openai/codex · error · io::Error

`additional_developer_instructions` from {} exceeds the mode

Error message

`additional_developer_instructions` from {} exceeds the model-context limit of {MAX_MANAGED_DEVELOPER_INSTRUCTIONS_TOKENS} estimated tokens ({estimated_tokens} including context markers)

What it means

Error "`additional_developer_instructions` from {} exceeds the model-context limit of {MAX_MANAGED_DEVELOPER_INSTRUCTIONS_TOKENS} estimated tokens ({estimated_tokens} including context markers)" thrown in openai/codex.

Source

Thrown at codex-rs/core/src/context/world_state/managed_developer_instructions.rs:69

}

/// Reject oversized policy rather than silently dropping part of its instructions.
pub(crate) fn validate_managed_developer_instructions(
    requirement: Option<&Sourced<String>>,
) -> io::Result<()> {
    let Some(requirement) = requirement else {
        return Ok(());
    };
    // Reserve the notice used when an existing conversation receives a new policy.
    let overhead = ManagedDeveloperInstructions {
        instructions: format!("{REPLACEMENT_NOTICE}\n\n"),
    }
    .render()
    .len();
    let rendered_bytes = requirement.value.len().saturating_add(overhead);
    if rendered_bytes > approx_bytes_for_tokens(MAX_MANAGED_DEVELOPER_INSTRUCTIONS_TOKENS) {
        let estimated_tokens = approx_tokens_from_byte_count(rendered_bytes);
        return Err(io::Error::new(
            io::ErrorKind::InvalidInput,
            format!(
                "`additional_developer_instructions` from {} exceeds the model-context limit of {MAX_MANAGED_DEVELOPER_INSTRUCTIONS_TOKENS} estimated tokens ({estimated_tokens} including context markers)",
                requirement.source,
            ),
        ));
    }
    Ok(())
}

/// The managed policy currently visible in retained model history.
#[derive(Clone, Debug)]
pub(crate) struct ManagedDeveloperInstructionsState {
    instructions: Option<ManagedDeveloperInstructions>,
}

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub(crate) struct ManagedDeveloperInstructionsSnapshot {

View on GitHub (pinned to 339751715c)

Solutions

1. Shorten `additional_developer_instructions` from the reported source to fit under the token limit.

When it happens

Trigger: Thrown at codex-rs/core/src/context/world_state/managed_developer_instructions.rs:69 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of openai/codex@339751715c (2026-08-25). Data as JSON: /api/errors/4ea9d96477271599. Report an issue: GitHub.