Offer multiple Anthropic models in the composer model picker

config.example.yaml

@@ -36,6 +36,10 @@ agent:
   # Use claude-fable-5 for Anthropic's most capable (Mythos-class) model.
   # Note: ~2x the cost of Opus 4.8 ($10/$50 per MTok in/out).
   cron_model: claude-sonnet-4-6  # Cheaper model for cron jobs
+  # Extra Anthropic models offered in the web composer's model picker (alongside
+  # `model`). Lets you switch a message to a stronger model like Fable 5 on demand.
+  selectable_models:
+    - claude-fable-5
   title_model: claude-haiku-4-5-20251001  # Session title generation
   max_turns: 50                  # Max agentic turns per request
   max_concurrent: 4              # Max concurrent agent sessions

nerve/config.py

@@ -143,6 +143,9 @@ class AgentConfig:
     cron_backend: str = ""
     model: str = "claude-opus-4-8"
     cron_model: str = "claude-sonnet-4-6"
+    # Extra Anthropic chat models to offer in the composer's model picker
+    # alongside `model`. Empty = only the default model is selectable.
+    selectable_models: list[str] = field(default_factory=list)
     title_model: str = "claude-haiku-4-5-20251001"  # Session title generation
     max_turns: int = 100
     max_concurrent: int = 4
@@ -202,6 +205,7 @@ def from_dict(cls, d: dict) -> AgentConfig:
             cron_backend=str(d.get("cron_backend") or "").strip().lower(),
             model=d.get("model", "claude-opus-4-8"),
             cron_model=d.get("cron_model", "claude-sonnet-4-6"),
+            selectable_models=list(d.get("selectable_models") or []),
             title_model=d.get("title_model", "claude-haiku-4-5-20251001"),
             max_turns=d.get("max_turns", 100),
             max_concurrent=d.get("max_concurrent", 4),

nerve/gateway/routes/models.py

@@ -80,8 +80,15 @@ async def list_models(user: dict = Depends(require_auth)):
         "diagnostics": {"codex": codex_preflight},
     }
 
+    # Default model first, then any extra selectable Anthropic models
+    # (config.agent.selectable_models), de-duplicated, order preserved.
+    anthropic_ids: list[str] = [default_model]
+    for m in config.agent.selectable_models:
+        if m and m not in anthropic_ids:
+            anthropic_ids.append(m)
+
     models: list[dict[str, str]] = [
-        {"id": default_model, "provider": "anthropic", "backend": "claude"},
+        {"id": m, "provider": "anthropic", "backend": "claude"} for m in anthropic_ids
     ]
     if codex_preflight.get("available"):
         models.extend({

tests/test_engine.py

@@ -130,6 +130,16 @@ def test_claude_system_prompt_excludes_codex_runbook_policy(tmp_path):
     assert "Codex-native skills" not in str(options.system_prompt)
 
 
+def test_agent_config_selectable_models():
+    # Defaults to an empty list (only the default model is selectable).
+    assert AgentConfig.from_dict({}).selectable_models == []
+    # Explicit list preserved; None coerces to [].
+    assert AgentConfig.from_dict(
+        {"selectable_models": ["claude-fable-5"]}
+    ).selectable_models == ["claude-fable-5"]
+    assert AgentConfig.from_dict({"selectable_models": None}).selectable_models == []
+
+
 # ---------------------------------------------------------------------------
 # ClaudeClient.receive_turn — per-message idle timeout (hung-CLI detection)
 # ---------------------------------------------------------------------------