Same build task, same planted bug, same refactor, same test suite. Here is what GPT-5 and Grok 4 actually shipped.
Editorial Note: This article is based on hands-on use of the tools from our own test accounts, combined with product documentation, benchmark data, and publicly available information. All features, pricing, and benchmark figures are verified through official sources. See our Disclaimer.
Short answer: ChatGPT (GPT-5) is the better coding assistant. It passed 10 of our 12 unit tests on the first generation against 8 for Grok 4, followed the written spec more faithfully, and backs it up with a real developer toolchain — Codex, a CLI and repo connectors — that Grok simply does not have yet. Grok is fast, blunt, and excellent at questions about libraries that changed this week, but on the code itself it finishes second.
This matchup gets asked a lot because Grok 4 posts strong numbers on public reasoning benchmarks and xAI markets it hard to developers. Benchmarks are not a codebase, though. So we put both through the identical three-task gauntlet we use for every coding comparison on this site, scored against a test suite written before either model saw the prompt.
Over four working days (July 27–30, 2026) we ran the same three tasks through the ChatGPT app with GPT-5 (Thinking enabled where relevant) and Grok 4 via grok.com, both on paid accounts we pay for ourselves:
We used the same tasks as our ChatGPT vs Claude for coding test, so the scores are directly comparable across all three models. Full methodology lives on our How We Test page.
| Dimension | ChatGPT (GPT-5) | Grok 4 | Edge |
|---|---|---|---|
| First-pass tests passed (of 12) | 10 | 8 | ChatGPT |
| Followed the written spec first try | Yes, sliding window as asked | No, fixed window | ChatGPT |
| Debug: found planted race condition | 2nd prompt | 3rd prompt | ChatGPT |
| Refactor behaviour preserved | 1 test broke | 3 tests broke | ChatGPT |
| Speed to first token | Moderate | Noticeably faster | Grok |
| Live web / X data for new libraries | Browse pass, often lags | Real-time, best in class | Grok |
| Coding agent | Codex (cloud + CLI) | None comparable | ChatGPT |
| Consumer price | $20/mo (Plus) | ~$30/mo SuperGrok, $40/mo Premium+ | ChatGPT |
| API price (input / output per 1M) | $1.25 / $10 | $3 / $15 | ChatGPT |
Our build prompt is deliberately picky. It asks in capital letters for a sliding-window algorithm, not a fixed window, because fixed windows allow burst traffic at boundaries — and three of our twelve tests target exactly that.
GPT-5 implemented the sliding window correctly on the first attempt, using a per-key timestamp array with pruning. It handled X-Forwarded-For behind a trust-proxy check and emitted all three RateLimit headers. It failed two tests: same-millisecond burst collisions, and a Retry-After value it rounded down instead of up. Both were fixed in one follow-up.
Grok 4 produced clean, readable code fast — and used a fixed-window counter, the one thing the prompt explicitly ruled out. That cost it the three boundary tests immediately, plus one more on header formatting. When we pasted the failing tests, Grok's response was refreshingly direct: it said it had chosen the simpler algorithm for performance reasons and then rewrote it properly. Two follow-ups later it reached 12/12. Its final code was the most compact of the three models we have run this task through, but with the fewest comments.
Takeaway: Grok writes tidy code but skims requirements. If your prompts are loose and you iterate conversationally, the gap is small. If you write precise specs and expect them honoured, GPT-5 respects them more consistently.
We gave both models the 340-line asyncio script with one line of context: "This script occasionally produces a wrong total. Find out why and fix it."
GPT-5 in Thinking mode narrowed to the right coroutine on its first reply but proposed a fix that changed the accumulation semantics; after we shared the failing output it identified the interleaving across the await boundary and applied an asyncio.Lock correctly. Two prompts total.
Grok 4's first reply blamed floating-point accumulation — a confident wrong answer. Its second reply suspected the queue consumer. Only on the third, after we supplied a reproduction with logging, did it find the actual race. It then fixed it cleanly and, to its credit, explained the failure mode better than GPT-5 did. Three prompts total.
Worth noting for context: Claude found this same bug on the first pass. If debugging is the bulk of your AI usage, neither model here is the category leader — see our best AI coding assistants ranking for the full field.
The 1,100-line jQuery-to-ES2022 conversion tests context handling and discipline. GPT-5 accepted the whole file and returned a refactor that broke exactly one integration test (a dropped event.stopPropagation()). Grok 4 also accepted the file — its 256K context is ample — but its output broke three tests: two event-delegation regressions and one changed default parameter. It also silently reordered several functions, which made the diff harder to review than the code quality warranted.
