bench Verified score (82.6 percent), an LMArena ranking (1481), and more than double the context window, it edges the Intelligence Index 55 to 54, and it is available in the EU. 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. This is not a points tally where the model with more table rows wins; it is a matchup where Grok 4.5's price advantage is so large — a fifth of the output cost — that it flips the decision for a whole class of high-volume, non-EU users, while GPT-5.5's independent verification, context, and EU reach are exactly what verification-critical and European teams cannot do without. Independent agentic coding is a genuine tie near 76. If your work is cost-sensitive, high-volume, and outside the EU — pick Grok 4.5 and bank the token savings. If your work needs independently verified capability, long context, or EU deployment — pick GPT-5.5. For many teams the rational endgame is routing: Grok 4.5 for cheap, fast, high-volume calls where a one-point capability gap does not change the outcome, and GPT-5.5 for the verification-critical, long-context, and EU traffic. For the tools and neighbors around this matchup, see our Grok 4.5 review, our GPT-5.5 review, our Grok 4.3 review, our Claude Opus 4.8 review, and our GPT-5.5 vs Grok 4.3 comparison and Claude Opus 4.8 vs GPT-5.5 comparison.

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 vendor positioning is labeled as such throughout.

• SpaceXAI — Grok 4.5 model documentation and pricing
• SpaceXAI — Grok product home
• OpenAI — GPT-5.5 API pricing
• OpenAI — GPT-5.5 model documentation and specifications
• 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. Grok 4.5 reached public availability on July 9, 2026 and is new, while GPT-5.5 has been in production since April 2026; we will revise this comparison as independent benchmark coverage of Grok 4.5 matures.