gemma4: render differently based on model size

Following up on #15560, this change now has e2b/e4b render differently
from 26b/31b.

For backwards compatibility, we take the existing renderer name `gemma4`
and make it do dynamic resolution based on the model name/size, but the
intended use is for the models to be republished with the renderer
variant specified explicitly: `gemma4-small` or `gemma4-large`.

model/renderers/gemma4.go

@@ -12,7 +12,8 @@ import (
 // <|turn>/<turn|> markers, <|"|> string delimiters, and <|tool>/
 // <|tool_call>/<|tool_response> tags for function calling.
 type Gemma4Renderer struct {
-	useImgTags bool
+	useImgTags          bool
+	emptyBlockOnNothink bool
 }
 
 const (
@@ -124,6 +125,9 @@ func (r *Gemma4Renderer) Render(messages []api.Message, tools []api.Tool, thinkV
 	// Generation prompt.
 	if prevMessageType != "tool_response" && prevMessageType != "tool_call" {
 		sb.WriteString("<|turn>model\n")
+		if r.emptyBlockOnNothink {
+			sb.WriteString("<|channel>thought\n<channel|>")
+		}
 	}
 
 	return sb.String(), nil

model/renderers/gemma4_reference_test.go

@@ -3,9 +3,9 @@ package renderers
 // TestGemma4RendererMatchesReference verifies our renderer matches the checked-in
 // Gemma 4 reference template.
 //
-// Current upstream Gemma 4 chat templates differ by model size, so the checked-in
-// reference intentionally uses the shared baseline without an empty generation-time
-// thought channel until renderer selection is split by size.
+// Current upstream Gemma 4 chat templates differ by model size. The checked-in
+// reference cases below use the small (e2b/e4b-style) baseline, with large
+// (26b/31b-style) checks covered separately in this file.
 //
 // To regenerate expected values, save the E2B template to
 // gemma4_e2b_chat_template.jinja2 and run:
@@ -1474,6 +1474,40 @@ Hi<turn|>
 	}
 }
 
+func TestGemma4RendererVariantsMatchExpectedGenerationPrompt(t *testing.T) {
+	messages := []api.Message{{Role: "user", Content: "Hello"}}
+
+	tests := []struct {
+		name         string
+		rendererName string
+		expected     string
+	}{
+		{
+			name:         "legacy_alias",
+			rendererName: "gemma4",
+			expected:     "<bos><|turn>user\nHello<turn|>\n<|turn>model\n",
+		},
+		{
+			name:         "small",
+			rendererName: "gemma4-small",
+			expected:     "<bos><|turn>user\nHello<turn|>\n<|turn>model\n",
+		},
+		{
+			name:         "large",
+			rendererName: "gemma4-large",
+			expected:     "<bos><|turn>user\nHello<turn|>\n<|turn>model\n<|channel>thought\n<channel|>",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := RenderWithRenderer(tt.rendererName, messages, nil, nil)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.expected, got)
+		})
+	}
+}
+
 func TestGemma4RendererMatchesJinja2ExpandedParity(t *testing.T) {
 	if os.Getenv("VERIFY_JINJA2") == "" {
 		t.Skip("set VERIFY_JINJA2=1 to run expanded Jinja2 parity checks")
@@ -1616,15 +1650,35 @@ func TestGemma4RendererMatchesJinja2ExpandedParity(t *testing.T) {
 		},
 	}
 
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			renderer := &Gemma4Renderer{useImgTags: RenderImgTags}
-			got, err := renderer.Render(tt.messages, tt.tools, tt.think)
-			assert.NoError(t, err)
+	variants := []struct {
+		name        string
+		renderer    *Gemma4Renderer
+		templateRel string
+	}{
+		{
+			name:        "small",
+			renderer:    &Gemma4Renderer{useImgTags: RenderImgTags},
+			templateRel: gemma4E2BTemplate,
+		},
+		{
+			name:        "large",
+			renderer:    &Gemma4Renderer{useImgTags: RenderImgTags, emptyBlockOnNothink: true},
+			templateRel: gemma431BTemplate,
+		},
+	}
 
