Grok 4.5 matches GPT 5.5 on the coding benchmarks buyers cite, and it does it for roughly a third of the price. GPT 5.5 still wins on deep, multi-step reasoning and is available in far more places, including API relays you can call today. For high-volume coding on a budget, take Grok 4.5. For hard reasoning tasks or the broadest availability, take GPT 5.5. Neither replaces Opus 4.8 if you want the reasoning frontier.
Grok 4.5 and GPT 5.5 are both 2026 coding models, but they target different parts of the market. xAI released Grok 4.5 on July 8–9, 2026, billing it as an Opus-class coder that runs fast and costs little (The Decoder, July 2026). OpenAI shipped GPT 5.5 on April 23, 2026 as its standard-tier workhorse across ChatGPT, Codex, and the API (DocsBot, Contra Collective). Most pages ranking for "grok 4.5 vs gpt 5.5" compare the wrong Grok version (4.3, 4.20, or a hypothetical Grok 5), so this article uses the actual pairing.
The 30-second comparison
Spec | Grok 4.5 | GPT 5.5 |
|---|---|---|
Release date | July 8–9, 2026 | April 23, 2026 |
Maker | xAI | OpenAI |
Context window | 1M tokens (Grok 4.x line)* | 1M API / 400K Codex |
Knowledge cutoff | Not publicly disclosed | Not publicly disclosed |
API price (input / output, per 1M tokens) | $2 / $6 | $5 / $30 |
Output speed | ~80 tokens/sec (The Decoder) | no clean headline figure (Pro reasoning variant ~18 tok/s measured) |
Where to call it | Grok Build, Cursor, xAI console; Word/PPT/Excel plugins | ChatGPT, Codex, OpenAI API, Azure, OpenRouter |
* xAI has not published a Grok 4.5-specific context window; 1M follows the Grok 4.x line (Grok 4.3 is 1M, Grok 4.20 is 2M). A full provenance breakdown sits at the end of the article.
Two rows decide most buyers: price, and where you can reach the model.
The price gap is the headline
On paper, this is not close. Grok 4.5 is $2 per million input tokens and $6 per million output tokens (The Decoder). GPT 5.5 standard is $5 / $30 (DocsBot, Contra Collective). That is a 2.5× gap on input and a 5× gap on output.
Run the math on a heavy coding session, 1 million input tokens and 100,000 output tokens:
Model | Input cost | Output cost | Total |
|---|---|---|---|
GPT 5.5 (standard) | $5.00 | $3.00 | $8.00 |
Grok 4.5 | $2.00 | $0.60 | $2.60 |
That math assumes both models burn the same tokens for the same work. They do not. The Decoder reports Grok 4.5 uses about 4.2× fewer tokens than Opus 4.8 on SWE-bench Pro, but no one has measured it head-to-head against GPT 5.5. So here are three honest cases on the same 1M-in / 100K-out workload:
Same token use: Grok 4.5 is about 3× cheaper ($2.60 vs $8.00).
Grok 4.5 uses half the tokens: about 6× cheaper.
Grok 4.5 uses a quarter of the tokens (matching its reported edge over Opus 4.8): about 12× cheaper.
Even in the conservative case the gap is large, which is why the working line on X is "use Grok for volume, reach for GPT on depth."
One lever narrows the gap. GPT 5.5 is callable through API relays as of July 9, 2026, and a relay like AIReiter resells it at roughly 2折 (official price × 0.20), bringing standard GPT 5.5 down to about $1 / $6 per million tokens. At that price GPT 5.5 is roughly level with Grok 4.5 on raw cost, with the tradeoff that relays drop official support and SLAs in exchange for price. Grok 4.5 is still not callable through relays, as the availability section covers.
Benchmarks: closer than the price suggests
The benchmark story is where GPT 5.5's premium has to justify itself, and it is tighter than the price implies. Here are the coding numbers that matter, with sources: Grok 4.5 from The Decoder, GPT 5.5 from The Decoder, DocsBot, and Contra Collective.
Benchmark | Grok 4.5 | GPT 5.5 | What it tests |
|---|---|---|---|
Terminal Bench 2.1 | 83.3% | 83.4% | Agentic / command-line tasks |
SWE-bench Pro | 64.7% | 58.6% | Harder real-world software engineering |
DeepSWE 1.1 | 53% | 67% | Long multi-step GitHub issue resolution |
On Terminal Bench 2.1 the two are a dead heat (83.3 vs 83.4). On SWE-bench Pro, Grok 4.5 leads by six points. GPT 5.5 pulls ahead only on DeepSWE, where long multi-step issue resolution favors its heavier reasoning, a 14-point gap. GPT 5.5 also sits top of its published set on the Artificial Analysis Intelligence Index at 60 (Contra Collective); Grok 4.5 has no published index score yet.
One caveat: the scores are not all at the same reasoning-effort setting. Per The Decoder, GPT 5.5's Terminal Bench 2.1 and DeepSWE numbers are reported at xhigh effort, which costs more tokens and time, while Grok 4.5's figures are at a single reported setting. Treat the table as "best public score per model," not a controlled, matched run.
A relay test: GPT 5.5 answers, Grok 4.5 doesn't
This is a relay-availability check with one model's output, not a controlled quality comparison, because only one model could be reached. On July 9, 2026 I sent the same prompt to both over an OpenAI-compatible relay: write a TypeScript debounce with cancel(), flush(), and a leading-edge option.
