Add per-model-family prompts (#3597)

Allows more flexibility in defining prompts.

codex-rs/core/src/client_common.rs

@@ -10,15 +10,12 @@ use codex_protocol::models::ResponseItem;
 use futures::Stream;
 use serde::Serialize;
 use std::borrow::Cow;
+use std::ops::Deref;
 use std::pin::Pin;
 use std::task::Context;
 use std::task::Poll;
 use tokio::sync::mpsc;
 
-/// The `instructions` field in the payload sent to a model should always start
-/// with this content.
-const BASE_INSTRUCTIONS: &str = include_str!("../prompt.md");
-
 /// Review thread system prompt. Edit `core/src/review_prompt.md` to customize.
 pub const REVIEW_PROMPT: &str = include_str!("../review_prompt.md");
 
@@ -41,7 +38,7 @@ impl Prompt {
         let base = self
             .base_instructions_override
             .as_deref()
-            .unwrap_or(BASE_INSTRUCTIONS);
+            .unwrap_or(model.base_instructions.deref());
         let mut sections: Vec<&str> = vec![base];
 
         // When there are no custom instructions, add apply_patch_tool_instructions if either:
@@ -185,8 +182,12 @@ mod tests {
         let prompt = Prompt {
             ..Default::default()
         };
-        let expected = format!("{BASE_INSTRUCTIONS}\n{APPLY_PATCH_TOOL_INSTRUCTIONS}");
         let model_family = find_family_for_model("gpt-4.1").expect("known model slug");
+
+        let expected = format!(
+            "{}\n{}",
+            model_family.base_instructions, APPLY_PATCH_TOOL_INSTRUCTIONS
+        );
         let full = prompt.get_full_instructions(&model_family);
         assert_eq!(full, expected);
     }

codex-rs/core/src/config.rs

@@ -9,6 +9,7 @@ use crate::config_types::Tui;
 use crate::config_types::UriBasedFileOpener;
 use crate::git_info::resolve_root_git_project_for_trust;
 use crate::model_family::ModelFamily;
+use crate::model_family::derive_default_model_family;
 use crate::model_family::find_family_for_model;
 use crate::model_provider_info::ModelProviderInfo;
 use crate::model_provider_info::built_in_model_providers;
@@ -865,15 +866,8 @@ impl Config {
             .or(cfg.model)
             .unwrap_or_else(default_model);
 
-        let mut model_family = find_family_for_model(&model).unwrap_or_else(|| ModelFamily {
-            slug: model.clone(),
-            family: model.clone(),
-            needs_special_apply_patch_instructions: false,
-            supports_reasoning_summaries: false,
-            reasoning_summary_format: ReasoningSummaryFormat::None,
-            uses_local_shell_tool: false,
-            apply_patch_tool_type: None,
-        });
+        let mut model_family =
+            find_family_for_model(&model).unwrap_or_else(|| derive_default_model_family(&model));
 
         if let Some(supports_reasoning_summaries) = cfg.model_supports_reasoning_summaries {
             model_family.supports_reasoning_summaries = supports_reasoning_summaries;

codex-rs/core/src/model_family.rs

@@ -1,6 +1,11 @@
 use crate::config_types::ReasoningSummaryFormat;
 use crate::tool_apply_patch::ApplyPatchToolType;
 
+/// The `instructions` field in the payload sent to a model should always start
+/// with this content.
+const BASE_INSTRUCTIONS: &str = include_str!("../prompt.md");
+const SWIFTFOX_INSTRUCTIONS: &str = include_str!("../swiftfox_prompt.md");
+
 /// A model family is a group of models that share certain characteristics.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct ModelFamily {
@@ -33,6 +38,9 @@ pub struct ModelFamily {
     /// Present if the model performs better when `apply_patch` is provided as
     /// a tool call instead of just a bash command
     pub apply_patch_tool_type: Option<ApplyPatchToolType>,
+
+    // Instructions to use for querying the model
+    pub base_instructions: String,
 }
 
 macro_rules! model_family {
@@ -48,6 +56,7 @@ macro_rules! model_family {
             reasoning_summary_format: ReasoningSummaryFormat::None,
             uses_local_shell_tool: false,
             apply_patch_tool_type: None,
+            base_instructions: BASE_INSTRUCTIONS.to_string(),
         };
         // apply overrides
         $(
@@ -69,6 +78,7 @@ macro_rules! simple_model_family {
             reasoning_summary_format: ReasoningSummaryFormat::None,
             uses_local_shell_tool: false,
             apply_patch_tool_type: None,
+            base_instructions: BASE_INSTRUCTIONS.to_string(),
         })
     }};
 }
@@ -114,7 +124,27 @@ pub fn find_family_for_model(slug: &str) -> Option<ModelFamily> {
             slug, "gpt-5",
             supports_reasoning_summaries: true,
         )
+    } else if slug.starts_with("swiftfox") {
+        model_family!(
+            slug, "swiftfox",
+            supports_reasoning_summaries: true,
+            reasoning_summary_format: ReasoningSummaryFormat::Experimental,
+            base_instructions: SWIFTFOX_INSTRUCTIONS.to_string(),
+        )
     } else {
         None
     }
 }
+
+pub fn derive_default_model_family(model: &str) -> ModelFamily {
+    ModelFamily {
+        slug: model.to_string(),
+        family: model.to_string(),
+        needs_special_apply_patch_instructions: false,
+        supports_reasoning_summaries: false,
+        reasoning_summary_format: ReasoningSummaryFormat::None,
+        uses_local_shell_tool: false,
+        apply_patch_tool_type: None,
+        base_instructions: BASE_INSTRUCTIONS.to_string(),
+    }
+}