-			jinja2Output := renderWithJinja2(t, tt.messages, tt.tools, tt.think)
-			assert.Equal(t, jinja2Output, got,
-				"renderer output doesn't match Jinja2 template output")
+	for _, variant := range variants {
+		t.Run(variant.name, func(t *testing.T) {
+			for _, tt := range tests {
+				t.Run(tt.name, func(t *testing.T) {
+					got, err := variant.renderer.Render(tt.messages, tt.tools, tt.think)
+					assert.NoError(t, err)
+
+					jinja2Output := renderWithJinja2Template(t, variant.templateRel, tt.messages, tt.tools, tt.think)
+					assert.Equal(t, jinja2Output, got,
+						"renderer output doesn't match Jinja2 template output")
+				})
+			}
 		})
 	}
 }

model/renderers/renderer.go

@@ -81,8 +81,10 @@ func rendererForName(name string) Renderer {
 		return renderer
 	case "nemotron-3-nano":
 		return &Nemotron3NanoRenderer{}
-	case "gemma4":
+	case "gemma4", "gemma4-small":
 		return &Gemma4Renderer{useImgTags: RenderImgTags}
+	case "gemma4-large":
+		return &Gemma4Renderer{useImgTags: RenderImgTags, emptyBlockOnNothink: true}
 	case "functiongemma":
 		return &FunctionGemmaRenderer{}
 	case "glm-4.7":

server/create.go

@@ -523,7 +523,7 @@ func createModel(r api.CreateRequest, name model.Name, baseLayers []*layerGGML,
 				arch := layer.GGML.KV().Architecture()
 				switch arch {
 				case "gemma4":
-					config.Renderer = cmp.Or(config.Renderer, "gemma4")
+					config.Renderer = cmp.Or(config.Renderer, gemma4RendererLegacy)
 					config.Parser = cmp.Or(config.Parser, "gemma4")
 					if _, ok := r.Parameters["stop"]; !ok {
 						if r.Parameters == nil {

server/gemma4_test.go

@@ -0,0 +1,78 @@
+package server
+
+import "testing"
+
+func TestResolveGemma4Renderer(t *testing.T) {
+	tests := []struct {
+		name  string
+		model *Model
+		want  string
+	}{
+		{
+			name:  "nil model falls back to legacy alias",
+			model: nil,
+			want:  gemma4RendererLegacy,
+		},
+		{
+			name: "explicit small passes through",
+			model: &Model{
+				Config: testConfigWithRenderer(gemma4RendererSmall),
+			},
+			want: gemma4RendererSmall,
+		},
+		{
+			name: "explicit large passes through",
+			model: &Model{
+				Config: testConfigWithRenderer(gemma4RendererLarge),
+			},
+			want: gemma4RendererLarge,
+		},
+		{
+			name: "legacy e4b tag resolves small",
+			model: &Model{
+				Name:      "gemma4:e4b",
+				ShortName: "gemma4:e4b",
+				Config:    testConfigWithRenderer(gemma4RendererLegacy),
+			},
+			want: gemma4RendererSmall,
+		},
+		{
+			name: "legacy 31b tag resolves large",
+			model: &Model{
+				Name:      "gemma4:31b-cloud",
+				ShortName: "gemma4:31b-cloud",
+				Config:    testConfigWithRenderer(gemma4RendererLegacy),
+			},
+			want: gemma4RendererLarge,
+		},
+		{
+			name: "legacy model type resolves small",
+			model: &Model{
+				Config: testConfigWithRendererAndType(gemma4RendererLegacy, "4.3B"),
+			},
+			want: gemma4RendererSmall,
+		},
+		{
+			name: "legacy model type resolves large",
+			model: &Model{
+				Config: testConfigWithRendererAndType(gemma4RendererLegacy, "25.2B"),
+			},
+			want: gemma4RendererLarge,
+		},
+		{
+			name: "legacy unknown defaults small",
+			model: &Model{
+				Config: testConfigWithRenderer(gemma4RendererLegacy),
+			},
+			want: gemma4RendererSmall,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := resolveGemma4Renderer(tt.model); got != tt.want {
+				t.Fatalf("resolveGemma4Renderer() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}

server/images.go

@@ -156,7 +156,7 @@ func (m *Model) Capabilities() []model.Capability {
 
 	// Temporary workaround — suppress vision/audio for gemma4 MLX models
 	// until multimodal runtime pipeline lands. Remove when imageproc.go is wired up.
-	if m.Config.ModelFormat == "safetensors" && m.Config.Renderer == "gemma4" {
+	if m.Config.ModelFormat == "safetensors" && isGemma4Renderer(m.Config.Renderer) {
 		capabilities = slices.DeleteFunc(capabilities, func(c model.Capability) bool {
 			return c == model.CapabilityVision || c == "audio"
 		})