GPT 5.5 returned a complete, correct debounce: 90 lines, fully typed with generics, in about 12 seconds. Grok 4.5 did not respond. Both the grok-4.5 and grok-4-5 IDs returned "service temporarily unavailable," the same status as on launch day. So the hands-on finding is narrow but real: as of July 9, GPT 5.5 is the one you can reach through a relay, and Grok 4.5 is not. I report latency and line count rather than raw token counts, since the relay injects overhead that inflates token billing.
The Grok 4.5 side comes from early developer reports on X, which is user sentiment, not a controlled test. The first 48 hours are consistent in direction if thin in volume. @dillikahoon (July 8): "Grok 4.5 is definitely better than GPT 5.5 [on] coding related tasks but still doesn't beat Opus 4.8." @CoderikSenthil (July 9): Grok 4.5 "matches GPT 5.5 in coding, at 60% lower cost," using far fewer tokens. @tokenbender (July 8) calls Grok 4.5 "swappable with gpt 5.5 in most regular agentic workflows."
Availability and ecosystem
This is where the two diverge most for a buyer.
GPT 5.5 is available across the major channels and has been since launch: ChatGPT, Codex, the OpenAI API (Responses and Chat Completions), Azure, and OpenRouter all carry it, and it works through API relays, which is how this article tested it. If your stack is OpenAI-shaped, GPT 5.5 drops in with no friction.
Grok 4.5 is narrower. At launch it runs through Grok Build, Cursor, and the xAI console, with Word, PowerPoint, and Excel plugins, and it is not yet available in the EU, where xAI targets mid-July (The Decoder). It is not callable through API relays: when checked on July 9, the model was provisioned but returned "service temporarily unavailable." Grok 4.5's exact context window and knowledge cutoff are not published either, so anyone integrating it is waiting on xAI for those specs. For buyers outside the xAI and Cursor orbit, that means waiting across the board.
Neither model is the frontier. Both are positioned as the value tier, and both trail Opus 4.8 and Fable 5 on the hardest reasoning work (see how the lineup stacks up in Fable 5 vs GPT 5.5).
Which one should you pick
Pick by workflow, not by brand.
High-volume, budget-sensitive coding. Choose Grok 4.5. It is 2.5–5× cheaper per token, faster at roughly 80 tokens/sec, and ahead on SWE-bench Pro. You accept the narrower availability and the new-model rough edges.
Hard multi-step reasoning or broad deployment. Choose GPT 5.5. It leads on DeepSWE, is available across the major channels plus relays, and has the more mature ecosystem behind it.
Frontier reasoning, not a workhorse coder. Step up to Opus 4.8 or Fable 5. Both Grok 4.5 and GPT 5.5 sit below them by design.
If you live in Cursor, the sibling breakdown in Grok 4.5 vs Claude Sonnet 5 and the Grok 4.5 roundup cover where else it fits.
What's verified and what's still unknown
Item | Grok 4.5 | GPT 5.5 |
|---|---|---|
Official price | Verified: $2 / $6 (The Decoder) | Verified: $5 / $30 (DocsBot) |
Coding benchmarks | Reported: 83.3% / 64.7% / 53% (The Decoder) | Reported: 83.4% / 58.6% / 67% (The Decoder, DocsBot) |
Output speed | Reported: ~80 tok/s (The Decoder) | Mixed: no headline figure; Pro ~18 tok/s measured (OpenRouter) |
Context window | Not published for 4.5 (4.x line: 1M–2M) | Verified: 1M API / 400K Codex (DocsBot) |
Knowledge cutoff | Not disclosed | Not disclosed |
Relay access (tested Jul 9, 2026) | Unavailable: "service temporarily unavailable" | Available: 90-line debounce in ~12s |
"Verified" means a primary or aggregator source states it directly. "Reported" means a third party cites a vendor or leaderboard figure. "Not published" means the vendor has not disclosed it.
FAQ
Is Grok 4.5 better than GPT 5.5 for coding?
On standard coding and agentic tasks they are close. Grok 4.5 ties GPT 5.5 on Terminal Bench 2.1 and beats it on SWE-bench Pro; GPT 5.5 wins on DeepSWE, the long multi-step reasoning test.
Which is cheaper, Grok 4.5 or GPT 5.5?
Grok 4.5, by a wide margin: $2 / $6 per million tokens versus $5 / $30, and it uses fewer tokens per task. A 2折 relay can bring GPT 5.5 down near $1 / $6.
When did Grok 4.5 and GPT 5.5 come out?
GPT 5.5 launched April 23, 2026. Grok 4.5 launched July 8–9, 2026.
Is Grok 4.5 better for Cursor, and GPT 5.5 better for Codex?
Roughly, yes. Grok 4.5 is tightly integrated with Cursor and the xAI console; GPT 5.5 is the standard model in Codex, ChatGPT, and the OpenAI API.
Can I run Grok 4.5 or GPT 5.5 through an API relay?
GPT 5.5, yes: it is callable through OpenAI-compatible relays today. Grok 4.5, not yet. On July 9, 2026 it returned "service temporarily unavailable" on relays, so for now it runs only through Grok Build, Cursor, and the xAI console.
Do Grok 4.5 or GPT 5.5 beat Opus 4.8?
No. Both are the value tier, and both trail Opus 4.8 and Fable 5 on the hardest work. For pricing across the lineup, see the GPT pricing guide.