Openai
developers.openai.com › api › docs › models › gpt-5.3-codex
GPT-5.3-Codex Model | OpenAI API
GPT-5.3-Codex supports low, medium, high, and xhigh reasoning effort settings. If you want to learn more about prompting GPT-5.3-Codex, refer to our dedicated guide. 400,000 context window ·
Reddit
reddit.com › r/githubcopilot › gpt-5.3 codex have a 400k context windows in gh copilot
r/GithubCopilot on Reddit: GPT-5.3 Codex have a 400k context windows in GH Copilot
February 9, 2026 - I don't think that comparison is between the right metrics. Both 5.2 and 5.3 Codex have a 400k total context window, INCLUDING both in and output. So, 400k - 128k = 272k. They should both be identical.
Videos
r/codex on Reddit: GPT 5.3 Codex stuck in the infinite loop & ...
06:11
GPT-5.3-Codex and Opus 4.6 in 6min.. - YouTube
r/codex on Reddit: Meet GPT-5.3-Codex-Spark
16:03
Codex App + GPT 5.3 Codex Is INSANE! - Full Tutorial - YouTube
17:22
I Tried New GPT-5.4 vs GPT-5.3-Codex: Is It Better? - YouTube
08:00
Codex with GPT-5.4 Is Actually Good Now - YouTube
What is the context window for GPT-5.3 Codex?
It features a 400,000-token context window. This allows the model to digest entire enterprise repositories in a single pass.
automatio.ai
automatio.ai › home › models › gpt-5.3 codex
GPT-5.3 Codex - Pricing, Context Window Size, and ...
Is API access available for GPT-5.3 Codex?
Yes, it is available via the OpenAI API using the identifier gpt-5.3-codex. It is also accessible through the Codex app and CLI.
automatio.ai
automatio.ai › home › models › gpt-5.3 codex
GPT-5.3 Codex - Pricing, Context Window Size, and ...
What makes GPT-5.3 Codex agentic?
It is designed to operate computers end-to-end including running terminals and self-correcting mistakes. It moves beyond writing code to executing software lifecycle tasks.
automatio.ai
automatio.ai › home › models › gpt-5.3 codex
GPT-5.3 Codex - Pricing, Context Window Size, and ...
OpenAI
openai.com › index › introducing-gpt-5-3-codex
Introducing GPT-5.3-Codex | OpenAI
February 5, 2026 - The model advances both the frontier coding performance of GPT‑5.2‑Codex and the reasoning and professional knowledge capabilities of GPT‑5.2, together in one model, which is also 25% faster. This enables it to take on long-running tasks that involve research, tool use, and complex execution. Much like a colleague, you can steer and interact with GPT‑5.3‑Codex while it’s working, without losing context.
OpenAI
openai.com › index › introducing-gpt-5-3-codex-spark
Introducing GPT-5.3-Codex-Spark | OpenAI
February 12, 2026 - At launch, Codex-Spark has a 128k context window and is text-only. During the research preview, Codex-Spark will have its own rate limits and usage will not count towards standard rate limits.
Turingcollege
turingcollege.com › blog › gpt-5-4-review-vs-gpt-5-3-codex
GPT-5.4 Review: Is It Worth Leaving GPT-5.3 Codex Behind?
March 7, 2026 - It absorbed 5.3 Codex's coding capabilities into the mainline, added a 1-million-token context window, pushed computer use past human baseline, and won the GDPval knowledge-work benchmark at 83%. ...
Zilliz
zilliz.com › ai-faq › what-context-limits-does-gpt-53-codex-have-in-practice
What context limits does GPT 5.3 Codex have in practice? - Zilliz Vector Database
January 14, 2025 - In the GPT-5.3-Codex system documentation, compaction is described as being used to prevent the context window from growing too large in long agentic evaluations (compaction triggered every 100K tokens in a particular eval harness) and as enabling sustained coherent progress across long horizons [GPT-5.3-Codex System Card] (https://cdn.openai.com/pdf/23eca107-a9b1-4d2c-b156-7deb4fbc697c/GPT-5-3-Codex-System-Card-02.pdf?utm_source=chatgpt.com).