server/images_test.go

@@ -118,6 +118,39 @@ func TestModelCapabilities(t *testing.T) {
 			},
 			expectedCaps: []model.Capability{model.CapabilityEmbedding},
 		},
+		{
+			name: "gemma4 small safetensors suppresses vision and audio",
+			model: Model{
+				Config: model.ConfigV2{
+					ModelFormat:  "safetensors",
+					Renderer:     gemma4RendererSmall,
+					Capabilities: []string{"vision", "audio"},
+				},
+				Template: chatTemplate,
+			},
+		},
+		{
+			name: "gemma4 large safetensors suppresses vision and audio",
+			model: Model{
+				Config: model.ConfigV2{
+					ModelFormat:  "safetensors",
+					Renderer:     gemma4RendererLarge,
+					Capabilities: []string{"vision", "audio"},
+				},
+				Template: chatTemplate,
+			},
+		},
+		{
+			name: "legacy gemma4 safetensors suppresses vision and audio",
+			model: Model{
+				Config: model.ConfigV2{
+					ModelFormat:  "safetensors",
+					Renderer:     gemma4RendererLegacy,
+					Capabilities: []string{"vision", "audio"},
+				},
+				Template: chatTemplate,
+			},
+		},
 	}
 
 	// compare two slices of model.Capability regardless of order

server/prompt.go

@@ -115,7 +115,8 @@ func chatPrompt(ctx context.Context, m *Model, tokenize tokenizeFunc, opts *api.
 
 func renderPrompt(m *Model, msgs []api.Message, tools []api.Tool, think *api.ThinkValue) (string, error) {
 	if m.Config.Renderer != "" {
-		rendered, err := renderers.RenderWithRenderer(m.Config.Renderer, msgs, tools, think)
+		rendererName := resolveRendererName(m)
+		rendered, err := renderers.RenderWithRenderer(rendererName, msgs, tools, think)
 		if err != nil {
 			return "", err
 		}

server/prompt_test.go

@@ -13,6 +13,14 @@ import (
 	"github.com/ollama/ollama/types/model"
 )
 
+func testConfigWithRenderer(renderer string) model.ConfigV2 {
+	return model.ConfigV2{Renderer: renderer}
+}
+
+func testConfigWithRendererAndType(renderer, modelType string) model.ConfigV2 {
+	return model.ConfigV2{Renderer: renderer, ModelType: modelType}
+}
+
 func TestChatPrompt(t *testing.T) {
 	type expect struct {
 		prompt string
@@ -397,3 +405,43 @@ func TestChatPromptGLMOcrRendererAddsImageTags(t *testing.T) {
 		t.Fatalf("prompt missing glm-ocr image tags, got: %q", prompt)
 	}
 }
+
+func TestRenderPromptResolvesDynamicGemma4Renderer(t *testing.T) {
+	msgs := []api.Message{{Role: "user", Content: "Hello"}}
+
+	tests := []struct {
+		name  string
+		model Model
+		want  string
+	}{
+		{
+			name: "small from name",
+			model: Model{
+				Name:      "gemma4:e4b",
+				ShortName: "gemma4:e4b",
+				Config:    testConfigWithRenderer(gemma4RendererLegacy),
+			},
+			want: "<bos><|turn>user\nHello<turn|>\n<|turn>model\n",
+		},
+		{
+			name: "large from model type",
+			model: Model{
+				Config: testConfigWithRendererAndType(gemma4RendererLegacy, "25.2B"),
+			},
+			want: "<bos><|turn>user\nHello<turn|>\n<|turn>model\n<|channel>thought\n<channel|>",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := renderPrompt(&tt.model, msgs, nil, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if diff := cmp.Diff(got, tt.want); diff != "" {
+				t.Fatalf("rendered prompt mismatch (-got +want):\n%s", diff)
+			}
+		})
+	}
+}

