diff --git a/internal/agent/t3code.go b/internal/agent/t3code.go
index 1ac9aa81..3145503e 100644
--- a/internal/agent/t3code.go
+++ b/internal/agent/t3code.go
@@ -9,7 +9,8 @@ package agent
 //
 //	{"providerInstances":{"<id>":{"driver":"claudeAgent","displayName":…,
 //	  "enabled":true,"environment":[{"name":…,"value":…,"sensitive":false}],
-//	  "config":{"customModels":[{"slug":…,"name":…}]}}}}
+//	  "config":{"customModels":[{"slug":…,"name":…,"capabilities":
+//	    {"optionDescriptors":[{"id":"effort","type":"select",…}]}}]}}}}
 //
 // A claudeAgent instance runs Claude Code (Anthropic's Agent SDK, the
 // user's ~/.claude settings read as Claude Code reads them) with the
@@ -18,7 +19,8 @@ package agent
 // own, "magpie": Claude Code pointed at the gateway (ANTHROPIC_BASE_URL and
 // the token Claude Code is routed with, so its requests are Claude Code's
 // to the gateway, tiers and all), every magpie model one of its custom
-// models, a 1M one marked [1m] as magpie marks it for Claude Code. It is
+// models, a 1M one marked [1m] as magpie marks it for Claude Code, with
+// a Reasoning pick of the levels it takes (t3Capabilities). It is
 // magpie's alone: the user's own instances, their custom models and T3's
 // other keys stay as they are, and off takes only it out. A binary path or
 // Claude home the user gave T3's own Claude is carried over, so it runs the
@@ -107,7 +109,11 @@ func t3InstanceJSON(path, gw string) map[string]any {
 	mark := claude1MFor("t3code")
 	models := []map[string]any{}
 	for _, m := range magpieModels("t3code") {
-		models = append(models, map[string]any{"slug": mark(m.ID), "name": m.Name})
+		e := map[string]any{"slug": mark(m.ID), "name": m.Name}
+		if c := t3Capabilities(m.ID, m.Efforts); c != nil {
+			e["capabilities"] = c
+		}
+		models = append(models, e)
 	}
 	config := map[string]any{"customModels": models}
 	for _, k := range []string{"binaryPath", "homePath"} {
@@ -130,3 +136,36 @@ func t3InstanceJSON(path, gw string) map[string]any {
 		"config": config,
 	}
 }
+
+// t3EffortLabels are T3 Code's names for Claude Code's levels, as its own
+// Claude models show them.
+var t3EffortLabels = map[string]string{"low": "Low", "medium": "Medium", "high": "High", "xhigh": "Extra High", "max": "Max"}
+
+// t3Capabilities is the pick T3 Code shows beside a custom model: without
+// one it shows none and sends no effort, so every magpie model ran at
+// whatever Claude Code took (KevinXC on Discord). It is Reasoning, the
+// levels of Claude Code's the model takes, medium chosen first as on T3's
+// own Claude models (else the lowest); T3 hands the level to Claude Code
+// as it is, which sends it to the gateway. nil for a model with no level
+// Claude Code can send.
