feat: support separate chat_template.jinja file (#1853)

lib/llm/src/model_card/create.rs

@@ -86,6 +86,7 @@ impl ModelDeploymentCard {
             tokenizer: Some(TokenizerKind::from_gguf(gguf_file)?),
             gen_config: None, // AFAICT there is no equivalent in a GGUF
             prompt_formatter: Some(PromptFormatterArtifact::GGUF(gguf_file.to_path_buf())),
+            chat_template_file: None,
             prompt_context: None, // TODO - auto-detect prompt context
             revision: 0,
             last_published: None,
@@ -124,6 +125,7 @@ impl ModelDeploymentCard {
             tokenizer: Some(TokenizerKind::from_repo(repo_id).await?),
             gen_config: GenerationConfig::from_repo(repo_id).await.ok(), // optional
             prompt_formatter: PromptFormatterArtifact::from_repo(repo_id).await?,
+            chat_template_file: PromptFormatterArtifact::chat_template_from_repo(repo_id).await?,
             prompt_context: None, // TODO - auto-detect prompt context
             revision: 0,
             last_published: None,
@@ -157,6 +159,19 @@ impl PromptFormatterArtifact {
             .ok())
     }
 
+    pub async fn chat_template_from_repo(repo_id: &str) -> Result<Option<Self>> {
+        Ok(Self::chat_template_try_is_hf_repo(repo_id)
+            .await
+            .with_context(|| format!("unable to extract prompt format from repo {}", repo_id))
+            .ok())
+    }
+
+    async fn chat_template_try_is_hf_repo(repo: &str) -> anyhow::Result<Self> {
+        Ok(Self::HfChatTemplate(
+            check_for_file(repo, "chat_template.jinja").await?,
+        ))
+    }
+
     async fn try_is_hf_repo(repo: &str) -> anyhow::Result<Self> {
         Ok(Self::HfTokenizerConfigJson(
             check_for_file(repo, "tokenizer_config.json").await?,

lib/llm/src/model_card/model.rs

@@ -62,6 +62,7 @@ pub enum TokenizerKind {
 #[serde(rename_all = "snake_case")]
 pub enum PromptFormatterArtifact {
     HfTokenizerConfigJson(String),
+    HfChatTemplate(String),
     GGUF(PathBuf),
 }
 
@@ -101,6 +102,10 @@ pub struct ModelDeploymentCard {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub prompt_formatter: Option<PromptFormatterArtifact>,
 
+    /// chat template may be stored as a separate file instead of in `prompt_formatter`.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub chat_template_file: Option<PromptFormatterArtifact>,
+
     /// Generation config - default sampling params
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub gen_config: Option<GenerationConfig>,
@@ -259,6 +264,11 @@ impl ModelDeploymentCard {
             PromptFormatterArtifact::HfTokenizerConfigJson,
             "tokenizer_config.json"
         );
+        nats_upload!(
+            self.chat_template_file,
+            PromptFormatterArtifact::HfChatTemplate,
+            "chat_template.jinja"
+        );
         nats_upload!(
             self.tokenizer,
             TokenizerKind::HfTokenizerJson,
@@ -308,6 +318,11 @@ impl ModelDeploymentCard {
             PromptFormatterArtifact::HfTokenizerConfigJson,
             "tokenizer_config.json"
         );
+        nats_download!(
+            self.chat_template_file,
+            PromptFormatterArtifact::HfChatTemplate,
+            "chat_template.jinja"
+        );
         nats_download!(
             self.tokenizer,
             TokenizerKind::HfTokenizerJson,

lib/llm/src/preprocessor/prompt/template.rs

@@ -26,7 +26,7 @@ mod oai;
 mod tokcfg;
 
 use super::{OAIChatLikeRequest, OAIPromptFormatter, PromptFormatter};
-use tokcfg::ChatTemplate;
+use tokcfg::{ChatTemplate, ChatTemplateValue};
 
 impl PromptFormatter {
     pub async fn from_mdc(mdc: ModelDeploymentCard) -> Result<PromptFormatter> {
@@ -37,13 +37,28 @@ impl PromptFormatter {
             PromptFormatterArtifact::HfTokenizerConfigJson(file) => {
                 let content = std::fs::read_to_string(&file)
                     .with_context(|| format!("fs:read_to_string '{file}'"))?;
-                let config: ChatTemplate = serde_json::from_str(&content)?;
+                let mut config: ChatTemplate = serde_json::from_str(&content)?;
+                // Some HF model (i.e. meta-llama/Llama-4-Maverick-17B-128E-Instruct-FP8)
+                // stores the chat template in a separate file, we check if the file exists and
+                // put the chat template into config as normalization.
+                if let Some(PromptFormatterArtifact::HfChatTemplate(chat_template_file)) =
+                    mdc.chat_template_file
+                {
+                    let chat_template = std::fs::read_to_string(&chat_template_file)
+                        .with_context(|| format!("fs:read_to_string '{}'", chat_template_file))?;
+                    // clean up the string to remove newlines
+                    let chat_template = chat_template.replace('\n', "");
+                    config.chat_template = Some(ChatTemplateValue(either::Left(chat_template)));
+                }
                 Self::from_parts(
                     config,
                     mdc.prompt_context
                         .map_or(ContextMixins::default(), |x| ContextMixins::new(&x)),
                 )
             }
+            PromptFormatterArtifact::HfChatTemplate(_) => Err(anyhow::anyhow!(
+                "prompt_formatter should not have type HfChatTemplate"
+            )),
             PromptFormatterArtifact::GGUF(gguf_path) => {
                 let config = ChatTemplate::from_gguf(&gguf_path)?;
                 Self::from_parts(config, ContextMixins::default())