For anything you have to review line by line before merging, reviewable diffs matter as much as correctness. GPT-5 was the safer collaborator here.
Two areas, and they are not trivial. First, speed: Grok is consistently quicker to first token, and for the dozens of small "what's the signature of this method" questions a developer fires off in a day, that responsiveness is genuinely pleasant.
Second, freshness. Grok's live access to X and the web is the best of any major assistant. When we asked about a breaking change published four days earlier in a popular Node library, Grok cited the maintainer's own post and the migration note; ChatGPT's browse pass returned the previous major version's docs and had to be pushed twice. If you work near the bleeding edge of fast-moving ecosystems, that is a real workflow advantage. For the wider non-coding picture, our Grok vs ChatGPT comparison goes deeper on personality, search and image features.
This is the least close section. ChatGPT ships Codex as a cloud sandbox and a CLI that clones a repo, edits files, runs tests and opens pull requests; plus connectors for Drive and GitHub, custom GPTs, and a mature API with structured outputs and function calling that most frameworks support out of the box. Grok offers a solid API and in-chat code execution, but no first-party agent that lives in your terminal and touches your repository. For developers whose workflow has moved toward agentic coding, that single gap outweighs most model-quality arguments.
ChatGPT Plus is $20/month. Grok's fuller access comes through SuperGrok at about $30/month or X Premium+ at about $40/month (verified on openai.com and x.ai pricing pages, July 2026). On the API, GPT-5 lists at $1.25/M input and $10/M output tokens against Grok 4 at roughly $3/M and $15/M. ChatGPT is cheaper on both the subscription and the API, which makes the value case fairly one-sided unless you specifically need Grok's real-time X data.
Yes, competent — 8/12 first-pass tests and clean, compact output. But it skimmed our spec, took three prompts to find a bug ChatGPT found in two, and has no terminal coding agent.
ChatGPT, clearly. Better spec compliance, better first-pass correctness, better debugging, cheaper, and a far deeper developer toolchain.
Roughly $30/mo (SuperGrok) or $40/mo (X Premium+) versus $20/mo for ChatGPT Plus. Grok's API is also about 2.4x more expensive on input tokens.
No first-party equivalent. In-chat code execution and API access exist, but nothing that autonomously edits a repo and runs your test suite.
Speed to first token, and real-time knowledge of libraries and breaking changes from the last few days — where it beat ChatGPT outright in our testing.
Choose ChatGPT if you want the better code, the better price, the better agent, and an ecosystem that plugs into everything. For the overwhelming majority of developers this is the correct default.
Choose Grok if you are already paying for X Premium+, you value blunt, fast answers, or your work depends on knowing what shipped and broke in the last 72 hours.
Our pick for a developer's single subscription in 2026: ChatGPT Plus. It won three of our four scored coding dimensions, costs a third less than Grok's comparable tier, and Codex alone justifies the price. Grok 4 is a legitimately good model attached to a developer story that is still incomplete — keep it on the free tier for real-time lookups and let ChatGPT write the code.
On July 27, 2026, we gave ChatGPT (GPT-5) and Grok 4 the identical build prompt below in fresh sessions on our own paid accounts, pasted each answer into a clean repo with no manual edits, and ran the same pre-written 12-test Jest suite against both.
| Metric | ChatGPT (GPT-5) | Grok 4 |
|---|---|---|
| Jest tests passed, first generation (of 12) | 10 ✓ | 8 |
| Followed sliding-window spec on first try | Yes ✓ | No — produced fixed-window counter |
| Memory-leak prevention included unprompted | Yes ✓ | No — unbounded Map |
| Proxy / IP handling correct | Yes ✓ | Yes ✓ |
| All three RateLimit headers emitted | Yes ✓ | Two of three |
| Prompts needed to reach 12/12 | 2 ✓ | 3 |
| Time from prompt to all tests green | 10 min ✓ | 14 min |
| Lines of code in final answer | 132 | 104 ✓ |
| Explanatory comments in final code | Thorough ✓ | Minimal |
| Winner | 🏆 ChatGPT | — |
Both have free tiers worth trying, but the paid plans unlock the models and agents we tested. ChatGPT won our coding gauntlet — and costs less.
Keep exploring — these related comparisons and guides help you decide.