server/renderer_resolution.go

@@ -0,0 +1,110 @@
+package server
+
+import (
+	"strconv"
+	"strings"
+
+	"github.com/ollama/ollama/format"
+)
+
+const (
+	gemma4RendererLegacy = "gemma4"
+	gemma4RendererSmall  = "gemma4-small"
+	gemma4RendererLarge  = "gemma4-large"
+
+	// Gemma 4 small templates cover the e2b/e4b family, while 26b/31b use the
+	// large template. Default to the small prompt unless the model is clearly in
+	// the large range.
+	gemma4LargeMinParameterCount = 16_000_000_000
+)
+
+func resolveRendererName(m *Model) string {
+	if m == nil || m.Config.Renderer == "" {
+		return ""
+	}
+
+	switch m.Config.Renderer {
+	case gemma4RendererLegacy:
+		return resolveGemma4Renderer(m)
+	default:
+		return m.Config.Renderer
+	}
+}
+
+func resolveGemma4Renderer(m *Model) string {
+	if m == nil || m.Config.Renderer != gemma4RendererLegacy {
+		if m == nil {
+			return gemma4RendererLegacy
+		}
+		return m.Config.Renderer
+	}
+
+	if renderer, ok := gemma4RendererFromName(m.ShortName); ok {
+		return renderer
+	}
+
+	if renderer, ok := gemma4RendererFromName(m.Name); ok {
+		return renderer
+	}
+
+	if parameterCount, ok := parseHumanParameterCount(m.Config.ModelType); ok {
+		return gemma4RendererForParameterCount(parameterCount)
+	}
+
+	return gemma4RendererSmall
+}
+
+func gemma4RendererForParameterCount(parameterCount uint64) string {
+	if parameterCount >= gemma4LargeMinParameterCount {
+		return gemma4RendererLarge
+	}
+
+	return gemma4RendererSmall
+}
+
+func gemma4RendererFromName(name string) (string, bool) {
+	lower := strings.ToLower(name)
+	switch {
+	case strings.Contains(lower, "e2b"), strings.Contains(lower, "e4b"):
+		return gemma4RendererSmall, true
+	case strings.Contains(lower, "26b"), strings.Contains(lower, "31b"):
+		return gemma4RendererLarge, true
+	default:
+		return "", false
+	}
+}
+
+func parseHumanParameterCount(s string) (uint64, bool) {
+	if s == "" {
+		return 0, false
+	}
+
+	unit := strings.ToUpper(s[len(s)-1:])
+	var multiplier float64
+	switch unit {
+	case "B":
+		multiplier = float64(format.Billion)
+	case "M":
+		multiplier = float64(format.Million)
+	case "K":
+		multiplier = float64(format.Thousand)
+	default:
+		return 0, false
+	}
+
+	value, err := strconv.ParseFloat(s[:len(s)-1], 64)
+	if err != nil {
+		return 0, false
+	}
+
+	return uint64(value * multiplier), true
+}
+
+func isGemma4Renderer(renderer string) bool {
+	switch renderer {
+	case gemma4RendererLegacy, gemma4RendererSmall, gemma4RendererLarge:
+		return true
+	default:
+		return false
+	}
+}

server/routes_create_test.go

@@ -928,6 +928,59 @@ func TestCreateDetectTemplate(t *testing.T) {
 	})
 }
 
+func TestCreateGemma4KeepsDynamicRendererAlias(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	p := t.TempDir()
+	t.Setenv("OLLAMA_MODELS", p)
+	var s Server
+
+	_, digest := createBinFile(t, ggml.KV{
+		"general.architecture":    "gemma4",
+		"general.parameter_count": uint64(25_200_000_000),
+	}, nil)
+
+	w := createRequest(t, s.CreateHandler, api.CreateRequest{
+		Name:   "test",
+		Files:  map[string]string{"test.gguf": digest},
+		Stream: &stream,
+	})
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected status code 200, actual %d", w.Code)
+	}
+
+	mf, err := manifest.ParseNamedManifest(model.ParseName("test"))
+	if err != nil {
+		t.Fatalf("parse manifest: %v", err)
+	}
+	if mf.Config.Digest == "" {
+		t.Fatalf("unexpected empty config digest for manifest")
+	}
+
+	configPath, err := manifest.BlobsPath(mf.Config.Digest)
+	if err != nil {
+		t.Fatalf("config blob path: %v", err)
+	}
+
+	cfgFile, err := os.Open(configPath)
+	if err != nil {
+		t.Fatalf("open config blob: %v", err)
+	}
+	defer cfgFile.Close()
+
+	var cfg model.ConfigV2
+	if err := json.NewDecoder(cfgFile).Decode(&cfg); err != nil {
+		t.Fatalf("decode config: %v", err)
+	}
+
+	if cfg.Renderer != gemma4RendererLegacy {
+		t.Fatalf("expected renderer %q, got %q", gemma4RendererLegacy, cfg.Renderer)
+	}
+	if cfg.Parser != "gemma4" {
+		t.Fatalf("expected parser %q, got %q", "gemma4", cfg.Parser)
+	}
+}
+
 func TestDetectModelTypeFromFiles(t *testing.T) {
 	t.Run("gguf file", func(t *testing.T) {
 		_, digest := createBinFile(t, nil, nil)