Reddit
reddit.com › r/githubcopilot › why does i have 272k context window for 5.3 codex?
why does I have 272k context window for 5.3 codex? : r/GithubCopilot
February 13, 2026 - This is just advertising the context window the same as everyone else. OpenAI advertises a 400k window (input + output): https://developers.openai.com/api/docs/models/gpt-5.2-codex
GitHub
github.com › openai › codex › issues › 9429
Increase effective context window 272000 -> 350000 · Issue #9429 · openai/codex
January 18, 2026 - This would trade off supporting 128k edge case support, for legitimate and broad improvement for users in large-context scenarios. I've been running this patch for about a week now, and the improvements are great. I can't go back to a 272k window now. ... diff --git c/codex-rs/core/models.json i/codex-rs/core/models.json index 537a42e27..72e08fe20 100644 --- c/codex-rs/core/models.json +++ i/codex-rs/core/models.json @@ -10,7 +10,7 @@ "limit": 10000 }, "supports_parallel_tool_calls": true, - "context_window": 272000, + "context_window": 350000, "reasoning_summary_format": "experimental", "slug
Author Zaczero
Artificial Analysis
artificialanalysis.ai › models › comparisons › gpt-5-3-codex-vs-gpt-5-1-codex
GPT-5.3 Codex (xhigh) vs GPT-5.1 Codex (high): Model Comparison
Comparison between GPT-5.3 Codex (xhigh) and GPT-5.1 Codex (high) across intelligence, price, speed, context window and more.
Automatio
automatio.ai › home › models › gpt-5.3 codex
GPT-5.3 Codex - Pricing, Context Window Size, and ...
March 10, 2026 - “GPT 5.3 Codex set the new high score on Terminal-Bench 2.0. 77.3% is a massive jump over the previous version.” ... “The ability to handle a 400k context window makes it possible to audit entire enterprise repositories in one go.”
OpenAI
openai.com › index › introducing-gpt-5-4
Introducing GPT-5.4 | OpenAI
March 5, 2026 - Context windows(opens in a new window) in ChatGPT for GPT‑5.4 Thinking remain unchanged from GPT‑5.2 Thinking. GPT‑5.4 is our first mainline reasoning model that incorporates the frontier coding capabilities of GPT‑5.3‑codex and that is rolling out across ChatGPT, the API and Codex.
GitHub
github.com › openai › codex › issues › 13799
Codex with GPT-5.4 (1M context window, set to compact at 500k) keeps stopping for no apparent reason, and forgetting to wait on subagents. · Issue #13799 · openai/codex
March 6, 2026 - Codex with GPT-5.4 (1M context window, set to compact at 500k) keeps stopping for no apparent reason, and forgetting to wait on subagents.#13799 ... bugSomething isn't workingSomething isn't workingmodel-behaviorIssues related to behaviors exhibited by the modelIssues related to behaviors exhibited by the model ... Codex repeatedly stops work or forgets to check on some in-progress task. GPT-5.3...
Author ariccio
Tensorlake
tensorlake.ai › blog › claude-opus-4-6-vs-gpt-5-3-codex
Claude Opus 4.6 vs GPT 5.3 Codex — Tensorlake
February 9, 2026 - A key aspect of GPT 5.3 Codex is its agentic design. It can work directly with terminals, files, and build tools, and continue operating across extended sessions while still allowing developers to guide and adjust the process without losing context.
X
x.com › chongdashu › status › 2029667206934503466
Chong-U on X: "GPT 5.4 has been released... + 1M context window! Here's how to enable in Codex: → 1. ~/.codex/config.toml → 2. model = "gpt-5.4" → 3. model_context_window=1000000 → 4. model_auto_compact_token_limit=9000000 Run codex → 5. /statusline → 6. toggle context-window-size I https://t.co/Zd40PFCTAX" / X
GPT 5.4 has been released... + 1M context window! Here's how to enable in Codex: → 1. ~/.codex/config.toml → 2. model = "gpt-5.4" → 3. model_context_window=1000000 → 4. model_auto_compact_token_limit=9000000 Run codex → 5. /statusline → 6.
Reddit
reddit.com › r/codex › only getting 258k context window on pro with gpt-5.4 in codex - thought it was supposed to be 1m?
r/codex on Reddit: only getting 258K context window on Pro with GPT-5.4 in Codex - thought it was supposed to be 1M?
March 6, 2026 -
as you can see from the screenshot, i'm on Pro and getting 258K context window for GPT-5.4 in Codex
thought the model supports 1M context - is this a Codex limitation or am i missing something in the settings?
