config.toml context window settings are not respected

[kkellyoffical]

What happened?

The context-related settings in config.toml do not appear to take effect. I tried configuring Codex from:

C:\Users\12768\.codex\config.toml

Relevant settings:

model = "gpt-5.5"
model_reasoning_effort = "high"
model_context_window = 960000
model_auto_compact_token_limit = 800000

After setting a large context window, for example around 1M, Codex still automatically reports/uses about 258k instead. This makes it impossible to control the effective context window from the config file.

Expected behavior

model_context_window and model_auto_compact_token_limit should be honored, or Codex should report a clear validation/error message if the configured value exceeds the supported model/client limit.

Actual behavior

The configured value is silently reduced/ignored. For example, setting approximately 1M results in Codex automatically changing/using about 258k.

Environment

• OS: Windows
• Config path: C:\Users\12768\.codex\config.toml
• Model configured: gpt-5.5

Why this matters

Users cannot reliably control context behavior through config.toml, and the silent conversion makes it difficult to understand whether the setting is unsupported, capped by the model, capped by the client, or being parsed incorrectly.

[github-actions]

Potential duplicates detected. Please review them and close your issue if it is a duplicate.

• Codex Pro GPT-5.4 long context regressed: ~672k worked Apr 22, ~290k fails Apr 23 #19142
• Codex CLI freezes near auto-compaction threshold and drifts with very large context windows #19116
• TUI runs out of context with gpt-5.5 despite auto-compact config #19183

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[LukyPlay]

gpt 5.5 doesn't have 1m context window with codex :(

[litaotju]

I can reproduce/confirm this on Codex Desktop for macOS as well, and it looks like the config is being loaded but then clamped by model metadata rather than ignored.

Environment I checked:

• Codex.app: 26.422.20832
• Bundled CLI: codex-cli 0.124.0-alpha.2
• Model: gpt-5.5
• Config included:

model = "gpt-5.5"
model_context_window = 1050000
model_auto_compact_token_limit = 900000

Observed model metadata from the installed app:

model	context_window	max_context_window	effective_context_window_percent
gpt-5.4	272000	1000000	95
gpt-5.5	272000	272000	95
crest-alpha	272000	272000	95

The relevant source path appears to be with_config_overrides, which clamps the configured context window to max_context_window:

codex/codex-rs/models-manager/src/model_info.rs

Lines 29 to 36 in 3f8c06e

	if let Some(context_window) = config.model_context_window {
	model.context_window = Some(
	model
	.max_context_window
	.map_or(context_window, |max_context_window| {
	context_window.min(max_context_window)
	}),
	);

So for gpt-5.5, model_context_window = 1050000 becomes min(1050000, 272000) = 272000. Then the effective context shown/used is further reduced by effective_context_window_percent = 95, which explains the ~258400 number.

The struct docs also describe max_context_window as the maximum allowed for config overrides:

codex/codex-rs/protocol/src/openai_models.rs

Lines 279 to 285 in 3f8c06e

	pub context_window: Option<i64>,
	/// Maximum context window allowed for config overrides.
	#[serde(default, skip_serializing_if = "Option::is_none")]
	pub max_context_window: Option<i64>,
	/// Token threshold for automatic compaction. When omitted, core derives it
	/// from `context_window` (90%). When provided, core clamps it to 90% of the
	/// context window when available.

And auto-compact is similarly capped to 90% of the resolved context window:

codex/codex-rs/protocol/src/openai_models.rs

Lines 310 to 318 in 3f8c06e

	pub fn auto_compact_token_limit(&self) -> Option<i64> {
	let context_limit = self
	.resolved_context_window()
	.map(|context_window| (context_window * 9) / 10);
	let config_limit = self.auto_compact_token_limit;
	if let Some(context_limit) = context_limit {
	return Some(
	config_limit.map_or(context_limit, |limit| std::cmp::min(limit, context_limit)),
	);

This makes the current behavior understandable but surprising: gpt-5.4 can use 1M because its catalog entry advertises max_context_window = 1000000; gpt-5.5 cannot because its catalog entry advertises max_context_window = 272000.

Expected improvement: if this is intentional because gpt-5.5 does not currently support 1M in Codex, Codex should surface a clear warning/status message when config values are clamped, e.g. model_context_window=1050000 was reduced to 272000 because gpt-5.5 max_context_window is 272000. If gpt-5.5 is supposed to support 1M, then the model catalog entry likely needs to advertise the larger max_context_window.

[cccat6]

#19208 (comment)
#19208 (comment)
It sounds expected, but I am unhappy with that...

[drixs2050]

setting to 400000 is not working as well