+func t3Capabilities(id string, efforts []string) map[string]any {
+	var options []map[string]any
+	for _, l := range claudeEffortsFor(id) {
+		if contains(efforts, l) {
+			options = append(options, map[string]any{"id": l, "label": t3EffortLabels[l]})
+		}
+	}
+	if len(options) == 0 {
+		return nil
+	}
+	def := options[0]
+	for _, o := range options {
+		if o["id"] == "medium" {
+			def = o
+		}
+	}
+	def["isDefault"] = true
+	return map[string]any{"optionDescriptors": []map[string]any{
+		{"id": "effort", "label": "Reasoning", "type": "select", "options": options},
+	}}
+}
diff --git a/internal/agent/t3code_test.go b/internal/agent/t3code_test.go
index 20ce26fd..4cc78c60 100644
--- a/internal/agent/t3code_test.go
+++ b/internal/agent/t3code_test.go
@@ -46,8 +46,20 @@ type t3Envelope struct {
 		BinaryPath   string `json:"binaryPath"`
 		HomePath     string `json:"homePath"`
 		CustomModels []struct {
-			Slug string `json:"slug"`
-			Name string `json:"name"`
+			Slug         string `json:"slug"`
+			Name         string `json:"name"`
+			Capabilities *struct {
+				OptionDescriptors []struct {
+					ID      string `json:"id"`
+					Label   string `json:"label"`
+					Type    string `json:"type"`
+					Options []struct {
+						ID        string `json:"id"`
+						Label     string `json:"label"`
+						IsDefault *bool  `json:"isDefault"`
+					} `json:"options"`
+				} `json:"optionDescriptors"`
+			} `json:"capabilities"`
 		} `json:"customModels"`
 	} `json:"config"`
 }
@@ -78,6 +90,23 @@ func t3Format(t *testing.T, raw []byte) t3Envelope {
 		if m.Slug == "" || m.Name == "" {
 			t.Errorf("custom model: %s", raw)
 		}
+		if m.Capabilities == nil {
+			continue
+		}
+		for _, d := range m.Capabilities.OptionDescriptors {
+			defaults := 0
+			for _, o := range d.Options {
+				if o.ID == "" || o.Label == "" {
+					t.Errorf("option: %s", raw)
+				}
+				if o.IsDefault != nil && *o.IsDefault {
+					defaults++
+				}
+			}
+			if d.ID == "" || d.Label == "" || d.Type != "select" || len(d.Options) == 0 || defaults != 1 {
+				t.Errorf("descriptor: %s", raw)
+			}
+		}
 	}
 	return e
 }
@@ -230,3 +259,58 @@ func TestT3CodeHomeAndInstance(t *testing.T) {
 		t.Error("the user's Claude instance is gone")
 	}
 }
+
+// Each magpie model in T3 Code has a Reasoning pick of the levels it takes
+// that Claude Code can send, medium chosen first, else the lowest (KevinXC
+// on Discord: every model ran at medium with no way to change it); none
+// for a model with no such level.
+func TestT3CodeEfforts(t *testing.T) {
+	type opt struct {
+		id  string
+		def bool
+	}
+	pick := func(id string, efforts []string) []opt {
+		c := t3Capabilities(id, efforts)
+		if c == nil {
+			return nil
+		}
+		raw, _ := json.Marshal(c)
+		var caps struct {
+			OptionDescriptors []struct {
+				ID, Label, Type string
+				Options         []struct {
+					ID, Label string
+					IsDefault bool
+				}
+			}
+		}
+		json.Unmarshal(raw, &caps)
+		if len(caps.OptionDescriptors) != 1 || caps.OptionDescriptors[0].ID != "effort" || caps.OptionDescriptors[0].Type != "select" {
+			t.Fatalf("%s: %s", id, raw)
+		}
+		var out []opt
+		for _, o := range caps.OptionDescriptors[0].Options {
+			if o.Label == "" {
+				t.Errorf("%s: no label: %s", id, raw)
+			}
+			out = append(out, opt{o.ID, o.IsDefault})
+		}
+		return out
+	}
+	for _, c := range []struct {
+		id      string
+		efforts []string
+		want    []opt
+	}{
+		{"codex/gpt-6", []string{"none", "minimal", "low", "medium", "high", "xhigh"}, []opt{{"low", false}, {"medium", true}, {"high", false}, {"xhigh", false}}},
+		{"ds/deepseek-v4", []string{"high", "max"}, []opt{{"high", true}, {"max", false}}},
+		{"claude/claude-opus-4-6", []string{"low", "medium", "high", "xhigh", "max"}, []opt{{"low", false}, {"medium", true}, {"high", false}, {"max", false}}},
+		{"claude/claude-haiku-4-5", []string{"low", "medium", "high"}, nil},
+		{"glm/glm-4.6", []string{"none", "minimal"}, nil},
+		{"glm/glm-4.6", nil, nil},
+	} {
+		if got := pick(c.id, c.efforts); !slices.Equal(got, c.want) {
+			t.Errorf("%s %v: %v, want %v", c.id, c.efforts, got, c.want)
+		}
+	}
+}