Top answer 1 of 4
16
You need to manually add: model_context_window=800000 model_auto_compact_token_limit=700000 to your config.toml. It's in the announcement post: https://openai.com/index/introducing-gpt-5-4/ and details on the config params here: https://developers.openai.com/codex/config-reference/ In the above example I've set context to 800k and compact threshold to 700k. It's working great. I left some daylight because I'm worried about degradation as it approaches the max.
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For what it’s worth, it completely falls on its face after 258k context just like Gemini and opus 1m. So you’re not missing anything at all. You’re better off with compaction.
Thesys
thesys.dev › blogs › gpt-5-3-codex
GPT-5.3 Codex: 77.3% Terminal-Bench & Spark Speed Analysis
March 3, 2026 - GPT 5.3 Codex marks a shift from AI that writes code to AI that collaborates with developers, enabling real-time steering, deeper context awareness, and agentic workflows.
Interconnects
interconnects.ai › p › gpt-54-is-a-big-step-for-codex
GPT 5.4 is a big step for Codex - by Nathan Lambert
March 18, 2026 - The final benefit of GPT 5.4, and OpenAI’s agentic models in general for that matter, is much better context management. In using them regularly now I feel like I’ve never hit the context wall or context anxiety point. The reasoning efficiency I suspect is the case above just lets the model do way more with its initially empty context window.
OpenRouter
openrouter.ai › openai › gpt-5.3-codex
GPT-5.3-Codex - API Pricing & Providers | OpenRouter
February 24, 2026 - GPT-5.3-Codex is OpenAI’s most ... of GPT-5.2. $1.75 per million input tokens, $14 per million output tokens. 400,000 token context window......
DataCamp
datacamp.com › blog › gpt-5-4
GPT-5.4: Native Computer Use, 1M Context Window, Tool Search | DataCamp
March 6, 2026 - The news comes just two days after the release of GPT-5.3 Instant, an update focused mostly on conversational flow. In ChatGPT with the new GPT-5.4 Thinking model, you can adjust ChatGPT’s output mid-response, receive better deep web research results, and you’ll find it’s better at maintaining context on longer problems. For users accessing GPT-5.4 through the API and Codex, you’ll have access to new native computer use features, 1 million tokens of context, and tool search.
Reddit
reddit.com › r/codex › 5.4 vs 5.3 codex
r/codex on Reddit: 5.4 vs 5.3 Codex
March 12, 2026 -
I have personally found GPT 5.3 Codex better than 5.4.
I have Pro so I don’t worry about my token limits and use extra high pretty much on everything. That has worked tremendously for me with 5.3 Codex.
Since using 5.4 I’ve had so many more issues and I’ve had to go back-and-forth with the Model to fix issues consistently (and often to many hours and no luck). It hallucinates way more frequently, and I would probably have to use a lower reasoning level, or else it’ll overthink and underperform. This was very noticeable from the jump on multiple projects.
5.3 Codex is right on the money. I have no issues building with it and have actually used it to fix my issues when building with 5.4. 5.4 is definitely slowed down workflow.
Has anyone else experienced this?
Top answer 1 of 5
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I use on high always (extra high overthinks too much IMO) and I’m having a good time with 5.4. I just noticed that it’s way faster than 5.3 Codex.
2 of 5
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I like 5.4's generality. I'm big on intent engineering, and I'll keep the business plan, customer profiles, and long-term strategy for the software in the repo as additional guiding docs. I've also got a soul.md file in there that I wrote to give it broader conceptual, moral, ethical, and philosphical meanings behind why it's doing what it's doing and how to think about things when in doubt. These docs give the agent the "why" behind the software's creation and implementation, which is hugely helpful for helping it to fill in the gaps correctly when we inevitably underspecify. 5.4's better broad generalization allows it to better align itself with organizational intent and guide the output towards the "right" direction/answer when I've failed to specify things clearly enough in the specs. I found that 5.3 ignored these docs more often in favor of the "right" way to do it from a pure computer science standpoint. But the problem is that it defaults to the mean, and that isn't always the "right" way, and it's never the "best" way. At least with 5.4 listening to my org intent docs better, it will steer implementation and planning more towards my version of the "right" way and it will ultimately make the "right" choice more often than if left to my own devices. If you ask your agent why you are building this piece of software and it can't answer it to your satsifaction with subtlety and nuance incorporated, then you're gonna have a bad time. It's going to drift over time and eventually do something in a way that may be technically the "right" way to do it based on the average, but is wrong in your particular situation. Too many of those kinds of mistakes and you've got yourself some hearty software soup.